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Title: Mechanics - The Science of Machinery
Author: Bond, A. Russell (Alexander Russell)
Language: English
As this book started as an ASCII text book there are no pictures available.
Copyright Status: Not copyrighted in the United States. If you live elsewhere check the laws of your country before downloading this ebook. See comments about copyright issues at end of book.

*** Start of this Doctrine Publishing Corporation Digital Book "Mechanics - The Science of Machinery" ***

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  Copyright, Ewing Galloway]

_The drop forge. A fourteen-ton hydraulic press is employed in forging
                 an immense open hearth steel plate._

                        POPULAR SCIENCE LIBRARY


                          GARRETT P. SERVISS


                       NORMAN TAYLOR    DAVID TODD
                        CHARLES FITZHUGH TALMAN
                              ROBIN BEACH

                      ARRANGED IN SIXTEEN VOLUMES
                          AND A GENERAL INDEX


[Illustration: LOGO]

                              VOLUME FIVE

                      P. F. COLLIER & SON COMPANY
                               NEW YORK

                            Copyright 1922
                    BY P. F. COLLIER & SON COMPANY

                       MANUFACTURED IN U. S. A.


                       THE SCIENCE OF MACHINERY


                            A. RUSSELL BOND


                      P. F. COLLIER & SON COMPANY
                               NEW YORK


ALTHOUGH strictly speaking the term “Mechanics” applies to that branch
of Physics that deals with the actions of forces on material bodies,
originally the word had a broader meaning embracing all machinery
and mechanical inventions. To-day popular usage is restoring to the
term its original broad interpretation, and it is in this popular but
rather unorthodox sense that “Mechanics” has been chosen as the title
of this book; for although certain elementary principles of mechanics
are described and explained, the major portion of the book deals with
machines and their evolution to their present stage of perfection.

Machines are man’s creation, and yet in a sense the man of to-day is a
machine product; for modern civilization owes its material and in large
measure its esthetic development to machinery. The story of machinery,
from primitive man’s first attempts to augment his physical powers with
mechanical aids down to the present era of gigantic, steel-muscled
machinery and marvelously intricate mechanisms, is the story of human
progress. It is this story that we have endeavored to tell in the
following pages, but the subject is too large to be covered in a single
volume or even a dozen volumes. Under the circumstances we have been
obliged to confine ourselves to a mere outline, selecting certain
avenues of progress more marked than others and presenting brief sketch
maps of them. We have aimed in this way to give a bird’s-eye view of
the whole story of human progress in things material.

The book has not been written for the mechanical engineer, but for the
layman who would learn of the mechanical contrivances that contribute
to his material welfare; hence technical terms have been avoided, as
far as possible, and where unavoidable have been explained and defined.



 CHAPTER                                             PAGE

      I. TOOL-MAKING ANIMALS                            9
     II. THE ANATOMY OF A MACHINE                      20
    III. MACHINES FOR MAKING MACHINES                  42
     IV. COUNTING SECONDS                              57
      V. PUTTING RIVERS TO WORK                        75
     VI. LIQUID LEVERS AND GEARS                       94
    VII. AIR _vs._ WATER                              109
   VIII. AIR SPRINGS AND CUSHIONS                     126
     IX. POWER FROM HEAT                              139
     XI. WHEN COAL AND OIL ARE EXHAUSTED              171
    XII. INVASION OF THE SEA                          182
    XIV. INVASION OF THE SKY                          219
     XV. HELPING THE FARMER                           239
    XVI. MACHINING THE EARTH                          251
   XVII. FROM FIBER TO FABRIC                         268
  XVIII. THE MAKING OF PAPER                          289
    XXI. ANIMATED MACHINERY                           326
   XXII. HEAT VACUUMS                                 345
  XXIII. ENGINES OF DESTRUCTION                       359


  THE DROP FORGE--FORGING A STEEL PLATE             _Frontispiece_

                                                       FACING PAGE

      PUMP USED IN EGYPT                                        32






  AIR LOCK OF A PNEUMATIC CAISSON                               96



  SUN-POWER PLANT IN EGYPT                                     129


  GIANT CAPRONI HYDROAEROPLANE                                 160

  CONCRETE STEAMSHIP “FAITH”                                   161



  BATTERY OF MULE SPINNING FRAMES                              225

  JACQUARD ATTACHMENT FOR LOOM                                 225






  MOLTEN METAL FROM A BLAST FURNACE                            320





  BLIND MAN READING WITH HIS EARS                              353



WHEN we review the marvelous achievements of modern civilization we
are quite willing to agree with the ancient psalmist that man is
“little lower than the angels.” But at the other end of the scale our
complacency is liable to receive a rude shock; apparently the boundary
between man and beast is not so very easy to draw.

We used to be told that one important superiority of mankind lies in
the fact that he makes use of tools, while the beast never uses any
implement except those that nature has furnished him as part of his own
organism. But a gorilla will throw stones at his enemy; and he knows
how to brandish a club and use it with telling force. Some of the apes
are known to use sticks to knock down fruit which is out of the reach
of their hands, and they will crack nuts with a stone. Clearly these
animals are tool users. A very intelligent orang-utan in the Bronx
Zoölogical Garden, New York, after trying for days to wrench off a
bracket from the wall of his cage eventually used the horizontal bar of
his trapeze as a lever and with it pried the offending bracket from its
fastenings. Here was real invention and the discovery of the principle
of leverage. The great black arara cockatoo of New Guinea uses his beak
as a saw to weaken the shells of hard nuts, and to keep his bill from
slipping off the smooth shell he is ingenious enough to wrap a leaf
around the nut to hold it steady.

Even in the insect world we find creatures resourceful enough to make
use of tools. Prof. Franz Doflein of the University of Breslau tells
of an interesting study of certain ants, known as the _Oecophylla
smaragdina_, who build their nests in bushes by fastening leaves
together with fine threads. But the ants that build the nests cannot
spin these threads, because they possess no spinning glands. They must
depend upon their larvæ for this product. When a rent was made in one
of these nests, a band of the tiny creatures ranged themselves side
by side along the torn edge of the leaf and reached across the gap
until they could catch hold of the opposite edge with their mandibles.
Then they drew back step by step, with perfect teamwork, until the two
edges were brought together. In the meantime, other ants had rushed to
the nursery and each one had picked up a larva, not with the idea of
bearing it off to safety, but in order that the babies might spin the
thread which the adult ants were unable to do. The larvæ were carried
to the breach in the nest and moved back and forth across the rent.
They were pressed first against one side of the tear and then the other
and all the while were squeezed tightly, evidently with the purpose of
making them spin. Gradually a fine silky web was woven across the torn
leaf and eventually the rent was completely patched.

Unquestionably these little ants are tool-using animals, because they
make their larvæ serve as spinning spindles and also as weavers’
shuttles. However, this can hardly be cited as a point in common with
even the lowest type of man, for the ants merely use the tools they
find at their disposal. They certainly cannot be credited with having
produced or even improved the tool which they use, whereas even in
the most primitive of men we find that the tools used are not only
carefully selected for the work to be performed, but are actually,
shaped, be it ever so crudely, to suit the job.

Clearly we must shift the boundary between man and beast,
distinguishing the former as the creature who artificially improves his
tools. But even here it is not absolutely certain that the boundary
will stand. Wilhelm Boelsche, a well-known German writer on natural
history, calls attention to the “blacksmith woodpecker” which will
thrust hard pine nuts into cracks in the trunk of a tree, so that they
are held as if in a vise, enabling the bird to operate upon the seed
more easily. Furthermore, this woodpecker will actually make a hole in
the tree to receive the nut if there is not a hole or crack handy, so
that evidently this animal does produce or artificially improve the
tool that it uses.

There are a few such examples in nature, just enough to cast a bit of
uncertainty on the boundary we have set. But although the actual line
of demarcation may not be clear, there is no question but that the
lowest type of humanity now existent, or of which we have any record,
is or was a tool maker. Chipped stones evidently fashioned by man
for some useful purpose are found even in the remains of the Middle
Tertiary Epoch. The spirit of inquiry, of experiment, of invention,
and the ambition to dominate over other members of the animal kingdom
or over the obstacles imposed by nature, are to be found more or less
active among all peoples, no matter how lowly a position they may
occupy in the scale of civilization.


The most primitive implements were probably developed for the purpose
of war. From the very earliest times, down to the present day, war
has been a most potent stimulus of invention. The first tools ever
used were probably intended to enable the user to cope with dangerous
enemies. They marked the first stage in the conquest of brain over mere
brawn. The primitive weapons were used not only in fighting other men,
but in fighting off dangerous animals, and then in hunting animals for
food. No doubt the first implement ever used was a club, which gave
a real advantage over the unarmed, scratching, tearing, and biting
enemy. This was a lever which increased the reach of the fighter, and
also increased the power of his blow. The heavier the club, the more
dangerous the weapon, particularly when most of the weight was centered
at the outer end of the stick. But he was a real genius who first
fastened a rock to the end of his club.


Then arose the art of breaking stones--breaking them skillfully, so as
to form a jagged cutting edge. When man began to fashion tools of stone
he left imperishable records of his craftsmanship which enable us to
trace his progress in invention. The first finished tool we find was
the fist hatchet--a stone roughly chipped to form a cutting edge and of
convenient shape for the grasp of the hand. This primitive tool very
slowly, through a period covering thousands of years, developed into
all manner of cutting implements, some with handles of wood and bone.
The ax head was followed by the spearhead and this finally by the
arrowhead, showing that man had at last found a mechanical substitute
for his muscles to hurl projectiles farther and with greater accuracy
than he could throw them by hand.

We marvel at the resourcefulness and skill of the primitive savage in
working so difficult a material as stone. It would baffle a modern
mechanic to be required to shape a piece of flint into an arrowhead
with no other tool than a piece of bone. He is so accustomed to using
tools which are harder than the material they are intended to shape
that he cannot conceive of making any impression upon a piece of flint
with a piece of bone, to say nothing of a stick of hard wood, and yet
such tools were used away back in the Stone Age. At first stones were
roughly shaped by hammering them together. Then the artisans became
more skilled. They discovered that certain stones could be chipped
more regularly and evenly, and the art of flaking off chips of flint
sprang up. Some specimens that belonged to ages long preceding that of
recorded history are beautifully done. The spearheads are symmetrically
shaped like a long narrow leaf, and the stone is evenly furrowed on
both sides with a keen edge all around.

Not only did primitive artisans shape the stone implements with hammer
blows, but they learned how to shape stone by pressure as well, using
a tool that was relatively soft. It is not a very difficult matter to
shape even so hard a substance as glass merely by pressure. If a piece
of glass is laid on a table with its edge slightly overhanging that of
the table, it is possible to chip off the overhanging edge by pressing
a nail or even a hard stick of wood against this edge. A small flake
of glass is thus removed, and, by continuing the process, arrowheads
of any shape may be formed. The tool is placed not against the upper
surface of the glass, but against the edge of the glass, so that only
the lower surface of it is split or flaked off. Then the glass is
turned over and a chip is taken off the opposite face.

In the Middle Stone Age we find the primitive craftsman equipped with
a very complete assortment of stone tools. He had hammers, chisels,
scrapers, drills, and polishing tools. He knew how to make useful
household implements, such as spoons and ladles, out of bone. He
polished his work and ornamented the implements with carvings of
animals. Ivory pins and needles show that he had begun to make himself
clothing from the skins of animals and that he sewed them together with
thongs or tendons.

In the Late Stone Age he had learned how to make vessels of fire-baked
clay. His axes were ground to a sharp edge, and he bored holes in the
ax head to receive the ax handle. The Swiss lake dwellers built houses
of wood and fitted them with all sorts of wooden furniture carved
with stone tools. Among the remains of these interesting settlements
may be found balls of clay which, from the fact that one of them was
discovered with a spool of flax still attached to it, were evidently
used as spinning “whorls” used for spinning flax into thread. Clothing
of skins was giving way to or being supplemented with clothing of woven


Prior to the Stone Age the club was undoubtedly used, in time of
peace--if there ever was a time of peace in those days--to batter down
trees, to beat through entanglements and to dislodge great stones.
Here the first idea of leverage was evidently employed. The club with
a rock tied to it, particularly if the rock was shaped with a sharp
edge, made a better implement for hewing trees. It is quite probable
that soon after this stage of development had been reached, some one
discovered the use of the wedge, particularly in splitting timber. Of
course, no one realized in those early days why it was that he could
pry up a greater weight with a lever than he could lift directly by
hand, or why he could split open a log by driving wedges into it. The
_art_ of mechanics was in existence long ages before _science_ of
mechanics began to be studied. But it was not until men began to look
into the why of things that rapid progress was made.

We can go on endlessly with our speculations on the evolution of tools
and machinery up to the time when historians began to record the
mechanical achievements of man. Unfortunately even after historians
began to write they were so filled with admiration for the destructive
work of man that they had no time to record his constructive work.
The warrior who spread havoc and terror received all the glory, and
his deeds were written on parchment, inscribed in clay and carved in
stone; but the humble artisan was not worthy of mention. Even when the
science of mechanics came to be studied, it was shrouded in a veil of
mystery, and it was beneath the dignity of the man of science to impart
his knowledge to the artisan. There was a lack of cooperation between
science and industry that has persisted to a certain extent even up
to the present time. Some of the most ingenious inventions of the
ancients were employed by a corrupt and crafty priesthood to produce
apparently miraculous effects and hoodwink the general public; and so,
in looking back to the early days of mechanics, we are obliged to draw
upon our imagination to trace its evolution, supplementing this by a
study of the tools of primitive people of more recent time. Practically
every form of hand tool we now use must have been known to the ancient


We are not going to attempt to write a history of the evolution of
machinery, but there is one invention whose origin is lost in the
remote prehistoric ages which deserves more than passing attention. It
is a pity that we have no clue as to who invented the wheel or how this
most important element that enters into the construction of nearly all
machinery was evolved. The invention called for a remarkable degree of
originality. There is nothing like a wheel in nature. Levers we have
in our own physical frame. But a wheel is something that is distinctly
a human creation. Whoever invented it must have been a real genius, a
James Watt or a Thomas Edison of his day. Certainly we owe more to the
invention of the wheel than we do even to so revolutionary a machine
as the steam engine, or the flying machine. How it was ever first
conceived is a mystery. Maybe this primeval genius got his idea from
seeing a stone rolling downhill, or he may have seen a tumbling weed
rolling along the ground before the wind. It may be that the forerunner
of the wheel was a roller shaped out of a log, for certainly primitive
civilization must have advanced enough to have known how to hew timber
before it would have been capable of fashioning a wheel. Some observant
man might have noticed that he could drag a heavy timber over a
rolling log much more easily than he could along the bare ground, and
gradually the roller evolved into a wheel.

We can speculate upon the evolution of vehicles and transportation,
once the wheel was invented. Of course, the first method of
transporting loads was to carry them in the arms. Possibly loads were
placed on skids and dragged along by one end. Away back in early times,
it was discovered that two persons could carry more than twice as much
as one, if the load were placed on a couple of poles. There was no
friction to contend with, and not only was the load cut in two, because
each man bore half of it, but the position of the load was such that
it could be borne more easily. After the wheel was discovered, some
one must have conceived of the idea of dispensing with an assistant by
placing a wheel between the poles of the stretcher, thus making a crude
wheelbarrow. It is more likely that two wheels were first used, making
a cart of the stretcher, because the crude workmen of those days could
hardly have produced anything but a very wobbly wheelbarrow. At any
rate, the wheel, or pair of wheels, robbed one man of his job. Only one
bearer was required where before two had been used. Labor costs were
immediately reduced 50 per cent.


In the very earliest days of invention machines began to displace men.
Had there been unions in those days, no doubt there would have been
strenuous opposition to the introduction of this substitute for an
honest worker. But among the ancients, even more than at the present
time, invention meant greater production rather than less work,
because the laborer of that time was not a hired man but a slave.
There was no object in cutting down labor when it cost practically
nothing. The only stimulus to invention was greater production.

The invention of the wheel meant the dawn of transportation, which
is the backbone of civilization, and from it resulted no end of
other inventions. It made it possible for communities to come into
closer touch with each other. It meant circulation--an interchange of
knowledge and of products. Food was transported from one locality to
another, enabling certain communities to dispense with agricultural
work and specialize in certain lines of manufacture; for they could
barter their products for food raised by other communities. There are
some tribes to-day which are most backward because they are separated
from other tribes by rivers, while other tribes similarly placed owe
their progress to the fact that they have developed sufficient skill to
build crude bridges and thus gain access to the outside world.


In Egypt the wheel had a wonderful effect on agriculture. In that dry
land water is, and always has been, most precious. No wonder the Nile
was venerated! It meant life--life to crops, and hence life to man.
How to raise water from this stream of life in time of drought was
the great problem of the Egyptian. As slave labor was cheap, it was
customary to haul up the precious water, a bucket at a time, and pour
it over the fields. Then some one discovered that this process could be
simplified by using a _shadoof_ or swape; in other words, a long pole
fulcrumed near one end, with a heavy rock for a counterbalance lashed
to the shorter arm, and a bucket tied by a long rope to the longer
arm of the lever. This primitive machine is still to be found in some
rural districts. With this contrivance, a heavier load could be lifted
than by hand, because, when raising the bucket, the weight of the rock
would assist in lifting the water. After the swape came all manner of
ingenious devices for lifting the water. There were seesaw arrangements
which would scoop up some of the water at each oscillation of the
seesaw, and in one ingenious contrivance there was a succession of
seesaws by which the water was raised to a considerable height, whence
it poured down into ditches that irrigated the fields.

Then some one invented a water wheel or a great wheel, fitted with
buckets, which was turned by human or ox power, and which poured a
steady stream of water into the irrigating ditches.

But the greatest invention was that of the engineer who actually made
the river turn the wheel. It was probably on the Nile that the _noria_,
as this machine was called, was first put into service.

The wheel was provided with paddles, so that the current made it
revolve, and the water spilled out of the buckets into a trough as
they were turned over by the wheel. We can imagine the triumph of the
ancient inventor who developed that machine. True, the river might
arise in its wrath now and then and wreck the machine, but in wrecking
the wheel it had to flood the land, which, after all, was exactly what
was aimed at. The anger of the river was short-lived; it soon quieted
down and went on placidly turning the wheel which robbed it of the
precious water. It was a great event in the history of engineering. The
Nile had been harnessed. One of the great powers of nature had been set
to work.



EVERY animal is a complex machine, provided with its own motive power
and a brain for directing the operation of its own mechanical elements.
Not satisfied with the mechanism that nature has put into the human
machine, man has reached for other elements and devised mechanisms
of his own in order to supplement the human machine and increase its
efficiency. At first, as we have seen, these elements were hand tools
of the crudest sort; but they were gradually improved and then they
were combined into what we term machines. In developing these machines,
he naturally took his own system as a pattern and was guided to a
large extent by an examination of his own physical structure. We see
this very clearly in the names of the different parts of machinery,
which are taken from the names of similar parts in the human frame.
Almost every member of the body is used in mechanical terminology. For
instance, we have the “head” and the “foot,” the “arms” and the “legs,”
the “fingers” and the “ankles,” “elbows,” “shoulders,” “trunk,” “hips,”
and various parts of the face, such as the “eyes,” “ears,” “nose,”
“mouth,” “teeth,” “lips,” and even the “gums,” to indicate parts of
machinery which have some remote resemblance to these features.

Before we can understand machinery we must have some general knowledge
of the elements of which it is composed. Probably most of the readers
of this book already possess a fair knowledge of machine elements and
mechanical movements and they can well afford to skip this chapter.
However, for the benefit of the uninitiated, we must put a machine on
the operating table, dissect it, and explain its anatomical structure.
We cannot attempt a very detailed study, but will confine ourselves to
the most important elements.

Every machine is made up of movable parts and fixed parts, the latter
serving to guide or constrain the motion of the former; for no
combination of elements will constitute a machine unless the parts are
_constrained_ to move in certain predetermined directions.


Among the moving elements the first to be considered is the lever,
which really forms a broad classification comprising many elements that
will hardly be recognized as levers at first blush. Levers in some form
are to be found in practically every machine. A wheel, a gear, and a
pulley are really levers in disguise, as will be explained presently.

Of course everyone knows that a simple lever consists of a rigid bar
that swings on a fulcrum. The fulcrum may be a knife edge, a shaft
passing through the bar or any element on which the bar can be swung
or oscillated. The purpose of the lever is to give a certain advantage
in the application of a force to a load. This may be a change of speed
and distance of travel, and hence of power, or merely a change of


There are three types or _orders_ of levers produced by varying the
relative positions of the points where the fulcrum, the force or
effort, and the weight or load are applied. These are shown in Figure
1. In the lever of the _first order_ the fulcrum is placed between the
effort and the weight; in the lever of the _second order_ the weight
is applied between the fulcrum and the effort; and in the lever of the
_third order_ the effort is applied between the fulcrum and the weight.
In each case that part of the lever which extends from the fulcrum to
the point where the effort is applied is called the _effort arm_, and
that which extends from the fulcrum to the point where the weight is
supported is the _weight arm_. The weight that can be lifted with a
given effort depends upon the ratio of the effort arm to the weight
arm. If the two arms are of equal length, the effort is equal to the
weight, but twice the weight can be lifted with the same effort if the
effort arm is twice as long as the weight arm. You can lift a ton with
an effort of only 100 pounds if your effort arm is twenty times as long
as your weight arm but the end of your effort arm would have to move
twenty inches to raise the ton weight one inch. We are assuming in all
these cases that the lever itself has no weight and that there is no
friction at the fulcrum.

Of course levers are not used merely for the purpose of lifting weight,
but to overcome any resistance or merely to apply pressure upon an
object. In almost every household we may find examples of the three
orders of levers. A pair of shears, for instance, is composed of two
levers of the first order, swinging on a common fulcrum. The effort is
applied at the handles, and the weight or load is the material that is
cut by the blades or, speaking more technically, the handles are the
_effort arms_ and the blades are the _weight arms_. A material that
is too tough to be cut at the tip ends of the blades may be easily
cut if we move it in near the fulcrum or pin that hinges the blades
together; for by doing this we shorten the weight arms, because the
weight arm is measured not to the end of the blade, but to the point
where it is cutting into the material. To cut very tough material, such
as heavy tin or sheet steel, we use long-handled short-bladed shears.
The cutting pressure depends upon the ratio of the effort arm to the
weight arm. If the effort arms are twice as long as the weight arms,
the cutting pressure is twice as great as that applied at the handles.

A nutcracker consists of a pair of levers of the second order. The
fulcrum is at one end and the effort or pressure is applied at the
opposite end of the levers or handles, while the equivalent of the
weight (in this case the nut) is placed between the effort and the
fulcrum. Again the _effort arm_ is measured from the fulcrum or hinge
pin of the tool to the point where the hand pressure is applied, and
the weight arm is measured from the fulcrum to the nut. The effort
arm may be four or five times as long as the weight arm, so that the
pressure exerted on the nut is four or five times as great as that
exerted by the hand on the ends of the handles.


In the case of a pair of sugar tongs we have another tool something
like the nutcracker in construction, but here the weight, i.e., the
lump of sugar, is seized by the ends of the tongs while the hand
pressure is applied somewhere between the fulcrum and the weight. Hence
we have here a lever or pair of levers of the third order. The _effort
arm_ of a pair of tongs is always shorter than the _weight arm_ and
the pressure on the sugar lump is always less than that exerted on the
tongs by the hand. Evidently the most powerful tool of the three is the
nutcracker, because the effort arms extend over the full length of the
tool and are always longer than the weight arms.

A lever need not consist of a straight bar; the effort arm may form
an angle with the weight arm, forming what is known as an angular or
bell-crank lever (Figure 2). When a common claw hammer is used to pull
out a nail, the claws that slip under the head of the nail form the
weight arm and the hammer handle the effort arm. A horizontal pull on
the handle produces a vertical lift on the nail.

Sometimes two or more levers are interconnected, as in Figure 3, the
effort arm of one being linked to the weight arm of the other. This
serves to increase the lifting force at the weight and at the same time
keep the mechanism within compact limits. Such compounding can go on
indefinitely and is subject to all sorts of variations.

[Illustration: FIG. 3.--COMPOUND LEVERAGE]

One thing we must not forget, and it is a matter that is commonly
overlooked by perpetual motion cranks, namely, that while a pound of
pressure on the effort arm may be made to lift two, four, or a hundred
times as many pounds on the weight arm by varying the relative length
of these arms, it has to move two, four, or a hundred times as far as
the weight arm, so that the work done on one side of the fulcrum is
always exactly equal to that done on the other side.



If we take a number of levers radiating from a common fulcrum like the
spokes of a carriage wheel, we have a primitive gear wheel. Two such
groups of levers may be mounted on parallel shafts so that when one
is turned its spokes will successively engage the spokes of the other
group and make the latter turn (see Figure 4). Each spoke is first
an effort arm on one side of the wheel and then a weight arm as it
turns around to the other side of the wheel, and as the effort arms
and weight arms are of the same length there is no multiplication of
power. A pound on one side of the wheel cannot lift more than a pound
on the other. The driven wheel receives the same power as the driving
wheel except for such loss as may be due to friction at the bearings or
where the spokes contact. The only advantage of such a pair of gears
is that the direction of rotation of the driven wheel is the reverse
of that of the driving wheel. If the spokes of one wheel are longer
than those of the other, we have at once a variation in the rate of
rotation proportional to the relative diameters of the two wheels. In
Figure 5, for instance, the diameter of the driving wheel A is twice
the diameter of the driven gear B, and so, for each revolution of A, B
must make two revolutions, i.e., the driver must make two revolutions
for each revolution of the driven wheel. In other words, the speed of
revolution is doubled. However, if we make B the driver the speed of
the driven wheel A will be half of that of wheel B.


In primitive machines spoke gears were seldom mounted on parallel
shafts because of the difficulty of keeping the spokes in alignment.
Instead, one shaft was mounted at right angles to the other so that
one set of spokes would cross the other (Figure 6), thus producing
the equivalent of a bevel gear. This was of advantage in changing the
plane of rotation. A later development was the _barrel_ or _lantern
gear_, which permitted transfer of power without changing the plane of
rotation. A cylindrical bundle of rods constituted one of the wheels
(as shown in Figure 7). Instead of being crudely formed of spokes, the
other wheel sometimes consisted of a disk with pins radiating from
its rim. Such gears in far more refined form are still used in modern
clocks and watches. A still further development for transmitting motion
to a plane at right angles to that of the driving shaft is shown in
Figure 8. Here we have a _crown_ gear in which the pins instead of
radiating from the periphery of the disk project from the side face of
the gear.



Turning back to our first spoked wheels, it is very evident that we
may put a rim over the spokes or even fill in between the spokes and
convert the wheels into solid disks that are in frictional engagement
with each other without getting away from the fact that we are dealing
with levers. Each wheel, then, consists of a continuous revolving
lever. Friction gears are used quite commonly in machinery when it is
desirable to have the wheels slip if subjected to excessive strain.


By forming teeth on one gear to mesh between similar teeth on the
other, we convert the friction gears into a pair of spur gears (Figure
9). We need not go into the intricacies of the form of gear teeth.
They are designed to be in continuous rolling contact while they are
in mesh. The novice is apt to call all spur gears “cogwheels” and
gear-teeth “cogs.” Mechanics, however, recognize a difference between
cog wheels and spur wheels. In the former, the teeth, or cogs, are not
cast upon or cut out of the wheel body, but are separate pieces fitted
to the wheel. Such wheels are found in old water mills. They consist of
wooden wheels with iron or steel teeth mortised in the wooden rim of
the wheel. In general it is safer to speak of spur gears because there
are few cogwheels now in use.

[Illustration: FIG. 8.--CROWN AND LANTERN GEAR]

When a small gear engages a large one, the former is commonly known as
a _pinion_.

[Illustration: FIG. 9.--SPUR AND PINION GEAR]

[Illustration: FIG. 10.--BEVEL FRICTION GEARS]

If two friction wheels are to turn at right angles one to the other,
they must have conical bearing surfaces, as in Figure 10. The angle
between the shafts of the two gears and the relative size of the gears
may be changed as desired, provided each cone surface has its apex at
the intersection of the two shafts or axes. It is easy to understand
how such conical friction gears may be converted into toothed bevel
gears (Figure 11), by forming teeth on the conical surfaces, and it
will be evident that the teeth must taper toward the apex of the two
cones. Two bevel gears of equal diameter, and with shafts set at right
angles one to the other, are known as _miter_ gears.

[Illustration: FIG. 11.--TOOTHED BEVEL GEARS]

So far we have not shown any combination of gearing that will multiply
power. In Figure 5, the driver A is twice the diameter of the driven
wheel B, and the latter makes two revolutions for one of A, but the
speed at the periphery of the two wheels is the same. A pull of one
pound at the point _a_ produces a pressure of one pound at _b_, and
this in turn produces a lift of one pound at _c_ because the levers
in each wheel are perfectly balanced, that is, each lever has equal
effort and weight arms. The way to obtain an increase of power and of
peripheral speed is to fasten two wheels of unequal diameters together
on the same center and apply the effort to one of the wheels (as in
Figure 12) and the weight to the other wheel. This gives us what is
technically known as a _wheel and axle_. The dotted lines show that
we have here a lever of the first order which can be used to multiply
power in the same way that a bar lever does. If one wheel is twice the
diameter of the other then a pound of effort will lift two pounds of



Figure 13 shows how the effort and weight can be shifted about in such
fashion as to give us a lever of the second and one of the third order.
The power may be enormously increased and the speed of the final wheel
greatly reduced by setting up a train of gears in which the effort
is received by the larger one of each couple and is delivered by the
smaller one. In Figure 14 the smaller wheels are half the diameter of
the larger ones. A pound of pressure at A will amount to 2 at B, 4 at
C, 8 at D, 16 at E, and 32 at F. On the other hand, point A will have
to move through 32 inches to make the point F move an inch.


A primitive pump still used in Egypt]



[Illustration: FIG. 14.--A TRAIN OF SPUR GEARS]

[Illustration: FIG. 15.--PULLEYS OF THE 1ST, 2D, AND 3D ORDERS]


A pulley is merely a modification of the wheel. Figure 15 shows how it
may be arranged to correspond to the three orders of simple levers.
If the pulley axis is fixed, as in the first order, the effort and
weight arms are equal and hence balanced. In the second order the
wheel is bodily movable, hence one pound will raise two pounds of
weight because the power arm is twice as long as the weight arm, while
in the third order it takes two pounds of lift to raise one pound of
weight. There is no end of possible combinations of pulleys which will
multiply power in the same way that bar levers do when compounded. A
common arrangement of block and tackle is given in Figure 16. There is
a four-sheave pulley block above and a three-sheave block below, but
in order to trace the rope clearly the pulley wheels or sheaves are
represented as of different diameters. The arrangement consists of a
series of levers of the first order in the upper pulley block coupled
to a series of levers of the second order in the lower block. To find
the weight that a given power will lift, multiply the effort by the
number of strands of rope that are supporting the weight. In this case
there are seven such strands, not counting the strand E, to which the
effort or pull is applied. This means that a pull of a hundred pounds
at E will lift 700 pounds at W. Of course a pull of seven feet at E
will raise the weight only one foot.



The inclined plane constitutes a second broad classification of machine
elements. The wedge, the screw, the cam, and the eccentric, all belong
to the family of the inclined plane.


A simple form of inclined plane is pictured in Figure 17, which shows
a weight W being rolled up an incline. The effort required to carry it
to the top of the incline depends, of course, upon the steepness of the
incline. The drawing shows a rise of 3 feet on a slope 5 feet long, and
the weight of the wheel is, say 20 pounds. To find the effort required,
the weight is multiplied by the rise (20 × 3 = 60) and divided by
the length of the slope (60/5 = 12) and we find that it takes only
12 pounds to roll the 20-pound wheel to the top of the incline. This
holds true when the pull is parallel to the inclined face. If the
pull is parallel to the base of the incline, as in Figure 18, we must
divide by the length of the base instead of the length of the incline
(60/4 = 15) and we find that it takes 15 pounds of effort to pull the
weight up the incline. If the pull is exerted at an angle both to the
base and the inclined face, we have a problem that is slightly more
complicated and we need not go into it here because it involves a bit
of trigonometry. In all cases, however, it may be noted that the amount
of rope that is taken in, in hauling the weight up the incline, bears a
definite relation to the amount of effort required to raise the weight.
In Figure 17, 5 feet of rope must be pulled in, in order to raise the
weight 3 feet, so that ⅗ of 20 or 12 pounds is all that is required
to pull up the weight, while in Figure 18, 4 feet of rope is hauled
in for a lift of 3 feet, so that ¾ of 20 or 15 pounds is required to
pull up the weight. In this respect the inclined plane is exactly like
the lever or the pulley, for the _effort_ multiplied by the _distance_
through which it is exerted is always exactly equal to the _weight_
multiplied by the _distance_ through which it moves. Thus in Figure
17, the effort 12 pounds multiplied by the distance 5 = the weight 20
pounds times the distance 3, and in Figure 18, effort 15 x distance 4
= weight 20 x distance 3. Of course, we are ignoring the weight of the
rope and the friction which, in actual practice, are important factors
to be reckoned with.

[Illustration: FIG. 19.--ENDLESS SCREW OR WORM GEAR]

So far we have considered a fixed inclined plane, but when the inclined
plane is moved between the weight and a fixed base it is known as a
wedge, and in this case, too, the effort required to move the wedge
multiplied by the distance the wedge moves is equal to the weight
multiplied by the distance it is lifted.

The commonest form of inclined plane is the screw which is merely an
inclined plane bent around a cylinder. A screw engaging a toothed
wheel, as in Figure 19, gives a combination known as an “endless
screw,” or, more commonly, as a worm gear. The screw or worm is always
the driver, and as it must make a complete turn to move the gear
through a space of one tooth, the power of this combination is very
great. It is practically impossible to turn the worm by using the gear
wheel as a driver because the friction developed at the point where
the worm and gear contact is very great. For this reason worm gearing
is used in the steering gear of automobiles. The shaft of the steering
wheel is fitted with a worm which meshes with a worm gear on the parts
connected with the wheels. It is very easy to turn the wheels by
operating the steering wheel, but if the wheels strike a rut or a stone
they are not deflected from their course, because the worm makes it
impossible for them to turn the steering wheel.

[Illustration: FIG. 20.--HELICAL OR SPIRAL GEARS]

The spiral gear shown in Figure 20 is a cross between a worm gear and
spur gear. The teeth are spirals set at an angle of 45 degrees to the
axis of the wheel. In this case either gear can be used to drive the
other, and the advantage of such a pair is that power is transmitted
from one shaft to another in a different plane and at right angles to
the first.

[Illustration: FIG. 21.--DRUM CAM]

[Illustration: FIG. 22.--PROFILE OR DISK CAM]

Cams are usually irregular revolving inclined planes. Figure 21, shows
a cylinder or drum cam. A groove is cut in the cylindrical wall of the
cam and an arm or lever is provided with a roller which rolls in the
groove. When the cam is revolved the lever is constrained to follow all
the twists and turns of the groove. A different form of cam is shown in
Figure 22. It is formed with an irregular periphery against which the
roller is pressed by a spring. As the cam wheel revolves, the roller
and the arm to which it is attached must move in and out over all the
hills and valleys of the periphery. The cam is one of the most useful
elements in modern machinery, for it provides a very simple means of
producing the most complicated and irregular motions.


We cannot attempt to describe all the different types of cams, but
reference should be made to the eccentric, which is a form of cam
commonly used to operate the valves of a steam engine. The cam in this
case is a perfectly circular disk, but the shaft that turns it does not
lie at the center of the disk, consequently an object bearing against
the periphery must move toward and away from the center as the disk
revolves. Instead of using a spring-pressed roller to bear against one
side of the disk, the whole disk is encircled with a ring of steel
known as an eccentric strap. This strap is bolted to a valve rod and
as the eccentric revolves the strap makes the valve rod move back and
forth. (See Figure 23.)

A description of all the various combinations of gearing, link motions,
ratchets, escapements, clutches, and miscellaneous movements would
easily fill the rest of this book, and we must therefore content
ourselves with this very brief survey of a few of the more important
elements employed in the construction of modern machinery.



WHILE we may glory in the wonderful mechanical progress of to-day, we
must not overlook the marvelous skill of the ancient artisan nor forget
that it is to his inventive genius that we are indebted for practically
every hand tool we possess. Only a few special tools owe their origin
to the modern inventor. All the rest date back beyond the twilight of
history. We have merely improved upon these tools by slight changes of
design or the employment of better materials in their construction.

As users of these tools we cannot begin to compare with the skilled
workman of ancient days. Our progress is shown not in the _development_
of skill, but in the _loss_ of it. We have taken the tool out of the
human hand and put it into an inanimate machine. It is only very
recently that the tool was delivered to the machine and that act marked
the dawn of the present remarkable mechanical era.

Machines for making machines date back to the time of the early
Egyptians. They had their pole lathes and bow drills, but these
machines only partially relieved the workman of his labors, and the
quality of the work still depended upon a degree of skill that was
acquired only through years of patient apprenticeship.

The pole lathe, by the way, consisted merely of a pair of centers
between which the work was mounted, a pole attached to the ceiling
and a strap or rope passed around the work and fastened at one end to
a pole and at the other to a pedal resting against the floor. (See
Figure 24.) When the pedal was depressed, the strap was pulled down
and the work was revolved. On releasing the pedal, the spring of
the pole pulled the strap up and reversed the rotation of the work.
Thus by alternately depressing and releasing the pedal, the work was
intermittently revolved against a chisel which was rested on a block
and guided by the workman. Small work could be turned out on such a
lathe with considerable precision, but when it came to large parts,
particularly parts of steel, the workman was easily tired by the effort
of operating the pedal and was apt to be irregular in the guiding of
the tool.

[Illustration: FIG. 24.--PRIMITIVE POLE LATHE]

Up to the middle of the eighteenth century practically no advance had
been made over the ancient lathe of the Egyptians, and when, 150 years
ago, the steam engine was invented the task of building the engine
seemed almost insuperable.

James Watt was a maker of mathematical instruments, a man of great
skill and precision as a craftsman, but he dealt with parts of small
dimensions. When he conceived of his steam engine, he mentally pictured
the various parts as turned out with all the accuracy and finish that
was possible in the diminutive members of a scientific instrument. To
him it seemed perfectly feasible to turn a cylinder which would be
practically perfect in contour, and to fit it with a piston around
which no steam could leak. With the lathe then in existence such a fit
was easily possible on small work. But when he undertook to have the
cylinder of his engine bored, he discovered that there was no machine
that could begin to do the work properly. In fact, when Smeaton, who
was a prominent engineer of that time, investigated Watt’s steam
engine, he declared that it was such a complicated piece of work that
neither tools nor workmen existed that could build it. In Watt’s first
engine, the cylinder was only six inches in diameter and two feet long,
and a special type of boring machine was devised to bore the forged
cylinders. But the boring was so irregular that when the piston was
inserted and the steam was turned on, nothing would stop the flow of
steam that leaked around the piston. In vain did James Watt use cork,
oiled rags, tow, paper, and even old hats to stop the leakage. However,
the boring machine was improved and later a cylinder, eighteen inches
in diameter, was bored with such accuracy that the large diameter
exceeded the small diameter in the worst place by only ⅜ of an inch.
This Watt considered a very good bit of turning. To-day cylinders of
that size that vary from true by half the thickness of the paper that
this is printed on would be thrown out as defective.

It was in 1769 that Watt invented the steam engine, but that great
event did not mark the dawn of the present era of machinery. For a
quarter of a century thereafter there was little progress in the
development of machine tools. A boring machine was built that did
fair work. There were a few sawmills in which wind power was employed
to drive the saw. But lathes were still driven by foot power and the
cutting tool was still held and guided by hand.


The real father of the present era was a very clever British mechanical
engineer, Henry Maudsley, who undertook to eliminate the uncertainties
of the human hand by clamping the cutting tool of the lathe in a rest
and arranging the rest to slide along the length of the lathe or
transversely toward or away from the center. These two motions made it
possible to accomplish all that the workman could accomplish by hand
and at the same time the tool was held so firmly that accuracy and
precision of turning was assured. Furthermore, he provided this slide
rest with a nut that engaged a screw driven through suitable gearing
by the lathe spindle. Then, as the work revolved, the slide rest
was compelled to move along the bed of the lathe at a uniform rate.
By varying the gearing, the speed of the slide rest and the tool it
carried could be varied at will, thus making it possible to cut screw
threads of any pitch desired with a degree of accuracy unattainable by

Remarkable as was this improvement, it met with the usual opposition
that every real advance in machinery received in those days. People
referred to the slide rest as Maudsley’s “go-cart,” but it proved such
an important element of the lathe and so very valuable that before
long it was universally adopted. From that time on the skill of the
workman began to lose its importance. The man began to give way to the
machine. Precision was possible in large as well as small work. The
human element was also dispensed with in the driving of the lathe. The
foot pedal was superseded by the steam engine, and the machine came to
be known as the engine lathe.

There are many ways of working metals now in common use. Metals may be
cast in a molten state, or they may be pressed and molded into shape in
a cold state, or they may be hammered either cold or hot, but in nearly
all cases in which metal is removed in order to form a piece of work,
the chisel is used as a cutting instrument. This is perfectly apparent
in lathes and planers, but not quite so apparent in sawing, drilling,
filing, and grinding. A drill is merely a spiral chisel which revolves
upon its own center. A saw is a gang of tiny chisels, and a file
consists of still smaller chisels which are broader than those of the
saw. In grinding we have rough surfaces in which particles of emery or
carborundum act as tiny chisels. The shears, the punch, and the cutting
torch are practically the only exceptions to the rule that metals
are always cut by chisels, and even the shears may be conceived as
consisting of a pair of broad coacting chisels, while it takes little
imagination to see a form of chisel in the punch. The cutting torch is,
of course, in no sense a chisel.

In the cutting of metals the work may move against a fixed tool or the
tool may move against a fixed piece of work. In a lathe, it is the work
that revolves or rotates against the tool. In the drill and the milling
machine the tool revolves against the work.

In the planer, the tool is fixed and the work slides against it. The
shaper reverses the operation; the work is fixed and the tool moves in
a rectilinear direction.

Up to the nineteenth century practically the only machines for
cutting metals were the lathe and a crude form of boring machine.
The machinists of that day had not reached the stage where they were
able to produce anything but round work on a machine. The planer had
not been born. It was for this reason that Watt had a great deal of
difficulty in getting rectilinear motion for the piston of his engine.
He had to invent a complicated system of links and levers in order to
obtain a practically parallel motion to guide his piston in and out
of the cylinder. When the planer was invented and it was possible to
produce straight surfaces with a considerable degree of accuracy, all
of Watt’s ingenious parallel motions, went into the discard and the
cross-head and guides took their place.

It was not until long after the planer had been invented that Eli
Whitney, the American genius of cotton-gin fame, conceived the milling
machine. He reversed the operation of the lathe by placing the cutting
tool on the revolving spindle and sliding the work against it. Milling
cutters consist of wheels formed with a number of cutting edges or
chisels which are arranged either on the periphery of the wheel or on
the face of the wheel.

Following the milling machine, came the grinder, in which a revolving
wheel of an abrasive material served to wear away the surface of a
piece of work, and with this form of machine steels of great hardness
could be finished with accuracy and a high polish.


The most notable advance in machine work came early in the nineteenth
century, when what was known as the “American System” of manufacture,
or the interchangeable system, was introduced. As long as mechanics
were obliged to perform their operations largely by hand, it was
impossible to attain great accuracy. Each workman put his own
individuality into the work. As a consequence, no two pieces were of
exactly the same size or shape. This was true even with the early
power-driven machine tools. The parts might be very close to the same
size, but careful measurements showed that they varied by a minute
fraction of an inch. Hence, when a machine was assembled the unyielding
metal parts had to be filed and trimmed and hammered to fit them
together. If any accident occurred to a machine, the damaged part
could not be replaced by another taken from stock. The entire machine
had to go back to the shop where an experienced mechanic would make a
new part to replace the damaged one. In those days a machine was not
manufactured but was built as an individual mechanism, just as a house
or a boat is built to-day.

With the advent of accurate machine tools came the idea of
standardizing the parts so that hundreds and thousands of pieces could
be made of exactly the same dimensions, and in assembling a machine
the parts could be picked at random from the stock and put together
without the use of special tools and without requiring any special
fitting. This was of special importance in the tools of warfare,
because armies need quantity production, i. e., rifles, cannon, etc.
More machines of the same kind were required for an army than for any
other organization or line of work. At the close of the Napoleonic
War the British Government had 200,000 parts of muskets either partly
finished or waiting repairs. Their muskets were made after the old
system. Each one was built separately with its parts individually
fitted together, so that whenever any part was injured, the musket had
to be laid aside and sent back to the workshop for repairs.

Long before that time, the idea of making standard guns had been hit
upon in France. Thomas Jefferson, while Minister to France, in 1785,
wrote of the French system which was then being developed by a mechanic
named Le Blanc. He was building a musket in which the parts were
of standard pattern, and which could be assembled by taking pieces
haphazard as they came to hand and putting them together without
special fitting. Thomas Jefferson called the attention of the American
Government to this system and showed that it was possible to produce
muskets cheaper by that method of manufacture. However, our Government
at that time failed to avail itself of the opportunity of utilizing
this system of manufacture.

Later on, the idea was taken up in this country by Eli Whitney and by
Simeon North. When Whitney attempted to introduce the system, he was
laughed at by French and English ordnance officials, and even our own
Government officials were skeptical, particularly when they found that
it required so much preparation in the way of machinery and designing
of parts before a single musket was completed. It seemed like a waste
of money to invest in so much preparation. But Whitney was soon able
to silence all his critics by taking to Washington ten pieces of each
part of a musket and then selecting at hazard from each pile of pieces
the requisite parts and putting together ten muskets. It was not long
before the foreign governments saw the importance of this method of
manufacture. Great Britain later adopted it in the making of her own
rifles and called the process the “American System.”

But it was not only in the field of rifles that interchangeable
manufacture made itself felt. The New England clock industry provides
an interesting illustration. At first the clocks were made of wood,
but early in the nineteenth century, a clock maker, Chauncey Jerome
by name, designed a brass clock in which the parts were made on the
interchangeable system. Instead of building each clock as a separate
piece of work, clocks were turned out by the thousands, and at an
extremely low price. Soon he had flooded this country with his clocks
and began to look around for other markets. Machinery had been used by
other clock makers in producing wooden clocks, and movements which had
cost $50 each in 1840 had been reduced to $5. But Chauncey Jerome’s
clock was made of brass and by means of the interchangeable system of
manufacture he could produce it for less than 50 cents. The clock was
such a success in this country that Jerome decided to try it abroad.
Consequently he made arrangements with an agent in England and shipped
over a large consignment. The British Government was astonished at the
low price of the clock and was convinced that it had been undervalued.
At that time, they had a simple and ingenious method of punishing a
consigner who undervalued the goods he wished to introduce into the
country. This consisted in promptly appropriating the property at the
price given in the invoice. In due course of time, much to Jerome’s
astonishment, he received a letter from the British Government stating
that his clocks had been confiscated, and with the letter came a check
paying for them at the invoice price. Jerome was not in the least
dejected by the rebuke; on the contrary, he was rather elated, for, as
far as he could figure it out, he had a spot-cash buyer for his goods
and no selling expenses. He did not mind at all letting the British
Government have the clocks at the invoice price. So he decided to try
again with a larger shipment. To his great delight this shipment met
the same fate as the first, and in due course another good British
check arrived. Thus encouraged, Jerome sent over a third and still
larger shipment, but by that time Johnny Bull began to suspect that the
Yankee clock maker was getting the best of the bargain and, finally
convinced that clocks really could be produced with profit at the
low invoice price, he permitted them to enter his country. With this
striking example, the fame of the Yankee system of manufacture spread
over the world.

In order to have two parts alike, they must be placed under a machine
in exactly the same way. In other words, they must be set in “jigs” or
frames which are fitted into the machine in such a way that the tools
will approach the work from exactly the same angle or penetrate the
work to exactly the same depth in ten, or a hundred, or a thousand,
or a million pieces, as the case may be. Making jigs and dies consumes
a great deal of time in preparation work, but once the preparation
stage has been passed, articles are produced with wonderful rapidity
and very little waste of time. Formerly it was necessary to determine
the location of each hole in a casting separately and spend precious
time in adjusting the work to the proper position under the tool. If
the hole was to be threaded, it had to pass through several separate


After the slide rest invented by Maudsley, the next great improvement
on the lathe was a turret head or a sort of turntable which carried
a number of tools. The tools are arranged to come automatically into
play one after the other. One tool, for instance, may cut a groove in
the work, another finish the face of the work, another bore a hole in
the piece and another tap the hole. In many cases, several of these
operations are performed simultaneously. The head of the lathe is
provided with a hollow spindle so that the work is automatically fed to
the tools through this spindle, and as soon as one piece is finished,
it is automatically cut off and the jaws of the clutch which holds
the work, or stock as it is called, open automatically so that a new
length may slide forward and be operated upon by the tools. The machine
requires no attention once the tools have been set up to the proper
angle, except that it must be kept supplied with bars of stock as they
are consumed, and with a copious flow of lubricant on the tools. One
operator can therefore take charge of a number of automatic lathes.
All he does is to feed them; they do the rest.

The modern drill has also gone through a great many developments in
order to speed up the work that it performs. When a casting is to have
forty or fifty holes drilled and tapped in it, instead of following the
old method of drilling each hole separately, a lot of separate drilling
spindles are used, each fitted with a drill, and these are brought
simultaneously into play. As many as fifty or sixty holes may be
drilled at a single operation, and after the holes have been drilled,
the drilling spindles move to one side to make way for the taps, which
thread such of the holes as are to receive screws. By first setting the
spindles in the proper position and then using jigs to locate the work
properly under them, the assurance is had that every one of the scores
of holes drilled will be accurately spaced apart and the spacing in
every casting will be identical.

The multiple tool system is also used in milling machines in which a
number of milling cutters either of the face or the end type come into
play simultaneously upon a piece of work set in a suitable jig, and cut
the piece with absolute precision, so that all castings will have faces
accurately spaced apart and cut to exactly the same level.

It is by such methods as these that we are able to produce such large
quantities of machinery at remarkably low cost. One of the most
notable examples of such work was the development of the Liberty
engine during the World War. This engine did not differ in principle
from others built in Europe or in this country, but its design was
carefully adapted to permit of interchangeable manufacture. No careful
finish was used except where indispensable. Special jigs, tools, and
fixtures were prepared. Ingenious wrinkles of American manufacture were
introduced. All this consumed time, and great was the irritation of the
general public. Under ordinary conditions, it would have taken years to
have developed the Liberty engine to the manufacturing stage, but under
the urgent stress of war, the whole work of design and preparation
for manufacture was crowded into a few short months, and then Liberty
engines began to be manufactured on a stupendous scale.


One of the most remarkable advances in machine tools was due to the
studies of Fred W. Taylor. He entered a large steel plant in 1880
and was immediately struck with the enormous waste of effort on the
part of the men in the plant. There was at that time considerable
dissatisfaction among the workmen, and when Taylor endeavored to speed
up work he was faced by the incontrovertible argument that he had no
idea how much work a certain machine ought to turn out. There was
nothing for him to do but either back down or study machine tools and
discover their maximum capacity. This led him to investigate the matter
of cutting speeds. For years he spent all of his spare time studying
this subject, timing machines and experimenting with different types
of cutting tools. He estimated that in the twenty-six years of his
investigation he converted 800,000 pounds of steel into chips. What
he wished to discover was the best depth of cut, the best speed of
cutting, and the best speed at which the tool should be fed into the
work. He soon discovered that, contrary to prevailing opinion, the
round-nosed tool was better than the diamond-pointed tool, that the
coarse slow-cutting speed was better than a fine cut at high speed. He
discovered that the best method of lubricating the tools was to keep
them bathed in a heavy stream of water, supersaturated with carbonate
of soda, so as to prevent the metal from rusting. The best tool steel
of that day was known as a self-hardening steel. Manufacturers of the
cutting steels had warned Taylor that he must not use water on these
tools. Taylor, however, was not satisfied to take the word of others,
but proceeded to investigate the matter himself, and discovered that
he could safely increase the cutting speed of his tools 33 per cent by
the use of a heavy stream of water for lubricating purposes. This led
Taylor and his associate, Maunsel White, to investigate the different
kinds of tool steels, and eventually they evolved a chrome tungsten
tool which could do from two to four times the work of other tools.
Later vanadium was added to the alloy, further improving the tool.

At the Exposition in Paris, in 1900, foreign manufacturers were
astonished to find enormous lathes operating at high speed with the
cutting tools taking such heavy cuts and feeding so fast that the nose
of the tool was actually heated to a dull red heat, and yet it kept its
cutting edge perfectly. This was a revelation to tool makers abroad,
and it led immediately to the adoption of American high-speed cutting

The development of the automobile, which began to take on serious
proportions at about that time, is responsible above all other machines
for improvements in American machine tools, and for the extension of
the American system of interchangeable manufacture. When automobiles
came to be made on the interchangeable system and in enormous
quantities so that the cost was reduced to within the limits of the
average man’s pocketbook, they began to make mechanics of men who
before that had never used a tool; and this new and widespread interest
in machinery stimulated the production of better and more efficient
tools. Hence the progress of machine tools in the past few years has
been simply phenomenal.



YOU CAN measure civilization by its timepieces. The higher the
civilization of a community the more it appreciates the value of time
and the more minutely does it measure the passage of time. The savage
divides his day into but two periods: the period of light and that
of darkness; the early Romans divided their day into eight watches,
four watches of daylight and four of night, but the higher and more
complex civilization became, the smaller became the subdivisions of
time. People began to feel the need of carrying the time with them,
and about 1500 A. D. watches came into use, but it was not until 1665
that watches began to be equipped with minute hands, and it was almost
exactly a century later that they were equipped with a second hand.
To-day time means so much to us that we will fight our way into a
subway express, instead of riding more comfortably in a local train,
merely for the sake of saving five minutes. The tiny second hands of
our watches divide the day into eighty-six thousand four hundred parts,
and in some operations we measure time intervals down to the thousandth
part of a second. Only among the most highly civilized nations are
timepieces carried by the common people.

It used to be that time was made for slaves, but now time has made
slaves of us. Shift the hands of the clock and the whole nation is
forced to change its habits.

Time-measuring mechanism is given early prominence in this book because
clocks were among the earliest machines invented, and they furnish an
example of the wonderful ingenuity of inventors before the dawn of
the modern era of machinery. Naturally this chapter must be largely

The first thought of measuring time came from the ancient astronomers
and astrologers, who, in watching the motions of heavenly bodies, the
sun by day and the moon by day and night, found it necessary to keep a
record of these motions and sought about for some mechanical means of
doing so. The studies of the old astrologers were closely associated
with religion, and as a consequence the most advanced intellects were
centered upon astronomical matters and incidentally upon horology.
Fortunately the design and construction of mechanisms for measuring
time were not considered beneath the dignity of the scientists of those
early days. Mathematicians felt free to record their investigations in
this branch of mechanics, and as a consequence of the early cooperation
of science and mechanics in this field much real progress was made, and
the development of timepieces was more rapid than that of any other


The ancient Egyptians early felt the need of a better clock than the
sundial, because it operated only on cloudless days and was absolutely
worthless to tell off the hours of darkness. Realizing that time is a
measure of motion, they sought for some slowly moving body whose motion
could be used to measure time, and naturally they turned to water. The
earliest form of clock consisted merely of a leaking bucket. Either the
bucket was filled with water which was allowed to escape through a very
tiny orifice, or else the heavily loaded bucket was placed in water
and the water was allowed to leak into the bucket until it sank. The
period it took for a bucket to run dry or for a bucket to fill and sink
indicated a lapse of an hour or some other standard of time.

The idea of subdividing this period was a later development. As
the water leaked out of a bucket, the water level descended, but
unfortunately not at a uniform rate. The weight of water in a full
bucket made the drops come faster than when the bucket was nearly
empty. Consequently the time graduations on the side of the bucket had
to be set farther apart at the top of the bucket than at the bottom.
Various ingenious schemes were devised for maintaining a uniform
discharge. In one type of water clock or clepsydra a conical bucket was
used so that there would be a constant relation between the head of
water and the volume in the bucket and the time graduations could be
spaced uniformly.


The most remarkable clepsydræ were those invented by an old Alexandrian
mathematician, Ctesibius, who lived about 250 years before Christ.
Ctesibius introduced the siphon principle into his clocks, and also
employed gear wheels and even a cord and pulley. Furthermore, he was
the first man to employ jeweled bearings in a timepiece. The use of
jewels in timepieces was reinvented in 1704 A. D. However, Ctesibius
used his jewels in a very different way from that in which they are
used now, as will be described below.

ABOUT 250 B. C.]

Figure 25 illustrates the most interesting clock he built and it was
arranged to run year in and year out. The clock had a cylindrical face
mounted on a hollow pedestal in which the mechanism was concealed.
The column was divided off into twenty-four hours and a pointer that
rose vertically marked off the lapse of time. But here he was faced
with a serious complication. Hours in those days varied with the time
of the year. A day from sunrise to sunset consisted of twelve hours.
In summer, when the days were long, the hours were long, and in the
short days of winter the hours were correspondingly shortened. To be
sure, the variations in the length of the day are not so great in Egypt
as they are in our latitude, because it is nearer to the equator;
nevertheless there is a difference which the precise old mathematician
had to take into account. In order to provide for variations in the
hours, Ctesibius ran the lines spirally around the column and arranged
his cylindrical clockface to turn slightly each day, so that in the
winter months the clock hand or pointer moved over that part of the
face where the daylight hour lines were closer together and the hours
of night were farther apart, while in summer, the reverse would obtain.
At the bottom of the column were two little cherubs. The cherub on the
left was a sad little fellow who was constantly weeping. Tears trickled
from his eyes and dropped into a basin. The tears passed into the
hollow pedestal of the clock and gradually filled a cylinder formed in
the base of the clock. A piston in this cylinder supported the other
cherub. As the water gradually filled the cylinder this cherub was
slowly raised and a wand he held in his hand pointed off the hours on
the clockface. When the twenty-fourth hour was reached, a siphon came
into play, which suddenly emptied the cylinder, permitting the pointer
to drop. The siphon discharged its water into a small water wheel,
which, by means of the system of gears, turned the column slightly
to bring the hour lines in proper positions for measuring the time
intervals of the next day. The column made one complete turn in 365
days. The jeweled bearings, referred to above, were placed in the eyes
of the weeping boy, so that the holes that pierced them would not be
enlarged by the constant wear of the water and thereby increase the
rate of flow.


We have dwelt at considerable length upon this old clock of the
pre-Christian era to show the ingenuity of inventors of that day, and
also the careful study that was made of time by ancient mathematicians
and astronomers. Of course water clocks were used before the time of
Ctesibius. In fact, we read of them in the comedies of Aristophanes,
written 400 B. C. Water clocks were used to limit the long speeches
of orators at court, and in one place we find Demosthenes accusing
a man of “talking in my water,” while at another time, when he was
interrupted, he called to the officer to stop the water, showing that
he valued every moment of time allotted to him for his speech.

In 807 Charlemagne was presented with a clock by the King of Persia.
This consisted of an elaborate mechanism in which were all manner of
wheels, and the clock would actually strike the hours. The driving
power, however, was water.

But there were serious disadvantages in the use of water for the
measurement of time. No great accuracy was ever obtainable with it,
owing to the fact that its volume varied considerably with the
temperature, and also with the dryness or moisture in the surrounding
atmosphere. The idea of using a weight instead of water is claimed to
have originated as far back as 990 A. D. The next important advance in
the motive power of clocks was in 1500, when Peter Hele of Nuremberg
invented the mainspring.

That was long before the pendulum made its appearance. The clock
mechanism was slowed down and kept under control by what was known as
a balance lever. (See Figure 26.) This was a horizontal lever mounted
to oscillate in a horizontal plane. The lever was fitted with sliding
weights, so that it could be carefully adjusted. The last wheel of the
train of gears was provided with escapement teeth, somewhat similar to
those used on our clocks and watches, but which would alternately move
the lever this way and that. The inertia of the lever with the heavy
weights on it was sufficient to prevent the mechanism from racing, and
by this means, the motion was governed and slowed down, so that it
measured time with a fair degree of accuracy.



The pendulum had an interesting origin. Galileo, while a student in
Pisa in 1581, was attending a service in the cathedral one day when
his attention was drawn to the swinging of a large hanging lamp. One
of the attendants had drawn the lamp toward him, so that he could
reach it more readily to light it. When he let go the lamp began to
swing slowly back and forth, and the observant young student noticed
that although the oscillations gradually slowed down the period of
oscillation was constant. He had no watch with which to measure the
length of the period, but being a medical student he knew that he had a
fair timepiece in his own heartbeats, and so by counting his pulse he
proved that it took the lamp just as long to complete each oscillation
when it swept through a long arc as when it died down to but a few
inches. He made note of this peculiar action and began experimenting
with pendulums of different lengths. Then it occurred to him that if he
could time the pendulum with his pulse he could time his pulse with a
pendulum. So he devised a pendulum whose length could be adjusted until
its oscillation would coincide with the throb of a patient’s pulse, and
then the length of the pendulum would give him the rate of the pulse
beat. The invention was seized upon by the medical profession of that
day, and the _pulsilogia_, as it was called, became an indispensable
instrument for physicians.




The idea of using the pendulum to control the action of the clock also
occurred to Galileo, and in later years, after he had lost his sight,
he passed the idea down to his son, Vincent. However, it is generally
conceded that the credit for introducing the pendulum and doing
away with the balance lever belongs to Christian Huygens, the Dutch
mathematician, whose first pendulum clock dates back to 1659.

About the same time Dr. Robert Hooke invented the balance spring
which made it unnecessary to use the pendulum in portable timepieces.
Prior to that watches were fitted with balance levers and they gave
a great deal of trouble, because the time varied with the position
in which they were carried. But the balance wheel overcame all these
difficulties and made it possible for a person to carry an accurate
timepiece in his vest pocket, although the early watches were very
bulky mechanisms.


The importance of having accurate timepieces aboard ship was felt as
far back as the time of Columbus. When ships began to go out beyond the
sight of land, it was highly important that they be equipped with some
means of locating their position at sea. By noting the elevation of the
sun at noon with a sextant it was possible to determine the latitude of
the ship, but there was no means of determining its longitude, except
by dead reckoning, that is, using a log to measure the speed of a ship,
and estimating its position by calculating the number of miles it
had traveled since leaving port. If ships could be provided with an
accurate timepiece which would keep the same time as that of some fixed
observatory, it would be possible definitely to locate the position of
the ship east or west by noting how fast or slow the sun was at noon on
the particular day on which the observation was taken. This use of the
chronometer is common in these days, but up to 150 years ago there was
no timepiece sufficiently accurate to permit a navigator to tell with
any certainty just where he was.

It was John Harrison, the son of a Yorkshire carpenter, who was the
first to build a chronometer worthy of the name. A prize of 10,000
pounds was offered by the British Parliament for anyone who could
invent and sell a chronometer which would enable a ship to take a
voyage from England to any of the West Indian islands and back and keep
track of the longitude within one degree. If this could be defined
within two-thirds of a degree, the prize would be 15,000 pounds.
Harrison made a bid for this prize, and after years of effort and
patient labor, he succeeded in being granted a trial. His son, William,
was sent on a ship to Jamaica with the now celebrated chronometer,
which was mounted on a large cushion. The instrument was constantly
attended by the young man, its position being adjusted from time to
time to suit the “lie” of the ship. When the ship was eighteen days
out, the vessel was estimated by dead reckoning to be 13° 50′ west of
Portsmouth, but the chronometer indicated the position as 15° 19′.
The timepiece was immediately condemned as worthless, but William
Harrison had not lost faith in the instrument, and insisted that if
the ship continued on the same course, a certain island, if properly
marked on the chart, would be seen the following day. True to the
prediction, the next morning at seven o’clock the island appeared.
By means of his chronometer William Harrison was able to predict the
appearance of the other islands, and at the end of the voyage, which
occupied sixty-one days, the chronometer was only nine seconds slow.
When he returned to Portsmouth, after an absence of five months, the
error of the chronometer was only one minute and five seconds, giving
an error in distance of only eighteen miles, whereas thirty miles was
the margin of error allowed by the prize conditions. Such accuracy
seemed so incredible that the chronometer had to be tested on a second
voyage, during which it was kept under lock and key and when William
Harrison had to wind the instrument he was obliged to do so in the
presence of two witnesses, lest he move the hand of the chronometer
surreptitiously. At the end of the second voyage there was no further
doubt that Harrison was fully entitled to the prize. Chronometers soon
came to be used extensively, until now they are one of the most perfect
of machines made by man, and operate with an accuracy that is almost
incredible. Usually a ship is provided with several chronometers, so
that one may be used as a check upon another. They are mounted in ball
sockets and gimbal joints, so that they are not affected by the roll of
the ship, but always lie in a horizontal position.


While we may well marvel at the precision of the chronometer, it is
equally marvelous, if not more so, that we may equip ourselves for
a few dollars with a timepiece which is so wonderfully accurate as
to vary little more than a second per day. If one took the pains to
regulate his watch carefully, any of the better makes could be adjusted
to such accuracy.

There is nothing very mysterious about the mechanism of a watch. It
consists merely of a train of gears which slow down the motions of
the mainspring to a convenient speed; and these gears moreover keep
the proper relation between the hour and minute and second hands. But
when we reflect that a small watch possesses a tiny second hand which
travels something like ten miles in a year, and that if carefully
regulated it will not vary from that of another watch in the whole
journey by more than six or eight inches at the most, we certainly have
a reason to marvel. There are 86,400 seconds in a day, and a watch is
usually arranged to make five beats per second or 432,000 per day.
The interval between beats must be adjusted with such minuteness that
one beat must not differ from another by 1/86000 part of a second,
else the watch will register more than a second fast or slow at the
end of a day. And yet watches capable of such precision are being
turned out daily by the thousands. Of course, such perfection would be
absolutely impossible without the use of extremely accurate machine
tools. It would have been impossible as long as we had to depend upon a
watchmaker to make a watch by hand.


If we look at the works of a clock the most conspicuous feature is
the rapidly oscillating balance wheel which, by the way, is the most
important part of the watch, for it governs the release of the power
stored up in the spring.

It controls the escapement which brings the whole mechanism of the
clock to a standstill five times each second--in fact it is the
pacemaker of the watch, for it gives the watch a step-by-step movement
and fixes the rate at which the steps are taken.

[Illustration: FIG. 27.--ESCAPEMENT OF A WATCH]

The last wheel of the watch train is what is known as an escape wheel.
It is formed with teeth of an odd shape, such as shown at A in Figure
27. These teeth are engaged by a pair of pallets B and C, carried by
a three-armed lever D. The pallets are usually bits of sapphire or
similar hard stone to prevent wear. The third of the lever is slotted
at its extremity to engage a sapphire pin E, carried by a disk F,
which is mounted on the staff of the balance wheel. The escape wheel
A revolves in the direction of the arrow, being impelled by the
mainspring acting through the train of gears. One of the teeth of this
wheel engages the pallet B, causing the lever D to swing on its axis
and push the sapphire pin E toward the left, thereby giving the disk
F an impulse in the same direction. Here a delicate coil spring, known
as the hairspring, comes into play. Without the hairspring the parts
would stand still, the escape wheel being blocked by the pallet B. The
hairspring is attached at one end to the shaft or staff of the disk
F and the other to the frame of the watch. It tries to hold the disk
F in a fixed position, but is disturbed by the action of the escape
wheel and is constantly oscillating the disk in its effort to bring
it back to its normal position. When the disk swings over to the left
the pallet B is clear of the teeth of the escape wheel. This releases
the escape wheel and it springs forward in the direction of the arrow,
but before it can move through an interval of one tooth it is arrested
by the second pallet C, which has been projected into its path by
the swing of the lever D. The lever swings back until the pallet C
clears the escape wheel and the pallet B engages the next tooth. And
so the action continues, the lever swinging back and forth and at each
complete oscillation releasing one tooth of the escape wheel.

The hairspring takes up the shock of this intermittent motion and a
balance wheel carried by the staff to which F is fastened steadies
the oscillatory motion of the lever D. A watch is full of microscopic
parts. In a small timepiece there are machine-made screws so small
that without the aid of a magnifying glass one cannot see the screw
threads cut upon them. But the most marvelous part of the whole watch
is the delicate hairspring and the means of adjusting its tension
and compensating for its expansion and contraction with changes of


When working with minute intervals of time many factors must be
considered which are not even thought of in machines of grosser
proportions. It never occurs to the man in the street that not only the
animate world but the inanimate as well is in ceaseless and variable
motion. If our eyes were capable of taking in minute microscopic
details, we should see that everything is expanding or contracting,
swelling or shriveling, twisting and warping in response to the
atmospheric changes. Our steel bridges and skyscrapers are in constant
motion; solid concrete dams must be provided with expansion joints; the
Washington Monument goes through a diurnal gyration in response to the
sun’s rays. Of course all this motion is almost immeasurably small. A
bar of steel a mile long will expand ⅖ of an inch for every increase
of a degree Fahrenheit in temperature. The expansion of a hairspring,
which may be nine or ten inches long, is infinitesimally small and yet
this must be considered by the watchmaker. We must remember that the
escapement mechanism divides the day into 432,000 parts, each of which
contains some minute error, for absolute perfection is impossible,
and if we add up all these 432,000 errors they must not foot up to
more than a second per day. If the hairspring expands ever so slightly
its power is weakened, but this loss of power is compensated by an
ingenious form of balance wheel. The rim is in two parts, half of it
being attached to one spoke of the wheel and the other half to the
other, as shown in Figure 28. Each half rim is formed of two strips
of metal, an inner strip of steel, and an outer strip of brass fused
together. Brass expands and contracts almost twice as much as steel,
and hence when there is a rise of temperature the rim sections tend
to curl in, bringing their center of gravity nearer the center of the
wheel and making less of a load for the weakened hairspring to move,
while on the other hand, when the spring is contracted by cold, the
rims spread out slightly, giving it a greater load to oscillate. The
weight of the balance wheel is thus automatically adjusted against
variations in power of the spring.


Aside from this automatic variable adjustment, the balance wheel must
have a primary permanent adjustment. The rim of the wheel is loaded
by means of small screws. Screws placed near the free ends of the
rim sections will have a greater inward or outward play as the rim
contracts and expands, and by their locations in different positions
on the rims the balance wheel may be adjusted with great accuracy to
compensate for temperature variation in the hairspring.


[Illustration: FIG. 29.--PENDULUM ESCAPEMENT]

In the case of clocks such delicacy of adjustment is hardly necessary.
Pendulum clocks, if they are to run accurately, must have their
pendulums automatically adjustable for variations in temperature,
because the longer the pendulum the more slowly it oscillates. Many
years ago a grid type of pendulum was invented in which various alloys
were used, which reacted one against the other and preserved the center
of gravity always at the same distance from the center of oscillation.
The action of a pendulum movement is similar to that of a balance-wheel
movement described above. The pendulum operates a pallet lever similar
to that shown in Figure 29. The teeth of an escape wheel, which are
commonly somewhat different from those of the watch movement, strike
the pallets of the pallet lever, and the escape wheel is intermittently
stopped and permitted to proceed. The pressure of the escapement teeth
against the pallets is just enough to keep the pendulum swinging and
the speed of the clock is regulated by lengthening or shortening the

We have added little to clock or watch movements in recent years. About
the only conspicuous modern invention is the torsion pendulum. The
pendulum in this case is a heavy horizontal disk suspended by a wire,
and the disk rotates first in one direction and then in the other,
twisting and untwisting the wire. The advantage of this pendulum is
that the oscillations are very slow, and hence it is possible to keep
the clock going for a year at a single winding.

The electric regulation of clocks is another important improvement. A
clock need not be a very perfect timepiece, but if provided with an
electric regulator its hands are brought up to the correct time every
hour in response to an impulse sent from an accurate master clock which
in turn has its time corrected daily from the National Observatory in



FLOWING water exerts a strange fascination upon mankind, even to the
present day. Tourists travel hundreds of miles to view the glorious
spectacle of a riotous tumbling cataract. Is it strange, then, that in
the olden times, when the world was peopled with gods and genii and
strange spirits, the ancients looked upon ceaselessly flowing rivers as
the symbol of life? It was most natural for them to covet the endless
power of a river and eventually, despite their superstitions, to try to
utilize some of its energy.

It may be that sailboats antedate the first water wheel, but it seems
much more probable that flowing water was the first inanimate power
harnessed by man. Windmills were certainly a later development. They
possessed the advantage that they could be located anywhere while the
water mill had of necessity to be built along the bank of a stream.
However, the power of the wind is so unreliable and fluctuates so
widely that it was little used, except in flat countries, where there
was little if any available water power.

Water power predominated until the steam engine was introduced, when
it had to give way to an even more reliable power and one which could
be located at any place to which fuel could be transported. Now,
however, we are going back to our first power, seeking it out in the
most inaccessible mountainous regions, because we have discovered the
means of taking the power it yields and transmitting it hundreds of
miles, over hills and plains to the point where we can put it to useful
service. Hydroelectric power has very aptly been termed “white coal.”

The first prime motor was the current wheel, that is, a wheel fitted
with paddles, which was journaled over a stream with the paddles
projecting into the water. This was a very inefficient machine; it
converted very little of the energy of a stream into useful mechanical
power. The idea of damming the stream and letting the waters flow
over the dam through a raceway upon a water wheel was a much later


Three types of water wheel which were in universal use before the
advent of the steam engine were the undershot wheel, the overshot
wheel, and the breast wheel (Figure 30). In the undershot wheel the
water stored back of a dam is let out near the bottom of the dam and
strikes the under side of the wheel, so that the top of the wheel turns
toward the dam. In the overshot wheel, the water flows over the wheel
striking the paddles or buckets on top and on the forward side, so that
the wheel turns forward. In the breast wheel, the water strikes the
paddles half way up the wheel on the rear side and drives the wheel in
the same direction as that of the undershot wheel.

When we speak of water power we are apt to think of the water as
actually furnishing the energy. As a matter of fact, it is not water
but gravity that drives the wheel, the water being merely the medium
that gravity acts upon. By having the water drop from a great height,
its velocity is greatly increased and the power it imparts to the wheel
is much higher. In mountainous regions it is easy to obtain a high head
of water and thus generate a great deal of power from a relatively
small stream. However, the ancient type of wheel with its paddles or
buckets has now practically passed out of existence, being superseded
by the Pelton wheel for high heads and the turbine for low heads of




In California, a number of years ago, they made use of what was known
as the hurdy-gurdy wheel. This consisted of an ordinary wheel with
bucket-shaped paddles against which was directed a stream of water
at high velocity through a nozzle. There was a carpenter, named L.
A. Pelton, who used to make a business of building and repairing
such wheels and the flumes that carried the water to them. Although
uneducated, he was possessed of considerable native ingenuity and was a
very observant man. One day, when he was called in to repair a wheel,
he noticed that one of the buckets which had been misplaced received
the water from the nozzle without any splashing. The water struck the
edge of the bucket with practically no shock, whereas the other buckets
produced a great deal of splashing. Pelton had enough knowledge of
the principles of mechanics to realize that a splash means a waste of
energy, and that here was a bucket which, although out of plumb and
apparently defective, was really more efficient than any of the others
in the wheel. It occurred to him then that instead of having the jet of
water strike the middle of the buckets it ought to strike the edge, so
that all its power would be absorbed without any wasteful splashing. He
might have displaced the jet laterally so as to accomplish this result,
but he realized that that would have produced a considerable side
thrust on the wheel, which, of course, would have been objectionable,
and so he hit upon the plan of using double buckets and letting the
stream of water strike the pair of buckets along their dividing line.
(See Figure 31.) This would split the stream in two and let each half
strike the slanting face of the bucket, and follow the surface around
in the same way that it did on the single misplaced bucket, but the
reaction or side thrust on one bucket would be counteracted by that
on the other. This idea proved successful and out of it has grown
the Pelton wheel which is now universally used in all power plants
employing high heads of water.


A notable illustration of such a plant is the great installation at
Big Creek, Cal. Big Creek, despite its name, used to be a small stream
flowing down the mountains into a canyon. One would hardly suppose that
it was capable of yielding much power, but it had its source high up in
the Sierras and was fed mainly by melting snows. In the springtime, it
swelled to a good-sized torrent. By building three dams near the top of
the mountain, a lake was formed in which the water of the melting snow
was impounded, so that a steady stream of water could be supplied the
year round for power purposes. But even so, the stream hardly amounts
to very much if we consider only the quantity of water that passes
through it. The particular advantage of this installation is the fact
that in a distance of six miles from the dam the creek falls 4,000 feet.

An inhabitant of the Eastern States who is unused to mountain
heights may gain some conception of the meaning of this elevation by
gazing up to the pinnacle of the Woolworth Tower, which rises 795
feet above street level, then mentally multiplying its altitude by
five. Evidently even a small stream of water dropping from such an
elevation would develop an enormous amount of power. In fact, it was
considered inexpedient to use the entire fall at a single drop and so
it was divided into two stages. The water is carried through a tunnel
three-quarters of a mile long and then through a flow pipe along the
face of the mountain to a point where it may drop 2,000 feet to the
first power plant. After passing through this plant the water is
discharged into the creek and is then diverted into a second tunnel
four miles long and a series of steel conduits to a point from which it
may drop 2,000 feet more to the second power plant. In each power house
there are two electric generators, each fitted with a pair of Pelton
wheels. These wheels are a little less than eight feet in diameter and
each one develops 23,000 horsepower.

The water is directed into the buckets of the Pelton wheel in a stream
six inches in diameter, and it issues from the nozzle with a velocity
of 300 feet per second or about 210 miles per hour. A jet of water is
almost like a solid bar of wood. In fact, it is impossible to chop
through it with an ax. The water would swing the ax out of one’s hand
before it got part way through the jet. Traveling at such a high speed
the friction is so great that it would tear the skin off one’s hands,
if it did not actually tear the hand off the arm, and yet it strikes
the buckets of the wheels with no shock at all, for the first part of
the bucket it touches is nearly parallel to the jet, and as the water
sweeps around the curved face of the bucket it loses practically all of
its pressure and velocity and falls into the tail race. The electric
power generated by the two plants is stepped up to 150,000 volts and
sent out over transmission lines to points of service. The street cars
of Los Angeles are connected by a 240-mile electric harness to the
hydraulic horses of Big Creek.

Powerful as this stream is, a still higher head is used in Switzerland,
at Lake Fully, where there is a drop of over a mile in a distance of
2.8 miles. The water is carried by a short tunnel through the mountain,
and then makes a drop of over 5,000 feet to the power plant, where it
strikes the Pelton wheels at a velocity of 400 miles per hour, or about
seven times the speed of a fast express train.


In contrast to such high heads, we have the low-head power plants
which are employed where a large volume of water is available. The
most notable installation of this type, and the largest in the world,
is that at Keokuk, Iowa, where a dam has been thrown across the
Mississippi River. For many years it was thought impossible to make
any use of the vast volume of water that flows through this great
river. But above Keokuk there used to be a rapid extending back about
twelve miles. By building a dam across the river just below the rapid
it was possible to obtain a working head of about thirty-two feet, and
with the enormous volume of water available this provided sufficient
energy to make the development worth while. In marked contrast to
the installation at Big Creek, it is volume rather than velocity
that is employed, and hence turbines rather than Pelton wheels are
used. More water goes through a single turbine than is used in the
whole of the city of New York with all its elaborate aqueduct system.
Enormous turbines are used, fifteen feet in diameter, and when the
installation is complete there will be thirty units, each yielding
10,000 horsepower, or a total of 300,000 horsepower. A turbine, it may
be explained, differs from the ordinary water wheel in the fact that
the water runs through the wheel instead of around it (Figure 32). The
water may enter at the center and then flow out at the periphery, or
it may enter at the periphery and then be discharged from the center
of the wheel, or it may run axially through the wheel. In a Pelton
wheel there is a single jet which strikes but one pair of buckets at a
time, but in a turbine there are many jets distributed all around the
circumference of the wheel. The water is divided into a series of jets
by being forced through a stationary set of curved vanes. The blades of
the rotor or revolving part of the turbine are oppositely curved. If
the rotor were immovable the jets would have to change their direction
in passing through the rotor, but as the rotor is free to turn, the
jets react against these blades and set the wheel to revolving. The
turbine may be designed to run either on a horizontal axis or on a
vertical one.


The turbines used at the Keokuk plant are of the inflow type. The rotor
is mounted on a vertical shaft in a scroll-shaped concrete chamber,
something like a snail shell. Water pouring into this chamber is thus
given a swirling motion in the direction of rotation of the wheel. As
it flows into the wheel it passes first through a ring of fixed vanes,
which divide it into the jets.

The highest velocity of a wheel is naturally at the periphery and the
advantage of an inflowing turbine such as this is that the water is
traveling at its highest velocity when it strikes the periphery of the
rotor. As it loses its velocity it flows in toward the slower-moving
portions of the rotor. Finally it reaches the center, after giving up
practically all its energy, and falls into the tail pool through a
draft tube at the center of the rotor.

The scroll chambers at Keokuk are thirty-nine feet in diameter and the
draft tubes are eighteen feet in diameter. Water enters the scroll
chambers with a velocity of fourteen feet per second and comes out of
the draft tubes into the tail pool with its velocity cut down to but
four feet per second. Compare this with the velocity of the water jets
at Big Creek!

The current generated at Keokuk goes to St. Louis and surrounding towns
and serves a population of 1,120,000.

Now that we have learned how to transmit electrical power without
serious loss over enormous distances, it is only a question of time
before all the water power in the world is harnessed and put to the
service of man. The power costs nothing after once the plant has been
built; the only expense is that of maintaining the machinery and
keeping it in repair. It is estimated that there is some 200,000,000
horsepower available in this country, but this includes all flowing
water, much of which it would be impracticable, if not almost
impossible, to utilize. However, there is about 60,000,000 horsepower
commercially available, according to the figures of the U. S.
Geological Survey, of which we have developed so far only 6,000,000

The ancients used flowing streams not so much for power purposes as
to lift water to a higher level so that it would flow into their
irrigating ditches. Nowadays, electricity, steam, or air is used for
elevating water, but we have a very ingenious machine which makes
the stream lift a part of itself. This machine is very different in
principle from the old Egyptian noria. It depends upon the kinetic
energy of water in motion. You cannot push a nail into a piece of wood
with a hammer but you can easily drive it in by striking it with the
hammer. As the hammer is swung it acquires what we term kinetic energy
or energy of motion.


It is not generally realized that water in motion also acquires kinetic
energy. Whenever a faucet is turned off very quickly, there is a
hammering sound which is due to the fact that the moving water in the
water pipe is brought to an abrupt stop. This puts a severe strain on
the piping. A great deal of trouble was experienced from this source in
the early days of plumbing. At a hospital in Bristol, England, there
was a lead pipe leading from a cistern in one of the upper stories
to the kitchen. Every time the faucets were turned off abruptly the
momentum of the water caused the lead pipe to expand, and every now and
then the pipe was burst. In order to relieve the situation, a plumber
connected a pipe to the faucet and carried it up the side of the
building to the level of the cistern. His idea was that whenever the
water was turned off suddenly it would have a vent leading up to the
level of the water reservoir. Much to his surprise, the water issued
from the pipe in a jet of considerable height. To prevent the escape
of the water, he extended the pipe considerably, and still a jet of
water would issue from it. Eventually the relief pipe was carried up
twice the height of the cistern and even then the water would squirt
out occasionally when the faucets in the kitchen were turned off very
suddenly. Then the idea was conceived of placing a reservoir on one of
the upper floors of the hospital and letting the jet of water fill this
reservoir. Every time the faucet was operated in the kitchen a certain
amount of water flowed into the new cistern, and in this way it was
kept supplied with enough water to furnish that which was required for
the upper floors of the hospital.


It is on this principle that the hydraulic ram operates. Water from a
stream is made to flow down a pipe, and as it gains velocity a check
valve suddenly stops the flow which produces enough pressure to force
open a valve in an air chamber and let some of the water enter the
chamber. As soon as the pressure is relieved the check valve opens
and the valve into the chamber closes automatically until a moment
later the stream of water has gained sufficient velocity to repeat the
performance. Thus an intermittent jet of water is forced into the air
chamber and thence through a pipe to a reservoir. The height to which
the water will rise depends entirely upon the velocity of the water
flowing through the system. The air chamber is necessary to cushion
the action of the hydraulic ram and provide a fairly steady pressure
upon the water that flows up through the vent pipe. The check valve is
entirely automatic. It is held open against the pressure of the water
by a spring or a weight, but when the water is in motion is dragged
shut, only to spring open again when the pressure is reduced by the
escape of the water into the air chamber.

[Illustration: FIG. 34.--THE GYRATING WATER METER]

There is a very ingenious water-driven motor which is employed merely
to record the amount of water flowing through it. This is the Thomson
water meter which is illustrated in Figure 34. It consists of a
circular chamber with inwardly dished or conical top and bottom walls.
In the chamber is a flat disk with a ball and socket bearing. At one
side there is a vertical diaphragm in the chamber which passes through
a slot in the disk. This prevents the disk from revolving, but it
is free to oscillate. It has a motion similar to the gyrations of a
top when it is beginning to lose speed and die down, except that the
disk does not revolve. When the disk is in contact with the bottom
wall of the chamber on one side it contacts with the top wall on the
other so that the chamber is virtually divided into two compartments
by the disk, but by gyrating the disk these compartments are made to
revolve. Water enters at one side and discharges at the other side of
the vertical diaphragm. Now, if the disk is in the position shown in
Figure 34, the water, on entering, bears upon the upper face of the
inclined disk and wedges its way between the disk and the upper wall
of the chamber, making the disk oscillate on its ball center. As the
edge of the disk rises across the face of inlet port the water entering
the chamber bears against the under side of the disk, continuing the
gyratory motion. The water cut off on the upper side of the disk is
carried around to the outlet and discharges, while a fresh supply flows
in on the other side of the vertical partition and at the next half
turn the water in the lower compartment discharges at the outlet side
of the partition, while the compartment is filling on the other side of
the partition. A measured amount of water flows through the chamber at
each gyratory oscillation of the disk. A train of gearing is driven by
the gyrating disk which operates a set of dial pointers and a measure
of the amount of water passing through the meter is indicated.


We have referred to the enormous velocity of the jets used to drive
Pelton wheels. Where high heads of water are obtainable water jets are
used very effectively for excavating purposes, particularly in mining
plants for washing down gold-bearing gravel banks. If water is not
found near such banks expensive canals, flumes, and pipe lines are
constructed and even tunnels are bored to bring the water to the point
where it can be utilized. Some of the giant nozzles spout streams from
2 to 8 inches in diameter with a pressure of from 50 to 200 pounds per
square inch. The powerful streams tear into the gravel banks, washing
them away into sluices in which riffle boxes are placed to catch the
precious metal. The back pressure of these nozzles is very heavy and
the larger ones have to be provided with strong anchorages. Water in
motion resists any change of direction and long levers have to be
provided to permit the miners to guide the nozzles.

The hydraulic jet is also used for general excavating wherever water
power is available. Sometimes it is employed under water when clearing
a channel to level down piles of stones that are too large to be picked
up by a suction dredge. Hollow iron piles are driven into a sandy
bottom by means of hydraulic jets. No hammer is needed. Water is pumped
into the pile and on issuing from the bottom of the pile it carries
sand with it, making a hole into which the pile sinks. Wooden piles
are driven in the same way by loosely attaching a water pipe to them
so that the pipe may be withdrawn when the pile has been driven far
enough. The pile is grooved at the lower end so that the pipe outlet
may be centered at the bottom of the pile.



A very ingenious apparatus for compressing air was invented in the
earliest years of the iron age to furnish a continuous blast of air for
the Catalan forges. This compressor, known as a “trompe,” can hardly
be termed a machine because it contains no moving parts except water,
which is the motive power, and the air which it traps and compresses.
To understand its operation we must look into a peculiar property of
water flowing out of a reservoir into a pipe or nozzle. There is a
converging motion that tends to contract the jet of water just after it
leaves the pipe. This is known as the _vena contracta_. It produces
a partial vacuum in the pipe. If air ports are opened into the pipe
at this point, air will be sucked in to fill the vacuum and will be
carried out of the pipe by the friction of the water. In Figure 35 a
pipe is shown running from the _vena contracta_ to a water tank below.
The rise of water in this pipe indicates the degree of vacuum produced
by the jet.


This principle is used in the hydraulic-air compressor or “trompe” as
it is called. Water flows out of one reservoir through a pipe into
another reservoir lower down. (See Figure 36.) Air enters the pipe
through ports at the point where the vein of water contracts and is
carried down into the second reservoir. This reservoir is sealed so
that the air is trapped in it. The water passes out through a pipe
which is carried high enough to keep a certain pressure of air in the
reservoir and prevent it from blowing out.


There is a compressor of this type, constructed on an enormous scale,
in the northern part of Michigan. A sketch of the compressor is given
in Figure 37. The air reservoir in this case is a huge underground
rock-walled chamber nearly 350 feet below the surface, 8 feet wide, 26
feet high, and about 280 feet long. There are three intake pipes, 5
feet in diameter, each filled with an annular funnel-shaped head, which
sucks air into the water and carries it down into the chamber. At the
bottom of each intake pipe there is a concrete block with a conical
top projecting up into the pipe. The column of water flowing down the
pipe is spread out into an annular stream by the conical block and the
bubbles of air escape into the chamber. The water outlet of the chamber
is an inclined shaft which leads up about 270 feet to the surface of
the ground where it discharges into the tail race. The water is forced
up this inclined shaft by the pressure of the air trapped in the
chamber. The mouth of the shaft is, of course, below the level of the
water in the chamber so that there is no chance for the air to escape
unless the pressure becomes excessively high, when it will force the
water level below the mouth of the shaft and blow out. The discharge
sometimes forms a geyser 700 feet high. The air will continue to blow
until the pressure is reduced enough for the water level to rise and
cut off access of the air to the mouth of the shaft. Under normal
conditions there is a fall of 343 feet from the water level at the top
of the intake pipe to the water level in the chamber, and a vertical
rise of 271 feet from the water level in the chamber to the tail-water
level. The difference, or 72 feet, represents the working head. With
all three intakes operating, a total of 5,000 horsepower is developed.
Each intake delivers 11,930 cubic feet of air per minute at a pressure
of 128 pounds. Air enters the intake heads through tubes ⅜ inch in
diameter and there are 1,800 of them to each head. The air is employed
to operate machinery and tools in an adjacent mine.

One advantage of this type of air compressor is that it cools the air
while compressing it. This was hardly an advantage in the Catalan
forges, but when the air is used to drive machinery it is important
that it be precooled. When air is compressed by mechanical means
a great deal of heat is generated and the machines must be water
jacketed to extract this heat, but in the hydraulic compressor the
air bubbles are compressed as they pass down with the water to the
reservoir and the water absorbs the heat, delivering cool compressed
air at the bottom of the intake pipe.



MANY an inventor has strayed off into the delusive pursuit of perpetual
motion because he did not know that the pressure in a body of water
at any given point is equal in all directions, upward, downward, or

A cubic foot of water weighs 62½ pounds. Take a hollow column with an
internal cross-sectional area of one square foot and if it be filled
with water to a depth of ten feet there will be a weight of 625 pounds
of water in the column and hence a pressure of 625 on the bottom of
the tube or 4.34 pounds on every square inch of the bottom. But the
water presses on the sides of the tube as well and the amount of
this pressure depends upon the depth or “head” of water and not upon
the quantity of water. At the bottom of the tube the pressure on the
side walls is 625 pounds per square foot or 4.34 pounds per square
inch; at a depth of one foot the pressure on the side walls is 62.5
pounds per square foot or .434 pound per square inch; at a depth of
two feet it will be .864 pound per square inch, etc. The pressure on
each square inch depends not upon the mass of the water but upon its
depth. If the column of water had a cross-sectional area of a mile or
a thousand miles, the pressure at a depth of one foot would always be
.434 pound per square inch. (Of course there are slight variations from
this figure due to salt or other substances dissolved in water or to
changes in density produced by variations of temperature, but we need
not consider such minute differences here.) That is why a dam which is
strong enough to hold back the waters of a pond will be just as able to
hold back the waters of the whole ocean if it be placed in a sheltered
bay where ocean waves cannot tear it to pieces. The ocean, despite its
enormous mass, can exert no more pressure per foot of depth than the
water in a cistern.


It is because the pressure of water at a given depth is exerted upward,
as well as laterally and downward, that a ship floats. It is the
upward pressure of the water that holds up the boat. When an object
is placed in a reservoir of water it sinks into zones of increasing
pressure until it finally reaches a depth at which the pressure on
the bottom of the object balances the weight of the body. If the body
is entirely submerged before reaching such a point, it will continue
to sink to the bottom of the reservoir because water will flow over
the top of the object and keep adding downward pressure to offset the
increasing upward pressure. The amount of water in the reservoir makes
no difference. A battleship will float just as high in a flooded dry
dock as it will in the open ocean. If the dry dock were so narrow as
to leave a clearance of but a few inches of water around the ship, the
latter would still float even though the ship weighed considerably more
than the water in the dock.

There is a big difference, then, between the weight of water and the
pressure it exerts. In Figure 38 we have an L-shaped receptacle with
the lower arm of the L terminating in a chamber A. The top wall B
of this chamber measures ten square inches. The tube C has a cross
sectional area of one square inch. If tube C is filled to a height of
twelve inches above wall B we shall have an upward pressure of 0.434
pound on every square inch of wall B, or a total of 4.34 pounds. If
by means of a plunger D we add a hundred pounds of pressure to the
column of water in tube C, we shall be adding a thousand pounds to the
pressure on the wall B. The side walls and bottom of the chamber A
will also be subjected to a pressure of 1,000 pounds per inch plus the
pressure due to the depth or head of water.





Here, then, we have a convenient means of multiplying force or effort
and it is a means that is used very largely in certain classes of
machinery. Figure 39 is a diagrammatic representation of a hydraulic
press. It consists of a cylinder A in which is fitted a ram B. An
L-shaped tube C connects with the cylinder and is fitted with a plunger
D. The cylinder and tube are filled with water and then when the
plunger is depressed the ram B has to rise, If the area of the plunger
is one square inch and that of the ram thirty square inches, a 100
pounds pressure on the plunger will exert 3,000 pounds of lift on the


However, we must remember that in mechanics, as in all walks of life,
we cannot get “something for nothing.” If we multiply the pressure or
force, we must pay for it in some way, otherwise we should be getting
more work out of the press than we put in it, which is what the
perpetual motion crank is ever trying to do. As the cross-sectional
area of the plunger D is only 1/30th of that of the ram, the plunger
must descend thirty inches to raise the ram one inch. We need not
consider the difference in the head of water because it would not
amount to more than a few ounces at most, nor need we consider
frictional losses. The case is parallel to that of the lever. In fact,
we may consider the hydraulic press as a fluid lever with the water in
tube C as the effort arm and that in cylinder A as the weight arm. The
two arms are here so proportioned that the power arm must move thirty
times as far as the weight arm. The work put into the press is exactly
balanced by that we get out of it. An effort of 100 pounds exerted
through a distance of thirty inches is exactly balanced by the moving
of 3,000 pounds through a distance of one inch.

It is a decided disadvantage to have to move the plunger so far and
in actual commercial practice hand-operated hydraulic presses are not
worked in that way. A pump is used to force water into the cylinder
so that a great many short strokes may be taken in place of one long
one, and the pump handle provides an added leverage, enabling a man
with little effort to exert an enormous lift. The water enters the ram
cylinder through a valve, and the pressure is maintained on the ram
until relieved by the opening of an outlet port.


All this seems very simple and one would suppose that the inventor
of the hydraulic press must have been exceptionally free from the
troubles and trials that beset most inventors. However, there is a vast
difference between a laboratory apparatus and a commercial machine.
When, towards the close of the eighteenth century, Joseph Bramah,
the eminent British tool builder, invented the hydraulic press, he
experienced all sorts of difficulty in holding the water in the ram
cylinder. Of course, the ram has to slide freely into and out of the
cylinder, but how could he prevent the water from leaking out past the
ram? He resorted to all the plumbing expedients of the day. He used a
stuffing box and gland, but when this was packed tight enough to hold
the water in, it gripped the ram so tightly that the latter would not
move down into the cylinder on the return stroke. Bramah had in his
employ a very clever young mechanic named Henry Maudsley, who later
became famous as an inventor and designer of machine tools. We read
of him in Chapter III. Maudsley attacked the baffling problem of the
hydraulic press and provided a solution that survives to this day. In
place of the stuffing box which is a means of jamming a mass of cotton
waste about the collar, he provided a cupped leather collar. When the
pressure was applied it expanded the collar and made it bear tightly
against the ram, but on relieving the hydraulic pressure the pressure
of the cup leather was also reduced automatically.

There are many machines analogous to the hydraulic press in principle.
They do not use water in every case for the fluid lever. Where the
fluid is used over and over again oil is frequently employed. The
compactness of this form of lever makes it most useful wherever an
operation calls for the overcoming of a very heavy load or resistance
through a relatively short distance. For instance, there are machines
for bending pipe, for curving railroad rails, for punching holes in
metal, for pulling wheels off their shafts, for jacking up heavy
weights, for baling cotton, paper, and other materials, all of which
operate on the same principle as the hydraulic press. Water pressure is
supplied sometimes by a hand pump, sometimes by a power-driven pump,
and sometimes it is taken from a reservoir in which compressed air
imparts the requisite pressure to the water.


A novel use of water pressure has been developed in England. In certain
mines it is dangerous to use dynamite for blasting purposes owing
to the presence of explosive gases, and successful experiments have
been made with hydraulic cartridges. This consists of a cylinder of
steel fitted with a series of little plungers arranged in a row in the
cylindrical wall of the cartridge. As in powder blasting, a series
of holes are drilled in the face of the rock and the cartridges with
the plungers retracted are fitted into the holes. Then the cartridges
are connected to a high-pressure water supply. The water forces the
plungers out, exerting enough pressure to burst the rock. Not only is
this system perfectly safe, but it is economical, because the gallery
does not have to be cleared of workmen before every blast. There is
more certainty in the use of water cartridges, and the danger, common
where dynamite is used, of having the rock drill or pick strike and
explode a stick of dynamite which failed to go off with the rest of the
charge in a previous blast is avoided.

Hydraulic pressure is also used in jacks for lifting heavy weights. The
principle of the hydraulic jack is the same as that of the hydraulic


An interesting illustration of the use of these liquid levers was
afforded in the construction of the Quebec Bridge. This huge bridge, it
will be recalled, consists of two cantilevers which stretch out from
opposite shores of the St. Lawrence River and support between them a
center span 640 feet long and weighing 5,400 tons. The span was built
on barges, towed down to position between the cantilever arms and then
lifted up 150 feet to the floor level of the bridge. Eight 1,000-ton
hydraulic lifting jacks were used, two at each corner of the span.
They were ideally suited to this kind of work. The bridge span had to
be lifted with utmost care and the motion had to be simultaneous on
all four corners. If one corner were raised faster than another the
span would be twisted and subjected to serious strains. In the first
attempt the fastening gave way at one corner and the span crumpled up
and plunged down into the river. But a year later at the second attempt
the span was hoisted successfully to position. The jacks had a lift
of two feet, and, counting the time required to secure the huge plate
chains by which the span was suspended, move the jacks down and give
them a fresh hold, it took fourteen minutes to complete each two-foot
lift. The work was done only during the daylight hours and on the third
day the span was finally brought into position and made fast to the
cantilever arms by means of twelve-inch pins driven home at each corner.

Hydraulic power is used very largely in the operation of cranes. As
the plunger or ram has a very limited range of motion some means of
multiplying distance of travel is required. One simple scheme is to use
a set of pulley wheels or sheaves attached to the cylinder and another
set to the ram and pass the hoisting chain around them. If we refer
back to Figure 16, on page 34, we shall see that seven feet of rope
must be pulled in at E in order to raise the lower pulley block one
foot. It is very evident that the process can be reversed. Power might
be applied to spread the two-pulley blocks apart when a movement of one
foot would produce a travel of seven feet at E. That is what is done
on the hydraulic crane. The ram is lifted, spreading the pulley blocks
apart and thus multiplying the motion of the lifting cable to any
extent, depending upon the number of sheaves, so that a travel of but a
few feet will result in lifting a load forty or fifty feet.


The same principle is used in hydraulic elevators. The hydraulic
cylinder lies horizontally on the basement floor and by means of pulley
gearing a short motion of the plunger is sufficient to raise the car
several stories.

In a more modern type of elevator the plunger acts directly on the car.
The plunger is long enough to reach to the top story of the building
which means that it must sink far into the ground in order to let the
car down to the first story or basement. A steel pipe is sunk into
the ground and serves as the cylinder and in this the long plunger
operates. In one of New York’s tall buildings the cars are lifted to
a height of 282 feet. The plungers are 6½ inches in diameter and they
travel at a speed of over 400 feet per minute. The car which, when
loaded, weighs 1,617 pounds, is supported on the top of the plunger.
However, counterweights are provided which balance the weight of the
car, so that practically the only weight lifted by the plunger is that
of the passengers. The advantage of this type of elevator is that it
reduces the danger of accident. The motion of the car is steady and
easily controlled. The car cannot move down above a given speed and
the only possible danger is that the plunger might break. However, a
shaft of steel 6½ inches in diameter, even if hollow, is hardly likely
to give way even under the most extraordinary loads to which it might
be subjected in elevator service.


There is another type of elevator that completely dwarfs anything used
in office buildings. On some canals where it is necessary to make a
sudden change of level of considerable extent, instead of using a
flight of locks, a hydraulic elevator is employed to lift or lower not
only the vessel but the water it is floated in. There are two huge
tanks which ply between the upper and lower levels of the canal. These
are so connected that as one rises the other descends. The tanks are
big enough to take in the largest vessels that are likely to use the
canal. They are fitted with water-tight gates at each end, and after a
vessel has entered one of them, say at the lower level, the gate behind
it is closed. Then hydraulic mechanism is operated to lift the tank,
and when the top is reached the other gate is opened and the vessel
sails out into the upper level. It seems like a tremendous undertaking
to lift a heavy ship, but the two tanks balance each other and the
only work that has to be done is to overcome the friction and inertia.
No matter how heavy a vessel may be, it will not disturb the balance
between the two tanks. Nor is it necessary to have a ship in each tank,
for the same depth of water is maintained in the two tanks, and when
a ship enters the weight of the tank is not increased, for the ship
displaces its own weight of water.


Water is frequently used to take the place of toothed gearing for the
transmission of power, particularly where it is desirable to vary
speed. One of the disadvantages of toothed gearing is that a change of
speed can only be made by shifting gears. The speed cannot be varied
gradually but is changed by abrupt steps. The guns of a battleship must
be kept trained on the target, while the ship rolls in the waves under
them, so as to be ready for a broadside at any instant. A telescope is
secured to the barrel of the gun and a man known as a “pointer” tries
to keep the cross-hairs of a telescope on the target by constantly
elevating or depressing the gun. The speed of the elevating machinery
must be constantly changing; now running at high speed, the next
instant barely moving, and the next moment reversing.

To produce these variations a hydraulic variable speed gear is used.
The construction is somewhat complicated, but the general principle of
operation is simple. In a common pump water is lifted by operating a
plunger in and out of a cylinder. It will be readily understood that
the operation may be reversed, and if power is applied to the water to
force it through the pump, it will make the plungers move in and out of
the cylinder. In the hydraulic variable speed gear the driving shaft is
made to operate a set of little pumps which are connected to a second
series of pumps that act upon the driven shaft. Instead of water oil
is used, and the oil pumped by the driving pumps is forced into the
driven pumps. The latter pumps are so connected to the driven shaft as
to cause it to rotate. But by a simple mechanical expedient the stroke
of the driving pumps can be varied at will from maximum to zero, and
the motion of the pumps can also be reversed. The variable amount of
oil pumped into the driven pumps varies the speed of the driven shaft,
for if it takes two strokes of a driving pump to fill the cylinder of a
driven pump the driven shaft will travel at only half the speed of the
driving shaft.

In turbine-driven vessels some sort of gearing is required between the
propeller and the turbine. In order to operate at its best efficiency
a turbine must run at very high speed, but this speed is entirely
too high for the propeller. There is a limit to the rate at which a
propeller may be driven. If this limit is exceeded, the propeller
merely bores a hole in the water, forming a vacuum which produces a
drag on the ship. It is customary to interpose some form of gearing
between the propeller and the turbine shaft, but because of the high
speed and the vast amount of power to be transmitted it is a difficult
matter to design gearing that will be reliable. Furthermore, it is
desirable to vary the speed of the vessel and even to reverse it
without slowing down the turbine engine. In some cases a specially
designed system of toothed gearing has been employed, in another the
power of the turbine is converted into electricity and then reconverted
into mechanical power by means of a motor on the propeller shaft. This
provides a very efficient transmission, because the electricity can
be very conveniently controlled to accelerate, retard, or reverse the
speed of the propeller motor. The same thing can also be done by using
a hydraulic transmission gear. This, although quite different from
the variable-speed gear, yet operates on the same general principle.
The turbine drives a centrifugal pump and the water thus pumped is fed
to a horizontal water turbine on the propeller shaft. By an ingenious
arrangement of turbine wheels the speed of the propeller shaft may be
varied at will.

Hydraulic machinery is notable for its reliability. Sometimes water
or oil is used as a convenient means of transmitting pressure from
one part of a machine to another. If we take a tube filled with water
and fit a plunger in each end, then, when one plunger is depressed or
pushed in, the other will be expressed or pushed out. The pipe may be
twisted around in any direction or be tied up in a double bowknot, and
yet pressure applied to one cylinder will immediately be felt by the
other. This method of transmission may do away with a vast number of
gears or levers.

Water is comparatively incompressible and hence not a very adaptable
means of transmitting power, but a certain amount of flexibility is
secured in some systems by the use of what is termed an “accumulator.”
This consists of a large cylinder fitted with a plunger. The plunger
is heavily weighted and it maintains a constant pressure upon the
column of water in the cylinder. If, for instance, a hydraulic crane
is being used and suddenly a larger quantity of water is required than
would normally be delivered by a pump, it is automatically supplied
from the cylinder of the accumulator, and at a constant pressure. The
accumulator is arranged to control the throttle valve of the steam
pumping engine so that when the plunger of the accumulator reaches
a predetermined height the stream is cut off and the engine stops


During the war a new use of water for power transmission was discovered
and it is now being developed for the operation of mining machinery.
The inventor of the new transmission is George Constantinesco, a
Rumanian engineer. His first application of the invention was to a
mechanism for synchronizing the firing of a machine gun with the
rotation of an airplane propeller, so that it was possible to fire
through the propeller without danger of striking its blades. There were
several existing methods of gearing the propeller to the machine gun,
but Constantinesco’s system proved so much more reliable that it was
adopted and widely used by the British in their battle planes.

Instead of gears and levers, the Rumanian engineer used a column of
water in a heavy steel tube to conduct impulses from the propeller to
the machine gun. The pulsations produced by the propeller were too
rapid to cause an actual displacement of the whole column of water in
the tube, but a wave of pressure traveled through the water column at
an enormously high velocity.

We are wont to think of liquids as incompressible, but they are
actually slightly compressible and highly elastic. This is demonstrated
by the submarine telephone or the submarine bell. Water, we know, is an
excellent medium for the transmission of sound, but sound, we know, is
produced by a succession of pressure waves. If water were absolutely
incompressible, it could not convey sound from one point to another.
When sound travels through a speaking tube the whole column of air
does not move back and forth simultaneously, but it is divided into a
series of waves. Each particle of air has a local oscillatory motion
which it communicates to its neighbor, producing alternate compression
and rarefication, and it is this wave action that travels through the
column. The same is true of water, except that the rate of travel of
the pressure wave in water is much higher than in air, namely 4,800
feet per second. It is this wave transmission that Constantinesco
employed and which he calls “sonic” wave transmission.

To-day sonic wave transmission is used to operate rock drills. A wave
generator is used, which acts somewhat on the principle of a pump. A
pair of plungers are reciprocated at a rate of forty strokes per second
by means of an electric or gasoline motor, and they produce a train
of pressure waves in a column of water. The water is contained in a
specially designed flexible steel piping which runs to the rock drill.
The pressure waves operate a plunger in the drill and the plunger
carries the drill steel. The latter pounds the rock under the wave
impulses at the rate of forty strokes per second.

Sonic wave transmission is analogous to alternating current
transmission of electricity. There are direct equivalents in the wave
transmission, of volts, amperes, frequency, angle of phase, induction,
inductance, capacity, resistance, condensers, transformers, and
single-phase or polyphase systems.



THE STEAM engine had its origin in a kitchen; the modern clock was
first conceived in a cathedral; our laws of motion were discovered
under an apple tree, but, strangest of all, pneumatic engineering had
its beginning in a _barber shop_. In each case it was an inquisitive
boy who played the leading rôle.

We do not hear much about the youthful father of pneumatic engineering,
possibly because he lived so very long ago, but his story is fully
as interesting as that of Watt or Galileo or Newton. Young Ctesibius
dwelt in the city of Alexandria, Egypt, 250 years before the birth of
Christ. His father kept a barber shop, and the young lad used to watch
his father practice his tonsorial art on the Greek and Egyptian dandies
of the time. No doubt Ctesibius’s father expected to make a first-rate
barber of his son, but history does not tell us much about his early

The barbers of those days had their mirrors as do the barbers of the
present time. But a mirror in those days was a treasured possession.
It consisted of a brightly polished plate of metal in which a person
could see himself “darkly” or it might have been a plate of glass with
a black backing. These mirrors had to be carefully preserved from
injury and from moisture, and so, instead of having them mounted on the
wall as in a modern barber shop, they were stowed carefully away and
brought out only after the tonsorial artist had completed his operation
and was ready to exhibit his finished product to the customer.


Now in the tonsorial parlors of Ctesibius’s father the precious mirror
was suspended above the head of the customer and when the barber had
finished the shave or haircut he pulled down the mirror and let the
customer survey his remodeled countenance. After the customer viewed
himself to his heart’s content he merely released the mirror and it
was automatically drawn back into place by a counterweight that slid
in a case fastened to the wall. Young Ctesibius noticed that every
time the mirror was released a curious whistling sound came from
the case in which the counterweight moved. No doubt this phenomenon
had been recurring day after day for years, but it excited no more
curiosity than would a squeaky door, until, one day, the barber’s son
happened to notice it. Immediately he was all curiosity. No one knew
anything about air in those days and the boy could get no satisfactory
explanation of the phenomenon, so he started an investigation of his
own. He found that the counterweight fitted very closely in its case
and when it dropped it forced a stream of “wind” out of a crevice which
produced a whistling sound. That set Master Ctesibius to thinking. He
had discovered a method of harnessing the wind. No more barber shop for
him; he was launched upon a career of scientific research and invention.

The first use he made of his discovery was to build a pipe organ which
was driven by a water wheel and hence was known as a water organ. But
there were other and more lucrative fields for the newly discovered
power. Being invisible, compressed air proved a most valuable medium
for performing seemingly miraculous tricks with which the corrupt
priesthood of that time hoodwinked the public. Naturally such
air-controlled apparatus was kept secret, and we have only a meager
record of a few of the ingenious devices used in the temples. However,
Ctesibius made many scientific discoveries and became the most famous
mathematician and scientist of his age. We have read in Chapter IV
of his famous water clock adjusted to record hours of varying length
according to the season.

While Ctesibius is credited with being the first man to make scientific
use of compressed air, the use of free air or wind as a power far
antedates him. Sailing vessels were probably in use long before
windmills were invented. As pointed out elsewhere, windmills possessed
an advantage over water wheels in that they could be placed anywhere,
instead of being confined to the banks of streams. They were widely
used for pumping water, grinding grain, and sawing wood until the steam
engine arrived and displaced them.

Although wind power is but little used to-day, air is much more widely
used in modern machinery than is generally realized. A catalogue of the
various devices in which it plays a prominent part is likely to prove
astonishing. For instance, we employ it to bore through rock, to stop
the speeding express train, and even to quell ocean billows. Being
elastic and compressible, it makes an ideal spring for the storage of
power and a cushion for absorbing shocks. It is also used to fight
back water and permit men to work in the depths of the sea or in
water-bearing sand and earth.

Despite his extensive use of air Ctesibius knew nothing of the
atmospheric pressure. It was not until the seventeenth century that
atmospheric pressure was discovered and measured. It was then learned
that there is no such thing as suction.



A suction pump should be called an atmospheric pump. The operation
of such a pump is illustrated in Figure 40. A piston A slides in a
cylinder B. There is an opening in the bottom of the cylinder which
is normally closed by a clack valve C that opens upwardly. There is
a similar valve D in the piston A. When the piston is pushed down it
compresses the air in the cylinder, closing the valve C while valve
D opens, permitting the air to escape. Then on the upward stroke the
valve D closes and valve C opens permitting air to flow into the
cylinder. In this way the air in the pipe and cylinder are exhausted
after a few strokes. As the air is rarefied and the pressure is reduced
above the column of water in the pipe the greater pressure of the water
outside the pipe forces the column to rise until it eventually flows
through the valve in the piston and out of the spout of the pump.
The maximum height to which water can be raised by a suction pump
is thirty-four feet but in actual practice the lift seldom exceeds
twenty-six to twenty-eight feet because the fit between the cylinder
and piston is not perfect.


When water is raised to a greater height a force pump is used. Such a
pump is shown in Figure 41. The pump cylinder A has two valves B and C.
The valve B opens upwardly and valve C opens downwardly. The piston D
is a solid member containing no valve. When the piston rises the valve
C closes and valve B opens, letting water into the cylinder. On the
reverse stroke the valve B closes and the descending piston forces the
water out through valve C into pipe E. The height to which the water
may be lifted depends upon the power applied to the piston and not upon
atmospheric pressure. In a fire pump two force pumps are used which
alternately deliver water into an air chamber. The air is compressed
by the water that enters the chamber and exerts a steady pressure on
the water, forcing it out through the fire hose in a stream that is
practically steady.

It is a decided disadvantage to install a force pump in a deep well
because of the mechanical difficulty of operating the piston at a great
depth. Often the suction and force pump principles are combined. The
force pump piston and cylinder are located twenty-six and twenty-eight
feet above the level of the water in the well with a pipe leading down
into the water. The water is forced up into the cylinder by exhausting
the air in the cylinder and pipe and then is forced out of the cylinder
and up a pipe to the top of the well. This also has its disadvantages.
In deep wells the pump piston must still be located and operated at
considerable depth.


A much more simple pump for deep wells is the air lift in which there
are no valves and no piston. The pump consists of two pipes that are
let down into the water. (See Figure 42.) The larger pipe is open at
the top and bottom, and the smaller pipe discharges air into the bottom
of the larger one. This air being directed upward has a lifting effect,
and mingling with the water in the pipe produces a sort of froth which
is so much lighter than solid water that the atmospheric pressure on
the water in the well is sufficient to raise the froth. The water is
thoroughly aerated and to a large extent purified by this system of
pumping, so that the air lift commends itself particularly for city
waterworks. Sometimes a series of air lifts are used which lift water
by successive stages to a greater height than would be possible with a
single direct lift.




Centuries ago it was realized that it would be possible for men to
descend into the open sea if they were protected by a bell-shaped
chamber, for the air trapped in the chamber would furnish them with
oxygen requisite for breathing purposes, and would prevent the water
from drowning them out. This same idea of a diving bell is used on
land when sinking a shaft through quicksand or water-bearing strata. A
large box or caisson is used. (See Figure 43.) This box may be either
cylindrical or rectangular, and it is open at the top and bottom. The
lower edges of the box are shod with steel and form cutting edges that
will sink into the soil that is being excavated. At a height of about
seven feet above the bottom of the box there is a transverse diaphragm
known as the deck, and the space below is known as the working
chamber. This deck is very strongly constructed, as it has to support
the weight of the concrete shaft that is built above it. Laborers,
commonly known as “sand hogs,” enter the working chamber and dig out a
shallow pit in the floor of clay or sand. This pit is then extended to
the cutting edges of the caisson. The caisson thus undermined settles
down into the excavation and another pit is started. In this way, step
by step, the caisson is sunk into the ground. In order to overcome the
friction of the caisson against the sides of the excavation and to
insure its sinking, it is heavily weighted. When water-bearing sand is
reached, compressed air is admitted into the working chamber to force
the water out. When the air pressure is greater than the water pressure
it drives the water out of the sand in the working chamber, so that the
men can work in perfectly dry ground, even though the surrounding sand
may be so saturated with water as to form a quicksand.

Of course the farther the excavation proceeds below the water level the
greater the air pressure required, and the caisson would be blown up
out of the ground by this air pressure or would float on the water were
it not for the weights with which it is loaded. When an open shaft is
to be dug, pig iron is loaded on the caisson to force it down, but in
most work the object is merely to sink a concrete column down to rock
and so the caisson is filled with concrete above the deck. Sections
are added to the caisson as it sinks into the ground, and these
sections are filled with concrete. This method of building the column
facilitates the work of laying the concrete, and at the same time
provides the weight necessary to overcome the buoyancy of the caisson
and the skin friction on the side walls of the excavation.

After the caisson has been carried down to rock and a good seat has
been blasted out of solid rock, the working chamber is completely
filled with concrete and the concrete shaft is thus anchored to the


Access to the working chamber is had through a central shafting. In
order to hold the air pressure in the working chamber and yet provide
for the entrance of men and materials, an air lock is fitted to the
upper end of the shafting. This air lock, as shown in Figure 43,
consists of a chamber formed with a trapdoor at the top and the bottom.
Both doors open downwardly. To enter the caisson, the bottom door of
the chamber must first be closed and means are provided for doing this
from outside the air lock. The compressed air in the chamber is then
let out through a valve, and when the pressure drops almost to normal
the upper trapdoor falls open of its own weight, giving access to the
chamber. After entering, the upper door is closed while compressed air
is admitted into the chamber; the air pressure then serves to hold the
upper trapdoor closed. The bottom door, in the meantime, has been kept
closed by the air pressure below, which is greater than that above the
door. But after sufficient air has been introduced into the chamber to
equalize the pressure on both sides of the lower trapdoor, it falls
open of its own weight. The occupants of the chamber can then proceed
down a ladder to the working chamber. When leaving the caisson, the
action of the air lock is reversed. The bottom door is pushed up and
held closed for a moment while air is released from the chamber, when
the greater pressure beneath will hold the door closed, and after the
pressure within the air lock has been lowered practically to normal,
the upper door drops of its own weight, permitting the occupants of the
chamber to climb out. The same process must be undergone by buckets
loaded with sand or earth from the excavation and by empty buckets
returning to the working chamber.

More time is required for a man to pass through an air lock than for a
load of sand or any inanimate load. In some of the larger caissons a
separate small air lock is provided just for the use of the workmen.
In the air lock the pressure must be built up slowly so that it will
permeate a man’s whole system. When we realize that the pressure
that men have to support in caisson work may amount to from fifty
to one hundred tons on the whole body, it is difficult at first to
understand why the body is not flattened out like a pancake. It is only
by permitting the system to absorb the pressure so that there is as
much internal pressure as that outside that a man is able to enter a
compressed air chamber without harmful results.


Compression is rather annoying to a man who has not experienced
the sensation, but the principal danger comes in decompression,
particularly after a person has been in the working chamber for a
long time. When breathing compressed air much larger volumes of
oxygen are taken into the lungs at each breath than in the ordinary
atmosphere, and one feels decidedly exhilarated by this unusual supply
of stimulating oxygen. But with the oxygen large volumes of nitrogen
are taken into the system as well. The nitrogen permeates the blood
while the oxygen is consumed and exhaled in the form of carbon dioxide.
The longer a man is exposed to the pressure the more nitrogen does he
absorb. When the pressure is released suddenly the nitrogen begins
to froth, just as a bottle of soda water does when the stopper is
removed. The nitrogen bubbles in the small veins stop the circulation
and produce the dreaded “caisson disease” which makes itself felt in
the form of severe cramps and excruciating pains. Not infrequently this
disease ends in death. By reducing the pressure gradually the nitrogen
is enabled to pass off completely without bubbling or frothing, just
as it is possible to let out the gas from a soda bottle without
frothing by permitting it to escape through a pin hole in the stopper.
The surest cure for a victim of the caisson disease is to put him
immediately into what is known as a “hospital tank” and build up the
pressure in the tank equal to that which he has just been subjected to
in the caisson, after which the air in the tank is let out so slowly
that there is plenty of time for the nitrogen to pass off without
forming bubbles.

A pressure of forty-five pounds per square inch above that of the
atmosphere is considered a severe pressure for excavation work.
But work has been carried on in pressures up to fifty-two pounds,
corresponding to a depth of 120 feet below water level.

Now that the cause of the caisson disease is understood formulas have
been worked out to insure proper decompression. On one occasion a diver
descended 306 feet into the ocean where the water pressure was 133
pounds on every square inch of his body. This meant that the air which
was pumped down to him had to be compressed to the same pressure. The
diver actually remained at the bottom only a very short time, but it
took two hours and three-quarters to bring him to the surface. He came
up half the distance very quickly and then had to rest on the bottom
rung of a Jacob’s ladder. The rungs on this ladder were ten feet apart
and he was instructed to rest on each rung a certain specified time.
When he was ten feet below the surface he had to wait three-quarters of
an hour for the last trace of nitrogen absorbed by his blood to pass


It is comparatively simple to sink a vertical shaft into water-bearing
soil, but a horizontal shaft involves serious difficulties. The action
of a diving bell is easily illustrated by inverting a tumbler and
pressing it down into a basin of water. The air trapped in the tumbler
will keep the upper part of the glass dry, and by inserting a tube in
the tumbler it is possible to fill the tumbler so full of compressed
air as to drive out all the water. This is virtually what is done in
the caisson; but when excavating a horizontal bore, the caisson must be
turned on its side. Turn the tumbler on its side and it is impossible
to keep the water out of it, no matter how much air we may blow into
it. The reason for this is that the pressure on the open end of the
tumbler is not uniform. At the bottom, where the water is deeper, it
will be greater than at the top. If air is pumped in to equalize the
water pressure at the upper edge of the glass, it will not prevent
water from flowing in at the bottom; and if it be equal to that at the
bottom, the water pressure at the top cannot hold the air in and keep
it from pouring out.


Fortunately most of the soil through which a subaqueous tunnel is
driven is not very fluid. It is either sticky, as in clay, or sluggish
enough to prevent the water from flowing in rapidly. If there is enough
cover of silt or earth above the tunnel bore, it will help to hold
the air in the tunnel. When the bore comes very close to the surface
of the bed of the stream that is being tunneled, loads of clay are
dumped along the line of the tunnel to provide the requisite cover. In
tunnel boring a shield is used which is the equivalent of the caisson
in vertical boring. The shield is a cylindrical box with a diaphragm
across it corresponding to the deck of the caisson. (See Figure 44.)
In front of the diaphragm there is a small working chamber which is
protected above by an extension of the shield known as an apron. In
the diaphragm there are a number of doors at different levels, which
may be closed in case of danger. If work is proceeding near the top of
the shield, the upper doors are opened and the pressure is regulated
to equal the water pressure at that level. If the work is carried on
near the bottom of the shield, the upper doors are closed and only the
lower doors are open, and the pressure is increased to equal the water
pressure at that point. Sometimes the material is of such a nature
that the men can safely pass out of the doors into the working chamber
outside, but more often it is possible to work only within a limited
area immediately in front of the doors.

When the material is very soft it is often unnecessary to do any actual
excavation by hand in front of the diaphragm. The shield is merely
pushed forward through the mud or silt and the doors are opened to let
the material flow in through them. Workmen dig out this mud and it
is hauled out of the tunnel. Whenever bowlders are encountered it is
necessary for the men to work outside of the diaphragm to chip away the
rocks with compressed-air drills, or else bore them and blast them with
small charges of dynamite.

In quicksand the material is so fluid that it is unsafe to open the
ordinary doors of the caisson, and they are then provided with shutters
which are raised one at a time, to permit of operating on a very small
section of the head of the tunnel. After enough material has been
excavated from in front of the shield, the latter is pushed forward and
the excavating is renewed.

Unlike caisson work, the weight of the shield is of no assistance in
making it penetrate the soil, nor is it possible to move the entire
lining of the tunnel with the shield. The tunnel is lined with rings
of cast iron which are bolted together, the rings themselves being
made up of heavily ribbed curved plates. The shield is formed with a
“tail” which fits over the end of the tunnel line like a cap. When the
shield is to be pushed forward, a set of hydraulic jacks are fitted
between the end of the tunnel lining and the diaphragm of the shield,
and by means of these the shield is given a shove forward far enough
for a new section of the cast-iron lining to be added within the tail.
The tunnel-lining rings are usually sixteen inches wide so that it is
customary to move the shield ahead sixteen inches at a time or just far
enough for a new ring of lining to be installed. Of course, the tunnel
is fitted with air locks by which men can enter the working section
without permitting the compressed air therein to escape, and these
locks are just like those used in sinking a caisson, except that they
are horizontal instead of vertical.


Air is also used in another and very novel way to battle against water.
In this case it is not quiet water pressure, but the tremendous power
of ocean storms that is combatted.

The influence of a shoal upon ocean waves has often been observed.
A sand barrier even when submerged to a depth of twenty or thirty
feet will break the waves of a heavy storm and leave an area of
comparatively quiet water behind it. The reason for this is that the
water in the waves does not travel with the waves, but undergoes
local oscillatory motion. This motion is in the form of circular or
elliptical currents which travel in a vertical plane. When a sand bar
is encountered it interferes with these local currents and breaks up
the waves.

Knowing this to be the case, it occurred to Mr. Philip Brasher that
some other means of disturbing the rhythmic movement of the water
might be found, and he determined to try the experiment of using
compressed air for this purpose. Accordingly he laid a perforated pipe
under water and connected it with an air compressor. Then when a storm
arose air was pumped into the pipe and it rose in bubbles through
the water. The effect of this upward movement of air was instantly
observable. It upset the rhythmic water currents and the waves which
struck this wall of air bubbles curled and broke as if they had
encountered a shoal of sand.

Several exposed piers on the Pacific coast have had a pneumatic
breakwater built around them so as to protect them or ships lying
alongside from being pounded by the waves. There is no expense attached
to the breakwater except in time of storm when the air pumps must be
kept going. One important advantage of the breakwater is that it does
not block navigation. A ship can sail right over the wall of bubbles
and find refuge behind it.



UNLIKE water, air is a highly compressible, elastic fluid, and as such
furnishes an excellent medium for the storage of energy. It acts just
like a clock spring into which energy may be introduced and stored
by winding or compressing the spring. The energy remains locked up
in the spring and when the spring is released, it gives back just
as much energy as was put into it, except for slight frictional and
heat losses. Air is a much better spring than steel or any other
metal because it never loses its elasticity from fatigue and because
it has an enormous capacity for the storage of energy. It possesses
one serious drawback, however. Much of the energy that is expended
in compressing it is converted into heat. If the air were to be used
immediately and without transmitting it to a distance, there would be
no advantage in extracting the heat, but heat cannot be stored in air
for long and it would gradually escape from the storage reservoir or
air receiver and from the pipes leading the air to the machines that it
was to operate. As the heat escaped it would lower the pressure of the
air and hence much of the energy would be lost.


In Chapter V we described a hydraulic system of compressing air and
noted that one of the advantages of this system is that it delivers
air cooled to the temperature of the water. This, of course, does not
mean that there is no loss due to heat. The air bubbles as they are
compressed are cooled by the water that compresses them; in other
words, the heat of compression passes off into the water, making the
water warmer than it would otherwise be. Heat is not produced without
expenditure of energy and a certain proportion of the water power is
thus wasted.

In most cases air is compressed by steam or electrically driven
compressors, and in such machines the heat due to compression is a
serious matter. The air cylinders are water-jacketed to carry off the
heat. But air is a poor conductor; it acquires heat faster than it can
give it off to the water surrounding the cylinders. In compound air
compressors the air compressed in one cylinder is cooled before being
passed on to the next cylinder, where it is further compressed. The
heat loss in compressing air in a single stage up to 100 pounds gauge
pressure is about 30 per cent. Air that enters a compressor at the
normal pressure of the atmosphere and with an initial temperature of
60 degrees F., if not cooled will become heated to 415 pounds gauge
pressure. The higher the initial heat of the air, the greater the rise
of temperature. If a volume of air be subjected to 294 pounds gauge
pressure, it will occupy about one-tenth of its former volume. If the
air was introduced into the compressor at zero, it would acquire a
temperature of about 650 degrees; if introduced at 60 degrees, it would
show an increase of about 800 degrees; and, if started at 100 degrees,
it would show an increase of 900 degrees in passing through the
compressor. This shows the advantage of compressing the air in stages
and cooling the air between stages.

Sometimes the heat developed is sufficient to produce a disastrous
explosion. Air is noncombustible, but the oils used to lubricate the
compressor are vaporized by the heat and when mixed with air form a
powerful explosive. Care has to be taken that none but high-grade
oil with a high flash point be used in the compressor and that the
temperature of compression does not rise to near the flash point lest
the vaporized oil be ignited.

That fire can be produced by sudden compression of air has long been
known in the Philippine Islands. The natives use a small air tube with
a close-fitting plunger. Combustible matter is placed in the bottom of
the tube, and on striking the plunger a sharp blow this is ignited.

When compressed air is used in an air motor it expands and in so doing
absorbs heat. The more rapidly it expands, the more heat it absorbs.
This heat it extracts from the motor and from the atmosphere into which
it escapes, and it is a common occurrence to find a thick coating of
frost around the exhaust port. This is due to condensation of moisture
in the atmosphere or in the compressed air itself, which, because
of the rapid extraction of heat, is converted into snow. On cold
days enough frost may be produced in the exhaust pipe to clog it and
interrupt the operation of the motor, and frost sometimes clogs the air
lines leading to the motor.


Air issuing from the submerged perforated pipes breaks up the waves]



The fact that compressed air on expanding is cooled, makes it an ideal
power for use in mining machinery. Steam is inconvenient because of the
difficulty of transmitting it to the machines without loss of heat,
because it would heat the machines so that they cannot be handled
readily and because the exhaust steam would fill the mine with an
impenetrable fog; electricity is dangerous in mines that are apt to
contain explosive gases, because the wires are liable to be broken and
cause sparks by short circuiting, and because sparks are likely to form
between the brushes and commutators of the motors; but compressed air
has none of these objections, and, furthermore, the discharge from the
machines furnishes the operators with ample supplies of fresh cool air
which drives out disagreeable and dangerous gases.


The ordinary rock drill is really a pneumatic hammer. The tool, which
is chisel-shaped, is used as a hammer to pound a hole in the rock. The
tool is driven up and down or in and out by compressed air bearing
alternately on opposite sides of a piston. The elasticity of the
compressed air acts as a cushion to relieve the machine from shock. The
drill is mounted upon a tripod in such a way that it may be operated in
any direction.

The pneumatic riveter is another form of compressed-air hammer.
The machine is held in the hands, and the tool, which is rapidly
reciprocated by air pressure, pounds the red-hot shank of a rivet.
While this is being done an assistant holds a hammer against the head
of the rivet. However, there is a type of riveter which has a U-shaped
frame. One arm of the frame carries the reciprocating tool while the
other reaches around and bears against the head of the rivet.

All sorts of tools have been built in which a small air-driven motor
furnishes the motive power. There are hand drills in which the tool is
revolved by a set of pistons, shears for shearing sheep which operate
somewhat on the principle of hair clippers, and pneumatic chisels used
for chipping stone. Pneumatic motors are widely used in operating
cranes and air hoists. They consist of a simple cylinder and piston,
and are used for short, direct lifts of all sorts.


Air has played a most important part in transportation. When the air
brake was first introduced its purpose was to prevent collisions and
provide greater safety of operation. It was not generally realized that
efficient air brakes are not only a safety precaution, but a means of
increasing schedule speeds. The more quickly a train can stop, the
better speed it may make, particularly on a schedule that calls for
frequent stops.

In the first air brake invented by George Westinghouse, the locomotive
was provided with a reservoir in which air was stored and compressed
by means of a steam-operated air pump. The cars were each provided
with a cylinder and piston connected to the air reservoir through a
valve conveniently located in the engineer’s cab. The piston of the
air cylinder was connected with the air brakes so that whenever the
engineer wished to stop his train he merely turned on the compressed
air and all the brakes in the train were operated. This was a great
saving over the previous system of providing brakemen to operate hand

Unfortunately, the problem of stopping a train was not as simple as
all this. On a long train the cylinders near the engine were the first
to receive pressure sufficient to operate the brakes, and as a result,
the forward part of the train was retarded more than the rear part at
the start of the brake operation, and the train came to a stop with
a series of jolts. Another serious disadvantage was the fact that
an enormous reservoir was required to furnish all the air necessary
for a long train. But the most serious drawback was the fact that
occasionally a train broke apart and then the engineer was powerless
to control the brakes of the detached portion of the train. If the
accident occurred on a down grade, there would result a collision
between the cars running by their own momentum and gravity and those
attached to the engine. This led to the present system of reversing the
process which consists in keeping air pressure constantly in the train
pipe and setting the brakes by relieving the pressure in the train pipe.

Each car is provided with its own cylinder which furnishes the
necessary air for the operation of its brakes. There is, of course, a
main cylinder on the locomotive in which air is pumped at high pressure
by a steam-operated pump. When the pressure of the main reservoir
falls below a predetermined amount, the air pump starts operating
automatically and continues until the requisite pressure is restored.
Air from the reservoir is fed to the train pipe at a certain pressure
and feeds the local reservoirs on the cars of the train. At each car
it passes through a very ingenious triple valve, which consists of a
cylinder with a double piston, one operated by pressure in the train
pipe, and the other by pressure in the local cylinder. The piston
operated by the pressure of the train pipe is larger than the other and
consequently the valve piston is normally pressed back, uncovering a
small port through which air from the train pipe feeds into the local
reservoir. In this way the air in each local reservoir is maintained
at the same pressure as that of the train pipe. Whenever air is let
out of the train pipe, the piston is pushed out by the excess pressure
on the local reservoir side and uncovers another port which permits
air to flow from the local reservoir to the brake cylinder operating
the brakes. The advantage of this system is that each car is always
supplied with sufficient power to act on the brakes immediately without
having to draw its supply of air from the main reservoir. In case the
train breaks apart, the air in the train pipe escapes and the brakes
are set automatically.

There have been a number of improvements in air brakes aimed to make
the operation of the brakes more uniform and to insure immediate
action, even on a very long train. Modern express trains weighing 920
tons and traveling at a velocity of 60 miles per hour, can be brought
to a standstill in 860 feet, or practically their own length. Automatic
arrangements are provided to insure the application of the brakes
at graduated rate, except, of course, when the emergency brakes are
applied. As the speed of the train slows down the pressure is gradually
relieved, otherwise the train would stop with a severe jolt. The rate
of applying the brakes so as to provide a smooth retardation depends in
large measure upon the weight of the train.

On the New York subways, it is interesting to note, every passenger
who boards a train has his weight recorded by the brake mechanism, and
allowance is automatically made for the inertia that his mass adds to
the train when it is in motion. The weight operates through a system of
levers to control the amount of pressure that is applied to the brakes
so that when the engineer operates the brake lever, he does not have to
consider whether the cars are light or jammed full of passengers; the
brake mechanism itself takes care of this.


If air can be used to stop a train, why cannot air be used to propel
it? This question occurred to many inventors and they answered it by
building air-propelled cars and locomotives. Pneumatic cars were tried
out on street railways, but they have had to give way to electric
cars which do not need to carry their power around with them, but can
draw it from a central power plant through a trolley wire. In only a
few situations, such as in mines where electric sparking is feared,
are air-propelled cars and locomotives still used to any considerable

However, air plays another and highly important part in transportation
and here it is employed not to deliver energy stored in it, but to
serve as a cushion. Without the soft, flexible grip of the air-filled
rubber tubes with which automobile wheels are shod, high-speed
motoring would be practically impossible. There is nothing that can
compare with air for absorbing shocks and unevennesses in the road.
Whenever an obstruction is encountered, not only is the shock absorbed
by elasticity of the air, but the impact is immediately distributed
uniformly over the whole tire, so that the strain on the tire is not
localized and the life of the tire is correspondingly increased. There
have been many attempts to introduce substitutes for pneumatic tires,
such as combinations of metallic springs and straps, but these have
failed, chiefly for the reason that they cannot distribute the shock
as the pneumatic tire does. Consequently they are not only liable
to damage, but they do not absorb the obstructions as readily as the
pneumatic tire does and the vehicle which they carry is subjected to
heavy stresses and strains.

Air as a cushion is used to prevent the rebound of the springs of an
automobile and is also widely employed in machinery to absorb the
momentum of moving parts or to slow the action of a spring. In a door
check, for instance, a powerful spring is provided which would slam the
door shut were it not for the cushioning action of air. A plunger is
connected to the door and slides in a cylinder on the door frame. The
air compressed by the plunger can escape only very slowly through a
small port.


Air cushions are used in elevators to prevent too rapid a fall of
the car in case of accident. The lower part of the elevator shaft is
completely inclosed and fitted with steel doors to form an air pocket.
The car fits the shaft closely enough to compress the air under it when
it is moving downward. At normal speeds, this air escapes quite readily
around the sides of the car and through cracks in the doors, but when
the speed is excessive the air cannot escape fast enough and sufficient
pressure is built up to retard the car so that it will strike the
bottom with a moderate impact not at all dangerous to the passengers.

In the Woolworth Building, New York, the highest elevator shafts are
680 feet high and the air pockets are 137 feet deep--i. e., they reach
up to the tenth story. If the car broke away from its supports at the
top of the shaft it would be traveling at the rate of 132 miles an hour
when it struck the air pocket, but before it reached the bottom the
air would bring it practically to a stop. Imagine a heavy automobile
traveling at 132 miles per hour and brought down to a standstill in
half a city block! The passengers would be hurled out of their seats,
but in an elevator the passengers are standing and can brace themselves
against the pressure produced by their own momentum. The velocity
acquired in falling 543 feet to the air pocket must be overcome in 137
feet or ¼ of the distance. This means that the weight of each passenger
is multiplied by four. A man who weighed 150 pounds would find that
his pressure on the floor of the car had mounted to 600 pounds. One of
the inventors of the pneumatic cushion for elevators was killed when
testing out a car, not because of the impact of the car, but because
he was foolish enough to sit in a chair. The chair gave way under his
suddenly acquired weight and the poor man was fatally stabbed by one of
the splinters.

Air jets are used for a variety of purposes ranging from tamping
railway tracks to painting buildings. When a track is depressed under
the tamping action of trains passing over it the ties must be raised
and new ballast introduced under them so as to bring them up to level.
In order to save hand labor and insure the perfect filling of all
cavities a pneumatic tamper is sometimes used. The ballast, consisting
of sand or gravel up to ¾ inch in diameter, is fed out of a hopper and
meets a blast of air that hurls it into place like shot from an air
rifle. This furnishes a very solid and compact road bed.

It is in much the same way that weather-stained stone walls are
cleansed by means of a sand blast. The sand particles projected by the
jet of air act like myriads of tiny bullets which chip away the face
of the stone.


It is after this same fashion that the cement gun is used to project
cement against wire reenforcement to form walls of buildings. Carl
E. Akeley was led to the invention of the cement gun by his efforts
to find an expeditious and economical method of mounting specimens
of large animals for the Field Museum in Chicago. He constructed a
pneumatic device for spraying cement and water upon a canvas-covered
framework, thus building up a body upon which the skin of the animal
could be mounted. This machine was improved and tried out successfully,
on a large scale, in constructing buildings.

The machine as now constructed consists of a hopper into which a
proper mix of sand and cement is introduced. Compressed air blows this
mixture out of a nozzle. Here it meets a jet of water also propelled
by compressed air. The water, sand, and cement combine and strike the
wall or surface to be coated with such an impact as to make a compact
fine-grained coating known to the trade as “gunite.”

Large surfaces can be painted much more readily and more evenly with
compressed air than with a brush. A widely spreading air jet is used
which draws the paint out of a receptacle, breaking it up into minute
droplets that are projected as a mist against the surface, covering it
with a uniform coating.


So far we have been considering air as a compression spring. It may
also be employed in a manner somewhat analogous to a tension spring.
When air is exhausted from a receptacle we have a partial vacuum which
will produce work, but in the opposite direction from that produced by
compressed air. Of course there is no such thing as suction, and it is
the pressure of the atmosphere which is employed to do the work.

We are apt to overlook the fact that a vacuum cleaner depends upon
atmospheric pressure to drag the dust and dirt out of a carpet.
A vacuum cleaner would not work on the moon, where there is no
atmospheric pressure. The apparatus consists of an air pump, usually
driven by an electric motor, which exhausts, or partially exhausts,
the air from a foot piece that is dragged along the carpet. As the air
under atmospheric pressure rushes in through the carpet to take the
place of the air that has been pumped out, it carries with it all loose
particles of dirt. The dirt is filtered out of the air or a mechanical
trap is provided to catch and retain the dirt while the air is allowed
to escape. Large-scale vacuum cleaners are used for cleaning city
streets. The dirt is loosened by revolving brushes and is then drawn up
by atmospheric pressure into a tank.

Another use of atmospheric pressure is to be found in the pneumatic
tubes which convey mail from one post office to another. Air is
exhausted from the tube and when a carrier is inserted which fits the
tube closely the atmospheric pressure behind it forces the carrier
along to its destination. The same system is used to carry money to and
from the cashier’s office in department stores.

In later developments of the pneumatic mail carrier compressed air
was used back of the carrier, but the principle of operation was not
altered. In either case propulsion is effected by the difference of
air pressure on the opposite sides of the car.

In 1869 Alfred E. Beach built an experimental subway line under
Broadway, New York, near Warren Street. The line was only 200 feet
long. A cylindrical car large enough to hold eighteen people, fitted
the bore snugly and was propelled in one direction by compressing the
air in the tunnel and in the other direction by exhausting the air.



THE TERM “water power” is a misnomer. There is no power inherent in
water. It is gravity that makes water fall in cataracts or flow down
a river bed, and hence it is the force of gravity that is responsible
for the turning of our turbines and Pelton wheels. Water is merely the
medium through which the force of gravity acts.

In the steam engine, water, again, serves as a medium and it is the
energy of heat that is actually the working force. A closed vessel is
partly filled with water and heat is applied to it. The water grows
hotter and hotter until at a temperature of 212 degrees it begins to
vaporize. The temperature of the water remains stationary until the
space above the water is completely filled with steam at a pressure
equal to that of normal air pressure. The steam gauge then registers
zero. Continued application of heat raises the pressure of the steam
and also raises the temperature of the water. When the steam gauge
shows a pressure of 25 pounds per square inch, the water temperature
is nearly 267 degrees; at 100 pounds it is over 337 degrees; at 200
pounds it is 387 degrees; at 500 pounds it is about 467 degrees. As
steam is drawn off from the boiler a proportionate amount of water
turns immediately into steam to take its place. If the boiler should
burst, the entire mass of water would instantly flash into steam
because its temperature is far above the boiling point at normal air
pressure. That is why the explosion of a steam boiler is so violent. If
the boiler were entirely filled with steam the effect of an explosion
would not begin to be so destructive as if the boiler were half full
of water. It is really the explosion of water that does such serious

When the steam pressure in a boiler corresponds to the temperature of
the water it is said to be _saturated_. The water in a boiler boils
violently when the steam is drawn off rapidly and tiny droplets of
water are carried off in the steam, producing what is known as _wet
steam_. Steam that carries no water particles in suspension is called
_dry steam_. When the steam is heated above the temperature of the
water by means of an auxiliary heating device or by some peculiar
construction of the boiler, it is called _superheated steam_.

In order to economize fuel it is highly important that as much water
surface be exposed to the heat as possible. This may be done either by
passing the heat in tubes through the water or by passing the water
in tubes through the fire. Locomotive boilers are of the fire-tube
type. The flaming gases of the furnace pass through the boiler through
a series of tubes that lead to the stack. In the water-tube boilers
it is highly important that a good and rapid circulation of water be
maintained, otherwise there might be local generation of steam with
serious consequences.



As steam is used from a boiler the water is slowly exhausted and it
must be replenished with a fresh supply. In early days of the steam
engine, water was pumped in against the boiler pressure by the use
of powerful pumps, but in 1858 a man named Giffard invented a most
ingenious apparatus by which steam of the boiler was used to force
water in directly against its own pressure. This seems like lifting
oneself by one’s boot straps. When the injector was first invented it
seemed so impossible for it to work that engineers would not accept it
until it had repeatedly demonstrated its operativeness. Even after it
was accepted and in common use its mysterious operation was a subject
of discussion for years. A sectional view of a Giffard injector is
shown in Figure 45. Steam from the boiler comes down the tube A and
passes out in a jet from the nozzle B. A needle valve C may be moved
into the nozzle to reduce or shut off the jet of steam. The jet enters
a conical chamber D which has a tube E that runs down into the water
reservoir. The steam jet blows the air out of chamber D, producing a
partial vacuum which draws water up the tube E and into the chamber D.
When the water reaches the steam jet it is driven out of the chamber
across a short open space into a slightly diverging tube or receiving
cone F and through a check valve G into the boiler. At H there is a
glass window through which the action of the water jet as it rushes
into the receiving tube may be watched. I is an overflow pipe leading
back to the reservoir. When the steam flows into the cone B it gathers
momentum and issues from the nozzle in a jet of high velocity. On
striking the water it combines with the water and condenses, but at the
same time it imparts its momentum to the water so that the water is
given more than enough momentum to drive it into the boiler against the
pressure in the boiler.

The pressure of steam is utilized to drive the piston of an engine
or the steam may be set in motion by letting it issue from a nozzle,
when its momentum may be employed to drive a steam turbine in the
same way that a water jet drives a Pelton wheel but in either case it
is heat that does the work. The steam expands as it moves the piston
and as it passes through the nozzle its expansion is accompanied by a
corresponding loss of heat.

As we have already noted, it was for the purpose of raising water that
inanimate powers were first set to work. It was with the same object in
view that steam was first employed.


To be sure the first steam engine was invented by Hero, the disciple
of Ctesibius, in the second century before Christ, and it was not a
water-raising machine. It consisted of a hollow sphere (see Figure
46), mounted to rotate and fed with steam that entered it through the
journals. The steam issued from opposite sides of the sphere through
two bent tubes. The steam in issuing from the tubes reacted against the
tubes, pushing them back and causing the sphere to revolve.

Every action is accompanied by an equal and opposite reaction. A bullet
fired from a gun kicks the gun back. In order to push the bullet out of
the barrel, the powder must have something to push against and the push
against the gun is equal to the push against the bullet. Even if there
were no bullet to be pushed the discharge of the powder would react
against the gun. In order to push its own gases out of the gun, the
powder must push back against the gun.

[Illustration: FIG. 46.--HERO’S STEAM ENGINE]

In Hero’s engine, the steam, in order to push itself out of the sphere,
must push against the bent tubes. We have a similar reaction motor in
the revolving lawn sprinkler. The water issuing from the bent arms of
the sprinkler forces them back and causes them to revolve. Were the
arms radial and not bent the reaction would be there just the same, but
it would be exerted against the center of the wheel and hence there
would be no rotation.

Reaction has nothing to do with the pressure of the atmosphere as
so many people imagine. A gun would kick just as hard and the lawn
sprinkler or Hero’s engine would operate just as well and as fast in
a perfect vacuum. It was to demonstrate the principle of reaction that
Hero built his steam engine. As far as we know it was never put to
useful work and remained merely a scientific toy.


The first practical use of steam power was applied to the pumping
of water from the deep mines of Cornwall. Newcomen’s engine, which
antedated Watt’s by several decades, was known as an atmospheric
engine. It consisted of a cylinder fitted with a piston, but the top of
the cylinder was open. The piston was connected to one end of a lever
or walking beam, the other end of which was connected by a chain with
the plunger of a pump situated at the bottom of the mine shaft. Little
power was required to lift the piston because it was counterbalanced by
the chain and plunger attached to the opposite end of the walking beam.
The real work was done in pushing the piston down and thereby raising
the pump plunger. Steam under low pressure was let into the cylinder
under the piston to raise it and then a jet of water was sprayed into
the steam-filled cylinder. This condensed the steam, producing vacuum
and the atmospheric pressure acting on the upper surface of the piston
forced the piston down, raising the pump plunger. The engine ran very
slowly, making only about 15 strokes per minute. Later it was improved,
producing about 30 strokes per minute.


Watt was the first man to build an engine in which the real work was
done by the pressure of steam as in modern steam engines. As long as
the steam engine was used for pumping water the reciprocating piston
could be connected directly to the pump plunger and it was unnecessary
to exert power on both sides of the piston, but in 1782 Watt obtained a
patent on a double-acting engine. Steam was admitted first on one side
of the piston and then on the other. The walking beam was connected
by means of a connecting rod to a crank on a shaft that carried a
flywheel, and the seesaw motion of the beam was converted into rotary
motion of the wheel. This opened up new industrial opportunities for
the steam engine.

The steam was exhausted from the cylinder into a condenser, i.e., a
chamber, in which a spray of water converted the steam into water,
producing a vacuum, thereby relieving the piston of back pressure and
virtually adding that much more power to the steam operating on the
opposite side of the piston. A pump driven by the engine drew the water
and the air liberated from the condensed steam out of the condenser.

Watt invented an ingenious governor to control the flow of steam to
the engine and insure a uniform motion. (See Figure 47.) This governor
consisted of a pair of levers hinged to a revolving shaft and each
provided with a ball weight at its free end. The shaft was revolved
by the engine and if the engine tended to run too fast the balls were
thrown out by centrifugal action. In so doing they operated a throttle
valve cutting down the steam supply. When the engine slowed down the
balls would drop, admitting more steam. In this way the speed of the
engine was kept within close limits. The ball governor in improved form
is still widely used in stationary engines.


[Illustration: FIG. 47.--WATT’S BALL GOVERNOR]

Another of Watt’s inventions which has proved of highest importance
in steam engineering was the cut off. In his first engine the piston
was subjected to the full boiler pressure throughout its stroke, and
the steam that poured out of the exhaust port of the cylinder at the
end of the piston stroke was almost as hot as that which entered the
cylinder at the beginning of the stroke. The heat that goes out in the
exhaust represents just so much wasted energy. Watt realized this and
so he invented a valve which would cut off the flow from the boiler
before the piston had completed its stroke. Then the steam back of
the piston would continue to expand because of the heat within it
and would keep on pushing the piston. Of course, the pressure would
gradually diminish and there would be less power in the stroke than if
the full boiler pressure were pushing the piston all the way, but this
loss of power is offset by the saving in steam and in the fuel used
to heat the steam. The point at which the cut-off takes place depends
largely upon the pressure of the steam. If the steam is cut off when
the piston has made only one-fifth of its stroke, one-fifth as much
steam will be used at each stroke as would be the case if the steam
were used nonexpansively. However, in actual practice the expansion of
the cut-off steam instead of being five times would be only about four
times, because of the clearance that must be allowed between the piston
and the end of the cylinder. If steam of 100 pounds absolute pressure
is used, the average pressure throughout the piston will be only about
57 per cent of the full pressure of the steam in the boiler, but each
pound of steam will actually do .57 × 4 = 2.28 times as much work as
it would if used nonexpansively. All sorts of valve gear have been
invented to admit steam quickly and cut it off at the proper point to
produce the most efficient result.

In low-pressure cylinders in order to prevent loss of heat through the
wall of the cylinder, the latter is steam-jacketed. In other words,
there is an outer casing surrounding the cylinder and between this
casing and the cylinder steam is admitted to keep the cylinder walls

In order to make full use of the heat in steam it is, in some engines,
sent through a series of two, three, and even four cylinders. The
exhaust from one cylinder goes into a second larger cylinder. From here
after doing work on a piston it discharges into a third still larger
cylinder and from that may be led into a fourth cylinder. The cylinders
must be progressively larger to allow for the expansion of the steam.

The ordinary steam engine labors under the disadvantage of having
to start and stop its pistons at the end of each stroke. Every body
possesses inertia, whether it be moving or at rest. If it be at rest,
it takes much more energy to set it in motion than to keep it moving.
In fact it would keep on moving without further expenditure of energy
were there no friction and no forces acting against it. In order to
stop the body energy must be expended to overcome its inertia. The
more rapidly a body is started and the more quickly it is stopped, the
more work must be done in overcoming its inertia. In a steam engine
not only the piston but other parts connected to it may be required to
reciprocate several hundred times per minute. A great deal of energy is
uselessly expended in starting and stopping these parts.

Many efforts have been made to produce a rotary engine in which the
piston rotates instead of reciprocating, thus doing away with the
work of overcoming inertia. However, there are serious obstacles to
the construction of such an engine, and as yet no truly efficient and
practical rotary engine has been built.


However, there is another type of engine in which the steam is applied
continuously and all the parts revolve. Such an engine was the reaction
turbine invented by Hero, to which reference has already been made.
Modern turbines, however, are of very different construction. They
resemble the Pelton wheels and turbines used in developing water
power, differing from them mainly in the fact that use is made of the
expansive energy of steam which is lacking in water. In the De Laval
steam turbine a wheel is used which has a series of curved buckets all
around its periphery that are closed at the outer end by a circular
rim. (See Figure 48.) Steam is directed against this bucket, not
tangentially as in a Pelton wheel, but from the side. Several steam
nozzles are employed and as the steam jets strike the buckets and sweep
around their curved surfaces they react against the buckets and drive
the wheel around. In order to operate efficiently the velocity of the
steam must be very high and the wheel must also turn at high speed.
When steam flows through a diverging nozzle its velocity is greatly
accelerated by its expansive effort. Such nozzles are used in the De
Laval turbines and the steam issues from them with a velocity which
may be higher than that of a rifle bullet. The buckets are forged and
the hard-scale surface is left on them; otherwise they would wear away
quickly under the action of the powerful jets of steam.

[Illustration: FIG. 48.--THE DE LAVAL STEAM TURBINE]

The turbine wheel may revolve at a speed of 30,000 revolutions per
minute. Such a tremendous speed has its disadvantages. If a wheel is
to run smoothly it must revolve on its center of gravity. A lopsided
wheel, or one that is mounted a little off center, produces a pounding
action which imposes a serious strain upon the bearings and the
revolving parts. The wheel tries to turn on its own center of gravity
and will do so if permitted to. It is impossible to balance a wheel so
perfectly that the axis it turns on passes exactly through its center
of gravity. At ordinary speeds this slight eccentricity is so slight
that it is practically negligible, but when we have to deal with 30,000
revolutions per minute the least divergence between the center of
rotation and the center of gravity will produce dangerous strains. For
this reason the wheel of the De Laval turbine is mounted on a flexible
shaft and on floating bearings, so that it will automatically find
and turn on its own center of gravity. In order to utilize the power
developed in the wheel, gearing must be used to step down the speed.


The Parsons steam turbine resembles a water turbine in its action.
Instead of having a few nozzles directing steam against the buckets
there is a nozzle for each bucket, and instead of a single wheel there
is a series of them through which the steam passes, successively
passing through a set of nozzles between each wheel. The nozzles are
formed of blades on the periphery of stationary wheels. These blades
are curved in the opposite direction to the blades on the revolving
wheels, as shown in Figure 49. Steam in passing through the ring of
curved stationary blades is divided up into a series of jets which
strike the curved blades of the first wheel. In passing through this
wheel the direction of the stream is reversed, and it enters between
the second set of stationary blades, which turn it back again and
direct it against the next wheel. Thus the steam pursues a sinuous
course through the series of wheels. To allow for the expansion of
the steam the blades are made progressively longer and the wheels of
progressively larger diameter from the inlet to the exhaust end of the


The Curtis turbine combines the De Laval and the Parsons principles.
The steam enters through a series of nozzles which are of the expanding
type, then it goes through a series of moving and stationary blades, as
in the Parsons turbine, from which it enters another set of expanding
nozzles and gains velocity and momentum before passing through the
second series or stage of moving and fixed blades. (See Figure 50.)

Steam turbines are particularly adapted for use in electric power
plants. The speed of rotation of the Parsons and Curtis types is much
lower than that of the De Laval and hence the electric generators may
be directly driven by them without the interposition of any gearing.
They can be built of larger power than the reciprocating engines
because they are so economical of space.


A good comparison of turbine versus reciprocating engines is offered
by the 74th Street power station of the Manhattan Elevated Railway,
New York. This station, which was completed in 1901, was equipped with
eight huge reciprocating engines, each developing 8,000 horsepower
normally, and capable of delivering a maximum of 12,500 horsepower. The
whole plant, therefore, had a maximum capacity of 100,000 horsepower.
Gradually these units have been giving way to steam turbines of much
higher power, and in 1919 there was installed one powerful turbine
which alone was capable of developing as much power as the entire plant
of 1901. This is a triple-compound turbine comprising one high-pressure
turbine and a low-pressure turbine at each side. Steam enters the
high-pressure turbine at 205 pounds pressure to the square inch and
then exhausts into the low-pressure turbines, passing from them into
condensers which operate under 29 inches vacuum. Each turbine drives
a separate generator and the combined horsepower of the whole unit is
about 100,000, while the floor space occupied is only 50 by 52 feet.

The economy of space and of fuel offered by the steam turbine is of
great value in the power plants of ships, and this form of prime
mover has been installed on modern high-speed passenger liners and
also on high-speed war vessels. While in certain respects the turbine
is ideal for such service, there are two handicaps which must be
overcome. In the first place, the most efficient speed for the turbine
is considerably higher than the efficient speed of the propeller
and some means must be provided for stepping down the speed. In
the second place, the turbine cannot be as economically controlled
as a reciprocating engine and its direction of rotation cannot be
reversed, so that difficulties are encountered in maneuvering the ship
in harbors. It is no simple matter to gear down the high speed and
enormous power of a turbine, However, an elaborate system of gearing
has been provided for this purpose which has proved satisfactory even
in powerful battle cruisers. The British battle cruisers with a power
plant of 134,000 horsepower are driven by geared turbines. To reverse
the propellers separate low-power turbines are used.

A more attractive system of control is to have the turbines drive
electric generators and then use the electric power to drive the
propellers through motors mounted on the propeller shafts. The electric
power can easily be controlled from the bridge and the propellers may
be reversed by reversing the motors. However, the disadvantage of the
electric system is that it occupies a great deal of space, particularly
in plants running over 100,000 horsepower.



ONE OF the handicaps of steam power is that the heat produced by the
combustion of fuel is not used directly to drive the piston. A large
part of the heat energy in coal goes up the chimney or is wasted
by radiation from the furnace walls. With anthracite coal in the
furnace the loss may be as low as 22 per cent in the very best types
of boilers. In the engine other serious losses occur, so that in the
best condensing reciprocating steam engines the power delivered is
only 10 to 16 per cent of that stored in the fuel. In locomotives the
efficiency is as low as 4 to 6 per cent. In turbines the steam is used
to better advantage and the actual power delivered may run up to 20 per
cent of that in the fuel.

In internal-combustion engines the furnace and boiler losses are
largely overcome by burning the fuel right in the cylinder, where
the heat energy of the combustion may be utilized directly upon the
piston. There are other losses, however, so that the most efficient
gasoline engines deliver only 28 per cent of the energy in the fuel,
and coal-gas engines may run up to 31 per cent.

A wide range of fuels may be used in an internal-combustion engine.
They may be either gaseous, liquid, or even solid. In stationary
engines hydrogen, coal gas, natural gas, blast-furnace gas, and
producer gas are employed to advantage. Volatile fuels, such as
alcohol, bensol, gasoline, and kerosene, are turned into a mist or
vapor and then burned as a gas. In engines of the Diesel type any
liquid fuel ranging down to thick crude oils may be employed, and
in one type of engine, which, however, has not proved commercially
practicable, coal dust is burned in the cylinder.


Owing to the widespread use of automobiles, the general public is
better acquainted with internal-combustion engines than with steam
engines. Nevertheless, there are many elementary facts in connection
with gasoline engines that are not generally known. The average
motorist probably does not realize that he burns far more air in his
motor than gasoline, and he probably does not understand why it is that
the mixture of gasoline vapor and air must be compressed before it is
ignited, or why only one out of four strokes of the piston is a power

If a volume of gasoline vapor be thoroughly mixed with an equal volume
of air, the mixture will not explode. Only when there is an excess of
air will combustion take place, and the most intensive explosion takes
place when there are nine parts of air to one part of gasoline vapor.
Where gasoline is vaporized in a carburetor the best mixture is one
part of gasoline-saturated air to eight parts of pure air. Hence it is
mainly air that is burned in an automobile engine.

The energy of combustion is much greater when the mixture is
compressed. The particles of gasoline and air are forced into more
intimate contact by the compression. The same thing is true of
gunpowder. If gunpowder is ignited in the open air, it will burn
quickly, but not with explosive violence. If, on the other hand, the
powder is compressed in a cartridge and is then ignited, an explosion
takes place. Nearly twice as much gas was required in the early
noncompression-type motors as is required to-day in the compression
motors of the same power.

In an internal-combustion engine the cylinder serves as a furnace. This
“furnace” must be charged with fuel, and after the fuel has been burned
the “ashes”--i. e., the products of combustion--must be removed. The
piston serves as the furnace stoker.

In the ordinary four-cycle engine the action of the piston is as
follows: On the first or down stroke of the piston a mixture of air and
gasoline vapor is drawn into the cylinder; on the next or rising stroke
the charge is compressed. Then the charge is ignited by an electric
spark, and the rapid combustion of the charge produces gases which
drive the piston down. On the fourth stroke the piston rises again and
pushes the burnt gases out of the cylinder. The piston receives energy
intermittently, or only once out of four strokes, and a flywheel has
to keep it going the rest of the time. It is just like propelling a
bicycle with a single pedal and pushing the pedal every other time it
comes out. It can be done as long as the wheel is moving fast enough to
carry itself along between power strokes. Naturally a single-cylinder
motor cannot be slowed down very much without stalling, and it will not
start of itself because it needs outside help in stoking its furnace
before it acquires the power to do this job alone.


There is a two-cycle type of motor in which the burnt gases are removed
from the cylinder, not by the piston, but by the injection of the
unburnt fuel mixture. On the upward or compression stroke the piston
not only compresses the mixture in the cylinder, but draws in a fresh
charge of fuel into the crank case, and when the piston is driven
down by the combustion of the fuel in the cylinder, the charge in the
crank case is compressed until, near the end of its stroke, the piston
uncovers a port in the cylinder through which the fuel from the crank
case is forced in. (See Figure 51.) Just before this occurs the piston
uncovers an exhaust port in the opposite side of the cylinder, and
the burnt gases start to flow out before the fresh charge of fuel
pours into the cylinder. The incoming gas is directed upward so as to
completely scavenge the cylinder of all burnt gases.

There are no bothersome poppet valves in this engine. The piston itself
acts as a valve, opening and closing the inlet and exhaust ports as it
slides by them. Every other stroke of the piston is a power stroke, so
that the engine acts like a one-pedal bicycle, which receives a push
every time the pedal comes around. Unfortunately, the burnt gases are
never completely scavenged, and the fresh charge of fuel is always
more or less diluted by the product of combustion remaining from the
previous charge. This represents just so much loss of power, and
may interfere with the ignition of the charge. For this reason the
four-cycle engine is generally considered more reliable and efficient,
and is far more generally used, particularly on motor vehicles.

To overcome the intermittent character of the internal combustion
engine a number of cylinders are used, which come into play
successively. In the four-cylinder motor one piston is always on the
power stroke. In recent years the number of cylinders has progressively
increased from four to six, eight, and twelve cylinders, while in
racing power boats the number of cylinders has gone up as high as


The temperature of the combustion in a gasoline engine may be over
3,000 degrees Fahrenheit. Evidently it would melt the cylinder walls
were not special provisions taken to keep them cool. The usual method
is to surround the cylinders with water which absorbs the heat, and
then cool the water by passing it through a radiator. Air driven
by a fan through the radiator carries off the heat. Of course this
represents just so much wasted energy and lowers the efficiency of the
motor, but it is the most convenient way of getting rid of the intense
heat of combustion. Smaller motors, such as are used on motorcycles,
have their cylinders cooled by direct action of air on the outer
surface of the cylinder. The heat radiated depends upon the surface
exposed and the velocity of the air current. The radiating surface
of the cylinders is increased by forming them with external ribs or
flanges, so that the air that flows over them, while the machine is
in motion, carries off enough heat to keep the temperature of the
cylinders within safe limits. In some systems, particularly in the
case of stationary engines, to insure a good circulation, the air is
positively driven against the flanges by means of a fan.

There are serious disadvantages in using water to cool an engine.
Besides the bother of keeping the water system supplied with water
there is the danger of clogging the radiator with lime deposits, and
in extremely cold weather the water is liable to freeze and burst
the water jackets or the radiator; for this reason, air cooling is
recommended by some for automobile engines. In certain air-cooled
automobile engines the cylinders are air-jacketed; that is, they are
surrounded with casings through which the air is sucked by a powerful
fan driven by the engine shaft, so that the air is bound to flow if the
engine is turning. The cylinders are ribbed, so that they present a
large radiating surface.


  Copyright, Kadel & Herbert


Seating capacity 100 persons; power, eight 450-h.p. Liberty motors]



Length over all, 97 ft.; weight of engine, 684,000 lbs.; of tender,
214,300 lbs.; tractive power, simple, 176,600 lbs.; compound, 147,200]

Air-cooled engines have hotter cylinders than water-cooled engines
and hence in cylinders of the same size less fuel is drawn into the
air-cooled cylinder. But the fuel is used more efficiently because less
of its heat energy is wasted; so that air-cooled engines show a slight
fuel economy over water-cooled engines. On the other hand, when the
air-cooled engine is overloaded or is run at very high speeds it is
liable to become overheated and may ignite the incoming charge of gas


As has already been pointed out, compression of gas generates heat,
and one of the reasons for cooling the cylinders of an internal
combustion engine is to prevent the gas from exploding prematurely on
the compression stroke of the piston. In the Diesel engine, instead
of avoiding such a critical temperature it is deliberately sought,
because it is the heat of compression, instead of an electric spark,
which ignites the charge. Pure air is drawn into the cylinder on the
suction stroke. This air is under ordinary atmospheric pressure when
it enters, but on the return stroke of the piston it is compressed to
about 500 pounds per square inch. This raises the temperature up to
the neighborhood of 1000 degrees Fahrenheit. Into this highly heated
air a spray of oil is injected by air at still higher pressure and
immediately the oil flashes into flame and the gases resulting from the
combustion drive the piston down.

This is a very economical type of motor. Any liquid fuel may be used,
from light gasoline to heavy crude oils, or the oils that remain after
the more volatile fuels have been distilled from them. The heavy oils
have more heat value in them than is to be found in light volatile
fuels, such as alcohol, gasoline, and kerosene, and because the oils
do not throw off any inflammable vapors unless highly heated, they can
be stored more safely. This is of highest importance on submarines and
Diesel engines are commonly used for propulsion on the surface or to
drive the generators which charge the storage batteries for submerged

In order to inject the fuel into the cylinder against the pressure of
air therein, a powerful air pump is required. This does not need to be
of very large capacity, but it must compress the air to from 700 to
1,000 pounds per square inch. It may seem at first as if the work done
by the engine in compressing the air in the cylinder and in operating
the injector pump represents so much loss, but a moment’s consideration
will show that it is all recovered. The air in the cylinder acts like
a spring, rebounding when the piston starts down on its power stroke
and adding its energy to that of the burning gases, while the air from
the injector pump also enters the cylinder and helps to push the piston

Diesel engines are made to operate on the two-cycle as well as the
four-cycle principle.

In one type of engine, known as the semi-Diesel, a lower compression is
used in the cylinder. This is not high enough to ignite the oil that
is sprayed in, and so a hot tube or bulb is employed at the top of the
cylinder against which the fuel jet is directed. This bulb is heated to
a dark cherry red by means of a torch until the engine has developed
enough heat to keep the bulb at the requisite temperature.



An interesting modification of the Diesel engine is the Junker engine
(Figure 52) in which the cylinder consists of a tube open at each end.
In this there are two pistons which reciprocate toward and away from
each other. Air is compressed between them as they approach each other
and fuel is injected into this air, ignites and forces them apart.
Both pistons are connected to the same crank shaft, one pushing down
and the other pulling up. The pulling piston has a yoke on the end of
the piston rod from which a pair of connecting rods run down at either
side of the cylinder to a pair of cranks on the crank shaft. Between
these cranks on the opposite side of the shaft is the crank to which
the pushing piston is connected. The advantages of this arrangement are
that the moving masses are perfectly balanced, the construction of the
cylinder is very simple and especially adapted to high pressures, and
the reaction of the gases, instead of being directed against a fixed
part of the engine, is directed against a moving piston, thus reducing
the strain on the structure. Of course the power is not doubled or
increased, because each piston moves only half as far as it would for
a given expansion of gas were it operating in a cylinder closed by a
cylinder head.

The efficiency of Diesel engines, although greater than that of the gas
and gasoline engines, is still very low. The semi-Diesel will yield
about 30 per cent of the energy in the fuel, the Junker engine about 34
per cent, and the best Diesel, four-cycle engine in large units, about
36 per cent. This is a wonderfully high efficiency compared with that
of a locomotive, and yet it seems pitiably low when we consider that
nearly two-thirds of the energy stored in the fuel is thrown away.


The waste of energy is clearly evident in the exhaust pipe of an
internal combustion engine. The gases after doing their work on the
piston rush out with such velocity as to produce a sharp explosive
sound. The noise of the exhaust is highly objectionable in automobiles
and must be overcome, but instead of utilizing the boisterous energy of
the escaping gases and getting a little more useful work out of them,
means are provided for hushing their noise. This is done by passing
them through a series of baffles which reduces the pressure of the
gases before they are discharged into the atmosphere. By letting the
gases expand gradually instead of bursting suddenly into the atmosphere
the noise of the discharge is reduced. However, this must not be done
at the expense of the engine power. Unless the gases pass quickly
through the muffler they will choke and retard the exhaust and make
the engine do useless work in driving them through. Even the best of
mufflers will use up nearly 5 per cent of the engine power. The energy
that escapes at the exhaust is not the only loss. All the heat that
radiates from the engine represents just so much wasted energy. In
our water and air-cooled systems we deliberately abstract heat from
the burning gases and throw it away. If we had materials that would
stand the intense heat of burning gases and enable us to conserve all
the heat developed in the cylinder we could use our fuels much more

Many attempts have been made to utilize the wasted heat of internal
combustion engines, but they have not met with any considerable degree
of success, with the exception of the invention of William Joseph
Still. This engine, which was the result of many years of patient work,
was first made public in a paper read before the Royal Society of Arts
in London, May 26, 1919, and when it was shown that the new engine had
developed an efficiency of 38 to 41 per cent it was realized that here
was a remarkable advance over any other machine for turning heat into


The Still engine is a combined steam and gas or oil engine. The heat
that is ordinarily thrown away in the water jacket and in the exhaust
is utilized to produce steam, and this steam is employed to return the
piston to the top of the cylinder after the gases generated by the
combustion of fuel have driven it down. While in previous experiments
some steam had been developed from the exhaust gases it had not been
found possible to generate steam in the water jacket because of the
low temperature that had to be maintained. In the standard internal
combustion engine the cylinder walls are made of cast iron, thick
enough to withstand the heavy pressures to which they are subjected
should the charge be ignited prematurely. Around them the water
circulates under practically no pressure and so the wall of the water
jacket is made comparatively thin. Because of the thickness of the
cylinder wall the water has to be maintained at a comparatively low
temperature so as to keep the interior of the cylinder from growing
too hot. In the Still engine the cylinder wall is from one-third to
one-fourth the thickness of the standard cylinder wall, while the
water-jacket wall is of thick steel. The cylinder wall is formed with
ribs which extend to the water-jacket wall, so that the latter will
take care of any excessive loads due to premature ignition. Figure 53
shows how the cylinder and jacket of the Still engine compare with
those of the ordinary motor. The thin cylinder wall and the ribs
furnish a far better conduction of heat to the water which circulates
between the ribs. The necessary cooling of the cylinder can be
maintained with water at a much higher temperature than in the ordinary



A diagrammatic representation of a Still engine of the two-cycle
heavy-oil type is shown in Figure 54. This is shown with an auxiliary
boiler heated by an oil burner. The piston of this engine has a sleeve
which fits into an annular steam cylinder. The latter is an extension
of the combustion cylinder. Surrounding the steam and combustion
cylinders are the steam and water jackets. The drawing shows the piston
at the end of its downward stroke, having just been driven down by
the gases of combustion. In this position a scavenging-air port at
the left is uncovered and the burnt gases are swept out by a blast of
air, passing out of the exhaust. This consists of a bank of tubes or
flues which pass through a water heater. The gases leave the cylinder
with a temperature of 900 degrees Fahrenheit and they issue from the
exhaust with a final temperature of only 150 degrees Fahrenheit. Steam
now enters the annular steam cylinder from the steam jacket, through
the port shown at the lower right-hand side, forcing the piston up and
compressing the charge of air in the cylinder. Then oil is sprayed in
through a nozzle, not shown in the drawing, and is ignited by the heat
of the compressed air as in a Diesel engine and the piston is driven
down again by the gases of the combustion. The water surrounding the
combustion cylinder comes from the lower part of the boiler and flows
by the exhaust flues. It is maintained at a temperature of 350 degrees
in the water jacket, and here is turned into steam by the heat of the
combustion. Thence it passes into the steam dome of the boiler. On
the downward stroke of the piston a slide valve, shown at the lower
right-hand side, moves down and connects the steam port with an exhaust
port through which the steam flows out into a condenser. Water from the
hot well of the condenser enters the system at the combustion exhaust.
The arrows show the course of the steam and water and the temperature
at various points is given. As may be noted there are two systems of
steam and water circulation: one from the bottom of the boiler through
combustion exhaust heater to the water jacket and back to the top of
the boiler; and the other from the steam dome of the boiler to the
steam jacket, to the steam cylinder, to the steam exhaust, to the
condenser and back again from the condenser into the combustion exhaust
heater, whence it enters the boiler by way of the water jacket.


When water turns into steam a certain amount of heat is absorbed, which
does not show in the thermometer. This is known as latent heat. If
cold water is placed in a kettle and is then heated the thermometer
will gradually rise until the water reaches the boiling point. Then
there will be no further rise of temperature, although heat is still
applied to the kettle, until all the water is turned into steam, after
which the thermometer will begin to show a rise of temperature, showing
that the steam is beginning to grow sensibly hotter. In the engine,
shown in Figure 54, a boiler pressure of 120 pounds gauge pressure
is maintained, and therefore water will not boil until it reaches
350 degrees Fahrenheit. The water in the water jacket registers 350
degrees and is therefore far hotter than it could possibly be in the
open atmosphere. However, the heat from the combustion does not raise
the temperature of the water, but expends its energy in converting
the water into steam. The cylinder wall is kept at a temperature
of at least 350 degrees all the time, so that the air that enters
the cylinder gathers heat from the cylinder as well as from its own
compression, and its temperature at the end of the compression stroke
is higher than it would be in a cold cylinder, thereby insuring the
ignition of the fuel when it is sprayed in.

The Still engine can also be used as a common gasoline or gas engine of
either two or four cycle and the efficiency in such types is from 31 to
33 per cent. This is much better than the best airplane engines, which
show an efficiency under 27 per cent. Although 41 per cent for the best
Still heavy-oil engine is a remarkable accomplishment, yet it does not
begin to compare with the efficiency of the best water turbines and
Pelton wheels, which turn into useful power from 75 to 87 per cent of
the kinetic energy in the water that drives them.



IN PREVIOUS chapters we have indulged in a great deal of historic
retrospect. It may be well at this point, while we are dealing with the
subject of power, to look into the future and the prospects that it
holds out to us.

It was about fifty thousand years ago, according to conservative
estimates, that primitive man first began to use tools, and he managed
to exist and thrive and develop to a very high degree of civilization
during practically the whole of that period without touching the stores
of energy that lay beneath his feet. It was only yesterday that the
steam engine was invented, and when it was discovered how to turn heat
into work and what a wealth of power was stored up in the deposits of
coal there started a lavish and profligate squandering of the precious
heritage of the Carboniferous era. The fossilized vegetation of by-gone
ages is now employed to drive our locomotives and steamships, to turn
our factory wheels, to extract metals from the ore and help us shape
them according to our needs and desires, to convert iron into steel
and to heat and light our houses. We all know that there is a limited
supply of coal in the world and that some day the stores will be
exhausted, yet we go on using larger quantities of the fuel each year.

For the last century our demands for coal have been doubling every ten
years, until to-day the world is using about 1,200 million long tons
per year. It is conservatively estimated that if our demands for coal
do not increase there is enough left in the whole world within a mile
of the surface to last 1,500 years. Fortunately this country is better
supplied than many others, and it is probable that we can get along on
our present rations for 2,000 years. England, however, faces exhaustion
of her coal supplies within two hundred years.

After living fifty millenniums on earth as a being clearly superior to
other animals, man comes into an inheritance which he squanders in one
or at most two millenniums. It is not creditable to our civilization
that we have taken no precautions to ration out this precious store of


As was shown in a previous chapter, we utilize very little of the
energy in coal. Our steam railroads squander from 94 to 96 per cent of
the coal they burn and our best turbine power plants throw away about
80 per cent. The coal we burn in domestic furnaces is most wastefully
squandered. Maybe we shall learn how to use the energy in coal more
efficiently and make it last longer, but eventually it will all be gone
and then what are we going to do?

Of the other fuels available, petroleum takes the leading place,
but we are hardly more economical in our use of this fuel and our
oil supplies are diminishing much more rapidly than the stores of
coal. In 1919 the United States produced 376,000,000 barrels of oil
and consumed 418,000,000 barrels, having had to draw on Mexico for
42,000,000 barrels. Natural gas cannot last much longer and peat bogs
are estimated at about half of one per cent of the coal supplies. Where
shall we turn for heat and power when all these stores of energy are

It has been estimated that the water powers of the earth, if fully
developed, would probably supply about half of the energy that we now
get out of coal. This is a never-failing supply of energy, and no doubt
before we have begun to scrape the bottom of our coal magazines every
river on earth that is capable of turning a wheel will be doing so to
the limit of its capacity. Then there will be a readjustment of the
manufacturing centers of the earth and remote regions such as Iceland,
for instance, which has more available water power than Switzerland,
will hum with machinery, while such countries as Great Britain, which
is relatively poor in water powers, will have to give up manufacture
and revert to agricultural pursuits.

But are there not other powers that can be used? If we could capture
all the energy of the winds we should have ample power to do all the
work that is now done on earth with a large margin to spare. It has
been estimated that the winds contain 5,000 times as much energy as is
obtained from coal, but how may we capture so fickle a power as the
wind. It is so variable, sometimes exerting enough power to lift houses
from their foundations and uproot giant trees, and again sinking to an
absolute calm. In some places wind power is turned into electricity and
then stored up in batteries; but the cost of doing this is high and at
present uneconomical.


The ocean Is a vast storehouse of energy. The quiet but powerful rise
and fall of ocean tides, and the tremendous energy of ocean waves, have
been looked upon with envy by engineers. All sorts of schemes have
been devised for capturing a part of this energy and putting it into
the service of man. Water power has been aptly called “white coal”
and ocean power “blue coal.” Wave energy is but another form of wind
energy and hence just as fickle. There is plenty of power to be had,
but it is a costly matter to build a power plant on the shores of the
ocean and any day a storm may arise which will dash the machinery to
pieces and sweep away the whole plant or convert it into a pile of
wreckage. In a few places, however, Nature has provided a plant which
the ocean has been unable to destroy and man has adopted the plant to
furnish him with power. There is a rocky cave on the California coast
which is exposed to the ocean swells. As the swells sweep into the
cave they compress the air therein and this compressed air is trapped
in a reservoir. Then the air that has been pumped by the ocean is put
to useful work. There are similar caves on other rocky coasts which
could be made to deliver power when coal becomes scarce and it becomes
commercially practicable to exploit them, but the amount of power they
would furnish would be a mere drop in the bucket.


The ocean tides are also immensely powerful, but the rise and fall of
the water is so slight and so gradual in most places that an enormous
plant is required to obtain any appreciable amount of power. In
certain regions, however, tidal power is actually in use to-day. At
high tide water flows into a large basin and at the ebb of the tide the
outflow of the basin operates a water wheel or turbine. Power can be
obtained while the basin is filling as well as while it is emptying.
One serious objection to this plan is that the turbine operates
intermittently and at irregular intervals, sometimes by day and
sometimes by night, depending upon the tide. However, tide mills need
not be exposed to the fury of ocean storms as are plants that seek to
employ the power of ocean waves. In certain localities the conformation
of the coast is such as to accumulate the tidal flow and produce
enormous differences of level between ebb and flood tide. In the Bay
of Fundy, for instance, the tide rises seventy feet and an appreciable
amount of power could be obtained from the flow of water into and out
of the bay. If a sea-level canal were dug across the Isthmus of Panama
there would be a flow of water back and forth through it because the
tides at the Pacific side have a rise and fall of only two feet while
on the Atlantic side the tide rises twenty-two feet. Some power might
be obtained from the tidal flow through this canal, but a fall of
twenty feet in fifty miles would not produce a very swift current.


If tidal power is to be utilized at all it must be done on a grand
scale. A French engineer, R. Esnault Pelterie, has proposed a vast
tidal power system in the English channel where the tide rises high.
(See map Fig. 55.) The plan is a most ambitious one, but the power that
could be obtained is enormous. He proposes to build concrete dikes
across the channel at the Straits of Calais inclosing a large basin
about twenty miles wide and turbines would be operated by the flow of
water into and out of this basin. Of course locks would have to be
provided to permit the passage of ships through the basin. Other and
larger basins could be formed by walling off the estuary of the Thames
and the bay of the Seine on the French coast. The Gulf of St. Malo
could be inclosed by running a dike from Cape La Hague to the island
of Guernsey and thence to the mouth of the Trieux. These basins would
furnish a minimum of 800 horsepower for each square mile, hence the
basin across the Straits of Calais alone would furnish nearly half a
million horsepower while the Gulf of St. Malo would furnish about a
quarter of the power that France now uses in her industries. The first
cost of the installation would be heavy, but there would be no expense
for fuel and the supply of power would be endless. It has been proposed
to dam the estuary of the Severn (England) where the spring tides rise
thirty feet, and it has been estimated that half a million horsepower
would be developed. Part of the power would be used to pump water into
an elevated reservoir which would serve as a storage battery, so that
when the tidal plant was idle because of the turn of the tide, water
flowing out of the reservoir would operate an auxiliary plant, thereby
furnishing a continuous supply of power.


With the exception of the tides all the energy we use on earth comes
from the sun. It is the sun’s energy that is stored in coal beds and
oil fields; it is the sun’s energy that raises water from the ocean
to the tops of our mountains; it is the sun’s energy that makes the
winds blow, and through them disturbs the surface of the ocean, and
even the tides owe a part of their energy to the attraction of the
sun. Why can we not utilize the energy of the sun directly, instead
of at second hand? In the sunshine that beats upon the earth there
is seventy-thousand times as much energy as we now obtain from coal.
Unfortunately the energy of the sun is so widely dispersed that it
cannot be used economically except in a very few places where clouds
do not often interrupt the direct passage of the rays to the earth’s

Near Cairo, Egypt, there is a plant erected by an American inventor,
Mr. Frank Shuman, which develops about fifty horsepower. This consists
of a series of five huge trough-shaped mirrors that focus the sun’s
rays upon boilers and thus generate low pressure steam. The mirrors
measure 13 feet in width and 304 feet in length and these are mounted
on a light steel framework with their axes running north and south so
that they may be turned from east to west to follow the course of the
sun across the sky. In order to prevent the mirrors from shading each
other in the early morning and late afternoon they are set twenty-five
feet apart. Mirrors are made of thin sheets of window glass, silvered
at the back. The troughs are parabolic in cross section and at the
focus of each is hung a tubular boiler painted black to absorb the heat
rays. The five boilers feed a common steam reservoir from which steam
is fed to a pump. This pump raises about 6,000 gallons of water per
minute, which is used for irrigating purposes. Of course at night the
supply of energy is cut off and on cloudy or rainy days no steam is
generated, but such days are few in the region of Cairo, and continuous
operation is not essential to the operation of irrigating systems.

There are localities in Africa, Asia Minor, and even in the United
States where the lack of water and the pitiless rays of the sun have
turned vast regions into deserts. Here the very rays which have parched
vegetation may be utilized to pump water over the thirsty lands and
convert them into rich agricultural regions.

There is another mighty source of power in the internal heat of the
earth. Here and there all over the earth are vent holes through which
the pent-up energy makes its escape in the form of steam, gases, or
molten lava. There is no question as to the enormous stores of energy
in active volcanoes, and as we appreciate the value of heat energy
our eyes turn covetously to these great chimneys of the subterranean


It seems like the height of daring to attempt to harness the volcanoes,
and yet there is a plant in Italy which utilizes volcanic energy and
develops useful power from it. At Volterra, in the province of Tuscany,
there is a volcanic region where jets of very hot steam issue from
cracks in the ground. These steam jets, known as _soffioni_, are laden
with gases and mineral matter. For many years the boric acid that
they contain was abstracted from them, but the steam was allowed to
escape. In some few instances it was piped into houses and used for
domestic heating. In 1908 an attempt was made to convert the energy
of the steam into useful power. Holes were bored into the earth and
steam of a temperature of 302 degrees Fahrenheit came up the pipes.
This steam was applied directly to a forty horsepower steam engine,
and for the first time volcanic heat was set to work. The steam,
however, contained so many impurities that it was impracticable to use
it directly in the engine. The valves and cylinders were soon clogged
with deposits of boric acid. Then instead of trying to obtain power
directly from the steam, the latter was used to heat a boiler in which
pure steam was generated. This plan proved perfectly practical and a
300 horsepower condensing steam turbine was driven by the energy thus
obtained indirectly from volcanic heat. This power was converted into
electricity and the power was transmitted to the surrounding villages.
After the World War broke out and Italy began to feel the shortage
of fuel, the price of coal having risen to $50 per ton, the use of
volcanic power was extended. A 3,000 kilowatt plant was installed and
electric current was transmitted to Florence, Leghorn, Volterra, and
other towns of Tuscany. The exhaust steam from the boilers was utilized
in the boric acid industries.

Other projects for utilizing the internal heat of the earth have been
given serious consideration in Italy. Near Naples there is the dormant
volcano, Solfatara, the crater of which is filled with a sea of very
hot mud underlying a cool thin crust of earth. Holes bored into this
mud to a depth of a few feet send forth steam hot enough to do useful
work and a plan to utilize this store of energy is under way.


There are regions where the ground is red-hot at a depth of a hundred
feet. While there is no water present to furnish steam, it is a simple
matter to sink a water pipe down to the heated earth and then, around
this pipe, to drive a ring of smaller pipes through which steam may
find its way up to the top and be fed either into water heaters or
directly into steam engines. In fact it has been suggested that such
a scheme might be used almost anywhere. If we bore into the earth, we
find that the temperature grows higher the deeper we go. The rate of
increase of temperature varies with different localities, but it is
very evident that anywhere on earth temperatures that will give a steam
pressure of ten or more pounds per square inch can be obtained if we
dig down far enough, and when we find it worth while to do so we shall
probably riddle the earth’s crust with perforations through which
water will be sent down to the subterranean furnaces and it will return
to us laden with heat energy.

After all, we shall not be plunged into dire want when our stores of
coal are exhausted. There will be other sources of power to draw upon,
most of which will be inexhaustible. Furthermore, we have recently
discovered in atoms of matter stores of energy incomparably greater
than any that have heretofore been used to work the will of man. How to
utilize this energy we have not yet learned, but the energy is there,
and no doubt, some day, probably long before coal takes its place in
museum collections, we shall be possessed of a new slave, far more
powerful than that which has served us so far.



THE POSSIBILITY that the wind was the first inanimate power utilized
by man, has already been referred to. There are records of the use of
sailing vessels in Egypt that date as far back as 6,000 years before
Christ. Navigators of that early date, however, could hardly claim to
have mastered the wind. They merely used wind power when the wind was
disposed to help them. If the winds were adverse, they had no recourse
other than to furl their sail, step the mast and depend upon oars to
propel them to the desired port. It was not until thousands of years
later that primitive mariners learned how to tack and pursue a zigzag
course against the wind. When this knowledge was acquired we do not
know, but it is certain that the Phœnicians, who rounded the continent
of Africa 1,200 years before Christ, knew how to make use of the power
of opposing winds. Of course they could not explain how it was that a
breeze could be made to drive a vessel in a direction across and even
opposed to that in which it was blowing. In order to understand this
apparent paradox ourselves, we must go back to the very elements of


The popular conception of force is something that produces motion,
but its true definition is “that which tends to produce _or resist_
motion.” There are forces in existence when there is no motion. When
you hold a weight in your hand there is a force tending to pull the
weight to the earth, but this force is opposed by an equal force
exerted by your muscles in holding up the weight. There is no motion
because the two forces are perfectly balanced. If they were unbalanced,
there would be motion in the direction of the greater force. If the
pull of the arm is greater than that of gravity, the weight will be
lifted, and if the weight is too heavy for the arm to support, it will
go down despite muscular efforts to prevent it. In one case the force
of gravity will endeavor to destroy motion by opposing the lift of the
arm, and in the other case the arm will endeavor to resist motion by
opposing the pull of gravity. A book on a table is motionless and yet
it is acted upon by two forces which are opposed to each other and
hence balanced. The table furnishes a force which resists and balances
the force exerted by gravity. If the book were heavy enough, in other
words, if the force directed downward were great enough, the table
would be crushed.

When two forces are in perfect balance they must be equal and opposite.
Unless the directions of the two forces are exactly opposite, there
will be motion in some new direction. Suppose we use an apparatus such
as shown in Fig. 56 to study the result of three coacting forces. It
consists of a T-shaped frame with a pulley _P_ at each end of the cross
arm. These pulleys turn very freely on their axes, so that we need
not be concerned with any appreciable amount of friction. Two fine
cords running over these pulleys are knotted at _O_ to a third short
cord. Each cord is provided with a hook on which weights may be hung.
Now if we put a pound weight on each cord the two _A_ and _B_ will
raise the weight _C_ until the angles between the cords at _O_ are all
equal. In other words each force of one pound is balanced by two other
forces of one pound each pulling at an angle of 120 degrees to it and
to each other. If we put a 3-pound weight at _A_, a 4-pound weight at
_B_ and a 5-pound weight at _C_, the cords will come to rest in the
position shown in Fig. 57. The weight _B_ being heavier than weight _A_
will pull the knot _O_ to the right until the angle between the cords
running to these weights is a right angle.



Although a force is something that cannot be pictured it can be
represented graphically by means of a line, letting the direction of
the line represent the direction of the force and the length of the
line the strength of the force. In Figure 58 we may measure off 3
inches from _O_ to _a_ to indicate the 3-pound force and 4 inches
from _O_ to _b_ to represent the 4-pound force and 5 inches from _O_
to _c_ to represent the 5-pound force. Now if from _a_ a line is
drawn parallel to _O b_ and from _b_ a line is drawn parallel to _O
a_ we shall have a parallelogram _a O b d_, and if we extend the line
_O c_ it will bisect the parallelogram, running diagonally from _O_
to _d_, and this diagonal will be found to measure exactly 5 inches
which represents the 5-pound force. This is what is known as the
_parallelogram of forces_. It shows us the resultant of any two forces
that are not directly opposite and it gives us the direction as well
as the strength or magnitude of this resultant. It is only because we
happen to choose the forces 3, 4 and 5 that the angle at _O_ is a right
angle. In Figure 59, where the forces are all equal, our parallelogram
is lozenge-shaped and the line _O d_ is just as long as the line _O a_
and _O b_, showing that its magnitude is the same as that of the two
forces that balanced it.


The greater the angle between the two lifting forces the less weight
can they lift. If two men are carrying a ten-pound satchel, each will
be lifting five pounds, if the pull is directly upward; but this is a
rather inconvenient way of carrying the bag and usually they pull at a
slight angle from the vertical, and so each must carry more than half
the weight. If they move so far apart that the angle between them is
more than 120 degrees, each will be carrying more than the full weight
of the bag.



Now that we know something about the parallelogram of forces we
may return to the problem of sailing across and against the wind.
In Fig. 60 we are looking down on the deck of a ship and the wind
is represented by the arrow. The dotted line _A B_ represents the
direction in which the boat is traveling and the line _C D_ represents
the plane of a sail. If the line _E F_ represents the magnitude and
direction of the force of the wind at the center of the sail, then
we can tell how much pressure is being exerted directly against
the sail, by drawing the line _g F_ perpendicular to the sail and
completing the parallelogram by drawing from _E_ a line parallel to
the sail intersecting _g F_ at _G_ and another line parallel to _g F_
intersecting the plane of the sail at _H_. Then the length of the line
_G F_ represents the pressure against the sail. If the line _G F_ is
half as long as the line _E F_, then only half of the force of the wind
is exerted in the direction _G F_. In other words, a wind pressure of
one pound per square foot blowing in the direction of _G F_ will do as
much work as two pounds in the direction _E F_. The force of the wind
has been broken up into two “components,” one (_G F_) at right angles
to the sail, and the other (_H F_) edgewise to the plane, and of course
the latter has no effect upon the propulsion of the boat.


If there were nothing to prevent it, the boat would sail in the
direction _G F_; but the keel of the boat offers resistance to motion
in this direction, and we must construct another parallelogram around
the force _G F_ to find the magnitude of the force exerted in the
direction _A B_. The line _K F_ is drawn at right angles to _A B_, and
then the parallelogram is completed by drawing a line from _G_ to _K_
parallel to the line _A B_ and another from _G_ to _M_ parallel to _K
F_. We have then resolved to force _G F_ into two components _M F_ and
_K F_. The former tends to push the boat along its course while the
latter tends to make it drift to leeward. The length of the line _M F_
is little more than a quarter of the length of the wind force _E F_
and the leeward acting force _K F_ is actually considerably greater
than the forward acting force _M F_. Even with a deep keel there will
be some drift to leeward. This is corrected by means of the rudder of
the ship which is turned to head the ship further into the wind so that
although the boat does not actually travel in the direction of its axis
it may be made to travel along the course _A B_. Of course the boat
cannot sail directly against the wind, but it can accomplish the same
result by tacking alternately to port and starboard so that eventually
it can reach a port that lies in the direction from which the wind


Before the advent of the steamship, sailing vessels were developed to
a high degree of efficiency. The speedy clippers of 1816 to 1845 used
to cross the Atlantic at an average speed of 6 to 9 miles per hour and
sometimes even better, which compares favorably with a common steam
freighter of to-day. The largest sailing vessel ever built was the
_Thomas W. Lawson_, a seven-masted schooner. She was launched in 1902,
but foundered in 1907 off the Scilly Islands. This great ship was a
steel vessel 395 feet long, with a displacement of 10,000 tons and a
cargo capacity of 7,500 tons. She had a sail spread of 40,617 feet.


Although a century has elapsed since the first steam-driven vessel made
its way across the Atlantic Ocean, sails have been as yet by no means
swept off the face of the sea. Nevertheless, even when sailing vessels
had no competitors they did not furnish a perfectly satisfactory means
of transportation. The fickleness of wind power was felt in this
application as well as in that of windmills, and inventors racked their
brains for some more certain means of propelling ships. Naturally, when
the steam engine was a proven success, efforts were made to apply this
newly discovered power to ships. How to make steam drive a ship was a
problem. At first it was proposed to use a system of oars which would
be moved back and forth in imitation of oarsmen and John Fitch’s first
steamboat in 1786 was driven by a set of paddles operated in a manner
similar to that of paddling a canoe. It was a very natural evolution
from oars to paddle wheel, which consists of a series of oars mounted
in a wheel so that they will come into play one after the other. The
propeller, although not invented by Col. John Stevens (as has been
popularly supposed), was first applied by him to steam navigation when
he constructed a small steamboat on the Hudson River in 1804. But the
simplicity of the paddle wheel and its high efficiency, particularly
in quiet harbors and shallow inland waters, gave it preference over
the propeller. In rough seas, however, the paddle wheel was far from
ideal. It was too easily broken by heavy waves and between 1855 and
1865 the propeller displaced it completely for ocean-going vessels.


Another curious form of propulsion, which dates back to the eighteenth
century and is still periodically revived by inventors, is the water
jet. The idea was to have the engine operate a pump which would drive
a stream of water out of the stern of the boat and drive the boat by
reaction. The British Government actually built two jet-propelled
steamers. One of them, called the _Waterwitch_, was a 1,100-ton vessel
and the other, the _Squirt_, was a small torpedo boat. The latter
attained a speed of but twelve knots while a sister ship of the same
steam power driven by a propeller attained a speed of seventeen knots.
The _Waterwitch_ was even less efficient. Some years ago experimental
water-jet vessels were built in New York in which a jet only ⅝ inch
in diameter with a pressure of 2,500 pounds per square inch was used,
but the experiment proved a failure. The propelling force of a jet is
the reaction of the stream of water against the orifice from which
it issues. The action is just like Hero’s reaction steam turbine
referred to on page 143. The propulsion would be the same were the jet
discharged in the open air or in a vacuum or against a solid stone wall.


It takes very little power to move a boat slowly because the resistance
that has to be overcome is merely the parting of the water at the
bow and closing in of the water at the stern and the skin friction
along the sides of the hull. In addition to this there is a similar
resistance offered by the air. At very low speeds the resistances
of the water and the air are practically negligible. In perfectly
quiet water with no air stirring the pull of a cord will move a ship
weighing hundreds of tons, but the motion will be very slow indeed.
Unfortunately the speed of a ship does not increase directly in
proportion to the power that drives it. Doubling the power does not
double the speed. If it takes ten horsepower to drive a vessel at a
speed of ten knots it will take not 2 but 2³ or 8 times as much power
to drive it at a speed of twenty knots. In other words, the horsepower
goes up as the cube of the speed. This is an average condition for
ordinary speeds. For very high speeds the horsepower may have to be
increased as the 4th and even the 5th power of the speed. The shape
of the bow and the stern is of utmost importance. The parting and
displacement of the water at the bow and the replacement at the stern
produce waves and the forming of these waves represents so much wasted
energy. The swell that is kicked up by a steamer is evidence of power
uselessly expended. Much of this loss can be overcome by careful design
of the ship’s lines. A vessel that kicks up a high bow wave--one that
sails with a “bone in its teeth”--may present a very pleasing spectacle
and may seem to be traveling at high speed, but the best designed
vessel--the one that slips through the water with no fuss--is much more
economical of power. It is easy to understand that the bow must be
carefully designed to cut through the water, but it is not so apparent
that the stern must also be shaped to permit the water to flow in
readily and fill in the void behind the ship. If the stern is not
carefully shaped, there will be a serious drag on the vessel. The skin
friction of the vessel is greatly increased by fouling of the hull with
marine growths. At high speeds the wind pressure on the superstructure
is considerable. Every spar and line adds its quota. A boat that is
traveling in still air at a speed of twenty-two knots or twenty-five
miles per hour is encountering the equivalent of a twenty-five mile
wind which will exert a pressure of over three pounds per square foot
of frontage.


Instead of cutting through the water modern speed boats are designed
to ride over it. The boats have flat bottoms which are arranged as a
series of flat planes known as hydroplanes. These planes form steps
and are set at such an angle as to make the boat rise up on the water
in the same way that a kite rises in the air. The higher the speed the
higher the boat rises so that at full speed it skims on the surface.
Hence there is comparatively little power wasted in displacing the
water. Some of these boats are driven by air propellers so that water
resistance to the propeller gear is avoided. These hydroplanes (they
must not be confused with hydroaeroplanes) almost fly over the water.


It was in 1807 that Robert Fulton built the _Clermont_ and established
steam navigation by running a regular service between New York and
Albany, and it was twelve years later that the Atlantic Ocean was
first crossed by a steam-driven vessel. It was an American vessel,
the _Savannah_, that made the trip. She was a 380-ton ship equipped
with steam power to help her along when the wind failed. Seventy-five
tons of coal and twenty-five cords of kindling wood were taken aboard
to feed her furnace. This was thought to be ample for the voyage, but
before the trip was completed the fuel was all gone. The log of the
_Savannah_ bears this entry the night before sighting the Irish coast:
“2 A. M. Calm. No cole to get up steam.” However the captain did raise
steam just before reaching Kinsale, Ireland, by burning wood. Watchers
ashore beholding the smoke issuing from her stack were convinced that
the vessel was afire and boats were dispatched to the rescue. The
_Savannah_ made the trip from Savannah to Kinsale in 23 days and was
under steam propulsion for only 80 hours of this time.

Regular trans-Atlantic steam service was not inaugurated until 1838,
but for many decades steamers were equipped with sails to assist them
when the wind was favorable.

The most notable of early steamships was the _Great Eastern_, a
combined screw and paddle-wheel ship, 692 feet long, built in 1858.
She held the record for size until 1899 when the _Oceanic_, 704 feet
long, was put into service. At present the _Leviathan_, formerly
the _Vaterland_, holds the record with a length of 920 feet. It is
difficult to judge of the size of a vessel out on the open water. If
the _Leviathan_ were placed in Broadway, New York, she would span
nearly four blocks. Because of her 100-foot beam she would be too wide
to be wedged in between the skyscrapers that border lower Broadway. If
she were set up on end she would tower 158 feet above the pinnacle of
the Woolworth Building. Her power plant consists of four turbines which
total 90,000 horsepower and the huge vessel is driven at a speed of
25.8 knots or nearly thirty miles per hour.

The wonder of these huge floating structures lies not merely in their
gigantic proportions but in the fact that they are able to weather
the terrific wrenching strains of heavy ocean storms. A skyscraper
is built to withstand only the steady and direct pull of gravity and
the variable thrust of the wind which, except in western cyclones,
seldom amounts to thirty pounds per square foot. Bridge building is
more difficult because of the leverage of the parts overhanging the
foundations. Wind pressures must be calculated and also the live load
of objects moving over the structure. In naval architecture enter
the problems of building construction combined with those of bridge
building, complicated by the fact that there is no fixed foundation
for the structure to rest upon. At one moment a ship may be spanning a
trough in the seas and at the next it may be seesawing over the crest
of the wave. Of course the bottom of the boat is seldom if ever out
of the water and a certain amount of support is provided throughout
the length of the vessel, but the ship is subjected to the strains
of a cantilever bridge when she is passing over a wave, and to the
strains of a truss bridge when spanning a wave trough. These strains
are increased by the fact that the structure is in constant motion. A
certain degree of flexibility is demanded of the materials which go
into the structure and of the joints between the frame members.


Originally wood was used for the hulls of ships; then between 1845 and
1855 iron supplanted wood, Between 1875 and 1885 steel supplanted iron
and to-day efforts are being made to supplant steel with concrete. The
advantages offered by concrete are cheapness and speed of construction.
The first large vessel built of this material was the _Faith_, an
8,000-ton ship. This boat stood up very well in heavy weather despite
the rigidity of her structure. It is doubtful, however, that a large
boat comparable in size to the _Leviathan_ could weather a severe ocean

The proposal to build ships of cement created almost as much of a
popular sensation as did the first iron boat. Although the public
had accepted iron and then steel as a perfectly proper material for
shipbuilding, concrete seemed too much like stone and it did not seem
possible that artificial stone could be made to float. They did not
realize that a cubic foot of steel weighs four times as much as the
same volume of concrete. Of course concrete does not begin to have the
tensile strength of steel and consequently the walls of a concrete ship
must be made relatively thick. For this reason a concrete vessel is
heavier than a steel vessel. She draws more water and requires a larger
power plant, and because of her greater mass she is not so readily


As was explained in Chapter VI, a body will float only so long as it is
lighter than the volume of water it displaces. It is almost impossible
to keep a body suspended in water unless some portion of it is exposed
above the surface. If it starts sinking it will keep on going down
until it reaches the bottom of the sea. There is a popular notion that
at great depths water becomes dense enough to float solid iron, but
water is practically incompressible and its density at a depth of five
miles is only slightly greater than that at the surface. An object must
therefore either float on the surface or sink to the bottom, unless its
weight is exactly equal to the difference between the upward pressure
of the water under it and the downward pressure of the water above it.
Such an ideal balance it is practically impossible to obtain unless the
object itself is compressible.

How then can a submarine navigate under water without sinking to the


The first solution to this problem dates back to the seventeenth
century. Doctor Cornelius Van Drebel, a Netherlander, who was a guest
at the court of King James I of England, built three submarines between
1620 and 1624. These were rowboats covered over with a water-tight
deck and propelled by twelve oarsmen. It is recorded that Van Drebel
discovered a means of holding the boats submerged by observing some
fishermen towing baskets full of fish up the Thames. The barks to which
the baskets were attached by cables were weighted down by the load they
were towing, but when the cables slackened the boats rose a little bit.
Van Drebel’s method of applying this principle was evidently to attach
a weight to the boat which trailed along the bottom. When the oarsmen
propelled the boat, she was pulled down under the surface by the drag,
but when the rowing ceased the boat would float up to the surface. King
James himself is said to have made a journey of several hours’ duration
in one these boats, which was kept at a depth of twelve to fifteen
feet below the surface. Progress must have been very slow because the
range of the submarine was given as five or six miles.

During the Revolutionary War David Bushnell built a submarine with
which attempts were made to sink a British frigate lying in the Hudson
River. This submarine was driven by a hand-operated screw propeller.
The boat was provided with water ballast tanks, and by pressing a valve
with one foot he could let in water enough to submerge the boat while
with the other foot he could operate a pump to empty the tanks and
bring the boat to the surface. When the boat was ballasted so that she
would barely float, a vertical screw propeller was operated to raise
or lower her as much as desired. A 200-pound lead weight was attached
to a long cable which passed up through the bottom of the boat, and by
letting out this cable the submarine could be made to rise instantly in
case of an accident.


To Robert Fulton, however, belongs the credit of building the first
submarine operating on the principle that is now universally used.
His boat was also driven by a hand-operated screw propeller and was
furnished with water tanks which could be filled or pumped out at will,
but after the submarine was weighted until only the conning tower
showed above water, she was submerged or raised by means of horizontal
rudders or hydroplanes which could be tilted to any angle desired. Of
course these rudders, like any other rudders, would not operate unless
the boat were in motion. Such is the case with modern submarines. Like
bicycles, they must keep on going or they will fall. If they are
heavy, they will fall to the bottom, and if light they will “fall”
to the surface. When in motion the hydroplanes will either hold them
down or lift them up according to the angle to which these horizontal
rudders are tipped.

Robert Fulton’s _Nautilus_ had a fish-shaped hull of copper plating on
iron ribs and was twenty-one feet three inches long by six feet five
inches at her greatest diameter. The screw propeller was operated by
two men. When the boat was on the surface a sail was raised to assist
in driving the boat. This sail could be folded up like a fan when it
was desired to submerge.

Fulton deserves full credit for anticipating so many of the essential
features of the modern submarine, but of course the _Nautilus_ was
a mere toy compared to the marvelous machines which swim under the
surface of the sea to-day.

The German U-boats at the outbreak of the war were 150 feet long and
could make only nine knots submerged and twelve knots on the surface,
but later they grew to a length of 300 feet with a submerged speed of
twelve knots and a surface speed of eighteen knots. The British in
the meantime developed a submarine that was 340 feet long and had a
displacement submerged of 2,700 tons as against 800 for the largest
German U-boats. The speed of this big British boat is twenty-four knots
on the surface and ten knots submerged.


Despite their name, submarines are really surface boats. Only when
necessity demands are they submerged. During the war even the U-boats
did 90 per cent of their sailing on the surface. Origially submarines
were built primarily for submerged travel and consequently they were
given the form of a fish or of a fat cigar, but such a shape was not
adapted for surface sailing. Water piled up on the nose of the boat and
tended to bear her down. To overcome this, submarines are now shaped
more like a boat with a bow high enough to part the waves without
burrowing into them.


The gasoline engines that were formerly used for propelling the boats
have now given way to heavy oil or Diesel engines, because of the
greater efficiency of these engines and the greater safety of handling
heavy oil. Some submarines have been equipped with steam power plants.
Such is the power used on the big British submarines above referred to.
Of course any power that involves the burning of fuel can only be used
on the surface. As has already been explained, an internal combustion
engine burns seven to nine times as much air as oil and it would be
impossible to store enough air on board to keep the engines going very
long; hence they can be operated only while the hatches are open to the

Coupled to the shafts of the engines are dynamos which generate
electricity and feed it to storage batteries. A dynamo will serve as
a generator when turned by some mechanical power and on the other
hand when current is fed into it, it serves as a motor, so that when
traveling submerged and fuel can no longer be used, the generators are
disconnected from the engines but remain connected to the propeller
shafts and driven by the very current they previously stored in the


Amidships there is a bridge from which the vessel can be navigated when
on the surface and a conning tower from which she can be navigated
when running awash. Most of the submerged travel is maintained at a
comparatively shallow depth so that the submarine can keep an “eye” on
the surface. The eye is the periscope of which there are two so that
in case of damage to one the other may be used. Periscopes date back
to the “Fifties” when they were used on some experimental European
submarines. In the Civil War, when the river monitor _Osage_ ran
aground in the Red River, her captain, now Rear-Admiral Thomas O.
Selfridge, rigged up a periscope with which he could look over the high
banks of the river and direct the fire of his guns upon a Confederate
force that was attacking him. This periscope consisted merely of a
three-inch pipe with a hole at each end cut in opposite sides of the
pipe. Small mirrors were set in the pipe so that the light coming in
through the upper hole was reflected down through the pipe and out of
the lower hole. This crude periscope is the same in principle as the
modern submarine periscopes except that the latter are provided with
lenses to gather and focus all the light possible on the eyepiece so
that the operator will have a perfectly clear view. Periscopes extend
fifteen to twenty feet above the roof of the conning tower. While
periscopes are insignificant objects on the broad seas when a submarine
is moving very slowly, they are made conspicuous by the wake of foam
that follows them when the boat is traveling even at a moderate speed.
For this reason during the war the Germans developed a telescoping
periscope which could be shot up to the surface whenever desired in
order to give the commander a glimpse of his surroundings.

The submarine is submerged by letting water into the ballast tanks and
then turning the hydroplanes to a diving angle. There is an after as
well as a forward pair of diving rudders.

When running completely submerged the submarine is blind and solely
dependent upon the chart and compass. It is impossible to see far under
water. Searchlights are of no value at all. They will not make visible
an object a hundred feet away. The submarine commander cannot see even
the bow of the boat he is piloting. The ordinary magnetic compass will
not operate when entirely incased in steel as it is in the hull of the
submarine and so a gyroscope compass has to be used instead.

While the compass serves as a guide for travel in the horizontal plane
the depth gauge must be watched to see that the boat does not dive too
deeply. The pressure of the sea increases at the rate of 64 pounds per
foot of depth. Two hundred feet below the surface the pressure amounts
to about six tons on every square foot of the surface of the submarine.
Few submarines can stand a greater pressure than that without being
crushed or at least springing serious leaks. When coming to the surface
the hydroplanes are used and if the boat is to remain on the surface
water is blown out of the ballast tanks.


Although submarines may be blind under water they are not deaf. Sound
detectors are used which enable them to locate other vessels by the
throbbing of their engines or the beat of their propellers and so they
can avoid collisions when coming up to the surface.

Despite the perfection of the submarine the sea is still a great
mystery to us. We know only its surface and its shallows. We have
sounded a few deep holes and brought up samples of deep-sea life, but
we have not been able to penetrate in person its profound depths and
explore with our eyes and hands the world that is buried beneath its
waves. Three quarters of the globe is covered by water and if we are to
claim complete mastery of the earth we must find some way of descending
into the heart of the ocean and exploring its deepest valleys.



IN ALL forms of transportation friction plays a most important part. If
there were no such thing as friction, it would be impossible for us to
set an object in motion by the means that are now commonly in use, and
once the object were moving it would be impossible to stop it except by
bringing it up against a wall set squarely across its path.

In transportation on land friction is a much more serious bar to motion
than it is in marine or aerial transportation. There are two kinds
of friction that we have to contend with; sliding friction when two
contacting surfaces are dragged by each other; and rolling friction
when one surface rolls upon another. It is impossible to obtain two
surfaces that are absolutely smooth; there are minute elevations in
each that sink into minute depressions of the other like intermeshing
teeth and a grinding action takes place as these microscopic
inequalities are broken away. Oil reduces the friction by filling up
these inequalities, but the oil itself offers a certain amount of
friction just as water does along the sides of a moving ship.


Rolling friction is of a different kind. The intermeshing inequalities
or microscopic teeth are lifted out of contact with, one another
just as the teeth of gear wheels are carried out of mesh. But there
is another cause of friction due to the fact that no objects are so
microscopic that they do not sink into each other to some extent. A
wheel is always rolling out the surface it is turning on just as a
rolling pin rolls out dough. If the surface is of elastic material
such as a steel rail, it springs back into place immediately after
the passage of the wheel, but the wheel must constantly travel in
the trough of a wave which accompanies it along the rail. There is a
similar wave in the wheel itself and this ironing-out action produces
heat in the wheel and the rail. It is particularly noticeable in the
flexible tires of automobiles which, after a run on even a smooth road,
become too hot to be grasped with the bare hand merely because of the
waves of compression and decompression to which they are subjected.

Both rolling and sliding friction are increased by pressure because
the depression is greater and because inequalities are brought into
more intimate engagement with one another. The degree of friction also
depends upon the nature of the substances in contact, but theoretically
the area of contact does not make any difference. It is just as hard to
push a block along a smooth surface on its edge as on its side.


As intimated in Chapter I the forerunner of the wheel was probably the
roller. It was much easier to move a heavy object on rollers because
rolling friction was substituted for sliding friction, but the rollers
would not stay under the object; they traveled only half as fast as
the load they carried. To make them keep up with the load they had to
be mounted on axles which were fastened either directly to the load or
to a cart body on which the load was supported. Thus the wheel came to
be invented, but except for the fact that it stays by its load and does
not roll out from under it a common wheel is not to be compared with a
roller for efficiency. To be sure, it substitutes rolling friction for
sliding friction where it contacts with the road, but the friction at
the axle is sliding rather than rolling. However, drawing an object on
wheels is a decided improvement over sliding it along the road, for two
reasons: the sliding friction at the axle is reduced to a minimum by
choosing materials that will slide upon each other with comparatively
little resistance, by polishing them smooth and by lubricating them.
But even if these precautions were not taken there would be a distinct
advantage in the use of wheels because of the relatively shorter travel
at the axle than at the rim of the wheel. If a wheel is thirty inches
in diameter and turns on an axle one inch in diameter, it will travel
thirty times as far at the rim as it does at the axle; hence the
sliding friction at the axle is far less than it would be at the point
of contact with the ground, were the wheel locked so that it could not
turn. But it is not necessary to have any sliding friction at the axle
if we revert to the old roller system that prevailed before the day of
the wheel. The axle may be considered the load and the axle bearing
the road. We can then put rollers between load and road. Because the
road is a circular one that travels with the load we can line it with
rollers throughout its length, and the load will never lack for rollers
to roll upon. Thus we have the roller bearing which is so widely
used in modern vehicles. Ball bearings operate on the same principle
except that the balls furnish less contacting surface and are not so
suitable for supporting heavy loads, as are rollers. Sliding friction
is almost completely eliminated and unless heavily loaded a wheel on
ball bearings will not heat even when the bearings are not lubricated.


While there is little friction between a wheel and the roadway upon
which it travels, the roughness of the road is a very important factor.
Every time a wheel goes over a stone the entire vehicle must be lifted;
this represents so much wasted energy. The advantage of the pneumatic
tire lies in the fact that it absorbs small inequalities without making
it necessary for the entire vehicle to rise over them. This means less
load lifted and hence less work done. Large wheels are better than
small ones because they do not sink so deeply into depressions and
because they surmount small obstacles more readily. On a steel track
the size of the wheel does not make so much difference as it does on a
road because the track surface is smooth and is but little depressed
by the wheel. It has been estimated that a horse can pull ten times as
great a load on rails as on an ordinary macadamed road. Some years ago
broad steel tracks were laid in some of our city streets for the use of
horse-drawn trucks. They served very well as far as the vehicles were
concerned. The road friction was reduced considerably, but the fact
was overlooked that the horses needed a good friction surface under
their feet. Two horses could not pull a truck along the track without
walking on the track and the smooth steel made such slippery footing
that the tracks had to be torn out and replaced with common paving.


The difference between sliding and rolling friction is well illustrated
in a locomotive. The driving wheels are turned around by steam power.
They must either roll or slide on the track and the load they will
pull without slipping is a measure of the excess of sliding friction
over rolling friction. To increase the traction or the adhesion of the
locomotive to the track it is provided with a number of driving wheels.
In some of our largest locomotives driving wheels are placed under the
tender so as to obtain a maximum of traction.


When it was first proposed to substitute steam propulsion for the horse
it was not realized that a rail would furnish enough traction to permit
of hauling heavy loads, and some of the early locomotives that ran on
rails were provided with toothed wheels that engaged in racks alongside
the rails. In fact, the earliest locomotives were not built to run on
rails but on ordinary roads; in other words, they were automobiles.
The motor car can therefore boast of a more ancient lineage than the
railroad engine. Joseph Cugnot of France is said to have built a
three-wheeled steam carriage in 1769 which was so top-heavy that it
upset when making a sharp turn at three miles per hour. Several steam
carriages were built in England in the eighteenth century, but they
were not successful. The real father of steam traction was Richard
Trevithic, of Camborne, Cornwall, whose first steam carriage, built
in 1801, carried eight passengers. His third machine, built in 1804,
was the first to run on rails. This was strictly a locomotive intended
to haul cars. It ran with its load at the astonishing speed of five
miles an hour. Trevithic was the first to exhaust the steam from the
cylinders into the smoke-stack and thereby increase the draft through
the furnace and generated steam at higher pressure.

All the early locomotives used toothed gears to turn the driving wheels
until George Stephenson introduced connecting rods to drive the driving
wheels direct from the pistons. George Stephenson’s “Rocket,” built in
1829, won a prize of 500 pounds in a speed contest when it established
a record of 24 1-6 miles per hour. It also established the doubtful
honor of being the first mechanical speed monster to exact the toll of
human life. On its prize run it ran over a man and killed him.


[Illustration: FIG. 61.--STEPHENSON’S LINK MOTION]

Stephenson’s son Robert is commonly credited with the invention of
an ingenious link motion, although the invention is also claimed for
W. T. James of New York. We must pause a moment for a description of
this ingenious link motion, because it became a standard in locomotive
construction that is still in service. As explained in Chapter IX steam
should be used expansively in order to obtain a maximum of efficiency.
After a certain amount of steam has been admitted into the cylinder
it is cut off from the boiler and it pushes the piston by its own
expansion. The speed of the locomotive must be varied by varying the
point of cut-off, and the direction of motion of the locomotive is
reversed by reversing the motion of the valve. In the Stephenson link
motion this is all effected by the operation of a single lever. Fig.
61 shows the arrangement. The valve is moved back and forth by the
rod _A_ which is connected to the arm _B_ suspended from the frame of
the locomotive. The drive shaft is shown at _C_ and it carries two
eccentrics projecting on opposite sides of the shaft which move the
rods _D_ and _E_ back and forth. The outer ends of these rods are
connected to opposite ends of a curved link _F_ and a pin _G_ on the
arm _B_ engages a slot in the link. The link is held up by a rod _H_.
As the drive shaft rotates the slotted link is oscillated back and
forth on its own center. When the link is lowered so that the pin _G_
is at the center of the slot there is no motion of the valve rod _A_,
but when the pin is at the top or at the bottom of the slot the valve
rod has its greatest motion. As the top of the link is moving in one
direction while the bottom is moving in the other direction, it will
be plain that the action of the valve when _G_ is at the top of the
link will be the reverse of the action when _G_ is at the bottom. The
link is raised and lowered by means of a lever _I_ which is connected
to one arm of a T-shaped lever _J_ which on one side of its fulcrum is
connected to the rod _H_ and on the other to the counterweight _K_.

There are certain defects in the Stephenson link motion that we cannot
discuss here. These became serious as engines grew larger and more
powerful so that to-day it has been largely superseded by other valve
gears. The most important of these is the Walschaerts gear, invented by
a Belgian engineer. This gear, unlike Stephenson’s, is conspicuously
placed outside the drivers and is particularly noticeable because
of its peculiar grasshopper motion. The action of the gear is so
complicated that a description of it would be out of place in this book.


We cannot enter minutely into the development of the locomotive from
the crude machine of Trevithic’s time to monsters of to-day. There has
been a progressive growth of locomotives in power and in speed. Our
biggest freight engines are so powerful that they cannot be used for
pulling alone because they can pull a greater load than the draw-bars
of the cars can stand. If placed at the head of a long train they would
yank the forward cars loose from the rest. Hence they are placed at the
rear of the train to act as pushers or in the middle of the train where
half their energy is expended in pushing the cars ahead of them and the
other half in pulling the rest of the train.

The most powerful steam locomotive of to-day (1921) weighs 342 tons and
its tender 107 making a total of 449 tons. Its length is 105 feet and
its boiler 8 feet 7⅛ inches in diameter. Its low pressure cylinders (4
feet in diameter) are larger than the locomotive boilers of 50 years
ago. Its high pressure cylinders are 30 inches in diameter and the
stroke is 32 inches. It may be operated either compound or simple, _i.
e._, the smaller cylinders may exhaust into the larger ones or they
may take steam direct from the boiler. The tractive effort compound
is 147,200 pounds and simple 176,600 pounds and the total horsepower
developed is 5,040. Each cylinder drives five coupled drivers, in other
words there are twenty power-driven wheels with a pair of trailers and
a pair of pilot wheels. Six and a half tons of coal are consumed per

In the matter of speed a mile per minute has become common and regular
scheduled runs over long distances at an average well above sixty miles
per hour have been maintained, but the present tendency is to reduce
speed somewhat in favor of safety.

There are two inventions that have made possible the high speeds
of modern railroad travel: the air brake, which has already been
described; and the block signal system. The latter, of which there are
a number of different types, being electrical, does not properly belong
in this book.

Stoking a large freight engine or a high speed passenger locomotive is
strenuous work. Three tons of coal per hour is not an uncommon rate of
consumption. The fireman on a fast express train gets little rest. To
relieve him of this exhaustive work automatic stokers are now being
used. These convey the coal from the tender to the fire box and feed
the fuel at a uniform rate. In place of solid fuel, oil is extensively
used in regions where it may readily be obtained. This simplifies
the task of firing the locomotives. There has also been some use of
powdered coal which is blown into the furnace in much the same way as
oil is.

To-day steam locomotives have found a serious competitor in the
electric locomotive, which is steadily increasing in favor.

Where traffic is heavy, where long tunnels make the smoke and gases
of a steam locomotive dangerous, where electric power is plentiful,
the steam locomotive must give place to electricity. As the cost of
coal mounts, the electrification of railroads will spread and it will
be only a matter of time before the electric locomotive, which is far
more economical in its use of power, will completely supplant the steam


As we have already noted, the automobile antedated the railway
locomotive. It was an accident that took the primitive steam carriage
off the high roads and put it on rails. In 1802 Richard Trevithic,
while speeding along a road at the frightful speed of ten miles per
hour, lost control of his machine, ran into a fence and ripped off
a number of palings. That accident spelled the doom of the early
automobile. So dangerous a machine was not allowed to run at large.
Special tolls and restrictions were placed on power-driven road
vehicles. As late as 1896 when the automobile had become a practical
machine in France and was being rapidly developed in this country,
England still had a law prohibiting any power-propelled vehicle to
travel over the highways at a higher speed than four miles per hour
and required further that the vehicle be preceded by a man bearing a
red flag.

The most important early American road car was that built by Richard
Dudgeon in 1855, which made a record speed of forty miles per hour.
In 1889 Serpollet, in France, invented the flash boiler and interest
in steam-driven automobiles was revived. In a flash boiler water is
turned into steam as it is used by injecting small quantities at a time
in a red-hot tube. In the meantime, however, the internal combustion
engine was being developed. Lenoir, in France, was the first to build
a motor car driven by an internal combustion engine. He obtained a
patent on such a vehicle in 1860. However, the real father of the
modern automobile was Gottlieb Daimler of Germany, who patented a motor
vehicle in 1884 driven by an internal combustion engine. The next year
Karl Benz, another German, built an automobile.


Pioneer work in this country began with Charles E. Duryea in 1891.
Five years later he took one of his machines to England, where it
entered a fifty-two-mile race between London and Brighton. There were
many entrants from France, Germany, and other European countries.
The American car won the race by nearly an hour over its nearest
competitor. Commercial building of automobiles began in America in
1894. However, it was not until the opening of the twentieth century
that America took hold of the motor car in real earnest. Since then the
rise of the automobile industry has been phenomenal. American methods
of manufacture were applied and cars were turned out in quantity.
In 1916 the annual production exceeded a million and to-day the
production is about two million passenger cars and over three hundred
thousand trucks. The motor car industry is largely responsible for the
wonderful progress in American machine tools that has been made in the
past two decades.

On the race track the motor car has established a record speed of 131
miles per hour, but of greater utility has been the motor truck which
now competes with railroads in the transportation of freight. Owing to
New York’s inadequate terminal facilities, it takes less time to haul
a load from New York to Philadelphia by motor truck than to take the
same load from the warehouse, transport it across the Hudson River, and
load it on a freight car. It has made the country a part of the city. A
short run brings the farmer’s produce to the markets and his passenger
car keeps him in close touch with city life. The motor tractor has
lightened his work on the farm and has enabled him to conduct farming
operations over vast areas. Animal power is gradually giving way to
mechanical power. This, however, is a special branch of automotive
engineering which we must look into.


The success of the automobile depends upon the character of the roads
it has to traverse. Wheels provide the best form of transportation
over a smooth, hard road, but if the road is soft, the wheel will sink
into the surface and will be greatly impeded. In traveling over mud or
sand runners are preferable to wheels because they have a broader and
longer bearing surface. In the snowy regions of the north and the sandy
regions of Africa and Asia Minor, sledges are used in place of wheeled
vehicles. Sliding friction is less than rolling friction under such
conditions. In fact, only where man has constructed special roads is
it possible to use wheeled locomotion. It is because in nature we must
contend with all sorts of surface conditions, soft and hard and seldom
smooth, that the rolling principle of locomotion is not to be found
in any species of animal. The legs of an animal are levers, just as a
wheel is a system of levers, but in the former case the levers can be
folded or extended to adapt themselves to all the unevennesses of the
ground. No animal can begin to run as fast as an automobile on a good
road, but on the other hand we have yet to build a machine which will
run as fast as a horse on soft and uneven ground.


Farm operations must be conducted on loose and broken surfaces for
which the ordinary wheeled vehicle is unfitted. In some cases broad
wheels are used to keep them from sinking into the soil and they are
furnished with cleats so as to give them a good grip on the ground,
but long ago it was realized that if the horse was to be completely
displaced on the farm a more adaptable form of locomotion than that of
wheels must be furnished. Inventors sought to make machines that would
walk. One interesting machine of this class which met with a certain
degree of success attempted to combine walking and rolling. Large
wheels were used which were provided with a series of feet or tread
plates connected by knuckle joints to the wheel rims. As the wheels
revolved, these treads came successively into contact with the ground
and the machine actually walked on its feet. The feet were broad
enough to prevent the machine from sinking into the ground and they
adapted themselves to inequalities in the surface. Instead of having to
roll over a rock that lay in its path the machine would plant its feet
on the rock and lift itself over.

A very curious machine of the walking type has been developed for
excavating machines that operate in soft swampy ground. The machine
actually walks over surfaces that a light carriage could not negotiate.
It consists of a large central turntable flanked on each side by a pair
of broad and long tread plates which serve as feet. When the dredge is
to be moved, it plants the feet on the ground, lifts up the turntable,
moves it forward, and sets it down again; then the feet are lifted,
moved forward, and planted on the ground again while the turntable is
moved forward again. When it is desired to make a turn the machine is
swiveled around to the desired direction while sitting on the turntable
with its feet raised clear of the ground. Of course the speed of such a
machine is very low, but transportation is of secondary consideration.
The main purpose of the machine is to excavate ditches in soft ground
and only occasionally does it have to move its position. The turntable
provides a broad base that distributes the load over a comparatively
large area which prevents the machine from sinking into the mud, and if
it should sink into a soft spot it lifts itself out vertically instead
of having to roll out.


Long ago it occurred to inventors that a machine could travel over
trackless wastes if they carried their own tracks with them. The idea
dates back more than a century, but only in comparatively recent times
has it been developed to a practical stage. The track-laying mechanism
takes different forms, but in one prominent type it consists of a
series of plates linked together to form a chain or belt that passes
around a series of wheels. As the machine progresses the plates are
successively laid down in front of the wheels and picked up behind
them. The wheels consist of a large number of rollers whose axles
are spring-supported so that they are capable of a certain amount of
vertical movement and as the belt they roll upon is made up of separate
plates they can adjust themselves to irregularities of the ground and
creep over an uneven surface. Its close resemblance to the creeping
locomotion of a caterpillar has led to the adoption of the trade name
“caterpillar” by one of the large tractor manufacturers. The tractor
belt is driven by spur wheels at each end and the rollers serve merely
to distribute the weight of the machine along the belt. The traction is
exceedingly great because the belt is broad and long, giving it a large
gripping surface. For the same reason it will not sink into plowed
ground. Because of its flexible tread surface it will creep over rocks
and stumps, waddle down into a ditch and climb up the opposite bank. So
powerful is it that it will crash through underbrush with ease and even
small trees yield before it. It will run over soft mud, deep sand, and
even snow with equal facility. The tread belts on either side of the
tractor are separately driven and by making one belt run faster than
the other it is possible to steer the machine. In fact it can be made
to turn around in its own length by stopping the belt on one side and
driving the belt on the other.

Such a machine is ideal for plowing and other are hauled with ease over
the soft plowed ground. For ordinary farming purposes speed is not
essential, but the possibility of rapid travel with tread-belt traction
was demonstrated in the World War when small “tanks” were built which
could run at the rate of twelve miles per hour.



FROM the day when man began to assert his superiority over other
animals he began to cast longing eyes at the sky. Fired with ambition
and stirred with a spirit of mastery he chafed at the bonds that bound
him to earth; but the heavens remained a forbidden kingdom to him. Many
a bold adventurer who dared to emulate the birds paid the penalty of
his temerity with a broken limb and even with his life. It seemed as if
man were destined forever to grovel on the bed of the atmospheric ocean
with never a chance to rise except in dreams and fancy.

It was not until near the close of the eighteenth century that a means
of rising off the earth was discovered. Two brothers, Stephen and
Joseph Montgolfier, of Annonay, France, were sitting before a fire,
watching the smoke curl up the chimney, when it occurred to one of them
that smoke might serve as a vehicle to carry them up into the air. They
belonged to a prominent paper-manufacturing family and naturally turned
to that material as the most suitable for trapping and harnessing the
smoke. They began their experiments with a large bag of thin paper
which they filled with smoke and floated up to the ceiling. The next
step was to fasten a dish filled with burning embers to the bag, so
that the balloon carried its own smoke generator. The experiment was
tried in the open air and the balloon arose to a great height. Larger
bags were made of linen and paper and on the fifth clay of June, 1782,
a public exhibition was given. A pit was dug in the ground in which a
fire was lighted and over this was placed a huge balloon which weighed
300 pounds. Eight men were required to hold it down while it was
filling with heated air and, when released, it shot up to an elevation
of about 6,000 feet and came to earth about a mile and a half away.


When the news of this event reached Paris a professor of physics named
Charles suggested that hydrogen, being much lighter than air, would
raise the balloon without the use of fire. By a popular subscription
funds were raised to defray the expenses of securing enough iron
filings and sulphuric acid to generate the hydrogen necessary to fill a
balloon of 22,000 cubic-foot capacity. On the 27th of August, 1783, a
flight was attempted. The big bag arose without mishap and disappeared
in the clouds. Three quarters of an hour later it landed in a field
fifteen miles away much to the astonishment of the villagers thereabout
who gathered around the strange bobbing monster with mingled fear and
curiosity. One of the number, more daring than the rest, advanced and
shot the balloon, whereupon the crowd closed in and tore it to pieces
with their pitchforks.

In November of the same year the Montgolfier brothers built a balloon
48 feet in diameter and 74 feet high, and Jean François Pilatre de
Rozier, a professor of natural history, made several ascents with the
balloon held captive. Then, in company with the Marquis d’Arlandes, the
balloon was cut loose and the balloon voyage was undertaken. Below the
car of the balloon was an iron vessel in which a fire was maintained to
furnish the heated air. The aeronauts each carried a bundle of fuel to
feed the fire and a wet sponge to extinguish sparks that might ignite
the bag. Despite this precaution a number of holes were burnt in the
envelope, but nevertheless the flight was successful and the daring
voyagers came to earth without mishap after a short journey.

M. de Rozier’s career as an aeronaut was a short one. The first man
to be carried up in a balloon, he was also the first balloon victim.
He undertook to combine the Montgolfier and the Charles systems by
building a balloon that employed both the hot air and the hydrogen
principles, but the balloon took fire and De Rozier with his companion,
the Marquis de Maisonfort, were both killed. Two months after De
Rozier’s first balloon ascension a flight was made at Lyons in a huge
fire balloon which carried seven passengers. This big bag was 100 feet
in diameter and 130 feet high, with a capacity of 590,000 cubic feet.
The invasion of the air was now well under way, although for a time
it made little real progress. Owing to the danger of fire, hot air
eventually gave way to hydrogen and later to coal gas, which, although
it did not have half the lifting power of hydrogen, possessed the
advantage of being much cheaper.


It seems hardly necessary in this day and generation to explain that a
balloon rises because it is lighter than the air it displaces, but it
does seem astonishing that a balloon weighing several tons may yet be
lighter than an equal volume of air. We do not ordinarily think of air
as having any weight. We know that the ocean of air bears on the earth
with a pressure of about 14½ pounds per square inch, or about a ton per
square foot at sea level. This amounts to 28 millions tons per square
mile and, when we multiply this figure by the number of square miles of
surface in the total area of the earth, we find that the whole ocean
of air has a weight of 5,500,000,000,000,000 tons--a figure which is
far beyond our conception, but it does impress us with the fact that
air is a ponderable substance. Of course, the atmosphere that exerts
a pressure of 14½ pounds per square inch is scores of miles deep, but
even a small quantity of air has appreciable weight. If weighed in a
vacuum a cubic foot of air would tip the scales at 1¼ ounces, and 100
cubic feet would weigh close to 8 pounds. The air in an empty room 10
feet square and with a 10-foot ceiling weighs nearly 80 pounds at a
temperature of 32 degrees Fahrenheit. In other words, if we had a box
measuring 10 feet on each side and weighing less than 80 pounds in a
vacuum it would float in the atmosphere when the thermometer was down
to the freezing point, provided there was no air in the box to weigh it

Vacuum balloons were proposed long before the time of the Montgolfier,
but the problem was to construct a vessel strong enough to resist the
crushing pressure of the atmosphere. The best bracing for the walls
of the vessel is some gas dense enough to exert a pressure equal to
that of the atmosphere but whose weight is less than that of the air.
The weight of the vessel must then not exceed the difference between
the weight of the gas and an equal volume of air. The Montgolfier
brothers used heated air to keep their box or envelope distended. Air
expanded by heat is lighter than cold air. However, it does not make a
very good filler because 1,000 cubic feet of air heated to 212 degrees
Fahrenheit weighs 59 pounds, leaving only 21 pounds on a freezing cold
day for the absolute weight of our 1,000-cubic-foot box. Coal gas,
on the other hand, weighs about 40 pounds per 1,000 cubic feet at 32
degrees Fahrenheit, while the same volume of hydrogen weighs only 5½
pounds. If coal gas were used to brace our box against the pressure
of the air we should have a surplus of about 40 pounds for the weight
of the box, while hydrogen would allow us 74½ pounds. Of course, the
weight of a volume of gas depends upon its density. No matter how small
a weight of gas we placed in the box it would fill the box completely,
but when we speak of a 1,000 cubic feet of gas or hydrogen we mean a
volume sufficiently dense to bear against the container with the same
pressure that the atmosphere presses outside; _i. e._, 14½ pounds per
square inch. Temperature also affects the pressure. In the case of
fire balloons the hot air inside the envelope is less dense and hence
lighter than cool air outside, but the pressure is equal because the
former is expanded by heat. The volume of gas in a hydrogen or coal-gas
balloon varies greatly with the temperature to which it is subjected.
For instance, if on rising through a cloud or a blanket of fog, the
balloon should encounter the rays of the sun, the heat would burst open
the envelope were no vent provided. The mouth of the bag is kept open,
however, for just such emergencies so that the surplus gas may escape.
On the other hand, sudden chilling of the gas will contract it and send
it down to earth, or the balloon might encounter a downward current
of air, when the only salvation of the aeronaut is to throw out the


Balloons seem like very helpless craft, and yet they are capable of
skillful navigation at the hands of an experienced pilot. Although the
balloonist has no means of self-propulsion and must drift with the
winds, he is capable of controlling motion in the vertical direction
and can choose the particular air currents on which he desires to
ride. By throwing out sand ballast the bag may be made to rise and
by letting out the gas it may be made to descend, and a pilot who
is familiar with prevailing currents of the atmosphere or able to
interpret meteorological indications, may locate the air stream that
will carry him to his destination. Sand is the balloonist’s fuel; when
that is gone the balloon may as well come to earth at once. Its course
can no longer be directed and there is nothing to prevent it from being
suddenly dashed to earth should it run into an “air hole,” which is
another name for a downward air current. When a balloon comes to earth
it is liable to be dragged by the wind and many accidents from dragging
occurred in the early days of aeronautics until John Wise, an American,
invented the rip panel by which the envelope may be ripped open by
pulling a cord, thus freeing the gas and permitting the bag to collapse


Note the belt of cards that determine the pattern that is to be woven]




The greatest altitude ever attained by a balloon has been claimed
for Glaisher and Coxwell, who in 1862 went up to a height of seven
miles. Both men were overcome by the extreme rarity of the atmosphere.
Coxwell, however, although nearly paralyzed and unable to move his
arms, succeeded in seizing the safety valve rope in his teeth and
pulled it before he lost consciousness. The balloon was then at an
altitude of 29,000 feet and rising at the rate of 1,000 feet per
minute. Thirteen minutes elapsed before he regained his senses, and
then the balloon was falling at the rate of 2,000 feet per minute.
From the data furnished, it has been estimated that an altitude of
37,000 feet was reached. While there has been much dispute as to the
authenticity of this record, the altitude of 35,100 feet established in
1901 by Professor Berson and Dr. Suring in the German balloon Preussen,
probably represents a higher ascent than that of Glaisher’s balloon.

The new system of aerial transportation proved very useful in the
nineteenth century. During the siege of Paris, in 1870-1871, sixty-six
balloons arose out of the beleaguered city, and all but seven made
their escape in safety. In our own Civil War captive balloons were
first used to direct the fire of artillery. It was in one of these
balloons that Friedrich von Zeppelin, who was a German military
attaché with the Union forces, made his first aerial ascent. He was
so impressed with the advantages of military observation from such a
lofty aerie that he became from that moment an aeronautical enthusiast,
and on his return to Germany urged upon the military authorities the
importance of the balloon in war. It was then that he began his
aeronautic studies and experiments which culminated in the construction
of the gigantic ships of the air with which Germany undertook to carry
the terror of war into England.


In the World War captive balloons were extensively used by both sides,
an important development being the kite balloon. The common spherical
captive balloon is very unsteady except in perfectly still air. It bobs
around and swings and turns, making an unfavorable base for careful
observation. In heavy winds it is liable to be dashed to earth by
sudden gusts. The kite balloon is held up not only by its own buoyancy,
but also by the wind in the same way that a kite is supported. The
bag is elongated (sausage-shaped) and is fastened to the anchor line
in such a way that it is tilted like a kite. To assist in holding it
in this position the balloon is ballasted at the after end and the
ballast, if you please, is air. A big air-filled bag hangs from the
stern of the balloon and serves as a rudder while two other horizontal
bags serve as stabilizing fins.


No sooner had the Montgolfier brothers proved that it was possible to
rise off the earth upon a bubble of hot air, than inventors began to
devise schemes of propelling the bubble and controlling its course.
The first dirigible balloon was built in 1784 and, strangely enough,
oars were used to propel it. The balloon had a fish-shaped body, just
like that of modern airships, and the bag was kept inflated by means
of air as it is to-day. It was realized even at that early date that
the envelope must retain its shape if it is to plow through the air
with a minimum of friction. As the gas would gradually leak out of the
envelope the bag would become flabby and present a crumpled bow to the
ocean of the air and, to overcome this, a double envelope was provided
and air was introduced between the inner and outer skin. Means were
provided for pumping air in as the gas slowly escaped, thus keeping
the envelope fully inflated. As the air was pumped in sand ballast was
thrown overboard so that the buoyancy of the airship was not impaired.
To-day air is used to keep gas envelopes inflated, but instead of
placing the air in an outside envelope it is introduced into a small
bag inside called a “ballonet.”

From time to time other means of propulsion were proposed and tried. In
1852 Henri Giffard, who is known as the Fulton of aerial navigation,
built and operated a dirigible driven by a steam engine, which he hung
at a considerable distance below the gas bag, so that the fire box
would not be liable to ignite the highly inflammable gas. A draft was
maintained in the fire box as it is in a locomotive by letting the
steam discharge into the smoke stack, but in this case the stack was
inverted and the smoke and gases were blown downward and away from the
coal gas with which the balloon was inflated. The danger of fire and
the difficulty of building a power plant light enough to be carried
aloft and powerful enough to give the craft any material headway were
the chief obstacles that had to be overcome. At the close of the
nineteenth century, Santos Dumont, a Brazilian inventor, built a
balloon that was driven by a gasoline engine. Despite the apprehension
of other aeronauts this machine proved an unqualified success. Two
years later, in 1900, Count Zeppelin introduced the rigid dirigible,
which to-day is the standard for large airships.


There are three types of dirigible airships; the flexible, the
semirigid, and the rigid. In the flexible type, as we have observed,
the envelope must be kept tightly filled in order to hold its shape
when driven against the air. The car is suspended from the gas bag. In
the semirigid type a rigid frame or backbone serves as a keel for the
gasbag and helps to prevent it from crumpling up. In the rigid type a
casing incloses the gas or rather bags; for the gas Is contained in a
number of separate bags fitted into separate compartments. The casing
is composed of a framework of duralumin, which is an alloy of aluminum,
with a percentage of copper and nickel. It weighs but little more than
aluminum, but is five times as strong. Over the duralumin framework is
stretched a sheathing of rubberized fabric. Because of the weight of
this casing rigid dirigibles must be made in large size.


Before the war large Zeppelins were built that were fitted with
luxurious cabins and dining rooms and made regular scheduled voyages.
The big British dirigibles are of the Zeppelin type. The R-34, was
672 feet long and 79 feet in diameter. It was fitted with nineteen
gas bags and had a total capacity of over two million cubic feet of
hydrogen. It was driven by five engines, each developing from 250 to
275 horsepower, and was capable of making from 50 to 75 miles per
hour, depending upon whether or not the engines were pushed. The big
dirigible left the Royal Naval Air Station, near Edinburgh, on the
2d of July, 1919, and landed at the Roosevelt Field near Mineola on
the 6th, having made the trip in four days and two hours. The course
covered about 3,100 sea miles, but the actual air mileage was about
6,300 miles because head winds were encountered. In aeronautic voyages
it is the distance through the air that must be reckoned rather than
the distance over the ground or sea. An airship may be traveling at
the rate of 50 miles per hour through the air, but if there is a wind
of 30 miles per hour blowing against the course of the dirigible, the
latter will be making only 20 miles per hour over the ground, or if the
wind is blowing with the airship it will be making 80 miles per hour
over the ground. Because of the head winds the transatlantic flight of
the R-34 was so much longer than had been anticipated that its stores
of fuel were almost completely exhausted. And yet, when the airship
started out from Edinburgh, it carried 81 tanks of gasoline, each
containing nearly 70 gallons, or a total of 4,900 gallons. This fuel
weighed nearly 16 tons. Almost a ton of oil and 3 tons of water added
to the load and the baggage and crew amounted to 4 tons more. The total
weight carried was over 24 tons and the dirigible fully loaded weighed
altogether about 60 tons. When the dirigible started out it had to fly
low, but as the fuel was consumed it grew lighter and rose higher. The
surplus hydrogen had to be pumped into steel tanks where, owing to its
compression, it was heavy and served as ballast which could at any time
be fed back into the gas bags to increase the buoyancy of the airship.
We can no longer think of air as having no weight when we consider that
all this tonnage was supported by air.

The R-34 was by no means the largest dirigible built, but we dare not
boast of the size of the airships of to-day when the aeronautics is in
its in-fancy, because our present dirigibles may seem puny alongside
the big aircraft that may be built to-morrow. The dimensions of the
R-34 have been given because of the historic interest in this first
dirigible to span the Atlantic Ocean.


Marvelous as was the achievement of the Montgolfiers and wonderful
as were the aeronautic developments that followed the invention of
the balloon, the dominion of the birds was not really conquered until
man had learned how to fly in a machine heavier than the air. Captive
aeroplanes date back to the remote ages of ancient history. Kites are
really “heavier-than-air machines.” They maintain themselves in the air
because they travel through the air at a considerable velocity. True, a
kite may be stationary, or practically so with respect to the ground,
but if we detach ourselves from the ground and view the situation from
a drifting balloon, the earth will appear to be moving under us and the
kite will rush past us as it is dragged by the earth to which it is
tied. The idea of propelling a kite through the air, not by tying it to
the earth, but by furnishing it with its own propeller and power plant,
was conceived long ago, but the problem was to find a power plant
light enough. The honor of being the first man to rise off the ground
in an aeroplane belongs to C. Ader, who made several short flights
between 1890 and 1896 in a machine driven by a twenty-horsepower steam
engine. Our own S. P. Langley did some most important pioneer work in
flying and built a man-lifting, steam-driven machine in 1903 which
would have flown had it not been for an accident to its launching gear.
In fact, this very model was flown successfully a number of years
later. However, it was not until the gasoline engine was developed that
the power plant problem was solved. The internal-combustion motor was
made more and more powerful in proportion to its weight until now there
are several types that weigh less than two pounds per horsepower.

But the power plant was only one obstacle to be overcome. The real
problem was to learn how to control the machine after it rose into
the air. Otto Lilienthal attempted to learn how to fly in a motorless
flying machine. He provided himself with wings and, jumping off a
height or running down a slope, depended upon gravity to furnish him
with the necessary propulsion through the air. Unfortunately after five
years of gliding experiments a fatal accident terminated his aeronautic


In this country the Wright brothers, Orville and Wilbur, took up the
work of Lilienthal and they, too, undertook to learn to fly before they
built a flying machine. In all his years of experiment, Lilienthal
did not have more than five hours of experience in the air. The
Wright brothers determined to spend more time in the air and less in
theoretical speculations at home, so they built a gliding machine that
would sustain a man at a speed of eighteen miles per hour and picked
out a spot on the Atlantic coast where they were assured of fairly
constant winds of sixteen to twenty-five miles per hour. At first
the machine was used as a kite and various experiments were made in
balancing it. Then short gliding flights were made from the tops of the
sand dunes. Not until the art of balancing the glider and controlling
it in unsteady air currents was any attempt made at building a
motor-driven flying machine. It was by these experiments that the
Wright brothers discovered the system of warping the wings so as to
preserve the lateral balance of the machine. After several seasons of
experimental gliding, and not until they felt that they had learned
how to fly, was a power machine built. This made its first flight on
December 17, 1903. The first flight lasted only twelve seconds, while
the fourth flight lasted fifty-nine seconds. Many months were spent in
perfecting the machine and in solving the various problems of flight,
and not until September, 1905, did the Wright brothers feel that they
had mastered the art of flying. After that three years elapsed before
the world was actually convinced of the reality of airplane flight and
recognized the work of the pioneers.


The development of the heavier-than-air machine is so recent and is
still advancing so rapidly that we dare not give more than a brief
outline of its progress here. The more important advances are familiar
to most of us and a record of achievements to-day will be hopelessly
out of date to-morrow. The war gave a tremendous impetus to flying.
Pilots were trained by the thousand. Machines grew in speed up to 150
miles per hour. Huge bombing machines were built, with a wing spread
of over 125 feet, and weighing ten to fifteen tons. These were capable
of carrying a load of four to five tons. The first flight across the
Atlantic was made in June, 1919, by the United States navy flying boat
NC-4, which flew to Newfoundland, then to the Azores, and from there
to Lisbon, Portugal. The trip was finally completed by a flight to
Plymouth, England.

The first nonstop flight was made in the same month by a Vickers Vimy
bomber which, with a favoring wind of thirty miles per hour, made the
trip in less than eighteen hours at a rate of 120 miles per hour.
To-day all-metal aeroplanes are being flown successfully. Plans are
under way to build aeroplanes for service at extremely high altitudes,
where greater speeds are possible owing to the tenuity of the air and
the consequent lowering of head resistance. These machines are to have
inclosed bodies in which air at normal pressure will be maintained by
means of blowers. The blowers would also furnish the engines with air
necessary for proper combustion of the fuel.

We are not going to give a history of the progress of aviation since
the invention of the Wright biplane, but instead we shall look briefly
and in a very elementary way into the principles underlying the flight
of heavier-than-air machines.


What is it that makes a plane or a kite stay in the air? The answer is
inertia. The balloon shows us that air possesses weight; the aeroplane
shows us that air possesses inertia. This is a natural consequence.
Every body possesses inertia and the heavier the body the greater its
inertia. By inertia we mean resistance to change of motion or rest. The
pressure of air against the face of a fan is due to its resistance to
a change from state of rest to a state of motion, while the pressure
of wind against a surface represents the resistance of air in motion
to being brought to a state of rest. The more sudden the change the
higher is the resistance or pressure developed. If an open newspaper
be laid over one half of a ruler, while the other half extends beyond
the edge of the table, the ruler may be broken by a sharp blow on the
overhanging end, not because the other end is held down by the weight
of the newspaper, but because the inertia of the air bearing on the
broad area of the paper prevents the ruler under the paper from rising
in response to the sudden blow at the overhanging end. It is the
inertia of the air, _i. e._, its resistance to rapid displacement that
keeps a parachute from falling like a solid shot to earth.

Figure 62 shows how a kite is maintained in the air. The line _AB_
represents the plane of the kite, the line _CO_ at right angles to this
plane is the pressure against the center of the kite surface. The wind
pressure _DO_ is resisted by the pull of the kite string and exerts
a lift _EO_, which resists the vertical pull of gravity. The sum of
the forces _DO_ and _EO_ must be equal to the force _CO_. If _EO_ is
greater than the force of gravity the kite will rise, and if it is less
the kite will fall. The magnitude of the force _EO_ depends upon the
velocity of the wind _DO_ and the angle of the kite _AB_ to the wind.
If the plane of the kite were parallel to the direction of the wind
the angle would be zero and the lift would also be zero.


[Illustration: FIG. 62.--FORCES WHICH HOLD UP A KITE]

In an aeroplane conditions are just the same as in a kite, except
that a propeller drives the plane through the air with a force equal
to _CO_. The plane is slightly curved, so that air which is deflected
or forced down at the forward edge will continue to press against the
plane all the way to the rear edge. The shape of the top of the plane
is also important. As the plane is driven through the air a partial
vacuum is formed above the plane, so that the difference in pressure
between the two sides is increased and there is a greater lifting
effect. This partial vacuum is known as “cavitation.” In the early days
of the aeroplane it was not realized how important was the effect of
cavitation on rapidly moving objects. Every spar and member of the
airplane as it plows through the air builds up a head resistance in
front and is followed by a wake of rarefied air unless it is given
a stream-line construction. This is illustrated in Figure 63, which
shows at the left a rectangular body traveling through the air and at
the right a stream-lined body. The flow of the air is indicated by the
lines and it is evident that head resistance and cavitation are reduced
by forming the body with a bulging bow and tapering stern. To-day all
the exposed parts of aeroplanes are stream-lined as far as possible.
In the early Wright machines wire braces were extensively used. It was
not supposed that a wire would offer much resistance to the air, but,
upon investigation, it was found that the wire braces would vibrate
laterally and present virtually a broad surface which materially
increased the head resistance.


The angle of the plane determines to a large extent the head resistance
of the plane. If the plane is horizontal the head resistance is at a
minimum, but the lift is also very slight. If the wing planes were
perfectly flat, there would be no lift at all, but because of the
curve of the wings there is a certain amount of lift when they are
horizontal, and even when they are tipped slightly downward, provided
the machine is traveling at high speed. The angle of an aeroplane’s
wings is therefore much flatter than that of a kite.


In order to maintain itself in equilibrium the center of gravity
must coincide with the center of pressure, otherwise there will be a
turning action about the center of gravity and the machine will upset.
The location of the center of pressure depends upon the angle of the
plane. The greater the angle the farther it is from the forward edge
of the plane and the pilot can maintain fore-and-aft equilibrium by
tilting the horizontal planes of his rudder so as to change the angle
of the machine, and hence of the main or forward planes. Unfortunately
the air is a turbulent ocean filled with invisible air currents and
the aeroplane must be capable of adjustment to meet the variations
of pressure due to sudden gusts of wind. This is particularly true
of lateral balance. A gust coming from the side will put a greater
pressure on one side of the aeroplane than on the other. To meet this
the angle of the plane at one side must be less than that at the
other. This was discovered by the Wright brothers and their method of
overcoming the lateral variations of pressure was the key to their
early success. They warped their wings or twisted them so that the
angle of the wing was reduced on the side from which the gust came
and was increased on the other, and thus the center of pressure over
the whole wing was kept on the line of the center of gravity. At the
same time there was a variation in head resistance which had to be
corrected by moving the rudder, and the Wright brothers used a single
lever to warp the wings and at the same time to operate the rudder so
as to keep the aeroplane on its course.

Before the Wright brothers made public their invention other aeronauts
had great difficulty in making turns. When turning, one side naturally
has to move through the air faster than the other. This produces
an increase of pressure on one side over the other which may be
counterbalanced by warping the wings. The same effect is produced by
the use of small wing planes, called “ailerons,” at each side of the
main planes. An automatic means of stabilizing an aeroplane has also
been devised, a description of which will be found in Chapter XXI.



THE FIRST efforts at directing the forces of nature and employing them
in the service of man were made by the farmer. The task of growing food
was quite the most important of primitive occupations, and although
the virgin soil was rich and the yield abundant there were regions
where crops could not be raised except at the expense of constant toil.
Infrequent rains made it necessary to carry water by hand from wells
and rivers and pour it over thirsty lands. As the grain fields grew
more extensive, irrigating ditches were used which saved the toil of
carrying the water, although it still had to be raised by hand. Then
machines were invented by which water could be raised by animal power
and, finally, as we have already seen, automatic water-lifting machines
were constructed by which the river itself was constrained to lift a
part of itself and pour this part into the irrigation ditches.

While it is true that the earliest machines were built to lighten the
work of the farmer, the attention of inventors was soon attracted to
other fields of endeavor and the farmer was left to toil slavishly
from daybreak to sundown with no further mechanical aid. The tools
he used were improved in form and quality. Oxen were used to draw
the plow. The wooden plow made out of a forked stick gave way to a
bronze plow and, finally, to one of iron. The curved knife or sickle
went through a similar process of evolution from flint to iron. It was
the only implement used for cutting the standing grain, and not until
comparatively recent times did it give way to the scythe. Practically
all the work of tilling, seeding, cultivating, harvesting and threshing
was done by hand in practically the same way and with practically
the same tools from the time of the Pharaohs down to the end of the
eighteenth century.


To be sure, there is a record of a harvesting machine built in Gaul,
while that province was under Roman dominion. Pliny described this
machine in 70 A. D. It consisted of an ox cart which was _pushed_
through a field of grain, instead of being _pulled_ by the ox. This
cart carried a rack or comb which caught the heads of the standing
grain, tearing them off and delivering them into the body of the cart.
Unfortunately this primitive, but useful, harvester was not extensively
employed and in time it was lost to agriculture. Farmers reverted to
the time-honored method of reaping by hand and the ox-pushed machine
was forgotten. From time to time in recent years this machine has been
reinvented and a machine similar in principle is used to-day to gather
clover seed.

The scythe was a distinct improvement over the sickle. It enabled a man
to use two hands at the work of reaping instead of one. It provided a
much longer and heavier blade, and hence a much broader swath was cut
at each stroke. A distinctly American improvement on the scythe is the
grain cradle, consisting of a set of fingers above the blade which
catch the grain and lay it in a swath at the end of the stroke. This
important improvement rapidly spread to all parts of the world and is
still used to-day where it is impracticable to use a mechanical reaper.
It is claimed that one man can cut and bind more grain with the cradle
than three men could with the sickle.


The plow has undergone important developments in comparatively recent
years. Wooden plows were still in use in America in Revolutionary
times; usually the point was shod with wrought iron. However,
these wooden plows speedily gave way to metal when iron came to be
manufactured in considerable quantity in this country. A plow has to
contend with two conditions of service that apparently conflict with
each other. The constant friction of the soil against the blade tends
to wear it away very rapidly, hence a very hard surface is requisite.
On the other hand, the plow is apt to encounter buried stones and
rocks which will shatter it unless it is soft. The problem then is to
make the plow both hard and soft. The chilled iron plow was invented
by Oliver, in 1855, to meet the first condition. When molten iron is
poured into an iron mold the surface that comes into contact with the
mold is suddenly chilled, producing a very hard surface that takes a
good polish. This effect is accentuated by using a hollow mold through
which water is circulated. The hard surface of the chilled iron wears
well in sandy and gravelly soil, it does not rust deeply, and it clears
well in sticky soil. However, it is very brittle and is liable to break
if struck a sharp blow. A more recent improvement is the soft-center
steel plow. This is both hard and soft. It is composed of three layers
of metal; the outer layers are of hard cast steel and the center one
of soft steel. These metal layers are heated to a welding heat and
then rolled together, producing a plow that has a hard outer wearing
surface and at the same time is tough because the center layer of soft
steel acts as a cushion to absorb sharp blows. To increase the wearing
qualities of the plow still further a patch of very hard cast steel is
welded over the point of the share. Thus both conflicting requirements
of softness and extreme hardness are met.

We think of the plow as a very simple tool, but the modern implement
is a product resulting from a vast amount of study and research into
the materials most suitable for its construction and into the best form
of share and moldboard. In place of a single plow for all purposes the
modern farmer is offered a large assortment to suit various classes
of work. At least three different kinds of plows are indispensable on
every farm; the sod plow, the stubble plow, and the corn-cultivating
plow. The sod plow is used for turning over the sod and breaking the
clod. This is provided with a jointer or diminutive plow point set
above the share, which turns over the edge of the furrow to prevent
grass from growing up between the furrows. The stubble plow has a
moldboard with less twist than that of the sod plow. This is used for
plowing land that was under cultivation during the previous year.

The plow of to-day has become more than a hand-guided, horse-drawn
tool. It has developed into a real machine, mounted on wheels, with a
disk or coulter wheel that cuts the furrow cleanly, means for leveling
the plow and regulating the depth of the plow, and a seat for the
plowman. It works upon soil with the same precision that a planer works
upon a slab of cast iron. The furrow is neatly sliced, lifted, and
turned over with mechanical accuracy. As the furrow slice slides over
the moldboard of the plow the soil is pulverized by friction. The front
furrow wheel runs in the furrow previously cut which serves as a track
to guide the machine. The front and rear furrow wheels are inclined
from the vertical so as to balance the thrust of the plow and they
may be given a lead toward or from the “land” or unplowed part of the
ground to regulate the steering automatically. The proper adjustment
and balancing of a plow calls for considerable skill.

Agricultural operations are now conducted on such a vast scale that
the single plow cannot begin to do the necessary work. Instead, sets
of gang plows are used so that from a dozen to two dozen furrows
may be turned at a time. Steam or gasoline tractors of the wheel or
track-laying type are required to furnish the tractive effort needed to
haul these huge plows. The larger tractors are so powerful that they
haul not only the plow but a harrow behind the plow to break up the
clods and a seeder behind the harrow to sow and cover the seed so that
all three operations are performed simultaneously.

The disk type of plow is used in very dry and hard soil and also in
very sticky soil. A rolling disk takes the place of the moldboard and
share, and in this way friction is reduced very materially, with the
result that less tractive effort is required to draw the machine.

There is scarcely any agricultural operation for which a machine has
not been designed. We cannot attempt to describe them all. For tilling
the soil there are plows, harrows, drags, and rollers of many different
varieties; for seeding and planting there are grain and seed drills,
corn planters, potato planters, etc.; for cultivating or working the
growing crops there are cultivators, weeders, fertilizer drills, corn
plows, etc.; and for harvesting or gathering the crops there are
mowers, hay rakes and tedders, reapers and binders, potato diggers,
corn binders and huskers, corn shellers, etc.


Most interesting of all are the reapers because they represent
the first successful efforts to introduce machinery into farming
operations. Toward the close of the eighteenth century the Royal
Agricultural Society of England offered a prize for the invention
of a successful reaper, which stimulated inventive effort in this
field. But although many patents on reaping machines were granted by
the British patent office, nothing was produced that completely met
the requirements. In fact even as late as 1851 when a World’s Fair
was held in London the British had no really successful reaper to
exhibit. In the meantime, American inventors had been at work and two
inventors in particular, Obed Hussey of Maryland and Cyrus McCormick of
Virginia, had developed machines which had so far proved their worth
that they were extensively used on American farms. These two inventors,
working independently, produced machines that were very similar in
basic principles. As our patent regulations of that period did not
call for an extensive search of the prior art there was no official
investigation to show which was entitled to the honor of priority of
basic principles or whether both did not include in their applications
much that was old. Hussey filed his patent on the last day of 1833 and
McCormick in June of 1834.

The main stumblingblocks of earlier inventors of reaping and mowing
machines was in finding a suitable method of cutting the grain.
Revolving combs for tearing off the heads of grain, fingers for
gathering the grain and holding it against a revolving cutter,
horizontally reciprocating knives--all these methods were tried
without success. Nearly three years before Hussey obtained his patent,
Manning, of Plainfield, New Jersey, solved the problem by inventing a
reciprocating cutter with spear-shaped blades cooperating with a finger
bar that guided and held the grain against the blades. This invention
was apparently unknown to either Hussey or McCormick and their patents
show cutting means that were broadly the same as that of Manning.


Of the two rivals, McCormick showed the better business ability in
perfecting his invention and promoting it so that he eventually became
to be considered the “Fulton” of agricultural machinery and the public
forgot the pioneer work of Hussey. As a matter of fact, McCormick
built his first successful reaper three years before he obtained his
patent. Four horses were hitched to the machine and he went out into a
neighboring field of oats to demonstrate it. In less than half a day
he had reaped six acres, which was a remarkable performance when we
consider that a single acre was considered a day’s work for one man.
McCormick’s machine had a reel above the cutter to hold the grain
against the knife and as the grain was cut it dropped upon a platform.
A man walked alongside the machine and removed the grain with a rake.
And so the reaper with two men to operate it did the work that had
formerly required twelve men with the cradle.

The next important improvement was to provide a seat at one side of the
reaper so that the man with the rake could ride. While this reduced the
labor of the man it did not materially increase the efficiency of the
machine. The next step, however, was of material importance. In place
of raking off the hay by hand an automatic rake was furnished and the
services of the extra man were dispensed with. One man could then do
the work of twelve. McCormick had had difficulty in introducing his
machine into public use, but now its superiority over hand labor was
so marked that reapers came to be extensively employed on American
farms. The reaper had reached this stage of its development when the
World’s Fair of 1851 was held in London and McCormick’s machine was
sent across the Atlantic to be displayed at the exhibition. At the same
time Hussey sent over one of his machines which had reached the same
stage of development. There was a British machine also on exhibition
based on the invention of Rev. Patrick Bell of Scotland in 1826, but in
a competition with the American machines it could not begin to compare
in efficiency. The work of the American machines was a revelation
to the British farmers. The prize was carried off by McCormick’s
machine, which was declared by the judges to be worth the whole cost
of the exposition. Unfortunately Hussey was not on hand to direct the
operation of his machine, which may have had something to do with its
failure, for in another test the Hussey reaper was found superior to
the McCormick.

The excellence of American reapers was now well established and their
fame spread throughout Europe. In a competitive test held near Paris
in 1855, America won the highest honors by cutting an acre of oats in
twenty-two minutes as against sixty-six minutes for a British machine
and seventy-two for an Algerian machine. In 1878 McCormick was made a
member of the French Academy of Sciences in honor of his achievements.


After the self-raker was introduced the next important improvement was
in the binding of the grain. At first the cut grain was raked into a
receptacle which was dumped by the driver of the machine when enough
had accumulated to form a bundle and the bundles were bound by men
following the machine. As in the evolution of the raker, the next step
was to provide a platform for these men on the machine so that they
could ride as they bound the grain and finally in 1873 a self-binding
attachment was invented which increased the efficiency of the machine
manifold. This self-binder, however, called for the use of wire which
did not meet with favor as a binding material because of the difficulty
of cutting it without a special tool. Efforts were therefore made to
introduce twine instead. But twine cannot be fastened by mere twisting;
it has to be tied and a mechanical means of tying a knot was far from
an easy problem to solve. While it is true that the human body is a
machine and every movement of which it is capable may be reproduced by
mechanical means, the difficulty is to copy many operations without
involving such complexity of members as to make the mechanism wholly
impracticable. The human hand is really a very intricate piece of
mechanism which by long generations of evolution and development has
become wonderfully deft. It exhibits this deftness and complexity of
movement in tying knots and the very intricacy of this operation was
enough to baffle the majority of inventors. There was one inventor,
however, who was not to be thwarted even by so formidable an obstacle
as this. In 1864 Jacob Behel secured a patent on an attachment for
binders which would actually tie a knot. The mechanism passed the twine
around the gavel of grain, formed a loop in the two ends, and tied a
simple overhand knot in much the same way that the hand ties this knot.
Ten years later Marquis L. Gorham improved the mechanism and built a
successful twine binder. Finally in 1879 John F. Appleby perfected the
binding mechanism, completing the last stage in the development of the
modern automatic self-binding reaper.

To keep pace with the reaper, other agricultural machines had to be
invented and developed. The vast quantity of grain harvested could not
be threshed by hand and the old-fashioned flail had to give way to
the steam-driven threshing machine. Finally to meet the requirements
of the vast western wheat fields, the combined harvester and thresher
was developed which, with a crew of four men, will reap, thresh, and
bag between two and three thousand bushels per day. According to
statistics of the U. S. Department of Agriculture it took a man three
hours and a half to produce a bushel of wheat in 1830 as against ten
minutes in 1896. Surely the world owes a tremendous debt to Hussey and
particularly to McCormick for introducing machinery into agriculture
and starting the train of inventions which in the space of two-thirds
of a century have led up to the present remarkable era of machine

There still remains one task of the farmer that has not yet been
accomplished with unqualified success by machine. The harvesting of
the corn crop is a tedious and disagreeable task and one which the
farmer would only too gladly turn over to the machine. To be sure, many
corn-harvesting machines have been built and put into service with more
or less success, but none has reached the perfection of other classes
of agricultural machinery. The difficulty lies not in the machine,
but in the fact that corn is so easily beaten down by storms that at
harvest time the machine seldom finds the stalks all standing up in
nice straight rows. Machines must therefore be provided with means for
lifting up the fallen stalks to vertical position. The stalks are cut
and bound into bundles and stood up in shocks.

Even more difficult than cutting and binding is the task of husking the
corn. This work was always dreaded by farm hands, but now machines are
provided to husk the ears and shred the stalks for fodder. Thus the
farm is being relieved of its drudgery. Unfortunately it is only the
large western farms that can afford to avail themselves of the latest
agricultural machinery. On small eastern farms it does not pay to
purchase a machine which can be used for only a few weeks in the year
and then must be stored away until the next season, but small farmers
are now cooperating and clubbing together to buy the less frequently
used machines and so even the small farm is being relieved of its
drudgery, and the arduous burdens which have always had a tendency
to drive young men away from the farm are now being assumed by the
unfeeling machine.



THE ALBANIAN people have a story that the Creator recently visited
the earth and was astonished to find how it had changed. “Why, this
is not the earth I created,” He said. “Everything has changed. My
forests are cut down; My rivers have been diverted from their courses;
My hills have been blasted away, and My mountains have been robbed of
their minerals. The whole face of the earth has been altered.” But in
the course of His roamings, the Creator suddenly came upon the land
of Albania. “Ah!” He exclaimed in delight. “Here is a bit of earth
untouched by man. It is still just as I made it.”

Man’s ambition to make over the face of the earth to his own liking
dates far back of the present age of machinery. However, the work of
the ancient engineer was accomplished only at the expense of decades
and generations of hard manual labor. To-day, with powerful and
gigantic machinery to do our bidding, we do not hesitate to change the
course of rivers, to level off the hills, to carve highways through the
mountains and pierce them with tunnels, to bore into their depths for
treasure and drive deep holes into the bowels of the earth in quest of
liquid fuel. We are able to machine the earth in much the same way as
a piece of metal is machined in the machine shop. In fact, the drill,
the circular saw, the slotter, and even the milling machine have their
counterpart in the excavating machinery of to-day. Of course we cannot
expect to find the counterpart of such machines as the lathe, boring
mill, and planer, in which the work revolves against the tool, because
this planet of ours is rather too big a piece of stock to be placed
between lathe centers or to be bolted to a planer bed.


The twentieth century finds this planet again stocked with monsters
larger and more powerful than the gigantic saurians that dominated
the earth in the Jurassic and Cretaceous epochs, but our mighty
fire-breathing, steel-sinewed beasts are humbly subservient to the will
of man.

The spectacle of a large steam shovel at work makes one feel at once
very small and very big. Before the work of this monster the human
shoveler shrinks to the proportions of a mere insect. Seven to eight
cubic yards shoveled into a cart is considered a fair day’s work for a
laborer, but a big steam shovel can easily gobble up as much material
in two bites. However, when we contemplate that this mammoth machine is
a human creation and an absolute slave to human command, we are rather
inclined to be puffed up with the greatness of man.

Steam shovels are ideal machines for excavating railroad cuts and were
primarily developed for just such work. The general operation of the
machine is very similar to that of hand shoveling. The shovel proper
consists of a big scoop or dipper and a dipper handle which correspond
respectively to the blade and handle of a hand shovel. Like the
shovel, the dipper is supported at two points. The dipper is suspended
by a chain from the end of a boom while the handle of the dipper is
also supported in the boom. By loosening the hoisting chain the dipper
is lowered to the ground, and by moving the handle forward the toothed
cutting edge is made to bite into the ground or sand bank. The hoisting
chain then hauls up the dipper, making it scoop out the bank, after
which it is swung to one side over a car on an adjoining track. The
rear of the bucket is fitted with a door which is opened by a spring
latch and the contents are emptied out. Some of the largest steam
shovels for ordinary grading have dippers with a capacity of 5 cubic
yards. They are not confined to railroad grading, but are applicable to
any excavation where a firm footing is provided for the heavy machine.
They are even used for excavating the cellars of large city buildings.
The machine must be supported on road wheels or on skids. When used
for excavating sewer trenches, it is sometimes mounted on a platform
spanning the trench. However, the steam shovel is rather limited in
its reach. The largest ordinary steam shovels have a clear lift of but
sixteen feet and can make a cut only sixty feet wide at the top.

For more extensive excavating as well as for digging ditches and
trenches the drag-line excavator has recently come in to use. In these
machines a scraper takes the place of the dipper. This is suspended
from the end of a long crane and it is dragged along the ground by a
cable, scooping up a load of earth. In some cases the scoop or scraper
is merely attached to a cable leading from the hoisting engine to
an anchorage and back to the engine. To adapt excavating machines
for service in soft ground they are mounted on broad wheels or on
track-laying tractor surfaces. One peculiar form of walking traction
used by a drag-line excavator was described in Chapter XIII.


For digging narrow ditches and trenches, particularly for sewers, water
mains, gas-pipe lines, etc., a number of very interesting machines
have been invented which are of two general types, the endless chain
and the wheel excavators. The first type consists of a traction engine
with a ladder at the rear that drops down into the trench. About this
ladder runs an endless chain which carries a series of scoops or
buckets. These are dragged up against the breast of the work and carry
the excavated earth to the top of the ladder where it is dumped upon a
transverse belt conveyor and carried to one side of the trench. With
the larger sizes of chain excavators, trenches may be dug to a depth
of twenty feet and the width of the trench may be from two to six feet

The wheel type of trenching machine is similar in principle to the
chain excavator. Instead of the chain of buckets, it has a wheel fitted
with buckets. In one prominent type the wheel has no hub or spokes, but
consists of a rim that is supported on and is turned by four friction
rollers mounted in a rigid frame. This frame is mounted on a boom which
can be raised or lowered as desired. Such machines can commonly dig to
a depth of a dozen feet or so.

A ditch differs from a trench in the fact that its side walls are
sloping instead of vertical. A trench is usually a temporary excavation
for the laying of pipes or conduits while the ditch is left open and
serves for irrigation or drainage. There are chain ditching machines
in which the chain of buckets runs laterally across the course of the
ditch, dipping into the earth to form a V-shaped channel. In connection
with the draining of the Everglades of Florida, a peculiar wheel type
of ditcher was built. The wheel is of gigantic proportions, consisting
of a series of radiating shovels or scoops shaped to conform to the
outline of the ditch. As the wheel revolves it scoops up the mud which
slides down toward the hub of the wheel and is carried to one side by a
traveling conveyor.


The main difficulty in drainage work is to provide a good footing for
the machine which must necessarily be very heavy. Broad caterpillar
tread surfaces are about the only means of locomotion. In very soft
swampy regions dredges have to be used. Dredges are merely floating
excavators. In them the problem of support and locomotion disappear and
there are no limitations of size and weight to be considered. Floating
excavators are therefore much more powerful than excavators that run
on land. The ordinary dipper dredge is merely a floating steam shovel
with a much longer dipper handle and much larger dipper. When work on
the slides of the Panama Canal had proceeded far enough to admit of
using dredges in place of steam shovels material progress was made. Two
enormous dipper dredges were built, each provided with a dipper that
had a capacity of fifteen cubic yards or about twenty tons at a single
lift. The dipper was big enough to hold thirty men. The dipper handle
was seventy-two feet long and it could reach down to a depth of fifty
feet. A smaller dipper of ten cubic yards capacity was also provided.
The power of these huge dredges was illustrated when one of them, while
using its ten-yard bucket, picked up an enormous bowlder weighing forty
tons. It was much bigger than the dipper that had raised it and it was
far too big to be placed on the mud scow that was receiving the spoil
brought up by the dredge. Had it been rolled off on the scow it would
have crashed right through the bottom of the boat and so the big rock
had to be drilled and broken up on the dipper before it could be dumped
into the scow.

For work on a soft bottom, grab buckets are used in place of dippers.
These may be made of two scoops as in the clam-shell bucket or of
four leaves as in the orange-peel bucket. No rigid handle is provided
for these scoops. They are spread open as they are lowered into the
water and on hauling in the hoisting cable, the scoops or leaves come
together biting into the bottom and lifting up a load of mud. Grab
buckets are largely used for picking up coal, ore, gravel, etc.

The equivalent of the chain trench-digging machine is found in the
ladder dredge. A ladder is hung over the stern of the dredge and
carries a chain of buckets which dig into the bottom and bring up the
mud or sand.


It is a dredge of this type that is put to the peculiar task of gold
mining. The dredge eats its way into gold-bearing sands, the material
passing through a system of separators which extract the gold and then
being discharged at the rear of the dredge. The dredge floats in a pool
of water that it carries with it, for as it excavates ahead it builds
up sand banks behind. In this way it may travel far from the river from
which it first started.




Suction dredges are particularly adapted for excavating sandy bottoms.
One type used for dredging channels consists of a large steam vessel
with large bins into which the dredged material is pumped. At each side
of the boat there is a long pipe which may be let down into the water.
Each pipe terminates in a drag or footpiece with grated opening which
is designed to be dragged along the bottom as the vessel slowly steams
ahead. Powerful pumps suck a stream of water up the pipes which carries
with it a quantity of sand. The sand and water flow into the bins, the
solid matter settling to the bottom while the liquid flows out over the
top. When the settlings have filled the tanks, the drags are pulled
up and the vessel steams out to sea. Here doors in the bottom of the
bins are opened and the material drops through. The idea of opening
up the bottom of a boat to empty it seems rather startling until we
consider that the bins are sealed off from the rest of the boat and do
not contribute to its buoyancy. The sand that is dumped out of them is
much heavier than the water that takes its place when the bin doors are


The Ambrose channel in lower New York Bay was dredged by means of
suction dredges. The channel is forty feet deep at low water and the
bottom had to be excavated from ten to twenty-five feet to attain
this depth. About seventy million cubic yards of material had to be
excavated or nearly a third as much as was excavated in the Panama
Canal. The Ambrose channel is seven miles long while the Panama Canal
is forty-five miles in length. Two of the larger dredges each had a
capacity of forty-five hundred cubic yards in their bins or enough to
load a train about a mile long, composed of 175 cars. It took less than
three hours to fill the bins. The openings in the gratings of the drags
measured about eight by nine inches and any stones or solid matter
small enough to pass through them was easily sucked up into the bins.
When a pile of stones of larger diameter was encountered a deep hole
was dredged around it and then by means of a water jet the stones were
forced into the hole.

The material sucked up by a dredge is sometimes dumped into a scow
alongside. This makes the structure of the dredge less expensive, but
where work has to be conducted in bodies of water exposed to storms it
is more expedient to let the dredge collect the material within its own


The sand drawn up by a suction dredge is valuable material for land
building. In fact, a suction dredge is often used for the double
purpose of excavating and filling in low land. Sometimes its only
purpose is to fill in tide flats to above tide level. The material is
discharged through a pipe line which may be over a mile in length.
This pipe line is supported on a string of wooden or steel pontoons.
The pipe sections are connected by means of heavy rubber sleeves so as
to make the line flexible. This permits the dredge to move about and
also allows of moving the discharge end about to distribute the sand

Unfortunately all dredging does not consist of sand and mud. Sometimes
snags and matted roots are encountered which give trouble. For handling
such material rotary cutters are used. The bow of the dredge is fitted
with a hinged ladder about sixty to seventy feet long in which the
cutter is mounted. The ladder also carries the suction pipe close to
the cutter. The ladder is lowered to the bottom and the revolving
cutter chops up the roots into pieces which are drawn up into the
suction pipe. The size of the pieces that are sometimes sucked up is
remarkable. The greater part of the area of the New Orleans Inner
Harbor Navigation Canal was filled with stumps and matted cypress
roots. The cutters tore up and cut these roots and stumps and the
pieces were transported through a pipe line about 600 feet long. Stumps
that were too large to be handled in this way were undercut and sunk
below grade.

Cutters are used also for loosening packed hard bottoms and some of
them will dig into hard pan and even soft rock. A pressure of 100 to
150 pounds per square inch is maintained in a discharge pipe twenty to
twenty-four inches in diameter, which is enough to carry along heavy
bowlders dug up by the cutter.


So far we have dealt only with surface conditions, but man has not been
content to stay on the surface of this planet. True, we have scarcely
begun to explore the crust of the earth. The deepest mine in the world
is the Morro Velho in the province of Minas Geraes, Brazil. Here the
earth has been penetrated to a depth of 6,426 feet in quest of gold.
This is a depth of less than a mile and a quarter and it shrinks into
insignificance when we reflect that we must go more than 3,000 times
that distance to reach the center of the earth. However, we have
made material progress in shaft-sinking in recent years, and it is
quite likely that the lure of scientific research may prove even more
powerful than that of gold and that some day we shall be induced to dig
many miles into the crust of the earth just to learn something more
about this globe that whirls us through space.

We have not yet reached the point at which hand labor may be dispensed
with in tunnel work, but there are machines which will do what formerly
could only be accomplished with the manually wielded pick and shovel.
We have already (in Chapter VII) described the pneumatic tunnel shield
and explained how it is sometimes driven forward through soft silt
by means of hydraulic jacks without any excavation of material. This
method of tunneling which is analogous to driving a punch through soft
metal, has a very limited field of application. It is impossible to
force the shield in this manner through sand or through any but very
soft silt.


The city of Cleveland takes its drinking water from Lake Erie. In
order to obtain water that is not contaminated by the refuse of the
city, tunnels are carried out under the bottom of the lake about two
miles from the shore where they terminate in water intakes far enough
below the surface to avoid floating impurities and far enough above
the bottom to avoid impurities that have settled to the lake bed. The
material through which the tunnels pass is a stiff clay, that cuts like
cheese. So uniform is this material that a special machine was built
to bore the tunnel through it. This machine is somewhat similar to a
boring mill. It has an arm that revolves against the face of the tunnel
heading and carries a cutter that travels along the arm so that it cuts
a continuous spiral ribbon of clay. The clay ribbon passes back through
the machine and is loaded into a train of dump cars.

For boring tunnels in hard rock many different machines have been
invented, but not one of them as yet has proved an unqualified success.
One very interesting machine, which was tried on the New York subway
excavation at 42d Street and Lexington Avenue, consisted of a series
of chipping hammers which, by means of pneumatic mechanism, were made
to hammer and pulverize the face of the rock with repeated blows. The
hammers were arranged in a circle and were revolved as they hammered
so that the whole surface of the heading was attacked and a circular
tunnel was cut through the rock. A serious disadvantage under which
the machine labored was the fact that the rock had to be crushed to a
powder or into small chips before it could be removed.

In ordinary rock excavation holes are bored into the heading and the
rock is then blown out by means of dynamite or some other explosive.
Large fragments of rock are then broken up into pieces small enough to
be handled readily, but no energy is wasted in reducing the material
to a powder. The percussion drills with which the rock is bored have
already been briefly described. When boring holes for a blast in soft
material, such as bituminous coal, a drill is used which resembles in
many respects an ordinary twisted auger bit except that it is many feet
in length. It is driven by hand into the coal by the use of a common
bit brace. Percussion drills or punches are also used. These are driven
either by pneumatic or electric power.


When excavating coal the heading is first undercut, that is, a deep
slot is cut in the wall of coal along the floor line. Then blast holes
are bored into the coal above this cut so that when the charges are
fired the coal will be broken downward. To undercut the coal special
machines are used, driven by compressed air or electricity. These
have endless chains fitted with chisel or pick points that bite into
and cut the coal. After the material has been shattered and reduced
to fragments of convenient size special machinery may be employed to
shovel it away from the heading and into dump cars. One electrically
driven shoveling machine which was tried out on some of the Catskill
aqueduct excavation had a broad open shovel which could be driven into
the pile of rock fragments under the control of an operator and would
scoop up the material, delivering it upon a traveling belt conveyor
which carried it on to the train cars. Many types of mechanical
shoveling and loading machines have been built for use in mines. They
are driven either by pneumatic or electric power.


In all engineering work it is highly important to explore subsurface
conditions before starting any construction or even drawing up plans.
The ordinary pneumatic percussion drill will not serve for deep holes.
Instead a rotary boring motion is requisite. The tool is mounted with
black diamond cutters which cut through the hardest rock. Water is
introduced into the hole to lubricate the tool and also to wash out
the abraded material. By trapping this material the character of the
rock penetrated may be determined. The material, however, is pulverized
and does not furnish, as a general rule, a fair sample of the rock.
When it is highly important to determine the exact nature of the rock
or other material a core drill is used. In other words the drill is
a hollow tube set with cutting crystals about its periphery. As the
tool is revolved it cuts an annular slot in the rock leaving a central
core standing. This core is broken off and drawn to the surface and
furnishes a true sample of the material encountered by the drill.

There is an interesting type of core drill in which steel shot is used
in place of diamonds. The cutting end of the drill is a collar with a
notched edge. Steel balls are fed into the drill and under the cutting
head. The balls are caught in the notches and rolled around against the
rock surface. There is also a partial dragging action. The friction
is sufficient to wear away the rock. As the balls wear away they are
replaced with new ones. Very evidently such drilling costs less for
upkeep than diamond drilling, but it is not as rapid as the latter.


A notable illustration of exploration drilling was furnished by the
surveys for the Hudson crossing of the Catskill Aqueduct. To bring
water from the Catskill Mountains to New York City it was necessary to
cross the Hudson River. In order to furnish a permanent conduit it was
decided to carry the water in an inverted siphon bored through solid
rock. It was necessary to obtain a profile of the rock at the point
where a crossing seemed most feasible. Borings were therefore made
from a barge anchored in the river, but it was impossible with such
an unsteady working base to carry on the boring to any considerable
depth. Tides, the wash of passing steamers, floating ice, all combined
to obstruct the work. Drills were constantly broken. Finally it was
decided to do the boring from opposite banks of the river at such an
angle that bore holes would meet or pass each other under the middle
of the river. The exploration boring from the barges indicated that
solid rock lay at a considerable depth below the river bed and that
the bore holes would have to be set at a sharp angle to keep from
breaking through rock. The river at that point is about 3,000 feet
wide and a boring from the surface at the middle of the river had been
driven to a depth of 768 feet without striking solid rock. Two shafts
were sunk to a depth of about 250 feet and from these diamond drill
borings were started at such an angle that they would cross at a depth
of 1,500 feet. Excellent rock was encountered throughout the boring.
Then a second set of borings was made which crossed at a depth of 950
feet without encountering any appreciable amount of water. It was
accordingly decided to carry the aqueduct in vertical shafts, one at
each side of the river, at a depth of 1,100 feet below water level, and
then connect these shafts with a horizontal tunnel. It was important
to have a good solid rock cover over the tunnel because the aqueduct
reaches the river with a head of 400 feet which added to the 1,100 feet
of depth of the inverted siphon gave a total head of 1,500 feet or a
hydraulic pressure of about forty-two tons per square inch.

Although the diamond drill borings just mentioned were remarkable
because of their inclination and because of the cramped quarters from
which they were driven, they do not begin to compare in depth with some
of the borings made in search of water and of oil. The deepest boring
in the world to date is near Fairmount, West Virginia, where a hole six
inches in diameter was driven to a depth of 7,579 feet or nearly a mile
and a half. At that point an earth slide stopped further borings.


The time-honored method of boring for oil known as the percussive
system is to hammer through the earth and rock with a heavy steel
drill. The drill really consists of a long string of parts measuring
altogether as much as sixty feet in length. (See Figure 64.) The drill
proper or bit has a cutting edge adapted for the character of the
material it is to penetrate. The bit is attached to a steel bar known
as the “auger stem” which may be from twelve to forty-five feet in
length. Then come the “jars” or a link member which allows a play of
about sixteen inches. The purpose of this is to assist in freeing the
bit from the material it is penetrating by jarring it upward on the
upstroke of the drill. Above the jars there is another bar known as the
sinker, and this is provided with a rope socket to which is attached
the cable that carries the string of drill parts. The cable passes
over a pulley to a walking beam which gives the necessary up-and-down


The loose material in the bore is removed by a sand pump. To protect
the bore from caving a casing of steel pipe must be lowered into the
well. The boring may proceed at the rate of ten to sixty feet per day,
depending upon the material penetrated and the depth of the well. All
sorts of difficulties are liable to interrupt the work. The cable may
break, the string of tools may become unscrewed, or the casing may drop
into the hole, and then follows the tedious process of fishing for the
lost parts and hauling them up out of the well.

As the drilling proceeds, the bore becomes progressively smaller and
casings of smaller diameter must be used. The well is completed by
lowering a pipe within the casing through which the oil flows to the
surface and is carried to the storage tanks and thence by pipe lines to
the refineries.

While the percussive system of drilling is very generally used
throughout the American oil fields, rotary methods of drilling are
largely employed in California.



IT IS NOT very long since the spinning wheel and the clacking loom
were an indispensable furnishing of every farmhouse and of many city
dwellings as well. With infinite patience the fleece of sheep, the lint
of flax, the filaments of silk and the fibers of cotton were spun into
yarn and then woven into cloth, and it was the nimble fingers of the
housewife that carried the process through from the matted raw product
to the finished garment.

It is comparatively easy to comprehend the development of machines
for dealing with such gross material as earth, rock, iron, and wood,
but when we come to consider the infinitely delicate and almost
imponderable fibers that go to make up our textiles, the marvel is that
any but highly skilled human hands, guided by keen eyesight, could
combine the tangled and obstreperous filaments into fine yarn and
weave this yarn into complicated patterns of cloth. But the spinning
wheel and hand loom could not stand long in the path of power-driven
machinery, and now huge, blind machines, with stiff, unbending fingers
of metal, comb out the matted masses of raw material, remove the dirt
and twigs, straighten out the snarls far quicker and better than could
be done by hand, and transform the fibers into beautiful fabrics such
as in former days would have been the envy of kings.

We cannot attempt to describe all the machinery involved in the
spinning and weaving of yarn, but it is highly important that every
well-informed person have a general knowledge of textile machinery.
Because cotton cloth is more widely used than either linen or wool, we
shall confine ourselves to the cotton branch of the textile industry,
particularly as the difference between the treatment of cotton and
other textile materials lies chiefly in the preparation of the thread
or yarn.

The predominance of cotton among textiles may be traced back to the
invention of a young New Englander fresh from college, who went to
Georgia as a private tutor, only to find when he got there that some
one else had been engaged in his stead, leaving him stranded and
practically penniless in a strange land. We had occasion to refer to
this man in Chapter III. Eli Whitney was a born mechanic, and before
entering college had not only shown great skill but had actually built
up a thriving business in the manufacture of nails, hatpins and knife


The agricultural condition of Georgia and its neighboring States at the
time that Whitney arrived there was very poor. There was no market for
their products. A splendid cotton, with fibers from 1⅜ to 2½ inches
long, was growing on the islands along the coast, but this cotton
could not be raised inland. The upland product, known as “green seed”
cotton, had a fiber only half as long as the “Sea Island” cotton, but
the principal drawback to its use was the difficulty of separating the
fiber from the seed. It was a day’s work for one woman to separate a
single pound of the “green seed” cotton fiber.

His attention having been brought to this matter, Whitney undertook
to design a machine which would remove the fiber from the seed in a
small fraction of the time required by hand labor. He was visiting at
the time at the plantation of Mrs. Greene, widow of General Nathaniel
Greene, of Revolutionary fame, and he set himself to the task with
such limited materials and tools as he could find on the estate. In a
couple of weeks he had built a model which contained all the essentials
of the modern cotton gin, with which a single man could separate more
cotton in a day than could be produced by hand in a whole season.
This was in the winter of 1792. The effect of the invention was felt
immediately. Cotton production had been falling off steadily. In 1791,
189,316 pounds of cotton had been exported. The next year there was a
falling off to 138,328 pounds, but following the introduction of the
cotton gin exports rose to 487,000 pounds in 1793, 1,681,000 in 1794,
and 6,276,000 in 1795. Fifty years later the world production amounted
to 1,169,600,000, nearly seven-eighths of which was contributed by the
United States, and of this only a small amount was Sea Island cotton.

A cotton gin (Fig. 65) consists of a gang of circular saws (_A_), with
forwardly pointed teeth which pass between the ribs of an inclined
grating (_B_) that forms the floor of a chamber (_C_) known as a roll
box. In this box is mounted a toothed roller (_D_). The cotton is fed
into the box and the fibers are seized by the teeth of the saws and
dragged through the grating while the seeds, being too large to pass
through, are left behind and, rolling down the grating, drop into a
hopper. The action of the saws is such as to impart a rolling motion
to the mass of cotton, and hence to the roller in the roll box. This
tends to drag the cotton into the roll box and bring fresh supplies to
the saws. The fleece carried by the saw teeth is beaten off by a wheel
(_E_) fitted with wire brushes. These brushes, traveling in the same
direction as the saw teeth, but at a higher velocity, readily disengage
the fibers from the teeth and create an air blast that blows the cotton
fleece out of the gin.



Cotton as it comes from the bale is a compact, matted mass, mixed with
bits of seed, leaves, sand, and other impurities, and it must pass
through a number of machines before it comes out as a pure, light,
fleecy product, with the fibers combed parallel. Even for a medium yarn
a dozen machines are required to prepare the cotton for the spinning

A system of “counts” is used to indicate the size of yarn and it is
based on the number of hanks it takes to make a pound. A hank is always
840 yards and 50’s would mean that the yarn is of such fineness that it
would take 50 × 840 yards (=4,200 yards) of it to weigh a pound. Yarn
below 30’s is graded as _coarse_; between 30’s and 60’s as _medium_ and
above 60’s as _fine_. To prepare cotton as it comes from the bale for
a fine yarn of, say, 100’s, it must go through no less than sixteen
machines before it reaches the mule.

We have not the space to describe all of these machines, but in general
it will suffice to say that the cotton is graded by passing it through
a series of pickers. These machines throw out the fibers and beat
them so as to knock out the impurities and, at the same time, a blast
of air blows out the dust. The cotton is treated by a number of such
machines in succession and is finally delivered in a broad sheet known
as a “lap,” after which it passes through the carding machine which
combs out the tangled bunches and removes further impurities from the
lap. The lap is then gathered into a compact rope known as a “sliver.”
The sliver goes through the drawing rolls which serve to parallelize
the fibers and make the sliver of even thickness, and at the same time
to give a moderate amount of twist so that it will hold together, and
it issues from the machine as “roving.” In the case of fine yarn the
sliver issuing from the carding machine goes through a combing machine
so as to remove the finer fibers. The bobbins of the roving are then
placed in the spinning machine, which may be either the spinning mule
or the ring spinning machine. The principal difference between the two
is that the spinning mule is intermittent in its operation, while the
ring spinner not only spins the roving into yarn but at the same time
winds it up on a bobbin.



The first advance over the old-fashioned spinning wheel, which dates
back to the fifteenth century, was in 1770, when the first spinning
jenny was invented by Hargreaves. This consisted practically of a
multiple spinning wheel by which one man could spin a large numbers of
bobbins of yarn at the same time. It was at about the same time that
Arkwright invented the drawing rolls which have played a most important
part in the preparation of yarn, and this invention is worthy of our
attention because it contains an interesting mechanical principle. As
shown in Figure 66, a number of pairs of rolls are provided through
which the roving passes, but successive pairs operate at higher
velocities. Thus, the second pair of rollers through which the roving
passes run at a little higher speed than the first pair, the third a
little higher than the second pair, and so on. As a result, the roving
is drawn out by the operation and issues from the last pair of rollers
at a higher speed than it entered the first pair of rollers. The only
way in which it can accommodate itself to this accelerated motion is to
be attenuated or drawn out. Weights are used, as shown in the drawing,
to press the upper rollers against the lower ones.


Shortly after Arkwright’s invention came the mule spinner, invented by
Crompton between 1774 and 1779. Machines operated on the same general
principle as this are in general use to-day. In the old-fashioned
method of spinning by hand the worker took a small quantity of cotton,
pulled it out into a long sliver, attached one end to a bobbin and
gave the bobbin a twirl between his hands in order to spin the fiber
into yarn; then the yarn was wound up on the bobbin and the process
was repeated. The spinning mule does practically the same thing, but
infinitely faster and on a much larger scale. As shown in Figure 67,
the bobbins of roving (_A_) are mounted on a stand and passed through a
set of drawing rolls (_B_) which are regulated to pull the rovings out
to the desired thickness of yarn. The roving then passes to the nose of
a “cop,” or spindle (_C_), which is revolved at very high speed. The
cop is carried by a carriage (_D_) which moves away from the bobbins
of roving to the position indicated by dotted lines, while the cop is
revolving. The cop has a travel of about five feet during the time the
yarn is drawn out and spun. Then the carriage moves back toward the
stand upon which the bobbins of roving are mounted and the spun yarn is
wound up on the cop. The reason the yarn does not wind up on the cop
while it is spinning is because it runs to the nose of the cop and,
at each turn of the cop, the coil twists on the nose and slips off.
On the return of the carriage, however, a set of wires (_E_), called
“fallers,” press the yarn down so that the revolving cop will wind up
the slack.

[Illustration: FIG. 67.--DETAILS OF A SPINNING MULE]

The continuously operating ring-spinning machine is provided with a
ring frame (Figure 68) around the cop or spindle. This frame, together
with the spindle, revolves at high speed, but as the ring revolves a
little more slowly than the spindle it winds the yarn comparatively
slowly upon the spindle or bobbin.


Having now produced our yarn, we may pause to consider the different
types of fabric into which it may be formed, and to draw a distinction
between, woven, braided, knitted, and net goods. In weaving we have two
sets of threads, one set running transversely to the other; in braided
materials the threads all run longitudinally and are arranged to cross
each other diagonally, so that they are interwoven; in knitting and
netting there is a single thread. In the case of netting this thread
is knotted where it loops back upon itself, whereas in knitting it is
merely looped without knotting.


The loom can trace its genealogy away back to early Babylonian times,
and the modern power-driven machine does not differ in its broad
principles of operation from its ancient progenitor--the hand loom.

[Illustration: FIG. 68.--RING-SPINNING FRAME]

[Illustration: FIG. 69.--THE HEDDLES OF A LOOM]

Every industry has a vocabulary of its own to furnish names for its
machine parts and products peculiar unto itself, and in this respect
the textile industry is by no means an exception. The threads that run
lengthwise in a piece of woven cloth are known as the “weft,” “woof”
or “filling.” In the loom the warp threads are threaded through loops
on what are known as “heddles”; in fact, there are two “heddles,” _A_
and _B_, Figure 69. Alternate warp threads (_C_) pass through the loops
of one heddle, and the other threads through the loops on the other
heddle. When one heddle is raised and the other lowered, the threads
form a wedge-shaped space (_D_) which is known as a “shed.” The filling
thread is sent through the shed and is then pressed closely into the
wedge-shaped space against the cloth already woven by means of a “reed”
(_E_) which is a comblike member with teeth or flat pieces of metal
that pass between the warp threads. This done, the position of the
heddles is reversed, so that _A_ is now lowered and _B_ raised, thus
binding the warp thread in place and forming another shed for the next
warp thread; and thus the process continues.

The filling thread is placed in a shuttle (_F_) which carries a bobbin
on which the thread is wound. As the shuttle is thrown back and forth
through the shed, the thread is unwound and trails behind it. Formerly
the shuttle was thrown back and forth by hand, but years ago, long
before the invention of the steam engine, the flying shuttle was
invented. In other words, a mechanism was provided for striking the
shuttle a blow and throwing it across the warp from side to side. By
this means the speed of operations was greatly increased.

About the middle of the eighteenth century the drop box was invented.
This consists of a receptacle for shuttles carrying different colors of
thread which may be selected in a definite order and thrown back and
forth so as to vary the pattern of the cloth.

In present looms a special machine is provided for taking the threads
from the bobbins or cops and laying them in an even sheet to form the
warp of the loom. These are wound on a beam and the machine is known
as a _beam warper_. As the threads are apt to be somewhat fuzzy it is
necessary to size them, and a machine known as a _slasher_ is employed
for this purpose. This machine coats each thread of warp yarn with a
sizing compound or an adhesive and dries the sheet of warp preparatory
to its use in the loom.

In common weaving the weft or filling threads run alternately under
and over the warp threads with perfect regularity. A pattern can be
formed by passing the weft threads under and over alternate groups of
warp threads, and this is effected in the ordinary loom by threading
the weft in groups through the heddles, _i. e._, instead of having
every second thread pass through one heddle and the intervening threads
through the other heddle; the threads are arranged in alternate groups
of two or more. This gives a regular pattern, but it may be varied to
form ornamental designs if the groups are varied. Such designs used to
be worked out by hand very slowly and laboriously, with the result that
figured weaving was very expensive.


At the French Exposition of 1801 a loom was exhibited that made a
sensation. With seemingly human intelligence it selected individual
warp threads or groups of threads and raised them or lowered them so as
to work out elaborate ornamental designs. The inventor, Joseph Marie
Jacquard, of Lyons, received a medal for his marvelous invention and
was decorated with the Cross of the Legion of Honor.

The “brains” of the Jacquard loom is a set of pasteboard cards that are
perforated in accordance with a prearranged design. The warp threads,
instead of being passed through the loops of two heddles, are passed
through what might be termed individual heddles, one for each thread,
or for a small group of threads. These consist of cords in each of
which is an eyelet through which the warp thread passes. The cord is
weighted at its lower end and its upper end is fastened to a hook in a
box at the top of the machine. The hooks engage transverse bars known
as “griffes” or “knives,” and when the griffes are raised, the hooks
engaging them are also raised. In this way the warp threads that pass
through the eyelets that are connected to the hooks are raised. But
running horizontally across the hooks there are “needles” or rods with
eyelets or bends in them through which the hooks pass. These needles
may be moved lengthwise to make the hoops engage or disengage the
knives. The mechanism is illustrated in Figure 70, where the knives
are shown in section at _A_, the hooks at _B_ and the needles at _C_.
For the sake of simplicity only eight hooks and needles are shown;
in actual practice there are hundreds in a single machine. At the
right-hand end of each needle there is a spring which pushes the needle
toward the left, thereby bringing the hook through which it passes
into position to be lifted by its griffe. At the left-hand side of
the machine there is a card (_D_) which presses back the needles and
thereby bends the hooks out of position to engage the griffes. However,
there are perforations in the card through which certain of the needles
can pass, letting the hooks they control engage the needles. The cards
thus select the particular weft threads that are to be raised. In our
illustration most of the needles have entered holes in the card, but
the second, fourth and sixth from the top have been pushed back by the
blank wall of the card and their hooks have been bent back clear of
the griffes. Only four cards are shown in the drawing arranged in a
four-sided box or “cylinder,” and the cards are successively presented
to the needles. For more elaborate designs a large number of cards are
used, arranged in a slatted belt, and these come successively into
position. As many as thirty thousand cards have been employed to carry
out a single pattern.

[Illustration: FIG. 70.--DETAIL OF A JACQUARD LOOM]


We are wont to call Necessity the Mother of Invention; in many cases
Laziness has given rise to valuable inventions, but according to
legend, Cupid played the leading rôle in the development of the
knitting machine. It is said that in 1589 William Lee of England fell
in love, but the girl who was the object of his devotion was always so
busy with her knitting that she could not give him the attention he
sought or thought he deserved. However, Lee was not to be thwarted in
this fashion, so he built a machine to do the knitting in order that
the girl could devote herself more completely to him.

There is another less pleasant version of the story to the effect
that Lee became so attached to his knitting machine that he neglected
the girl. However, in either case, love was somehow mixed up in the
invention of the knitting machine.

We are not going to attempt to delve into the complicated mechanism
of a modern knitting machine, but will merely call attention to the
fact that modern machines perform automatically practically all the
movements of the human hand in hand knitting.

The tendency of modern machinery has been to relieve the housewife of
the tedious work she formerly performed and to take such work away
from the home to the factory. There is one important machine, however,
which has been introduced into the home, apparently to stay; for in the
majority of houses it is still considered indispensable. It is a fact
that the introduction of labor-saving machinery into the household has,
until recently, met with stern opposition on the part of the housewife.
It is all the more remarkable, therefore, that in the middle of the
nineteenth century the sewing machine began successfully to invade the


It was in 1844 that Elias Howe hit upon the brilliant idea of putting
an eye at the point of a needle. This enabled him to produce a
successful sewing machine, because it was unnecessary for him to pass
the needle completely through the cloth in order to pull the thread
through it. When the needle point penetrated the cloth a shuttle passed
through the loop of thread that was carried through with the point.
This shuttle carried a second thread which interlocked with the thread
of the needle forming what is known as a “lock stitch.” In Howe’s
machine the cloth was held vertically and the needle which was curved
was carried by a lever. The needle was driven through the cloth with
a swinging motion, somewhat like that of a pick-ax. The shuttle was
driven back and forth by a pair of strikers after the manner of the
flying shuttle of a loom. George Fisher, a friend of Howe, furnished
$500 with which the first successful machine was built in 1845, and
with this machine Howe sewed two suits of clothes, one for Mr. Fisher
and the other for himself. A public exhibition was held at which the
machine, crude as it was, beat five of the best hand-sewers that could
be found. In 1863 Howe was reaping a fortune in royalties from his
machine which were estimated at $4,000 per day.

The next notable improvement in sewing machinery was that of the rotary
bobbin, invented by A. B. Wilson, which was patented in 1852. This did
away with the flying shuttle and simplified the machine considerably.
It made the sewing machine comparatively quiet, thus adapting it for
domestic use. In Wilson’s machine, a rotating hook passed through the
loop of thread and carried it around the bobbin on which the lower
thread was wound. Wilson also invented the four-motion feed for feeding
the cloth under the needle. Sewing machines up to that time had been
operated by hand, but Isaac Merritt Singer introduced a foot-power
machine and by progressive business methods built up a thriving
industry and did much to establish the sewing machine, not only at
home, but abroad as well.


The single-thread machine was invented by a Virginia farmer who had
never seen a sewing machine. James E. A. Gibbs had seen a picture of
a sewing machine and, unaware of the fact that there was a shuttle
carrying a second thread on the rear, or under side of the cloth, fell
to puzzling over the problem of what happened to the thread carried
by the needle through the cloth. Somehow, it seemed to him, the loop
of thread must be held until the next stitch carried another loop of
thread through it, thus forming a chain stitch. This led him to invent
an ingenious revolving hook. With infinite patience he whittled out a
model of his invention, and it is this hook that is the outstanding
feature of the Wilcox and Gibbs machine.


A notable modern development of the sewing machine is its adaptation
to the making of embroideries and even laces. In the common domestic
sewing machine the cloth is fed step by step under the needle, and
the length of the step regulates the size or length of the stitches.
The feed may be set for short or long stitches. It is evident that
if a greater range of length of stitch were provided, and if, while
the machine was operating, the stitch could be varied at will, not
only in length but in the direction as well, it would be possible to
work out elaborate patterns of embroidery. This is what is done on
the power-driven embroidery machines. Like the original Howe machine,
the cloth is held vertically and a series of needles are used which
pass horizontally through the cloth. As the needle retreats, the
thread it carries forms a loop on the rear or “wrong” side of the
cloth, and through this a shuttle is driven which carries a thread
wound upon a bobbin. Between stitches the cloth is moved this way and
that, in accordance with a prearranged pattern, and thus the design
is embroidered. A single machine may have several hundred needles
and, as they all work in unison, each needle repeats the design. The
arrangement is such that one needle starts where the next one leaves
off, so that the embroidery is continuous. The shuttles which operate
on the wrong side of the cloth are small, boat-shaped parts which the
Swiss have named “schiffli” or “little ships,” and this name has come
to be applied to the whole machine.

The guiding of the cloth to produce the required design is accomplished
either by hand or automatically. In the hand-guided schiffli machine
a skilled “stitcher” seated at one side of the machine operates a
pantagraph, tracing an enlarged design mounted on a board before
him. As he moves the lever vertically and horizontally the frame
carrying the cloth is correspondingly moved before the needles. An
expert stitcher can put a great deal of individuality into the work,
which is impossible in the strictly automatic machine; accordingly
the pantagraph is used for the finer grades of embroideries. In the
automatic machines a perforated roll like that of a piano player is
used. The perforations control the movements of the frame that carries
the fabric.


These machines are of Swiss and German design, but American inventors
have recently developed a machine for producing fine needlework which
imitates very closely the work of the hand. In this machine the needle
passes completely through the fabric as in ordinary hand sewing, but
it does not have to be turned around for the return stitch because
it is pointed at each end and has the eye in the middle. The needles
are held by spring clips in a swinging frame. When the frame swings
toward the cloth the needles are pushed through the fabric and their
points are caught by spring clips in a frame on the opposite side. The
latter frame draws the needles completely through and a set of hooks
catch the thread and pull the stitch taut. The advantage of this type
of machine is that it produces the same design on each side of the
cloth; in other words, there is no “wrong” side to the embroidery. The
design is controlled by a “stitcher” operating a pantagraphic system of
levers and by skillful manipulation he can completely overcome the flat
machinelike appearance of the automatic schiffli machine.

Laces are very ingeniously produced on schiffli machines by using the
“burnt-out” system invented forty years ago by a German, named Beckel.
This consists in the use of thread of a different material from that
of the fabric, and after the embroidery is completed the fabric is
removed either chemically or by the application of heat, leaving only
the stitching, which forms a delicate lace. For instance, cotton thread
may be embroidered on a groundwork of wool, or silk thread is used on
a fabric of cotton. Laces made in this way are known as Plauen laces,
taking their name from the city where Beckel invented the process, and
they form a large part of the machine-made laces that are now so widely



  Copyright Kadel & Herbert





THE MAKING of paper is closely related to that of textiles. In each
case the same basic materials are used. A mass of interlacing fibers
is formed into a continuous sheet, but the method of interlacing the
fibers and holding them together is entirely different. Paper resembles
felt more closely than any other form of fabric. The fibers are not
woven but are matted together and compressed. In the case of felt the
fibers of wool or hair are held together mainly by the microscopic
barbs that they possess while paper fibers are held together by means
of sizing.

Although paper gets its name from papyrus the latter was not paper, for
it was a felt of pith rather than fiber. The ancients produced a very
fair writing material from the rushlike plants that grew in the swamps
along the Nile. The stem of the papyrus was stripped of its bark and
the pith was cut into thin ribbons which were laid side by side to form
a sheet. Over these and at right angles to them was laid another layer
of pith ribbons. The material was then soaked in water, pressed into a
continuous sheet and dried. These sheets were then pasted together and
rolled up into scrolls. Unquestionably they played a most important
part in the civilization of ancient Egypt, providing, as they did,
a ready means of recording knowledge and disseminating it among the


Like so many inventions that are of vital importance to modern
civilization, paper is a Chinese invention. The Chinese made paper from
the fibers of trees, a material to which we have reverted in recent
years. The invention dates from about 150 A. D., when some one devised
a process of reducing the bark of the mulberry tree to a pulp, beating
it and boiling it in lye and then matting the fibers on a screen and
pressing them into a finished sheet. The process was introduced into
Europe by the crusaders in the 12th Century. In 1150 a paper-making
plant was established in Italy and soon the new writing material
was being made in increasing quantities and became a common article
throughout Europe. It was not until the end of the 18th Century that
machinery for making paper came into use.

In the old hand process which is still used to a very limited extent
for special papers, the pulp, after being reduced to a thin milky
fluid, was dipped out of a vat with a rectangular sieve which had a
wire screen bottom of fine mesh. The water drained off, leaving the
fibers upon the screen. As the pulp was draining the sieve was shaken
about to distribute the fibers evenly and interlace them as much as
possible. The depth of the sieve determined the amount of pulp that
was dipped out and hence the thickness of the paper. The soft, matted
mass of fibers was turned out upon a felt mat and left to dry. Soon
other fibers came to be used and the finest grades of paper were made
from linen and cotton rags. The rags were carefully sorted out and
washed after which they were stored in a damp place to rot for a number
of weeks. Then they were cut and shredded and boiled until they were
converted into a pulp. The complete process of making fine paper by
hand took from two to three months. Paper was made in small sheets
limited by the size of sieve that could readily be operated by hand.

The first man to make a continuous web of paper was Nicholas Louis
Robert, a Frenchman who received a reward of 8,000 francs from his
government for his invention. Robert’s patent rights were acquired by
the Fourdrinier Brothers (Henry and Sealy), of England. They developed
and perfected the machine and to them is ascribed the honor of founding
the modern paper industry.


Paper is more commonly and extensively used to-day than any other
product of manufacture and is employed for an astonishing variety of
purposes, ranging from milk bottles to suits of clothing. One very
novel use we might mention, in passing, is to be found on the sugar
plantations of Hawaii. After the cane is planted the fields are covered
with a thick paper made, by the way, from sugar-cane fiber. This
covering prevents the weeds from growing, but the sharp spikes of the
sugar sprouts pierce the paper and grow through it. By the time the
paper has disintegrated and the weeds have a chance to grow, the cane
has such a start on them that they are kept shaded and cannot compete
with or choke out the cane.


Before we proceed to describe the modern Fourdrinier machine, we must
look into present day methods of preparing pulp. The finest papers are
still made from linen and cotton rags. Esparto grass is largely used in
Europe. This comes from Spain and North Africa. But by far the greater
part of the paper produced to-day is made from the fiber of trees.
Particularly is this true of our own country, which consumes half of
the world’s output of paper.

It used to be that only the poorest grades of paper were made from
wood pulp; now however not only newspapers but nearly all books and
magazines are printed on a forest product. Formerly only spruce wood
was considered suitable for paper manufacture, but the rapid depletion
of this raw material led to the employment of many other species of
trees and our Government scientists are constantly searching for and
experimenting with new woods for this purpose.

Because of the insatiable appetites of our large newspaper printing
presses and because a newspaper is not intended to be an imperishable
document but a fleeting record of passing events, quality is of little
importance in the preparation of pulp for newsprint and everything
must be sacrificed for speed. The pulp is made of “ground” wood
as distinguished from the chemically prepared wood pulp known as
“sulphite.” The wood is first stripped of its bark and then cut into
pieces running from two to four feet in length, depending upon the
size of the magazine of the grinder. The wood is pressed against a
revolving grindstone by hydraulic pressure and at such an angle that
the fibers torn off will be as long as possible. The fibers are borne
off by a stream of water which carries them through a set of screens.
These remove any unground slivers, and eventually the pulp is drained
of water and pressed into laps, or, if it is to be used immediately,
it goes directly to the beating engine. Here it is mixed with a
certain amount of “sulphite pulp,” usually from 20 to 25 per cent. To
correct the yellowish color of the pulp, a small amount of blue and
red coloring is added. To give body to the paper from 5 to 15 per cent
of clay is mixed into the pulp and, to bind the fibers together and
give the paper a finish that will be at least partly nonabsorbent, a
quantity of rosin and soda ash is added with enough alum to precipitate
the rosin upon the fibers. The beater thoroughly mixes the mass of
material and converts it into a fluid of the consistency of thin milk,
which then passes on to the Fourdrinier machine.


Paper made from ground wood pulp soon discolors and becomes brittle
owing to the presence of the lignin and resin of the tree. The
superiority of sulphite pulp is due to the fact that chemical processes
are used to remove these disturbing ingredients, leaving only the
“bones” of the tree, that is, the pure cellulose fiber. Spruce wood is
usually used and after being freed of its bark and thoroughly cleaned,
all knots are cut out and it is sawed into short lengths which are
then split and cut up into little chips from ¼ to ½ inch long. These
chips are boiled under pressure in a solution of sulphur dioxide
and slaked lime. The “digesters” in which the chips are boiled are
large steel cylinders lined with brick set in cement and coated with
litharge and glycerin, so as to prevent the sulphite liquor from coming
into contact with the metal. A steam pressure of seventy to eighty
pounds is maintained for eight to ten hours and then the digesters are
discharged into vats. The sulphite liquor in which the resinous matter
is dissolved is drained away and the pulp is washed.

Soft woods, such as poplar, basswood, etc., are boiled in caustic soda,
producing what is known as “soda pulp.” “Sulphate pulp” is made by
boiling in a solution of sodium sulphate, to which a certain amount of
sodium carbonate and caustic soda are added. This process is used for
producing pulp for so-called “Kraft” paper and brown wrapping paper.

Formerly pulp was always made in the paper mill and hence the mills had
to be located near the source of wood supply, but to-day the making
of pulp is carried on as an independent industry in remote forest
regions where water power is plentiful. The pulp is pressed into laps
and compressed into bales weighing about 400 pounds. These are sent
over long distances by rail or steamship to paper mills located in or
near the big cities, so that the paper may be made near the points of

Baled paper pulp has to be reconverted into a smooth milklike fluid.
A shredding machine is used for this purpose, which tears the pulp
apart and mixes it with water. Then it goes to the beater where it
receives its quota of sulphite pulp, coloring matter, clay, and sizing,
as explained before. After an hour of treatment in the beater, it
passes on to a tank in which it is further diluted with water and is
then put through a Jordan engine. This consists of a conical cylinder
in which is placed a conical roll. Both cylinder and roll are formed
with knives that extend longitudinally, but the revolving knives are
set at a slight angle to the fixed knives, somewhat after the fashion
of a lawn mower. The conical form permits of careful adjustment of the
roller in the cylinder. The pulp mixture enters at the smaller end and
discharges at the larger end. This machine gives the pulp its final
beating and reduces it to a very smooth consistency.


From the Jordan engine the pulp is passed on into the Fourdrinier
machine, which we are now ready to investigate. The principal element
of this machine is a traveling belt of copper wire gauze which takes
the place of the screen or sieve used in the hand process. To confine
the pulp to the belt there are two endless bands of rubber, known as
“deckles,” along each edge of the screen, which travel with the screen.
To insure proper interlacing of the fibers, as in the hand process,
the screen is shaken laterally at the rate of about 300 vibrations per

The fluid pulp enters the machine through a flow box, where a constant
hydraulic head is maintained, so as to preserve a uniform discharge to
the wire gauze. The milky stream issues through a narrow opening in
the flow box, known as a “slicer.” This may be adjusted to alter the
width and also the thickness of the stream. No one would suspect from
the appearance of the milky fluid that it is filled with fibers, but a
microscopic examination of a drop of the thin liquid shows that it is
filled with tiny particles floating in the water like logs in a river.
It is interesting to watch this stream, as it passes out upon the
screen, change magically before one’s eyes, from a milky stream into
solid mass of pulp.


  A.  Flow Box
  B.  Copper Gauze Belt
  C.  Rollers
  D.  Deckles Confining Pulp
  EE. Pulleys
  FF. Drums
  G.  Suction Boxes
  H.  Dandy Roll
  I.  The Final Suction Box for Drying
  J.  Couch Roll
  K.  Canvas Belt

In Figure 71, which is a diagrammatical view of a portion of a
Fourdrinier machine, the flow box is shown at _A_ and the copper gauze
belt at _B_. This belt is supported on a series of rollers, _C_. The
deckles which confine the pulp along the margins of the screen are
shown at _D_. These belts travel with the wire gauze for a certain
distance and then pass back over the pulleys, _EE_, while the wire
cloth passes on and around the drums, _FF_. As soon as the pulp flows
out upon the wire gauze, the water it contains begins to drain away
through the gauze. But it does not do this fast enough under the mere
pull of gravity and it must be helped by means of suction. At _GG_
there are boxes or troughs that fit against the under side of the wire
gauze. In them a partial vacuum is maintained by means of suction
pumps and a large part of the water remaining in the pulp is sucked
out here. A dandy roll is shown at _H_, which presses lightly upon
the moist pulp, squeezing out the moisture in it, and at _I_ there is
a final suction box which further dries the web of fibers. It is the
dandy roll that puts a patterned surface on the paper. If the face of
the dandy roll is of finely woven wire cloth with diagonal mesh, a
“wove” paper is produced, while if it is of such surface as to impress
parallel lines in the half-formed paper, “laid” paper is produced.
Water marks are also produced by placing a suitable raised or depressed
pattern on the dandy roll, producing a corresponding thickening or
thinning of the pulp. Even after passing the last suction box, the
thin web of paper is still very wet and so flimsy that it cannot be
handled. Right here comes the most delicate part of the whole process.
The web must be picked off the wire cloth and carried across a narrow
gap to a felt belt which conducts it through another set of rollers,
A felt-covered roll, _J_, known as a “couch” roll, presses down upon
the web and the latter clings to the felt in place of the wire cloth
which passes down around the roller _F_. In starting a web of paper
very skillful manipulation is required to transfer the web from the
couch roll to the felt belt, but after it has once bridged the gap it
has enough tensional strength to pull itself across the gap. The felt
belt carries the web through a pair of heavy rollers which press out
more of the water. Because the paper passes through the rolls with the
felt belt it receives an impression from the felt on the under side.
This is now corrected by running the paper through a second pair of
rolls in the reverse direction, and on a second felt belt, so that both
sides of the paper receive the same impression. From here on the paper
passes through a long series of steam-heated drying rolls and emerges
eventually as a perfectly dry sheet.

Our largest Fourdrinier machines make a web 200 inches wide and they
can be run at a rate of 800 feet per minute, or more than nine miles
per hour. The paper is made in lengths eight miles long, which are
wound up into rolls to be fed into the huge printing presses of our
metropolitan newspaper plants.

The difference between the making of news print and finer papers lies
chiefly in the quality of pulp used and the quantity of clay and sizing
added. After the finer grades have issued from the drying rolls, they
are put through calenders to give them a glazed surface. This consists
virtually in ironing the paper between smooth rolls of iron on one
side and compressed paper or cotton on the other. Just as in ironing
clothes, the paper must be moistened before being ironed and steam is
used to supply the necessary moisture. In some cases a high glaze is
given to one side only of the paper by means of friction. The paper
passes between two rollers of different size. The smaller one travels
faster than the larger one and consequently it slips on the paper,
giving it a very smooth surface.


There is another type of paper-making machine which is used for coarse
papers, pasteboard, etc. This is known as a cylinder machine. The wire
gauze is formed into a cylinder which revolves in the liquid pulp. A
slight suction is maintained in the cylinder which causes the water to
flow in through the gauze; leaving the fiber drained on the surface.
The cylinder revolves, carrying the drained pulp on its surface until
it encounters a felt roll that picks off the web and carries it to the
pressing and drying rolls. One disadvantage of this type of machine is
that the cylinder in dragging the drained pulp through the water causes
the fibers to be combed in a direction parallel to the run of the paper
web, so that the paper, while strong in the direction of its length, is
comparatively weak in the transverse direction. This is corrected to a
certain degree by the use of “riffles” or devices that produce eddies
which disturb the even flow of the pulp.

In the making of pasteboard, a number of cylinders contribute their
webs to form a single sheet of several plies.



“WHO WON the war?” The question immediately brings forth numerous
contenders who claim the honor, respectively, for the aviator, the
chemist, the engineer, the mechanic, the farmer, the shipbuilder, etc.
As a matter of fact, all these and many others as well were invaluable
contributors to the final success, and “there is glory enough for all.”

The question, “What branch of technology or what branch of machinery
has done most for civilization?” finds a similar division of opinion,
with partisans in favor of the steam engine, machine tools, electrical
machinery, iron manufacture, paper making, printing, etc. Again, it is
clearly evident that all have been most valuable contributors and none
may carry off all the honors. However, partisans of the printing press
are entitled to place that machine among the foremost because it has
certainly been most useful in preserving and disseminating all classes
of knowledge and in promoting the progress of civilization.


It is hardly necessary for us to refer to Johann Gutenberg’s invention
in 1436 of separate type for each letter. Many centuries before that
the Chinese had made wood engravings of complete pages and printed
them on paper. Their method was to prepare an ink copy on a sheet of
paper and then transfer the copy by pressing the paper on the wood
before the ink was dry, after which they carved away all the surface
except those parts which were inked. This gave them a reverse plate
from which any number of copies could be printed. The invention of
individual type which could be used over and over again for setting new
copy was a marked improvement over the Chinese system.


The primitive screw press saw little improvement except in minor
details down to the end of the eighteenth century. Then steam began
to take the place of hand power and the idea was conceived of using a
rotary cylinder in place of a flat press. The types were tapered so
that they could be fitted about a cylinder. The paper was fed between
the type cylinder and a soft impression cylinder faced with leather.
The ink was applied to the type by means of a roller which was fed by
an inking apparatus.

In 1814 two rotary presses were installed in the offices of the
London “Times,” making it possible to turn out that newspaper at
the marvelous rate of 11,000 impressions per hour. In this country,
Richard Marsh Hoe invented a machine in which four, six, eight, or
ten impression cylinders operated on a single form of type, thereby
increasing the output of the press correspondingly. The first machine,
a four-impression cylinder press, was used by the Philadelphia “Ledger”
in 1846, and it printed 8,000 papers per hour.

Next came the “perfecting” press that printed on both sides of the
paper, and then came the continuous web press, in which the paper was
fed from a roll as a continuous sheet and, after receiving the type
impression, was cut, folded, and delivered as a complete newspaper.


Meanwhile stereotyping was introduced into newspaper printing. In
stereotyping an impression in plastic material is made of the type
face and then a casting is made from this impression which, of course,
exactly duplicates the type face. The type is thus relieved from
wear in the press and it is immediately released for use in setting
up other copy while the printing is done from the stereotype plate.
While the use of stereotyping in book printing dates back to the
eighteenth century, it was not thought practicable for newspaper
printing because of the length of time taken in making the plate, but
in 1861 papier-maché was introduced as a matrix material and a system
of rapidly drying the mold was developed so that a plate could be cast
in a comparatively short time; furthermore, impressions could be made
from a flat face of type and then the mold could be bent so as to make
curved stereotype plates for use on the cylinder presses. In newspaper
work it takes but five minutes to make a stereotype plate. Stereotype
metal does not stand the wear of printing very long and the plates
must be renewed from time to time. This fits in well with newspaper
requirements because clean cut work is not called for, and as the news
keeps coming in new editions must constantly be printed, which means
that new plates must be made from time to time. For the finer printing
of magazines and books, copper-faced electrotype plates are used in
place of the soft stereotype plates of newspaper printing.


A modern large newspaper press is a bewildering sight to behold; there
is such a vast number of rolls and cylinders, and the web of paper
moves so rapidly. But, after all, the machine is multiplex rather than
complex. It consists of a large number of printing cylinders, all
operating in a single frame. Take, for instance, a double-octuple,
color-combination press. It consists really of two separate presses,
each operating on four webs of paper that feed from opposite ends
toward the middle. There are two type cylinders for each web, one for
each side of the paper. Each cylinder is long enough to take four
stereotype plates side by side, and since each plate extends but half
way around the cylinder we have eight pages printed on each side of
the web. This makes sixteen pages per web or sixty-four for each half
of the machine, giving a total of 128 page impressions at each turn of
the cylinders. It is seldom that a 64-page paper is required, hence
the webs are slit in two by a revolving knife blade and each section
of the press has two folding mechanisms so that two sets of 16-page
papers are printed, folded, and delivered by each section. Arrangements
are provided whereby the product may consist of 32-page papers. The
papers are delivered by a traveling conveyor and every fiftieth paper
is pushed out ahead of the others so as to provide a simple method of
keeping count of the product.


The cylinders turn at the rate of 300 revolutions per minute which
means that the paper runs through the machine at nearly 14 miles per
hour. Summing up all the webs we have a total consumption of 108 miles
of paper per hour. The paper is 6 feet wide and the weight of paper in
an hour’s run is about 18 tons and the hourly production is 150,000
sixteen-page papers. When color is used, the press will deliver 50,000
24-page papers per hour with the two outside pages printed in three
colors and black. The course of the color printed web must necessarily
be different from that of the plain black printed web. It must pass
through a number of printings; and to prevent the moist ink from
transferring to the impression rolls and from them back to a succeeding
page, thus soiling or blurring the impression, an extra roll of thin
paper is passed between the printed web and the impression cylinders.
This acts in a measure as a blotter. The offset paper is taken up on a
roll and used over and over again. It is used not only for color work,
but also when fine half tone engravings are to be printed so that a
cleaner impression may be obtained.

The inking system of printing press is very elaborate. It is highly
essential that the ink be spread upon the type surface in just
sufficient quantity to be picked up by the paper and that the ink be
uniformly distributed over the whole surface. There is an ink reservoir
and a set of inking rollers for each cylinder. The reservoir consists
of a trough running the whole length of the cylinder. At each turn
a revolving roller dips into the ink and transfers a thin film of
ink to a series of small rollers. These are grouped about a large
roller to which they deliver the ink. The small rollers have an axial
reciprocating motion whereby the ink is uniformly spread over the large
roller. The latter transfers its thin coating of ink to a pair of
rollers known as “form rollers” and these in turn deliver the ink to
the printing cylinder.


The folding mechanism of a printing press is interesting. The paper is
first fed over a wedge-shaped form which folds the paper lengthwise
and then it is given a cross-wise fold. Curiously enough the folding
mechanism for printing presses was first invented by a Yankee sea
captain, named Cromwell, who could not read a drawing but developed his
invention by whittling out wooden models. He also contributed other
valuable improvements for the printing press worked out in the same
primitive way.

The rotary press was evolved especially for the printing of daily
papers and for a long time magazines continued to be printed on
flat-bed presses. But as the circulation of magazines grew into
the hundreds of thousands it became necessary to build high speed
presses to turn out these large editions. Accordingly rotary machines
were constructed similar in design to newspaper presses, but with
refinements to enable them to produce the better class of work required
of magazine printing. Although there are many magazines still printed
on flat bed presses, particularly those which publish small editions of
less than a hundred thousand, all the big national weekly journals and
monthly magazines are printed on rotary presses and some of them even
use web presses.


When a newspaper leaves the press it is folded, cut, and ready for the
news stand. Not so with the book and magazine press. There are too many
pages to be handled by a single press, and, furthermore, the pages must
be bound together. Some large magazines contain regularly more than 500
pages and occasionally they will run over a thousand pages. Obviously
no single press could handle so many pages and it takes the product of
many presses to make up a single copy. Each press prints what is known
as a form or signature and these signatures from the different presses
are then gathered, wire-stitched, and bound into individual copies.
There are machines which will do this work of gathering and binding at
the rate of sixty 1,000-page magazines or catalogues every minute. The
machines are adjustable for pages of different dimensions. The forms
may consist of four, eight, sixteen, or thirty-two pages. A separate
compartment is provided for each signature. A large machine will handle
thirty-six 32-page signatures. The compartments are kept supplied by
an operator, there being usually six compartments for each operator to
attend to. The bottom signature in each compartment is brought into
position by a suction device which seizes the signature and draws
it out, depositing it in a steel trough. Here a belt conveyor moves
the signature along at the right speed to carry it before the next
compartment just as a signature is being withdrawn therefrom. Thus the
magazine or book is progressively built up and the signatures reach
the end of their course properly assembled. A very delicate adjustment
is provided to insure the proper adjustment of signatures. The grippers
are adjusted to receive signatures of a certain thickness. If the
operator should make a mistake and put a signature of a wrong size
in the compartment the whole machine would come to a standstill. The
adjustment is so delicate that even a variation of a single thickness
of paper is enough to operate the stop mechanism. Each assembly of
signatures as it reaches the end of the trough is squared up and then
bound with wire stitching. From this point it moves on to receive its
cover. A thin coating of hot glue is applied to the rear edge of the
signatures. The cover is automatically applied and firmly pressed into
place. The finished book is then carried on out of the machine and
deposited neatly on a pile of previously bound books. To operate such a
machine there are required one chief operator and an assistant and six
girls to feed the signatures to the compartments.


The publication of a modern daily newspaper with its many special
editions would be well nigh impossible if we still had to depend
upon hand setting of type. Tens of thousands of type characters are
required to make up a single newspaper page, and although skilled hand
compositors work with extreme rapidity it would take a large corps of
men to set type for even a small newspaper in the short time available.
Speed is of prime importance in newspaper work and the task of handling
thousands of little pieces of type metal and arranging them correctly
into words and sentences was long recognized as a serious handicap,
but the problem of doing this work by machine was by no means simple
one and baffled inventors for years. One of the principal difficulties
lay in the size and shape of the type and another was that of
justifying the lines, that is, providing just the right width of spaces
between words to fill out the lines completely so that they would all
be of equal length, giving a straight instead of a ragged margin to the
column. After that came the problem of redistributing the type.

The first really successful composing machine was the invention of
Ottmar Mergenthaler in 1888. Mergenthaler overcame the difficulties
that had balked other inventors by attacking the problem from a
radically new angle. Instead of setting precast type, his machine cast
its own type from a set of matrices. By operating a keyboard, the
matrices were assembled in a line which was justified automatically
after the line was composed and then the whole line of type was cast in
a single slug. Hence his machine earned the name “linotype.” Then the
matrices were returned automatically distributed to the proper channels
of the matrix magazine ready to be used over again for succeeding slugs.


[Illustration: FIG. 72--A LINOTYPE MATRIX]

A picture of a linotype matrix is shown in Figure 72. It is a plate of
brass formed with ears _A_ at the four corners. The type mold is shown
at _B_ and of course the thickness of the matrix varies with the width
of the type letter it is designed to cast. In the top of the matrix
there is a V-shaped slot _C_ formed with teeth which are designed to
engage grooves in a V-shaped bar over the matrix magazine. The teeth on
the matrices are variously cut away and serve as keys to the different
channels of the magazine. There is a different combination of teeth
for each letter of the alphabet and all matrices of the same letter
have the same combination of teeth. The teeth on the distributing
bar are also cut away according to various combinations. After the
line has been cast the matrices are all raised by their ears and fed
one by one upon the distributing bar. Each matrix moves along until
it arrives over the channel it is designed to enter when it comes to
a gap in the teeth of the bar that are supporting it and drops into
the magazine. Although there are but seven teeth on each side of the
V-shaped bar, there are more than enough combinations possible to
provide a characteristic one for every key of the keyboard. A matrix
always has at least one pair of teeth in engagement with the bar until
it reaches the gap that lets it fall into its own special channel of
the magazine. The number of matrices of each character varies with the
normal frequency of use of that letter. For instance, the letter _e_
is very commonly used, and there must be many more _e_ matrices than
_z_ matrices, but in any case the number need not be very large because
the process of casting a line and redistributing the type does not take
very long and the matrices are soon back in the magazine ready to be
used over again. The casting and distributing operations are entirely
automatic and while they are in process the compositor is setting a new

The method of spacing which was a later development of the linotype
is also very ingenious. The compositor does not have to bother with
the width of spaces required to fill out a line. He merely touches the
space key at the end of each word and and a space bar drops into place.
Each space bar is formed of a pair of wedges and after the line has
been assembled the space bars are automatically expanded to fill out
the line completely by mechanism which holds down one wedge member (A,
Figure 73) and slides up the other (B).


[Illustration: FIG. 73.--A LINOTYPE SPACE BAR]

The difficulties of casting the linotype slug proved a serious handicap
in the earlier days of the linotype. The product of the machine could
not compare in quality with precast hand-set individual type, although
it served very well for newspapers; but the machine is now so far
perfected that it is widely used for magazine and book composition.
However before this stage of perfection was reached the demand for a
machine that could do a higher grade of work led to the invention of
another machine known as the “monotype.” The monotype consists actually
of two machines, one of which is operated by a compositor and the other
operated entirely automatically by the product of the first machine.
The compositor operates a keyboard and thereby cuts perforations in a
long strip of paper. These perforations are arranged in characteristic
groups one for each key. The perforated paper is then run through
the second machine and in accordance with the various perforations
the separate types are cast and assembled into justified lines. Air
flowing through the perforations operates a pneumatic mechanism which
brings the proper molds into position and casts the separate types. The
method of justifying the lines is very interesting. As in the linotype
the operator merely touches a space key at the end of each word, but
at the end of the line the mechanism automatically estimates the
spaces to be filled and divides this by the number of spaces so that
a characteristic group of perforations is punched when the compositor
shifts to the next line. In the casting machine the paper ribbon runs
through backward and the space group of perforations is encountered
before the line is cast. This automatically adjusts the mechanism to
cast spaces of the requisite size to fill out the line exactly.


In one sense we have taken up the various machines employed in printing
in reverse order. Of course the first machine used is the typewriter,
after which comes the composing machine, and finally the press.

It was in 1866 that two inventors, C. Latham Sholes and Samuel W.
Soule, undertook to make a machine for printing numbers in serial order
upon the pages of a blankbook. Carlos Glidden, another inventor, who
was engaged in developing a spading machine designed to take the place
of a plow, saw their work and suggested that they make their machine
write letters and words as well as numbers. The three combined and
proceeded to evolve the new machine. By the end of the summer of 1867
they had produced a typewriting machine that could be operated fairly
rapidly and that produced fair work. It was one of the letters written
by this machine that brought James Densmore into the enterprise.
He furnished the money needed to improve the crude typewriter and
make it a commercial machine. Many models were built but nothing was
produced that seemed good enough for commercial production. This
development work was too slow and discouraging for Soule and Glidden
and they dropped out, but Sholes inspired by Densmore persevered until
at last in 1873 he had produced a machine which he could offer for
manufacture. The typewriter was then taken to the Remington factory at
Ilion, N. Y., and the next year it was placed on the market and began
its public career.

Such is the story of the early development of the typewriter. It has
become so widely used and is so indispensable a part of the business
office that it arouses the utmost astonishment to learn that there
still are a few old-fashioned houses so conservative and so far behind
that they continue to write their business letters with the pen. So
common a machine, it is hardly necessary for us to describe in detail
except to mention two steps in the development of the machine, namely
the arrangement of the type bars whereby the typewriting is visible
to the typist, and secondly the effort to overcome noise by limiting
the stroke of the type bar and making it impinge upon the paper with a
pressure stroke rather than a hammer blow.

A recent development is the “stenotype,” a small machine which prints
shorthand characters, thus expediting the taking of rapid dictation.



IT USED to be that wars were fought for gold, but nowadays the
possession of rich iron mines is enough to arouse the cupidity of
neighboring nations less favored by nature. In fact, even though an
ounce of gold is worth twice as much as a ton of iron, the value of
the iron we dig out of the earth each year is far greater than that
of gold. When that rough ore is converted into iron and steel and
then into thousands of useful articles, its value mounts so high that
it cannot be estimated. The qualities of iron and its alloys are so
excellent and so varied under different treatment that this metal may
truly be said to form the foundation of all our mechanical progress.
On the one hand it spans our wide rivers, carries the burden of heavy
freight trains, or, in the form of armor plate, resists the terrific
impact of high-powered shells; on the other hand the same metal, spun
into a hair spring, governs the ship’s chronometer, or, in the compass,
points a trembling finger to guide the navigator on his course.


The first use of iron in the service of man dates far back into the
ages. An iron tool was found in the pyramid of Kephron which must
have been used 3,500 years before Christ. However, because of the
difficulty of working it, iron was not extensively employed except for
swords and cutlery. The conversion of iron into steel and the tempering
of steel blades grew to be an art which gave Damascus and Toledo a
world-wide reputation that dates back over a thousand years.

The ancients used to smelt their iron ore in what was known as a
Catalan forge because of its extensive use in Catalonia, Spain. Whether
the forge was invented there or not we cannot say. Similar forges have
been found in India and other widely remote places. They comprised an
inclined tray leading to a pot which formed the furnace and in which
a charcoal fire was kindled. The ore and charcoal were placed on the
tray and from time to time were raked down into the furnace and air
was forced into the bottom of the furnace by means of bellows. In an
improved form of the Catalan forge air was furnished by means of an
air compressor operated by a stream of water. This has already been
referred to and illustrated on page 90. Limestone served as a flux to
melt the earthy matter. The iron obtained from these primitive furnaces
was not heated sufficiently to flow as a stream, but was merely reduced
to a pasty mass which was then hammered into shape by the blacksmith.
Ten or twelve pounds of metal per day was considered a fair output for
one of these forges.


It was not until the middle of the 14th Century that a blast furnace,
crudely similar to those we have to-day, was first built and with it a
temperature was obtained that was high enough to turn the metal into a
liquid which could be cast in molds. Charcoal continued to be the fuel
used until about four centuries later, when Abraham Darby discovered
that by baking coal to remove its free gases, he could produce a new
fuel known as coke which was a good substitute for charcoal. This gave
a wonderful impetus to the iron industry in England where there were
ample deposits of coal adjacent to the iron mines. Shortly after that,
Mr. Henry Cort of Gasport, England, invented the processes of puddling
and rolling the product of the blast furnace, thus converting the iron
into a tough, malleable metal.


We must pause here to learn the difference between cast iron, wrought
iron and steel. Iron, as we know, has a high affinity for oxygen. When
exposed to air and moisture it oxidizes, rusts very quickly. The iron
we find in nature is largely oxidized. In other words, it is rusty. It
is also found in combination with other elements as well. The object of
putting iron ore through a furnace is to rid it of oxygen and this is
most readily accomplished by melting it in a carbon fire. The highly
heated carbon combines with the oxygen and passes off as carbon dioxide
and carbon monoxide gas. But a certain amount of carbon unites with the
iron and it is this alloy of carbon and iron that makes cast iron so
stiff and brittle. The less carbon present the softer is the metal and
pure iron is very ductile.

It was to rid cast iron of its carbon content that Cort invented the
puddling process. As the metal came out of the blast furnace it ran
into a “reverberatory” furnace where, without coming in contact with
coke or other carbon fuel, it was exposed to flames from an adjoining
furnace which burned out the carbon, and then the carbon-free iron was
cast into large pieces known as blooms which were hammered to rid them
of slag. The final product was known as wrought iron. Wrought iron then
differs from cast iron in having no carbon. Steel, on the other hand,
stands half way between wrought iron and cast iron in having a small
percentage of carbon. How steel is made will be described later.


Of course machinery plays a large part in the modern iron industry. It
would be an endless task even to load one of the big blast furnaces
by hand and then the enormous output of molten metal--40 tons for
every pound produced by the old Catalan furnaces--could not be
handled without ponderous machines whose huge arms and fingers are
not scorched and blistered by the intense heat. Along the Great Lakes
vast loading machines fill the holds of ore vessels and at the plant
there are enormous unloading machines that travel on rails. These have
long bridgelike arms that reach out over the ore boat and drop huge
clam-shell buckets into their holds. The buckets quickly unload the
boats and dump the ore on shore where other buckets pick up the ore,
carry it back and pile it up in big heaps that look like mounds of
reddish earth.


Blast furnaces are towering cylindrical structures of steel lined with
fire brick. They are loaded from the top with alternate layers of
coke and ore. Limestone also is added to act as a flux for the earthy
matter, as explained above. Running around the furnace near the base
there is a large pipe known as the “bustle” pipe. Through this air is
fed to a set of “tuyeres” which lead to the base of the furnace and
admit blasts of air requisite to maintain combustion at an intense
heat. The gases of combustion are not allowed to escape freely into
the atmosphere. The top of the furnace through which the ore and fuel
is admitted is closed by an air lock and the flaming hot gases are led
into “stoves” where they give up a large part of their heat to preheat
the air which is pumped to the blast furnace. The gases being mainly
composed of carbon monoxide are further combustible and may be used for
heat, light, and power purposes. In fact, they are commonly used to
drive the air compressors which feed the blast furnaces.

The blast furnace has two openings, one above the other. Through the
upper one slag is drawn off while the molten iron which trickles down
and collects at the bottom of the furnace is tapped off through a hole
near the base of the furnace. The fiery stream pours out into a lot of
small trough-shaped molds and is thus formed into “pigs.” These pigs
are all connected to the main body of the metal stream and must be
broken off. To save the time of cooling and of breaking off the pigs a
machine is used which consists of a series of molds connected to form
an endless belt. The molten iron is poured into these molds which in
their course dip into a trough of water. Here the iron is cooled and
solidified. The molds then run up an incline and finally dump the pigs
directly into railway cars which haul them away.


The production of steel economically and on a large scale dates back
to the inventions of Henry Bessemer. While searching for an improved
method of making big guns, Bessemer hit upon the idea of forcing a
blast of air through the molten iron and thus burning away carbon,
silicon, and manganese in the cast iron. No fuel was supplied except
the carbon and silicon in the iron itself. In burning out this carbon
sufficient heat was generated to keep the metal fluid.

When Bessemer made the announcement of his new process before the
British Association in 1856, his paper met with skepticism, but he
was able to demonstrate by actual experiment that cast iron could be
converted into malleable iron in this way. However, when several firms
operating under licenses from the inventor endeavored to reproduce his
experiment on a commercial scale they were unsuccessful, and after
costly experiments the process was given up as a failure. Bessemer,
however, persisted in his efforts and succeeded eventually in producing
malleable iron of a quality equal if not superior to that on the
market. But iron makers after the failure of the first experiments
would have nothing to do with the new process until Bessemer began to
turn out quantities of iron at $100 a ton below the prevailing market
price. Then iron makers woke up and Bessemer had no difficulty in
placing his process with numbers of firms on a very profitable royalty

This process pertained to the making of iron and not steel. When
Bessemer tried to produce steel he was confronted with serious
difficulties. The steel he obtained was very brittle. He tried purer
ores with little better success. Then a solution of his problem was
offered by Robert F. Mushet, who discovered a compound which would be
added to the molten metal to purify it. This compound which is known as
“spiegeleisen” is composed of iron, carbon, and manganese. It removes
the oxide of iron and the sulphur and regulates the amount of carbon in
the steel.

A Bessemer converter furnishes by far the most spectacular operation
in steel manufacture. The converter consists of a large bottle-shaped
vessel lined with refractory material. In the bottom of the vessel
there are openings through which the air blast is admitted. The molten
metal is poured into the flask and then the air blast is turned on. The
metal begins to boil violently. A dazzlingly brilliant blast of flame
and sparks comes roaring out of the mouth of the converter. Bubbles
of metal are thrown high into the air where they burst into showers
of sparks. The effect is similar to that of a volcanic eruption. In
from ten to twenty minutes the eruption subsides and then a quantity
of spiegeleisen is added. The converter is mounted on trunnions so
that when the operation is completed the vessel is tilted over and the
charge of molten metal now converted into steel is poured out.






While the Bessemer converter provides a very economical and expeditious
method of converting cast iron into steel, it is difficult to regulate
the carbon content with great accuracy and hence the use of the
open-hearth furnaces which furnish a slower method of burning out the
carbon. Figure 74 is a diagrammatic representation of such a furnace.
Below the hearth of the furnace there are two pairs of chambers, _A_,
_B_ and _C_, _D_, filled with a checkerwork of bricks. Gas is passed
through one chamber _A_, and air through the other _B_, and they
combine to form a very intense flame above the hearth _E_ in which
the metal is placed. The burnt gases pass over and through the other
pair of chambers, _C_, _D_, on their way to the stack. By this means
the bricks in the latter chambers are raised to a white heat. Then the
process is reversed; air flows through the hot checkerwork of bricks
in the chamber _C_ and gas through the hot checkerwork in chamber _D_,
and after combustion in the furnace the burnt gases are drawn through
the bricks of the first pair of chambers. By alternating the direction
of flow the air and gas fed to the furnace are always preheated by the
stored-up heat of the previously burned gases. While it takes but a few
minutes to convert cast iron into steel in the Bessemer converter, the
open-hearth process occupies from eight to twelve hours.

The steel produced in the open-hearth furnaces is poured into ingot
molds. These are approximately rectangular in section and slightly
larger at the bottom than at the top. They are open at the top and
bottom, but at the bottom rest upon a base plate. As soon as the steel
has hardened the plunger of a stripping machine holds down the glowing
ingot while a pair of hooks lift off the mold, leaving the ingot
resting on the base plate.


In the manufacture of railroad rails the ingots are placed on a
traveling “table” consisting of a series of rapidly turning rollers.
These carry the ingot to a pair of large steel rolls between which it
passes. The rolls compress the ingot slightly and it is automatically
turned over and passed through a second pair of rolls. After passing
through four “stands” of rolls, turning over between each stand, it
is considerably reduced in cross-sectional area and correspondingly
lengthened. It is now termed a “bloom.” The bloom goes through a series
of rollers which gradually reduce its section until it is some forty
feet long. Then it is cut in two and each section passes through other
rolls, until finally it is reduced to the required rail section. Each
section is then about a hundred and twenty feet long and the glowing
writhing rail passes on to the saws where it is cut into ten-yard
lengths. A similar process is employed in rolling other forms of rails
and in making steel plates and sheets.


The largest machines employed in the steel industry are those used for
the manufacture of armor and big guns. A modern large high-powered gun
is not a single solid casting or forging, but is made up of a series
of steel tubes that are shrunk one upon another so that the inner tube
is compressed. The reason for this is that the explosives used are so
powerful that they would expand the inner tube or lining of the gun
beyond its elastic limit and in that way enlarge the bore. By having it
compressed to start with it can expand farther without exceeding the
elastic limit. This expansion takes place so suddenly that the lining
rebounds or returns to its original dimensions before the outer tubes
have felt the full pressure and they too are thus prevented from being
expanded too far. In some cases the compression is effected by winding
the gun with a heavy wire of rectangular cross section.


Steel for guns and armor is made in the open-hearth furnace where the
quality of the metal may be regulated to a nicety. Gun tubes are cast
in vertical molds and during the cooling of the ingot it is subjected
to pressure so as to prevent segregation and the forming of “pipes.”
Pipes are cavities that are liable to form in the center of the ingot
due to contraction during cooling. Steel, as we have learned, is not
pure iron, but an alloy, and the various constituents have different
temperatures of solidifying, consequently they exhibit a tendency to
segregate. It is to overcome such tendencies that a so-called “fluid”
compressor is used. This is virtually a hydraulic press with a plunger
that bears down on the fluid metal as it is solidifying. Modern big
guns are enormously large. A sixteen-inch 50-caliber gun, for instance,
is nearly seventy feet long, consequently the ingot must be even
longer than this and the fluid compressor for so large a piece must be
correspondingly powerful. After the ingot has been cast and cooled,
the ends are cut off and it is bored to form a tube. Then it is placed
in a furnace and raised to a white heat, after which a bar or mandrel
is inserted in the bore and the tube is placed under the hydraulic
forge press. This is a very powerful machine with an immense hammer
that is actuated by hydraulic pressure. The stroke of the hammer is
carefully regulated so that the forging as it is turned in the forge
is subjected to equal blows. In the forge the tube is roughly formed
to the dimensions it is eventually to have when finished. The process
of forging subjects the metal to strains which must be relieved and
so the tube has to go to the annealing oven where it is raised to a
temperature which destroys crystallization. In this oven it is allowed
to cool very slowly, letting the molecules of the metal adjust and
rearrange themselves. When the temperature of the tube has been lowered
to a certain point it is taken out and plunged into a bath of oil. This
sudden cooling tempers the metal, giving it a high degree of elasticity
and tensile strength. Again the tube must be annealed to relieve it of
any strains occasioned by the tempering, and then it goes to the shop
to receive its finish boring and turning.

The process as here briefly described seems simple enough, but we must
not forget the enormous size of these pieces and their tremendous
weight. They would be difficult enough to handle when cold, but much
of the work is done while the pieces are at a white heat so that the
men who control and operate the machinery that handles the big forgings
must keep their distance. The casting, annealing, and tempering
operations are performed with the piece in vertical position, and lofty
machines and cranes are required to deal with these tall castings. A
visit to a plant which manufactures big guns is bound to impress the
visitor with awe and give him increased respect for the men who are
able to handle such huge masses of metal and also for the men who have
conceived and developed such gigantic operations.



IN MARKED contrast to the massive machinery and apparatus described
in the last chapter, and fully as wonderful, is a class of machinery
to which we might apply the term “animated.” By this we do not
mean manikins or toys, but certain higher types of machines which
seem to be possessed of powers that we should expect to find only
in living beings--machines that have a sense of touch, sight, and
hearing--machines that will reason out a mathematical problem; that
will talk; that have the equivalent of a memory. In this broad
classification we may include such widely different machines as the
motion-picture camera and projector, and that mysterious mechanism
which seems animated with strange powers of its own--- the gyroscope.


Adding, subtracting, multiplying, dividing, and the working out of
complex mathematical problems by machine seems wonderful until we stop
to reflect that mathematics is the most precise and mechanical of
all sciences. In the simpler forms these machines are mere counting
mechanisms in which the counting is done very rapidly by the aid of
intermeshing gears. The adding machine is in no sense possessed of any
reasoning power, but blindly obeys the simplest of mechanical laws.
There are rows of wheels with numbers running from 0 to 9 printed on
their peripheries. One wheel represents “digits,” the next “tens,” the
next “hundreds,” etc. The wheels are interconnected by means of gearing
so that when the digits wheel makes a complete turn, the tens wheel
makes 1-10th of a turn, and when the tens wheel completes a rotation
the hundreds wheel makes 1-10th of a turn. Keys numbered from “0” to
“9” are provided, which respectively turn each wheel through angles
from 1-10th to 10-10ths of a rotation. Thus suppose the digit wheel has
already been turned through 9-10ths of a rotation and registers the
figure “9,” and the “8” key is depressed, the wheel will be given an
additional turn of 8-10ths of a rotation and will register the figure
“7,” but the tens wheel to the left will also move through 1-10th of
a rotation, so that the two wheels will register “17.” Such is the
underlying principle of the adding machine, but various refinements
are added. For instance, the numbers that are being added are recorded
in print, and the total sum of the numbers is not printed until the
operator desires to foot up the column.

More complicated, of course, are the mathematical machines which
work out involved equations, but they are all based on simple
mechanical operations. In the Weather Bureau at Washington there is a
tide-predicting machine, which has been called a “great brass brain.”
Its brass gears may be set to allow for all the varying factors of
apparent solar and lunar motions, and they will work out the tide
for any past or future data in a few moments, solving mechanically a
mathematical problem that, by hand, would take hours and hours of weary


It was in 1877 that Edison startled the world with a machine that could
actually talk. Others had been working on this problem for years, but
they had been trying to copy the human mouth and organs of speech.
Edison attacked the problem from a new angle. He was not aiming to
produce speech but to reproduce it. Let the human vocal organs modulate
the sound waves so that they would produce spoken words; he would
provide a machine with no mouth but only an ear and a very retentive
memory which would listen to these sound waves and make an impression
of them on its soft tinfoil or wax brain. Then, at any time by the
principle of “reversal,” the record could be made the transmitter
instead of the receiver of sound waves, and it would actuate the ear
so that it would repeat the sound vibrations it had formerly received.
Thus Edison made the ear of his machine serve the double office of
hearing and talking. When Edison’s phonograph was listening it had a
sharp needle attached to the ear-drum or diaphragm of the sound box,
which cut a hill and dale groove in the brain or cylinder record of the
machine; when reproducing, a blunt needle was used which faithfully
followed the hills and dales of the groove without cutting a path of
its own.

The next notable improvement in the phonograph was that of Emile
Berliner, who in 1887 invented the laterally vibrating needle which
cut a zigzag groove in the record instead of a hill-and-dale groove.
In other words, instead of having his recording needle move in and
out as in the Edison machine, it moved sidewise. He also invented
the flat-disk record, which has almost completely supplanted the
cylindrical record.


In a measure associated with the phonograph is the motion-picture
machine, a machine with an eye and a retentive memory, which records on
a sensitive retina a series of pictures that it is able to reproduce
at any time. The recording of still photographs is remarkable enough
in itself, but photography does not properly belong in a book on
machinery. The taking of motion pictures, however, and the projection
of these pictures upon the screen, involves the use of machinery, and
we must refer to these machines briefly, owing to their widespread use
at the present time.

Long years ago it was observed that when a picture is suddenly flashed
before the eye an image is impressed upon the retina, which persists
for a brief interval even after the picture itself has been withdrawn
from view. By preparing a series of pictures of a figure which show
it in progressive positions and flashing these pictures in rapid
succession before the eye, persistence of vision will bridge the gaps
between pictures and the figure will appear to move. This principle was
first used as early as 1834 in an ingenious toy known as “zoetrope,”
which consisted of a cardboard cylinder with a series of pictures drawn
on the inner surface. There were slots cut in the cylinder through
which these pictures on the opposite face of the cylinder could be
seen. As the cylinder was revolved the eye caught only momentary
glimpses of these pictures, one after the other, producing a sense of
motion. In 1870, Henry Heyl of Philadelphia prepared a progressive
series of photographs each separately posed before the camera.
From these he made glass positives and projected them on a screen
in rapid succession so that the picture appeared to move. In 1880,
Edward Muybridge set up a battery of cameras and took a succession of
instantaneous pictures of a galloping horse. The shutters were operated
by strings stretched across the course and as these were successively
snapped by the horse the pictures were progressively exposed. Glass
positives of these pictures were thrown on the screen by means of a
machine to which he gave the formidable name “zoöpraxiscope.”


No one at that early date had thought of using anything but glass
plates, and they were difficult to handle, both in the camera and
in the projector. It was not until 1887 that the celluloid film was
invented by Rev. Hannibal Goodwin, and then it became possible for
Edison to invent a camera with a film that was intermittently moved
so as to take a series of pictures. From the negative thus obtained
a positive film was then made and placed in a machine known as a
“kinetoscope.” Looking through a peephole in this machine the pictures
were flashed before the eye in rapid succession. Finally, in 1893, C.
Francis Jenkins, of Washington, developed a projector similar to those
now in use by which the pictures could be thrown on a screen. Thus was
born the motion-picture industry which has taken such a strong hold on
the public.

It is now possible to project pictures in their natural color so as to
add to their realism, but one more step is needed to give a sense of
real life. The figures on the screen must talk as well as move. Efforts
to combine the phonograph with motion pictures have so far been only
partially successful. Perfect synchronism is very difficult to obtain,
but it is highly probable that obstacles which hitherto have been most
troublesome and seemingly insurmountable will, in time, be overcome.
Then the “silent drama” will no longer be silent and we shall have
“animated pictures” that will be really animated.

In addition to machines that talk we have machines that hear--machines
that will respond to sound waves. A diaphragm flexed by sound waves
closes an electric circuit and starts the operation of a machine. Some
toys have been made which operate on this principle. Experiments have
been made with a typewriter that will respond to a spoken message,
but so far they have not been attended with much success. Boats have
been built whose steering gear may be controlled by sound waves, but
as yet nothing of commercial importance has been developed in machines
controlled by sound.


Much more has been done with machines that see. There is a delicate
device known as a “sun valve,” which is used on beacon lights so that
as soon as it grows dark or very foggy the lamp is automatically
lighted, and when the day dawns or light breaks through the fog the
light is extinguished. The sun valve has two rods, one brightly
polished and the other a dead black. Light and its attendant radiant
heat waves are absorbed by the black rod, but are reflected from the
bright rod. As a consequence, the black rod grows hotter than the
polished rod and expands. The difference of expansion between the two
rods is utilized to operate a valve which controls the supply of gas to
the lamp. This valve is very sensitive and marvelously responsive to
variations of light.

There is a chemical element called selenium, which is peculiarly
sensitive to light. When light shines upon selenium its electrical
resistance is lowered, and hence it can be used as a light-operated
valve to control the flow of electric current.


One of the most marvelous machines of the present day is one which will
actually read ordinary printed type, uttering musical sounds that vary
for each letter, so that a blind man after learning this new musical
language can read any book. This machine, known as the optophone, is
the invention of Prof. E. Fournier d’Albe, and was developed to a
commercial success last year (1920). With it blind operators are able
to read at the rate of twenty-five words per minute.

The operation of this wonderful machine can best be understood by
reference to the accompanying diagrams, Figures 75 and 76.

[Illustration: Diagrammatic Arrangement of Optophone.


[Illustration: FIG. 76.--SIDE VIEW OF THE OPTOPHONE]

There is an electric lamp in the machine before which there is a disk
that is revolved by a small motor. In this disk there are five circular
rows of slots and the light shining through these slots is cut up into
five pulsating beams of light. These beams are brought to a focus in a
vertical row upon the type page. From the paper they are reflected to a
selenium cell or bridge. The selenium bridge forms part of the circuit
of a telephone receiver and the diaphragm is thus made to vibrate at
the same frequency as the light beams do. By varying the number of
slots in each row in the disk the beams of light are given different
periods of pulsation or vibration and they produce a sound chord or
“scala” in the telephone receiver. The speed of the disk and the
disposition of the slots is so chosen that the notes produced are _G_
_C′_ _D′_ _E′_ _G′_ of the musical scale. Only white paper reflects the
light beams; the black surface of the printed type absorbs them. Thus,
as the row of beams is swept across a line of printed matter, the beams
will be extinguished in various orders of succession, or simultaneously
in accordance with the shape of the particular type-character they

The middle three beams correspond to notes _C′_, _D′_ and _E′_, and
play upon the small letters, while _G′_ plays up the upper part of
capital letters, and _G_ upon the tails of such letters as _y_, _p_,
etc. If the scala passes over the letter “V,” for instance, first the
top note _G′_ is silenced, then _E′_, _D′_, _C′_, _D′_, _E′_ and _G′_
in succession. This arrangement constitutes what is known as the “white
sounding” optophone, because the full chord is sounded constantly,
except when the type matter is encountered.

To simplify the reading an improved type of optophone has been made,
which is known as the “black-reading” optophone, With this machine
there is no sound produced except when the type is encountered. The
letter “V” is then identified by the _sounding_, instead of the
_silencing_ of the notes _G′_, _E′_, _D′_, _C′_, _E′_ and _G′_. The
letter “A” produces the sounds _C′_, _D′_, _DE′_, _DG′_, _DE′_, _D′_
and _C′_. This result is obtained by using two selenium bridges, as
shown better in the side view, Figure 76. There is a concave reflecting
lens, which reflects half of the light upon the second cell, known as
the balancer selenium bridge. Electric current passing through the
balancer opposes the current passing through the main selenium bridge,
and hence there is silence in the telephone receiver when the scala
passes over plain white paper, but when type is encountered and certain
of the beams are not reflected against the main selenium bridge the
sounds are produced through the balancer bridge.

The success of the optophone leads one to hope that it may be but the
forerunner of a machine that will translate the whole world of light
and color into one of music, and permit the blind not only to read by
ear, but also to see their friends and their surroundings through the
sense of hearing. In fact efforts to make such an apparatus preceded
the invention of the optophone.


As intimated above, we have included the gyroscope among the higher
type of machines, because it seems possessed of a stubborn will of its
own, and apparently defies the laws of gravity.

There is nothing mysterious about its mechanism. It is merely a wheel
with a heavy rim and with its axis mounted in gimbals, so that it may
turn freely in any direction. The wheel, when at rest, behaves no
differently from any other mechanism. But once the wheel is set to
spinning at a high velocity it seems to acquire marvelous powers and
obstinate notions of its own as to what it will do and what it won’t
do. You may lift it, or lower it, or move it sideways in any direction,
and it will not show the least sign of rebellion so long as the plane
of its rotation is not deflected, but attempt to twist its plane of
rotation and it will resist with the power of a giant. The resistance
that even a small gyroscope will develop is astounding. A wheel
weighing not more than 10 pounds may develop so much energy that a man
twenty times as heavy pushing with all his might cannot turn it over.
Not only does it resist the push, but it actually leans back against
the pusher. Then it has the peculiar habit of turning at right angles
to the direction in which it is pushed. Suppose, for instance, the axis
of the gyroscope is horizontal and it is resting freely on a pair of
supports, one at each end. Remove one of the supports and the gyroscope
does not fall. To do so it would have to swing around the other
point of support as a center; in other words, the plane of rotation
would have to be turned angularly and such a motion the gyroscope
resists. The unsupported end of the axis dips momentarily under the
pull of gravity, but immediately recovers and actually rises above the
horizontal, then it begins to revolve slowly in a horizontal circle
about the supported end of the axis--a motion which is technically
known as “precession”. The pull of gravity exerted in a downward
direction results in a horizontal motion at right angles thereto. It
seems as if the gyroscope was bidding defiance to laws that govern
other objects, but, of course, such is not the case. The gyroscope is
as submissively obedient to the laws of gravity as any other object
or machine, but the forces which act upon it are so complicated that
it is difficult for one to comprehend them without study. In fact, it
is almost impossible to explain the strange behavior of a gyroscope
without the use of mathematics that is too involved to be presented in
this book.

Of course, the underlying cause of gyroscopic action is inertia; _i.
e._, the tendency of a body to retain its state of rest or uniform
motion. A bullet is forced out of a gun by the sudden expansion of
gases behind it, but after it leaves the muzzle and the influence of
the gases, why does it keep on traveling? We may just as well reverse
the question and ask why it should ever stop. Having once acquired
a certain velocity it keeps that velocity because of its inertia or
mechanical helplessness, and it would keep on going forever were it not
for the resistance offered by the air and the pull of gravity, which
gradually draws it down to earth. It takes a deal of energy to divert
the bullet from its course. In a gyroscope we have a similar condition.


We may conceive of a gyroscope as consisting of a stream of bullets all
tied to a center, so that they fly around in a circle. Any effort to
deflect the bullets out of their course will be resisted by each bullet
as it comes to the deflector. Here each bullet acts individually, but
in a gyroscope wheel the equivalent of the stream of bullets is a
solid rim, each particle of which is rigidly connected to every other
particle, and so the whole wheel immediately feels the deflecting force
and resists it. As long as the wheel is maintained in its own plane
of rotation, or moved into parallel planes, there is such a perfect
balance of all forces that no more resistance is offered to the motion
of the wheel as a whole than would be offered by any other object of
equal mass. But when the wheel’s plane of rotation is moved angularly,
a complicated series of forces is developed.


Some idea of the nature of these forces and why they give rise to
precession may be understood by reference to the diagram, Figure 77.
Here we have a disk with a heavy rim turning on the axis X, X′. At
_A_, _B_, _C_ and _D_ are four particles whose flights we are going to
consider. Suppose the wheel to be at rest; then if _X, X′_ is tilted
in the direction of the arrows _x_ _x′_, the wheel will turn about
the line _Y Y′_; _D_ will move forward toward _D′_, and _B_ backward
toward _B′_, but _A_ and _C_ will remain where they are. Now, suppose,
the wheel to be revolving clockwise, or in the direction _A_, _B_,
_C_, _D_, then the particle _A_ will pursue a spiral course that will
bring it to _B′_, and _C_ will pursue a spiral course that will bring
it to _D′_. However, particle _D_ will have an irregular course, as
indicated by the dotted line, starting first to move forward and then
curving back toward _A_. The same will be true of _B_, except in the
reverse direction. The course of particles _D_ and _B_ is, therefore,
materially different from that of _A_ and _C_. Now, the particle
_D_ will resist being deflected from its course and will develop an
opposing force represented by the arrow _d_. A moment later this is
reversed as the particle bends back toward the axis _Y Y′_, and we may
represent the new force by the arrow _d′_. It may be proved that the
force _d′_ is more powerful than that of _d_. The particle _A_ in the
meantime exerts a force opposing its deflection, which is represented
by the arrow _a_. On the other half of the wheel there are similar but
opposite forces, _b_, _b′_ and _c_. The sum of these forces gives the
wheel a tendency to turn about the axis _Z Z′_. To avoid complicating
our diagram with too many arrows, we had better refer to a new diagram
(Figure 78) which shows only the resultant of the forces developed.
The application of the forces _x_ _x′_, which would have turned the
wheel on the axis _Y Y′_, had it been stationary, have resulted in the
development of forces _z_ _z′_ at right angles to _x_ _x′_, tending to
turn the wheel about the axis _Z Z′_. Now, if we go through the same
processes of reasoning as before, it will be evident that the forces
_z_ _z′_ will result in a third set of forces _y_ _y′_ at right angles
to _z_ _z′_ tending to turn the wheel about the axis _Y Y′_. The forces
_y_ _y′_ exactly balance the forces _x_ _x′_, and hence the wheel does
not turn about the axis _Y Y′_ in response to the original forces, but
starts instead to revolve slowly about the axis _Z Z_. Because the
forces _x_ _x′_ and _y_ _y′_ balance each other, there is no fourth
couple developed and hence no opposition to the forces _z_ _z′_.


The gyroscope was used as a toy ages ago. The top, which is one form
of gyroscope, was a favorite plaything of ancient Egypt. But although
known these many centuries, it is only in the past few years that any
real effort has been made to set the top to work. Because it persists
in maintaining its plane of rotation it has proved most useful on
submarine torpedoes to control the rudder and hold the torpedo on a
true course to its target.


Another most important use for the gyroscope is found in the submarine
itself. The needle of a magnetic compass is kept pointing north by
action of the magnetic lines of force which surround this earth.
Whenever a large mass of iron is placed near the compass the magnetic
field is distorted and the compass needle is deflected from the
true north. On modern steel vessels the compass has to be carefully
corrected by using iron masses to counterbalance other disturbing
masses. However, in a submarine the whole shell of the vessel is of
steel and the magnetic lines of force flow along this shell. The
compass needle is virtually insulated from the terrestrial magnetism
by the surrounding steel hull. But, fortunately, the gyroscope may be
used as a compass and it is in no way affected by magnetism. Once the
gyroscope is set spinning with its axis pointing to the North Pole
of the heavens it will continue to point in that direction no matter
how devious a course the vessel may pursue. If pointed in some other
direction, the precessional forces set up by the rotation of the earth
will turn it due north. As the vessel rolls or pitches, disturbing
precessional movements are likely to be set up. These are overcome by
special mechanism, so that the gyroscopic compass may now be depended
upon as a perfectly reliable instrument.


One of the most remarkable recent developments of the gyroscope is
its use as a stabilizer in ships to keep them from rolling in a heavy
sea. A comparatively small wheel is mounted in the hold of the vessel
with perfect freedom to turn in any direction. If the wheel is clamped
so that it cannot precess, the vessel will roll and pitch, but the
instant the gyroscope is released it exerts its wonderful powers. The
ship rides smoothly and its groaning and creaking ceases, showing that
it is no longer subjected to severe strains. Of course, it rises and
falls with the waves, but it maintains an even keel as if sailing in
smooth water. The object of stabilizing a ship is not merely to cater
to the comfort of passengers who are subject to seasickness, but to
save wear and tear on the vessel and also to economize time and fuel.
An unstabilized ship riding a heavy sea pursues a very sinuous course;
in other words, it must travel farther than it would in smooth water.
The rudder must constantly be turned to keep the ship on its course,
and this acts as a drag on the progress of the ship, slowing it down
and wasting the power of the engine. As the ship wallows in the sea it
displaces much more water than it does when riding on an even keel and
here there is a further loss. It has been estimated that a 15,000-ton
vessel running at 18 knots may waste as much as 1,000 to 1,200
horsepower in a heavy sea. If stabilized with a gyroscope, practically
all this wasted horsepower would be saved at the expense of a very
small amount of power used in keeping the gyroscope spinning.

The first man to stabilize a ship with a gyroscope was Dr. Schlick,
who demonstrated the powers of this mysterious mechanism in 1906.
His stabilizer, however, was not sensitive enough to provide perfect
stabilizing. The ship had to roll some before the gyroscope exerted its
corrective forces. Recently, however, Mr. Elmer A. Sperry has improved
the stabilizer, making it so sensitive that there is practically no
rolling or pitching of the vessel.

Curiously enough, the gyroscope may be used not only to keep a ship
from rolling, but also to make it roll. Should a vessel run upon a
mud flat it may be rocked by braking or accelerating the precessional
motion of the gyroscope. In this way the ship may work itself out of
the mud bank. Ice breakers are equipped with gyroscopes, so that they
may be rolled to prevent them from being frozen into an ice pack and to
assist them in crushing their way through the ice.


In 1907 a sensation was created by the exhibition of a car which ran
on a single rail. The inventor of this monorail car was Mr. Louis
Brennan. The public was astonished at the ease with which this car
maintained its balance on the rail, leaning in as it rounded a curve
to keep its equilibrium. Passengers could move about at will without
the slightest danger of upsetting the car; in fact, if a heavy weight
was placed on one side of the car that side would rise rather than
fall. The car could run with equal ease upon a cable of a crooked pipe
line. The gyroscope that maintained the balance of the car consisted
of a couple of small wheels which revolved in a vacuum chamber at the
rate of 7,000 revolutions per minute. Once started, little power was
required to keep them going. Interesting as this car was, it did not
offer sufficient advantages over the present-day double rail cars and
locomotives to justify its development on a commercial scale. Although
witnesses of the exhibition marveled at the strange spectacle of this
mechanical tight-rope walker, they did not realize that they themselves
had had gyroscopic cars in their midst for years. The gyroscopic
action of the wheels of a motorcycle is very marked. It is this action
which is mainly responsible for holding the machine upright. The same
is true of a bicycle, although the gyroscopic effect is not quite so
marked, because of the lower velocity of the wheels. However, we all
know that any tendency for the machine to fall to one side or the other
may be corrected by a slight turn of the front wheel in that direction
which at once has the effect of bringing the bicycle back to vertical


Still another recent development of the gyroscope is its use as an
“automatic pilot” on aeroplanes. Two sensitive gyroscopes are used
to stabilize the aeroplane. If a gust of wind tends to tilt the
machine, the gyroscopes immediately sense the deviation and by closing
electrical circuits operate the ailerons to bring the machine back to a
horizontal plane.

An aviator possesses a certain sense of balance which is highly
developed by experience and long practice, but at its best it does not
begin to compare with sense of balance possessed by the gyroscope. Not
only will it keep the machine from tipping laterally, but it will also
hold it on a level keel and can be used to steer the aeroplane in any
desired direction, so that the human pilot may surrender the helm to
the faithful mechanical pilot with perfect confidence in the ability of
this animated machine to hold the aeroplane on a true course despite
the vagaries of the wind. While this is theoretically possible, in
practice certain difficulties are encountered which up to the present
have prevented gyroscopic control of aeroplanes from being entirely



IN THE preceding chapter we dealt with high temperatures and their
employment in melting, molding, and working steel into useful forms. It
will be well for us to pause here to consider temperatures at the other
end of the thermometer scale, how they are obtained, and the important
part they play in modern civilization.

It is not absolutely correct to speak of producing “cold.” We are apt
to forget that cold is merely absence of heat. Strictly speaking, there
is nothing cold on earth. Everything is more or less hot. A piece of
ice at 32 degrees F. is hot compared with a lump of frozen alcohol, and
the latter at its freezing point is hot compared with a lump of frozen
air, while air at its freezing point is hot compared with a lump of
solid helium. In other words, frozen alcohol will be melted by the heat
in the ice; frozen air will be melted by the heat in frozen alcohol,
and frozen helium will be fused by the heat in frozen air. Everything
contains heat, and one object is colder than another only because it
contains less heat.

Of course, the temperature of ice may vary. One block of ice may be
ten, fifty, or a hundred degrees warmer than another, but ice cannot be
heated above 32 degrees F. at the normal pressure of the atmosphere.

Ice is really a partial heat vacuum, a chamber partially exhausted,
into which heat will flow if it gets a chance. We pack it away in
sawdust, granulated cork, or other materials through which heat can
with difficulty penetrate, and then in hot weather cakes of ice are
placed in our household refrigerators, so that the heat that is in our
food will have something to flow into. When we place our hands near a
cake of ice, they feel cool and it seems as if ice radiated cold just
as a stove radiates heat; but, of course, such is not the case. The
heat of our hands radiates more rapidly in the direction of the cake of
ice than in other directions, because there is a partial heat vacuum
for the heat to flow into and the result is a sensation of cold.

We no longer depend upon cold winters for our supply of ice. We have
learned how to pump heat and we can make heat vacuums, anywhere and
at any time, even in the heart of the tropics, and regions in which
no natural ice is ever obtainable have the benefits of refrigeration.
Furthermore, we are not dependent upon ice for cooling foods. In many
cases it is not necessary or even desirable to reduce temperatures
to the freezing point of water. A moderate chilling is all that
is required for certain foods. By the proper use of refrigerating
machinery any degree of temperature may be obtained and maintained.
To-day small refrigerating plants are constructed for domestic
purposes, so as to render the housewife independent of the ice man.

With refrigerator cars and refrigerating plants on shipboard,
fruit from the far west and from tropical lands may be brought to
our breakfast table. Meats from northern slaughterhouses may be
transported in perfect condition into hot southern climes. There
are also certain industries which are dependent on the use of the
low temperatures. In breweries, dairies, margarine factories, etc.,
refrigeration is of the utmost importance, and refrigerating machinery
is used for cooling and drying the air blast for blast furnaces.

In some few places refrigerating machinery is used to cool buildings
in warm weather and make life more bearable in summer weather. It is
highly probable that refrigeration of dwellings will be more and more
extensively developed. In winter time we can make the climate in our
houses anything we please. Why should we not control the indoor climate
in summer time as well?


The volume of a gas varies inversely in accordance with the pressure to
which it is subjected, and also directly according to the temperature.
If we start with a gas at the freezing point (32 degrees F.) and reduce
its temperature 1 degree (or to 31 degrees F.), we find that the volume
of the gas is reduced 1/492.6 of its original volume, provided, of
course, that we do not vary the pressure on it. In fact, for every
reduction of 1 degree below the freezing point there is a reduction of
1/492.6 of its volume, and for every degree of increased temperature
there is an increase of 1/492.6 of the volume. From this it is assumed
that at 492.6 degrees below the freezing point, or 460.6 degrees below
zero F., we will reach the absolute zero, or the point at which there
is no more heat in the gas.

We have not yet succeeded in reaching the extreme of low temperature,
although we have come very near it in laboratory experiments. Helium
is liquefied at -448 degrees F., which is very near to the absolute
zero. At the other end of the scale we have attained enormously
high temperatures. The heat of the electric arc, for instance, is
between 6,500 and 7,200 degrees F., and that is the highest degree of
temperature that we have been able so far to attain.

Human life occupies a very limited zone in this range of temperatures.
We must maintain our blood at a temperature of 98 degrees F. A
variation of 8 degrees either way is fatal. By piling on heat
insulators, such as fur clothing, to retain the heat of our bodies
and keep it from flowing out too rapidly, we can maintain the blood
temperature at 98 while the surrounding atmosphere may be 70 or 80
degrees below zero. There are internal fires within us that generate
heat which radiates from the body, and by checking this radiation by
suitable clothing we can maintain our blood at the normal temperature.

But what can we do when the surrounding temperature is higher than
blood heat? The outside heat may be kept from flowing in by surrounding
ourselves with heat-insulating clothing, but the internal heat then
has no means of radiating away from our bodies; it accumulates, and
we become overheated. However, Nature provides a cooling system in
the perspiration which oozes from our pores, and as this evaporates
it cools the skin and enables us to maintain our normal blood heat,
although submerged in an atmosphere of a higher temperature. If the air
is dry, the evaporation is more rapid and the cooling is greater than
in a moist atmosphere. That is why a temperature of 105 degrees on our
Western plains may be more endurable than a temperature of 95 degrees
in the moist atmosphere of New York. The importance of keeping down the
temperature of the blood is particularly appreciated by physicians, and
for this reason the earliest attempts at artificial cooling were made
by physicians.


Very early in his history man discovered fire, learned how to kindle it
and how to use it for his good. That discovery placed him immediately
on a level far above the beasts. However, it is only in comparatively
recent times that he has learned the uses of low temperatures. Nature’s
stores of ice were drawn upon, and methods of preserving ice through
warm weather were discovered in ancient times. Nero had ice houses
built for him in Rome, but he could stock these buildings only with the
ice that nature furnished him. Freezing mixtures of salt and ice, such
as we use in our ice-cream freezers to-day to obtain temperatures far
below the freezing point of water, were probably known in early times,
but the ancients did not know how to produce ice.

Artificial ice was probably first made in India, where it has long
been the practice to produce ice by evaporation. Water is placed in
shallow pans and then dry air is circulated over it, causing so rapid
a vaporization as to cool the water to the freezing point. The idea
of cooling water by evaporation belongs to very ancient times. Water
placed in porous earthen vessels was found to be cooler than water
kept in water-tight jars. The moisture that escaped through the vessel
would evaporate, and in so doing draw heat out of the vessel and its
contents. To-day campers keep water cool by putting it in canvas
buckets and hanging the buckets in the wind, so that the moisture
oozing through the canvas will evaporate quickly.

It was not until 1755 that a mechanical means of producing low
temperatures was developed. The inventor was Dr. Cullen, and he used an
evaporation system, expediting the evaporation by producing a partial
vacuum over the water. But nearly a century elapsed before the first
commercially successful refrigerating machine was built. Even then the
advantages of artificial refrigeration were not fully realized, and it
was not until late in the last century that real progress was made.
Since then the development of artificial refrigeration has been truly


There is a definite relation between heat and mechanical energy, in
fact the two are mutually convertible. The amount of heat required
to raise the temperature of a pound of water 1 degree F. is called
a British thermal unit or a B. t. u. This measure is taken at 39.1
degrees F., because at that temperature water is at its densest. Since
heat and mechanical energy are mutually convertible, we can express
foot-pounds or horsepower in B. t. u. One B. t. u. is equivalent to
778 foot-pounds of energy. In other words, the amount of heat that
would raise the temperature of a pound of water 1 degree F. would, if
converted into mechanical energy, be sufficient to raise a weight of
778 pounds to a height of one foot, or one pound to a height of 778
feet. A horsepower is equivalent to 2,545 B. t. u. per hour.

Heat from burning coal is used to generate steam, and this in turn
is used to operate a steam engine and thus heat is converted into
mechanical energy (unfortunately most of the original heat units in the
coal are wasted, as was pointed out in a previous chapter); but heat
will not flow from one body into another of higher temperature without
the expenditure of mechanical energy. It always flows from a hot body
into a cold one, and not from the cold body into the hot one, unless
it is actually pumped up to the higher heat level by some mechanical
means. A refrigerating machine is actually a heat pump with which we
produce a partial heat vacuum.

Whenever a gas is compressed, heat is generated. Anyone who has
operated a tire pump knows how hot the pump becomes from the heat
that is seemingly squeezed out of the compressed air. As was noted in
Chapter VIII, heat is liable to give trouble in an air compressor,
and sometimes the temperature rises to such a point that there is
an explosion of the air and the vapors coming from the oil used to
lubricate the machine. The compressed air is therefore cooled by means
of water jackets or coils of pipe through which water is passed.
In this way the excess heat is carried off. When, however, cooled
compressed air is relieved of pressure and allowed to expand again
the process is reversed. A partial heat vacuum is formed and heat
from surrounding objects flows into the vacuum. In other words, the
surrounding objects are cooled.


[Illustration: FIG. 79.--COLD AIR MACHINE]

It is a simple matter to make a machine which will alternately
compress, cool, and expand air in such a way as to produce a lowered
temperature. Such a machine is indicated diagrammatically in Figure
79. There are two cylinders, _A_ and _B_, and a condenser at _C_. When
the piston _a_ in cylinder _A_ descends it compresses the air in the
cylinder; this air flows into the condenser _C_. There is a coil of
pipe in this condenser through which water circulates. This carries off
the heat of compression and then a valve is opened which permits the
cooler air to pass off into cylinder _B_. As the air expands in this
cylinder it becomes chilled. This chilled air is then forced out of
cylinder _B_ by means of piston _b_ and flows into the refrigerator or
cold storage room _D_. As the air is liable to take up moisture and to
introduce objectionable vapors from oil used to lubricate the pumps, it
is usually confined in pipes in the refrigerator and then returned to
the cylinder _A_.


[Illustration: THE OPTOPHONE

An instrument which enables the blind to read common print]


This is a type of a refrigerating machine that is used very extensively
on ships for chilling perishable foods. However, air has only a very
low capacity for heat, and in order to obtain an appreciable amount of
refrigeration very large volumes of air must be handled. This means
that cold-air machines must be very large and bulky. The efficiency of
such machines is low, but they find favor on shipboard because there
are no inflammable or poisonous gases to be dealt with. In the standard
machine of the United States Navy air is compressed to 260 pounds; and
in the expansion is raised to 60 pounds pressure, which is enough to
reduce the temperature to between 70 to 90 degrees below zero.


Far more efficient are the machines which utilize latent heat. As
explained in a previous chapter, whenever a solid is converted into a
liquid or into a gas a certain amount of heat is absorbed and stored
up in such a way as not to become apparent to the senses or to a
thermometer. Such heat is known as “latent heat.” For instance, we can
add a pound of water at 50 degrees temperature to a pound of water at
200 degrees, and the mixture will have a temperature of 125 degrees, or
the mean of 200 + 50 degrees. But a pound of ice at 32 degrees mixed
with a pound of water at 200 degrees will not give us 116 degrees
((200+32)/2), but only 44½ degrees. In other words, about 143 heat
units will be rendered latent in converting solid water into liquid
water, reducing the temperature of the water to 57 degrees and then
the mean of 57 and 32 is 44.5 (200-143=57, (57+32)/2 = 44½). A more
striking experiment is to mix a pound of water cooled to 32 degrees F.
with a pound of water at 175 degrees F., and the result will be two
pounds of water at 103.5 degrees, but if we mix a pound of chopped ice
at 32 degrees F. with a pound of water at 175 degrees F., the result
will be two pounds of water cooled to the freezing point.

In passing from a liquid into a gas water absorbs far more heat and
renders it latent. For each pound of water converted into steam at
atmospheric pressure 970 B. t. u. are absorbed. This storage of latent
heat is utilized to good advantage in refrigerating machinery. The
vacuum machine invented by Dr. Cullen in 1755 was a latent heat machine.


As we have observed before, the boiling point of a liquid depends upon
the pressure to which it is subjected. Under the normal atmospheric
pressure of 14.7 pounds per inch the boiling point of water is 212
degrees F., but if the pressure be increased the boiling point rises,
and if it be reduced the boiling point is lowered. In a partial vacuum
of ten pounds absolute pressure the boiling point is 193.2 degrees, at
one pound it is 102.1 degrees, and if the pressure is reduced to .089
pound water will boil at 32 degrees, or its normal freezing point. Dr.
Cullen, by exhausting the air from a vessel containing water, made the
water boil or vaporize at a low temperature. In order to boil it had
to absorb heat, and not being supplied with any external heat it had
to draw upon itself, thus producing ice.


Dr. Cullen’s machine has been improved upon by using various chemical
substances to absorb the water vapor. Such a machine is shown in Figure
80. The vacuum chamber _A_ is partly filled with brine, which may be
cooled below the freezing point of pure water without congealing. A
pump, _B_, maintains a vacuum in the chamber. In the upper part of
the vacuum chamber there is a vessel, _C_, into which sulphuric acid
is sprayed from a reservoir, _D_. This acid has a strong affinity for
water vapor and hastens the evaporation by absorbing the vapor with
which it comes in contact. The mixed sulphuric acid and water flows
over into a receiver, _E_. The acid is reconcentrated by steam heat so
that it can be used over again. However, this feature of the process is
not shown in the diagram. Brine from the chamber _A_ passes through
a coil of pipe _F_ in the tank _G_, where the ice is made, and it is
returned to the vacuum chamber by an injector _H_, which at the same
time introduces fresh water into the chamber to take the place of that
absorbed by the acid. The fresh water and brine enter as a spray at
_I_, so as to increase the rate of evaporation.



Another form of refrigeration is known as the absorption system,
and strangely enough direct heat is applied to the machine in one
place in order to abstract heat from it in another. A diagrammatic
representation of the first machine of this type (which was invented
by Frederick Carré) is shown in Figure 81. Two vessels, _A_ and _B_,
are employed, which are connected by a tube _C_. The vessel _A_
contains ammonia solution. A lamp, _D_, is placed under the vessel _A_.
Sufficient heat is produced to vaporize the ammonia, whose boiling
point is very low, and distill it out of the water in the solution. It
passes through tube _C_ into vessel _B_. This vessel is surrounded by
a tank, _E_, containing cold water, which condenses the ammonia vapor
into liquid ammonia, then the process is reversed.

The circulation of water through tank _E_ is checked and water from
pipe _F_ is sprayed on vessel _A_. This cools the contents of vessel
_A_, producing a partial vacuum. The ammonia in chamber _B_ boils and
its vapors pass back into chamber _A_, where they are reabsorbed by the
water in that chamber. The rapid vaporization in chamber _B_ absorbs
heat from the immediate surroundings and will freeze water placed in
the tank _E_.

In commercial practice the absorption system is very extensively
employed. The ammonia is placed in a large cylinder known as a
generator and is heated by steam coils. The ammonia vapor passes
through an analyzer which traps any water vapor it may contain, and
then it goes through a series of condensing coils, which are cooled by
water. In these condensing coils the ammonia vapor is liquefied by the
pressure in the generator and collects in a receiver, whence it passes
through an expansion valve into the cooling coils in the brine tank.
From the cooling coils the ammonia gas passes back through an absorber
which reverses the operation of the generator. Here weak aqua ammonia
is sprayed on the ammonia gas and absorbs it. The rich ammonia solution
is then pumped into the generator.

There are several auxiliary apparatus which are omitted in this brief
description in the interest of clarity.



One more type of refrigerating machine remains to be described and
that is the compression type. This was invented by Jacob Perkins in
1834, but was not developed into a commercial machine until 1850.
This machine is the most important of them all. In some respects it
is like the absorption process, but in place of adding direct heat
a compressing machine is employed. Figure 82 illustrates the system
diagrammatically. At _A_ is the compressor which compresses ammonia
gas. The gas which is heated by the compressor is then cooled and
liquefied in the condenser _B_. Thence it passes into a brine tank _C_,
where it expands and absorbs heat. From this point it is drawn back
into the compressor, thus completing the cycle. In other words, the
ammonia must absorb as much heat from the brine as is taken out of it
at the condenser.



AT THE VERY beginning of this book we observed that war is a most
potent stimulus to invention among primitive men. Despite all our
advances in civilization we still have our wars, each more dreadful
than the preceding one; for each important conflict brings forth new
engines of destruction or stimulates the invention of new death-dealing
machines which are developed during intervals of peace. So terrible
has modern war become that with each great conflict it has seemed as
if its very dreadfulness would stay the hand of the invader and make
him hesitate to expose his men to the horrible monsters which science
and invention have created. To-day, after a titanic struggle which cost
millions of human lives, which destroyed billions of dollars’ worth of
property, and which made itself felt to the remotest corners of the
earth, serious efforts are being made to banish war, but at the same
time inventors here and abroad are busy inventing new and more powerful
engines of death, and the prospects are that the next big war, should
there ever be one, will be even more horrible and destructive than the
one we have just passed through.

Fortunately engines of death are not the only inventions produced
by war. Many machines, apparatus, and processes are originated or
developed which have a distinct value in time of peace; hence war is a
great constructive as well as a destructive agency. In this respect the
great World War was no exception and we are already reaping benefits
which in a small way compensate for the havoc that was wrought. It
advanced scientific research to a point it would not have reached in
fifty years of peace. The stimulus was felt in every field of science
from chemistry to acoustics, from geology to meteorology. Wonderful
progress was made in radiotelephony, in submarine navigation, in
aviation, and there were scores of inventions which will add to our
comfort and aid us in the mastery of Nature.

Many of these inventions have already been described; others do
not properly belong in this volume as they have to do chiefly with
electricity or chemistry. In this chapter we shall take up mainly the
machines built for the purpose of destroying men and their works.


Of course the main objects of war are offense and defense, the
destruction of the opponent and the protection of one’s self. This
first fighting was a hand-to-hand struggle which gave way to fighting
at a distance as spears and arrows were invented. Shields and armor
were then invented to ward off these missiles. Cities were surrounded
with walls to hold off the enemy. Then came the Roman war “engines,”
catapults and battering rams, to destroy the walls and towers which
would enable the besiegers to fight on an equal level and in personal
contact with the besieged. Although a battle might start with
long-distance fighting it was always a hand-to-hand encounter that
clinched the victory. Even to-day, although we have our big guns which
fight at ranges of five to twenty miles, it is the rifle or bayonet
which wins or loses the battle.


The introduction of gunpowder from China in the fifteenth century did
not immediately revolutionize warfare. It was used only in cannon or
mortars for hurling large stones at city walls. The range of those
cannon was so limited and the time it took to load and fire them was so
great that they were of little use on an open battlefield. A cannon,
although a comparatively powerful offensive weapon, was helpless
against attack and was only suitable for use in forts or behind
breastworks. Later when its range was increased and it came to be used
on the battlefield it had to be protected from capture by men supplied
with small arms.

This defect of the cannon also applied to the use of the hand gun. Its
range was small and consequently the blunderbuss type was invented to
spread the charge of shot as much as possible so as to tear a wide gap
in the enemy’s line and prevent it from closing in upon the operator
of the gun. But the loading and firing of these early firearms was
extremely slow and the battle-ax and even the arrow and the crossbow
were much more effective weapons. So unreliable were the muskets of our
Revolutionary War that in battle more dependence was placed upon the
bayonet than the firearm.


Three important improvements were necessary to make the small gun a
really effective weapon. First was the invention of a reliable means
of igniting the powder; second the rifling of the barrel so that the
bullet would not tumble but would hold a true course, and finally
the invention of a cartridge and a rifle that could be loaded from
the breech. These improvements were not completely effected until
the time of the Civil War. Since then there have been further marked
improvements: The power of cartridges has been increased; the bullets
have been given a stream-line form so as to increase the range of the
rifle and its power of penetration; the rifle has been equipped with a
magazine for carrying a number of cartridges; and a simple mechanism
has been provided for discharging empty shells and inserting fresh
cartridges in a minimum of time.

Gyroscopic action plays a very important part in the flight of a
bullet or shell. The spiral grooves cut in the bore of the rifle give
the projectile a twist that sets it to spinning rapidly. The spinning
bullet is virtually a gyroscope and maintains its axis in the line
of flight. Hence it is possible to use a long pointed bullet instead
of the round ball of earlier days and to give the projectile a shape
that will enable it to cut through the air with comparatively little
resistance. The same bullet fired from a smooth bore gun would begin to
tumble and would encounter so much air resistance that it would fall
short in the space of a few hundred feet, besides which it would wander
far off its course.


A rifle is really a machine for hurling small projectiles. During the
Civil War a Chicago physician named Gatling fell to pondering over the
inefficiency of using a machine that would fire only one bullet at a
time with a considerable interval of time between shots for reloading,
and he hit upon the idea of developing a machine that would discharge
a continuous stream of bullets. So he built a ten-barrel revolving gun
operated by a hand crank. The barrels were automatically loaded and
fired one after the other. Although it was slow to accept the Gatling
machine gun, the U. S. Army after once accepting it was loath to give
it up even after better machine guns were invented.


In the Gatling gun hand power was required to operate the loading,
firing and shell-ejecting mechanism, but it occurred to another
inventor that a small portion of the energy developed in exploding the
cartridge could very well be utilized to replace the hand power and
thus make the machine gun completely automatic. It was Hiram Maxim who
first carried out this idea to a successful conclusion. When a rifle
is fired the suddenly expanding gases push back against the breech of
the gun with just as much pressure as they do against the bullet and
this shows itself in the recoil or “kick” of the gun. Maxim utilized
the kick of the gun to cock the gun, open the breech, eject the empty
shell, take a fresh cartridge out of a magazine belt, insert it in the
breech chamber, lock the breech and fire the gun. All these operations
occupied but an instant of time and the gun kept on firing as long as
the belt of cartridges held out.

John M. Browning, inventor of the Colt gun, instead of using the
recoil, employed a small portion of the gases to operate the mechanism.
A minute hole in the barrel of the gun, near the muzzle, communicated
with a small cylinder in which was a spring-pressed piston. The gases
pursuing the bullet out of the barrel would find this tiny hole and,
entering it, push back the piston. The pressure against the piston
would be only a small fraction of that exerted against the bullet and
would last for only the briefest part of a second, from the time the
bullet uncovered the hole to the time it emerged from the barrel and
liberated the gases, but this minute portion of the energy of the
powder was sufficient to actuate the mechanism which performed all the
operations necessary to reload and fire the gun.


The advantage of these machine guns over Gatling’s lay not only in
the saving of human labor, but in the fact that a single barrel was
employed in place of ten, thereby greatly reducing the weight of the
gun. But a serious handicap was encountered in the heat developed
by the burning powder. Dr. Gatling, by using ten barrels, could let
nine be cooling while the tenth was discharging, but even he found it
necessary to place a water jacket about half the length of the barrels.
In the Maxim machine gun a large water jacket enveloped the whole
length of the barrel and when the gun was firing continuously at a
moderate rate the 7½ pints of water contained in the water jacket would
come to a boil inside of a minute and a half, and thereafter more than
a pint would be evaporated each minute of firing, or about a pint and
a half per thousand rounds. The necessity of using water-cooling added
considerably to the weight of the gun and made it occupy in the service
an intermediate place between the shoulder rifle and the big gun.

Another method of cooling was to use a barrel with a large outer
diameter and depend upon the radiation of heat from the outer surface
to prevent overheating. This was later improved by putting flanges
on the outer surface of the barrel, so as to increase the radiating
surface, in the same way that the cylinders of a motorcycle are kept
cool. The barrel was made easily detachable and a spare one provided,
so that as soon as the barrel grew excessively hot it could be removed
and replaced with a cool barrel. The fault of overheating is not that
it might explode the cartridge prematurely but that the bore will
be enlarged by heat expansion so that the bullets will not take the
rifling and will come out of the barrel as if from a smooth-bore gun.
In a test of a Hotchkiss machine gun which was fired continuously
the expansion was sufficient at the end of four minutes to make the
course of the bullets very uncertain and in seven minutes the bullets,
emerging without any spin, tumbled over and over and failed to carry
more than three hundred yards.


The next marked step in the development of the machine gun was to
make it fan itself and thus keep its barrel cool. Col. I. N. Lewis
designed a gun operated by gas pressure somewhat on the principle of
the Colt gun and around the barrel he fitted sixteen deep flanges or
fins of aluminum that ran lengthwise of the gun. Around these fins
he fitted a casing, thus forming 16 long narrow chambers about the
barrel. The casing was open at the breech end, but at the outer end was
contracted into a narrow mouthpiece that extended beyond the muzzle.
The mouthpiece was so formed that as the bullets passed through it
they sucked air through the chambers, thereby cooling the gun. The air
travels through the casing at the rate of about seventy miles per hour.

This design permitted Col. Lewis to build a very light gun. Its total
weight was but 25½ pounds and it could be handled by a single man
if the muzzle was supported on some sort of a rest. It represented
a marked step toward a shoulder machine gun which would increase
enormously the efficiency of infantry equipped with this weapon. The
difference between rifle fire and machine-gun fire has been likened to
the difference between trying to hit a tin can with a stone and with a
stream of water from a hose. In the latter case the hose may be raised
or lowered to correct the course of the stream and bring it to bear on
the target. In the same way by watching the effect of the machine-gun
bullets the leaden stream may be corrected to bring it directly upon
the target. The advantages of a weapon such as this, which may be fired
from the shoulder or from the hip, are perfectly obvious.

As the war was nearing its end John M. Browning produced two machine
guns, one a water-cooled heavy model fired from a stand. The total
weight of this gun was 34½ pounds and with the water jacket empty it
weighed but 22½ pounds. It was operated by the recoil of the gun, but
the mechanism was greatly simplified and there were but few parts.
These could be taken apart and replaced with new ones in a minimum of
time in case of breakage. The other gun was a shoulder rifle weighing
only 16 pounds, which carried a clip of twenty cartridges. These could
be fired singly or in rapid succession in the space of two and a half
seconds. Only a second was required to replace the empty clip with a
filled one. No special cooling apparatus was provided because it was
not likely that a shoulder rifle would be fired long enough at a time
to become excessively heated.


The latest development in machine guns is a pocket edition weapon--a
firearm weighing only 7 pounds and measuring but 22 inches over all.
This little gun which is too small to be classed as a rifle and yet
rather large for a pistol, has two grips so that it may be fired from
the waist line, and it may be fitted with a gun butt so that it may be
fired from the shoulder. It operates at the astounding rate of 1,500
shots per minute or three times the speed of the average machine gun.
The cartridges are fed either from a box magazine containing 20 rounds
or from a drum-shaped magazine loaded with 50 to 100 cartridges. The
operating mechanism of this gun is entirely different from anything
produced heretofore and depends upon a discovery made by Commander
Blish of the United States Navy. He found that a wedge of a certain
angle will hold a breechblock closed against the pressure of an
exploding cartridge while the pressure is high, but will slide when
the pressure falls. Apparently at first the adhesion due to friction
is too great to permit the wedge to move, but the adhesion falls off
more rapidly than the pressure does and a point is reached at which
the wedge yields to the pressure. In the “submachine” gun, as the new
weapon is called, the barrel (or rather an extension of the barrel)
and the receiver, in which the operating mechanism is contained, are
locked together by a wedge. The wedge slides in slots set at an angle
of 80 degrees with the axis of the barrel. When a cartridge is fired
the wedge remains fast while the bullet is traveling through the bore,
but when it emerges and the pressure of the gases falls off the wedge
slides, unlocking the breech mechanism. The gun is remarkable for its
simplicity and the fewness of its parts. It has been adopted by the
Police Department of New York City.


As has been stated above, gunpowder was first introduced in warfare
not for the purpose of destroying men, but for smashing city walls and
fortifications, so that infantry could pour through the breeches made
by the heavy stone or iron projectiles. As artillery grew more powerful
and the aim more accurate walls of masonry gave way to earthworks
and to masses of concrete and armored steel. However the World War
demonstrated the impossibility of building any fortifications above
ground that would stand up against modern high-powered guns.


In military parlance a “gun” is a long-barreled piece that fires
its projectiles with a flat trajectory, that is, the projectile is
fired at a low angle and describes a long flat curve. A “mortar” is
a short-ranged weapon which fires at a high angle so as to land its
projectile over the walls of a fortification. The barrel of the mortar
was formerly very short and had a smooth bore, but later the barrel was
extended and the bore rifled so as to give a greater range, developing
what is known as the “howitzer.” The famous 42-centimeter gun with
which the Germans started the war was a howitzer which fired a shell a
yard and a half long weighing 2,108 pounds. We have big guns to defend
our coasts which fire a shell 16 inches in diameter, which is half an
inch less than 42 centimeters, and the weight of the shell is 2,400
pounds. But the startling thing about the German big howitzers was that
they were portable and could be brought up to smash fixed defenses.
As the war proceeded enormous guns as well as howitzers were set on
railroad mounts and moved about from time to time to avoid discovery by
spying aviators.


The 76-mile gun which bombarded Paris fired projectiles of only
8.27-inch caliber. The projectile described a wide curve which carried
it about twenty-four miles above the surface of the earth or about
3½ times as high as the greatest altitude ever reached by man in an
aeroplane. Had it pursued a perfectly straight line from the forest
of St. Gobain to Paris its course would have carried it 3,750 feet
below the surface, because of the curvature of the earth. The range
of the projectile was very materially increased by rising to such a
great elevation because of the extreme tenuity of the atmosphere.
The air resistance that a shell is obliged to overcome is not
generally appreciated. In the denser strata of the lower atmosphere
the resistance is very great, but as a shell mounts to higher levels
the air resistance falls off considerably and at twenty miles it is
practically nonexistent.

It was not until the summer after the armistice that details of this
gun were disclosed. There were seven of these powerful guns that
participated in the various bombardments. They wore out very quickly
under the terrific strain to which they were subjected and were rebored
to a diameter of 9.4 inches. In the last bombardment a number of
shells of this size reached Paris. The guns were fired at an angle
of 55 degrees from the horizontal so as to pass quickly through the
denser layers of the air. The shell left the muzzle of the gun with
the velocity of about 5,000 feet per second and arrived in Paris about
three minutes later with a velocity of about half that amount. The
enormous muzzle velocity was obtained by using a very long gun so that
the powder could keep pushing the projectile for a comparatively long
time. The guns were built out of worn-out 15-inch naval guns. These
guns which were 56 feet long were rebored, fitted with a heavy tube and
pieced out to a length of 118 feet. The last 20 feet of the bore was
not rifled and served as a guide to keep the shell in perfect axial
alignment when it emerged from the muzzle. A comparatively slow powder
was used so as not to put too severe a strain on the gun at the breech,
but gradually to accelerate the shell in its travel through the bore.

Spectacular as was the performance of these huge guns, they were of
little military value. The slightest variation in the powder would
cause a wide variation of range and they could not hope to hit a target
smaller than a large city. All seven guns fired a total of 303 shells
in 44 days of bombardment, only 183 of which fell within the city. They
killed 256 persons and wounded 620. Far more damage at far less expense
could have been effected by dropping bombs from aircraft.


Just as a problem in ordnance, American officers designed a gun 225
feet long which would fire a 400-pound shell of 10-inch caliber. It
was estimated that with a charge of 1,440 pounds of powder the shell
would leave the muzzle with a velocity of 8,500 feet per second and,
if fired at an angle of 55 degrees, would have a range of 121 miles.
The shell would rise to a height of 46 miles above the earth and would
make the 121 miles in about 4 minutes. The gun was never built, because
its military value would in no way be commensurate with its cost of
construction and operation. The purpose of the German long-range
bombardment was to produce a moral rather than a military effect. The
Germans hoped to intimidate the French people by this spectacular
performance, and in this they failed completely.


In modern warfare large guns are used either to rain a storm of death
upon infantry or to destroy their defensive works. In earlier days the
effectiveness of gunfire against a charging enemy was increased by the
use of grapeshot. A cannon was thus converted into a gigantic shotgun.
But although a wide dispersion of projectiles was obtained the range
was very limited. This handicap was then overcome by having the gun
fire another gun which would discharge when it had reached the enemy’s
lines. In other words, the grapeshot or leaden balls were packed into
a shell which was fired like a solid projectile, and this exploded
when it struck the target, scattering death broadcast. An improvement
on this was the timed shell, which would explode while still in the
air and scatter its rain of lead over a wide area. The time fuse of
a shrapnel shell must be very delicately adjusted to explode at the
desired instant. A train of powder is used which may be short-circuited
to give the exact length required for any given distance. The powder
is ignited by a cap which is exploded by concussion when the gun is
fired. The fuse then burns until it reaches the main charge of the
shell. This explodes, bursting the shell open and scattering shell
fragments as well as the scores of lead balls with which the shell is
packed. Should the fuse fail, a detonating pin is provided which will
explode the shell when it reaches the ground. Where the object is to
destroy defensive works the shell is charged with a high explosive
which is detonated not by a time fuse, but by concussion when the shell
strikes its target.

The war brought forth many new types of projectiles: shells loaded with
lethal gases; shells which left a trail of smoke whereby their course
could be followed when fired at aircraft; shells that illuminated the
battlefield at night, etc. The searchlight shells carried a number of
“candles,” each furnished with a little parachute so that when the
shell exploded the burning candles would settle slowly to the ground,
all the while casting a brilliant light on operations below.


Obviously, hurling projectiles from the air is a much simpler matter
than projecting them from the ground. No propellant is required to
carry them to the target and no rifling is necessary to keep them
head-on in the direction of flight. They are pulled instead of being
pushed and can easily be kept in their course by means of rudder
planes. But hitting a target from an aeroplane is like hitting a
swiftly moving object from the ground. The target is seemingly flying
past the aeroplane and in calculating where the aerial bomb will strike
the speed of the plane through the air and its height above the ground
must all be taken into consideration.

Naval warfare is a fight of fort against fort and consequently the high
explosive projectile is the principal one used. The shells must be
able to penetrate heavy steel armor and explode within the hull of the
vessel. In addition to these we have the torpedoes fired by destroyers
and submarines which explode an enormous quantity of high explosive
against the hull of the vessel. No attempt is made to penetrate the
skin of the vessel, but the explosive, tamped by a considerable depth
of water, delivers a very heavy crushing blow against the side of the


It is wrong to speak of firing a torpedo. A torpedo is really an
automatic, self-propelled, submarine boat. All that the destroyer or
submarine does is to set the steering gear in this little boat and then
launch it at the enemy with a blast of air that ejects it from the
torpedo tube. Most of the body of the torpedo is filled with compressed
air which drives a small air motor coupled to a pair of propellers.
These propellers run in opposite directions so as to balance each other
and they drive the torpedo through the water at a speed of about forty
miles per hour. The speed falls off gradually as the air supply is

To hold the torpedo on its course horizontal and vertical rudders are
employed. The vertical rudder is controlled by a gyroscope which turns
it this way or that according as the torpedo tends to veer off its

The value of a torpedo lies in its concealment. Were it to travel on
the surface the vessel against which it was directed might be able to
avoid it; furthermore the action of the waves would tend to disturb
the gyroscopic steering mechanism and the torpedo would pursue an
erratic course. For this reason it must travel under water at a depth
sufficient to avoid surface disturbances. There is also a distinct
advantage in having a good cover of water over the torpedo when it
strikes its target because the force of the explosion, although felt
in all directions, is mainly expended along the line of the least
resistance. If the depth of water over the torpedo is slight, most of
the force will be expended upward and only a comparatively small part
will act against the hull of the vessel. It was the practice of the
Germans to set their torpedoes for a depth of about ten feet.

To hold a torpedo at a fixed depth a very delicate hydrostatic valve
is employed which operates the diving rudders. The valve is set for a
certain depth or weight of water. If the torpedo goes below this depth,
the weight of the water bearing on this valve presses it down and
thereby tilts the diving rudders until the torpedo comes back to the
required depth. If it rises above the depth for which it is set, the
valve feels the reduction of water pressure and tilts the rudders in
the opposite direction to correct the deviation from the predetermined
line of travel. Once the valve has been set the torpedo takes care of
itself automatically. It may be discharged from any depth or be dropped
from torpedo tubes on the deck of a ship and after a few undulations it
will find its depth and hold it as long as it keeps running.

Torpedoes have actually been discharged from aeroplanes and it is
possible that in the next great war swiftly flying aeroplanes may
actually bring death and destruction to powerful dreadnoughts. In fact
winged destroyers and battle cruisers of the air may render obsolete
all our modern fighting machines.

As we have already observed, it was war that first aroused the
inventive instincts in man. Fortunately this instinct was not confined
to destructive devices and engines, and the mechanical conquest of the
earth, although it continues to derive much benefit from the stimulus
of war, may well afford to break off relations with so grim and
horrible a partner and proceed to develop under the stimulus of its own



THE REAL beginning of the present age of machinery dates from Watt’s
invention of the double-acting steam engine which was patented in 1782.
Prior to that date the steam engine was used merely for pumping water,
but now in its new form it was adapted for use in driving industrial
machinery. But, as we have shown in another chapter, it was not until
John Wilkinson invented his boring machine in 1774 that it was possible
to bore the cylinders that Watt used in his engine.

In the field of machine tools there were several notable inventions.
Henry Maudslay invented the slide rest for lathes and later in 1797
the screwcutting lathe. Joseph Bramah invented the hydraulic press and
Maudslay furnished the cup leather packing that made it a success.
Woodworking machinery, and particularly mortising machines for making
pulley blocks, were invented by Samuel Bentham and patented in 1791 and

In the textile industry we find the spinning jenny invented by
Hargreaves in 1770, Richard Arkwright’s roll-drawing spinning machine
invented in 1769 and 1775, and Crompton’s mule spinner invented between
1774 and 1779, but never patented. In addition to this there was the
invention of the cotton gin in 1794 by our own Eli Whitney and Dr.
Cartwright’s series of patents on the power-driven loom granted
between 1785 and 1788. In 1799 Louis Roberts invented a machine that
would make a continuous web of paper. The machine was developed in
England by the Fourdrinier Brothers and has ever since borne their name.


Just before the Nineteenth Century dawned the patents on Watt’s steam
engine expired and the invention became public property.

Trevithic applied steam power to the propulsion of a coach in 1801.
This was the forerunner of the automobile and it led to the invention
of the first steam railway and locomotive three years later. Steam was
also applied to the propulsion of boats in this decade and reached
the practical stage when Fulton built the Clermont in 1807. The first
application of steam to the driving of a loom is accredited to William
Horrocks in 1803. Jacquard’s loom attachment for producing various
patterns was invented in 1801. The first knitting machine in which the
latch needle was used was patented in France in 1806 by Jeandeau.

Among the machine-tool developments the most important were Bramah’s
invention of the planer in 1802 and Brunel’s mortising machine in 1801.
A process of making malleable iron castings was invented by Lucas in
1804. The percussion lock for guns was invented by Forsyth in 1807.


The second decade saw a much wider application of steam and
considerable development in locomotives. Hedley’s “Puffing Billy” was
built in 1813, and Stephenson’s first locomotive in 1814.

In the same year Fulton built the first steam war vessel and five years
later the Atlantic was crossed for the first time by a steamer, the
Savannah. The rotary steam printing press belongs to this decade.

The circular knitting machine was invented by Brunel in 1816. About
1818 Eli Whitney invented the milling machine, and in 1819 Blanchard
invented his “gun-stocking” lathe with which irregular forms could be
turned out. The breech-loading musket was patented in this country by
Thornton and Hall in 1811.


In this decade we find the conversion of electricity into mechanical
motion and many other important electrical developments, which,
however, are omitted from this list as we are confining ourselves
to mechanical inventions. There were marked developments in steam
railroads. Stephenson built the “Rocket” which won prizes on the
Liverpool and Manchester Railway, and the first locomotive was imported
into this country in 1829. The tubular locomotive boiler was invented
by Seguin in 1828 and Ericsson’s portable steam fire engine was built
in 1830. In the previous year an important improvement in spinning
mules was made when John Thorpe invented the ring frame.


Important railroad developments mark the opening of this decade. The
famous locomotive “John Bull” was imported from England in 1831 to
operate on the Camden and Amboy Railroad. The following year saw the
first American-built locomotive, “Old Ironsides,” which was built
at Philadelphia by the Baldwin Locomotive Works. Stephenson’s link
motion, also claimed by W. T. James, was invented in 1832.

However, the most important development of the decade was the invention
of the reaper. Hussey’s patent was obtained in 1833 and McCormick’s the
following year.

Colt’s revolver (1836); Perkin’s portable ice machine (1834); Anthony’s
(1831), Tolle’s (1834), and Burden’s (1835) developments in machines
for making horseshoes; and Isaac Babbit’s antifriction-bearing metal
are other notable developments.


It was in 1841 that F. E. Sickels invented the drop cut-off valve gear,
and the Corliss valve gear was patented in 1849 and 1851. Nasmyth’s
steam hammer was invented in 1842.

Hoe’s revolving printing press was invented in 1845. The next year
Sloan patented the gimlet-pointed screw. In 1847 Savage invented the
time lock, and in 1849 Hibbert patented the latch needle for knitting
machines. American machine-made watches appeared in 1850. However, the
most important invention of the decade was Howe’s sewing machine in


The year 1851 saw an important improvement in the harvester when
Seymour invented his self-raker, also an advance in firearms when
Maynard invented the breech-loading rifle. Three years later Smith &
Wesson came forth with their magazine rifle which was the forerunner of
the “Winchester.” In that year Wilson invented the four-motion feed for
sewing machines.

One of the most notable inventions of the decade was Bessemer’s
converter for producing steel (1855), and the following year Siemens
produced the regenerative furnace.

Gifford’s injector (1858) marked a most important advance in steam
engineering. The hand-turned turret for lathes was invented by Stephen
Fitch about 1853, and the automatically revolving turret was brought
out in 1855.

Other inventions of the decade were Herman’s diamond drill (1854),
Ericsson’s air engine (1855), the pedal-operated bicycle by Ernest
Michaux (1855), use of wood pulp in the manufacture of paper by Voelter
(1858), and the ammonia absorption ice machine invented by Carré.


The Civil War directed attention of inventors to military and naval
improvements. Dr. Gatling invented his machine gun in 1862, the same
year that Ericsson built the “Monitor.” It is interesting to note that
the revolving turret was patented in that year by Theodore R. Timby.
Dynamite was invented in 1867, and the Whitehead torpedo in the same
year. Barbed wire was invented in 1861. The same year saw the first
passenger elevator invented by Otis; the shoe-sewing machine invented
by McKay, and Col. Green’s invention of the drive well, which was
brought about by the necessity of supplying his troops with water.

The pneumatic rock drill was invented by Burleigh in 1866, and
Westinghouse invented the air brake in 1869. The latter, with Sholes’s
invention of the typewriter in the previous year, were undoubtedly the
most notable inventions of the decade.

In 1865 the cylindrical grinder marked a decided forward step in
machine tools.


This decade was marked by great activity, particularly in the field of
electricity. While we are confining ourselves to mechanical inventions
we cannot but mention Bell’s telephone (1876), Edison’s carbon filament
lamp (1878), and Berliner’s transmitter and Edison’s carbon microphone
which belong to the decade, although their patents were not issued
until 1891 and 1892 respectively.

The web printing press was invented by Hoe in 1871. Ingersoll’s
compressed air rock drill appeared in the same year. A marked
improvement in the Westinghouse air brake was patented in 1872, and the
automatic car coupler appeared in 1873. The positive motion loom was
invented by Lyall in 1872.

The harvester was improved by Gorham’s twine binder in 1874, and in the
same year a machine for making barbed wire was produced.

The Centennial year saw an important development in milling processes
when the roller mill was introduced to take the place of the
time-honored millstones. The middlings purifier was invented by George
T. Smith in 1875. The hydraulic dredge was invented in 1876, also the
universal grinder, and a machine for making cigarettes.

Edison’s invention of the phonograph and Otto’s invention of the gas
engine give prominence to the year 1877 and the Remington typewriter to
the year 1878.


The inventions of most far-reaching importance in this decade were
Mergenthaler’s linotype machine, which was invented in 1884 and
further developed into a practical machine in 1890; Gottlieb Daimler’s
invention of the automobile in 1883, and J. B. Dunlop’s invention of
the pneumatic tire in 1890.

Berliner in 1887 invented the flat-disk talking machine known as the
“Gramophone.” The snapshot “Kodak” camera appeared in 1888. In this
year De Laval invented his steam turbine, while Harvey invented his
process for annealing armor plate.

The following year nickel steel was invented. In 1883 Sir Hiram Maxim
invented the machine gun. Hugo Bilgram’s generating system of gear
cutting was invented in 1881.

A less prominent, though very important, invention of the same year was
the buttonhole machine patented by Reece.

Incidentally this decade saw the completion of the Brooklyn Suspension
Bridge in 1883, and the Great Forth Bridge in 1890.


The last decade of the Nineteenth Century gave us Parson’s steam
turbine (1891) and Curtis’s steam turbine (1896); also Rudolf Diesel’s
heavy-oil engine.

Langley’s model for a motor-driven airplane was built in 1896 and
actually flew. Santos-Dumont made his first ascension in a dirigible in
1898, and Count Friedrich von Zeppelin built his first rigid dirigible
in 1900.

J. B. Holland built a steam-driven submarine, and Simon Lake
constructed the first submarine to be driven by an internal combustion

This decade was largely devoted to the development of the automobile,
which gradually evolved into a truly commercial machine. About 1900,
Benjamin Holt invented the “caterpillar” tractor. The decade also
saw the invention of the Lanston “monotype,” and Henry Wise Wood’s
“autoplate” machine which revolutionized stereotyping.

In 1899 William Draper brought out a loom with an automatic
shuttle-changing mechanism. Hulett invented the automatic ore unloader
in 1898. Improvements were also made in automatic machine tools. J. E.
Gleason improved the Bilgram gear cutter in 1898, and at the close of
the century Taylor and White brought out their high-speed cutting tools
which revolutionized machine tools.

The decade was also remarkable for the invention of X-rays, wireless
telegraphy, and certain chemical processes, none of which really belong
in this summary.


In this decade the automobile reached a marvelous state of perfection
and a tremendous industry was built up which had a marked influence
on the development of machine tools and the production of iron
and steel. James A. Gailey invented a dryblast process for steel
production, getting rid of the moisture in air by subjecting it to
a freezing process. Fellow’s gear-cutting machine was perfected and
Bullard brought out the vertical turret lathe. There were important
developments of the steam turbine.

There is one invention that makes this decade stand out from among all
others. On December 17, 1903, the Wright brothers made a successful
flight in a biplane driven by a gasoline engine, and opened up a new
world for conquest. Man took to wings and the dream of ages was
realized. During the decade rapid progress was made in developing the
flying machine. The invention of the monoplane soon followed.

It was in this decade that the gyroscope emerged from the laboratory
and toy shop and began to be applied to practical uses. Schlick
utilized the gyroscope to prevent ships from rolling. The gyrocompass
was invented and reached a commercial stage in 1910.


It is difficult to pick out the most important inventions of this
decade because sufficient time has not elapsed to determine which are
most deserving of mention. The Great World War stimulated invention in
all civilized lands. Aeronautics developed faster in the five years of
war than it could in twenty-five years of peace. Of course, engines of
war developed to a remarkable degree. Among the lighter pieces we saw
the development of the Lewis gun, and then the Browning gun. The most
important invention was the tank. Many advances should be classed as
remarkable developments rather than basically new inventions. The war
of and against the submarine brought forth many ingenious devices.

Of the peace-time inventions, the most remarkable is the optophone, the
instrument which enables the blind to read ordinary printed matter.

       *       *       *       *       *

And thus the march of progress continues unchecked. We are tempted to
give our imaginations free play and forecast the developments that the
future holds in store for us, but unfortunately we cannot claim any
prophetic instinct or inspiration.


--Obvious print and punctuation errors were corrected.

*** End of this Doctrine Publishing Corporation Digital Book "Mechanics - The Science of Machinery" ***

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