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Title: Electricity for Boys
Author: Zerbe, J. S.
Language: English
As this book started as an ASCII text book there are no pictures available.

*** Start of this LibraryBlog Digital Book "Electricity for Boys" ***



[Illustration: Fig. 1. WORK BENCH]



A working guide, in the successive
steps of electricity, described in
simple terms


By J. S. ZERBE, M.E.


[Illustration: Printer's Mark]




INTRODUCTORY                                                      Page 1

EVENTS                                                            Page 5

 The Study of Electricity. First Historical Accounts. Bottling
 Electricity. Discovery of Galvanic Electricity. Electro-motive Force.
 Measuring Instruments. Rapidity of Modern Progress. How to Acquire the
 Vast Knowledge. The Means Employed.

II. WHAT TOOLS AND APPARATUS ARE NEEDED                          Page 11

 Preparing the Workshop. Uses of Our Workshop. What to Build. What to
 Learn. Uses of the Electrical Devices. Tools. Magnet-winding Reel.

III. MAGNETS, COILS, ARMATURES, ETC.                             Page 18

 The Two Kinds of Magnets. Permanent Magnets. Electro-Magnets.
 Magnetism. Materials for Magnets. Non-magnetic Material. Action of a
 _Second_ Magnet. What North and South Pole Mean. Repulsion and
 Attraction. Positives and Negatives. Magnetic Lines of Force. The
 Earth as a Magnet. Why the Compass Points North and South. Peculiarity
 of a Magnet. Action of the Electro-Magnet. Exterior Magnetic Influence
 Around a Wires Carrying a Current. Parallel Wires.

ELECTRICITY                                                      Page 29

 Three Electrical Sources. Frictional Electricity. Leyden Jar. Voltaic
 or Galvanic Electricity. Voltaic Pile; How Made. Plus and Minus
 Signs. The Common Primary Cell. Battery Resistance. Electrolyte and
 Current. Electro-magnetic Electricity. Magnetic Radiation. Different
 Kinds of Dynamos. Direct Current Dynamos. Simple Magnet Construction.
 How to Wind. The Dynamo Fields. The Armature. Armature Windings.
 Mounting the Armature. The Commutator. Commutator Brushes. Dynamo
 Windings. The Field. Series-wound Field. Shunt-wound. Compound-wound.

V. HOW TO DETECT AND MEASURE ELECTRICITY                         Page 49

 Measuring Instruments. The Detector. Direction of Current. Simple
 Current Detector. How to Place the Detector. Different Ways to Measure
 a Current. The Sulphuric Acid Voltameter. The Copper Voltameter. The
 Galvanoscope Electro-magnetic Method. The Calorimeter. The Light
 Method. The Preferred Method. How to Make a Sulphuric Acid Voltameter.
 How to Make a Copper Voltameter. Objections to the Calorimeter.

VI. VOLTS, AMPERES, OHMS AND WATTS                               Page 60

Understanding Terms. Intensity and Quantity. Voltage.
Amperage Meaning of Watts and Kilowatt. A
Standard of Measurement. The Ampere Standard. The
Voltage Standard. The Ohm. Calculating the Voltage.

LIKE APPARATUS                                                   Page 65

 Simple Switches. A Two-Pole Switch. Double-Pole Switch. Sliding
 Switch. Reversing Switch. Push Buttons. Electric Bells. How Made. How
 Operated. Annunciators. Burglar Alarm. Wire Circuiting. Circuiting
 System with Two Bells and Push Buttons. The Push Buttons, Annunciators
 and Bells. Wiring Up a House.


 Storing Up Electricity. The Accumulator. Accumulator Plates. The Grid.
 The Negative Pole. Connecting Up the Plates. Charging the Cells. The
 Initial Charge. The Charging Current.

IX. THE TELEGRAPH                                                Page 90

 Mechanism in Telegraph Circuit. The Sending Key. The Sounder.
 Connecting Up the Key and Sounder. Two Stations in Circuit. The Double
 Click. Illustrating the Dot and the Dash. The Morse Telegraph Code.
 Example in Use.

X. HIGH-TENSION APPARATUS, CONDENSERS, ETC.                      Page 98

 Induction. Low and High Tension. Elastic Property of Electricity. The
 Condenser. Connecting up a Condenser. The Interrupter. Uses of
 High-tension Coils.

XI. WIRELESS TELEGRAPHY                                         Page 104

 Telegraphing Without Wires. Surging Character of High-tension
 Currents. The Coherer. How Made. The Decoherer. The Sending Apparatus.
 The Receiving Apparatus. How the Circuits are Formed.

XII. THE TELEPHONE                                              Page 110

 Vibrations. The Acoustic Telephone. Sound Waves. Hearing Electricity.
 The Diaphragm in a Magnetic Field. A Simple Telephone Circuit. How to
 Make a Telephone. Telephone Connections. Complete Installation. The
 Microphone. Light Contact Points. How to Make a Microphone.
 Microphone, the Father of the Transmitter. Automatic Cut-outs for
 Telephones. Complete Circuiting with Transmitters.


 Decomposing Liquids. Making Hydrogen and Oxygen. Purifying Water.
 Rust. Oxygen as a Purifier. Composition of Water. Common Air Not a
 Good Purifier. Pure Oxygen a Water Purifier. The Use of Hydrogen in
 Purification. Aluminum Electrodes. Electric Hand Purifier.
 Purification and Separation of Metals. Electroplating. Plating Iron
 with Copper. Direction of Current.

XIV. ELECTRIC HEATING. THERMO-ELECTRICITY                       Page 135

 Generating Heat in a Wire. Resistance of Substances. Signs of
 Connectors. Comparison of Metals. A Simple Electric Heater. How to
 Arrange for Quantity of Current Used. An Electric Iron.
 Thermo-Electricity Converting Heat Directly into Electricity Metals.
 Electric, Positive, Negative. Thermo-electric Coupler.


 Direct Current. Alternating Current. The Magnetic Field. Action of a
 Magnetized Wire. The Movement of a Current in a Charged Wire. Current
 Reversing Itself. Self-Induction. Brushes in a Direct Current Dynamo:
 Alternating, Positive and Negative Poles. How an Alternating Current
 Dynamo is Made. The Windings. The Armature Wires. Choking Coils. The
 Transformer. How the Voltage is Determined. Voltage and Amperage in

XVI. ELECTRIC LIGHTING                                          Page 161

 Early conditions. Fuels. Reversibility of Dynamo. Electric arc.
 Mechanism to maintain the arc. Resistance coil. Parallel carbons for
 making arc. Series current. Incandescent system. Multiple circuit.
 Subdivision of electric light. The filament. The glass bulb. Metallic
 filaments. Vapor lamps. Directions for improvements. Heat in electric
 lighting. Curious superstitions concerning electricity. Magnetism.
 Amber. Discovery of the properties of a magnet. Electricity in
 mountain regions. Early beliefs as to magnetism and electricity. The
 lightning rod. Protests against using it. Pliny's explanation of


 Early beliefs concerning the dynamo. Experiments with magnets.
 Physical action of dynamo and motor. Electrical influence in windings.
 Comparing motor and dynamo. How the current acts in a dynamo. Its
 force in a motor. Loss in power transmission. The four ways in which
 power is dissipated. Disadvantages of electric power. Its advantages.
 Transmission of energy. High voltages. The transformer. Step-down
 transformers. Electric furnaces. Welding by electricity. Merging the
 particles of the joined ends.

XVIII. X-RAY, RADIUM AND THE LIKE                               Page 184

 The camera and the eye. Actinic rays. Hertzian waves. High-tension
 apparatus. Vacuum tubes. Character of the ultra-violet rays. How
 distinguished. The infra-red rays. Their uses. X-rays not capable of
 reflection. Not subject to refraction. Transmission through opaque
 substances. Reducing rates of vibration. Radium. Radio-activity.
 Radio-active materials. Pitchblende. A new form of energy. Electrical
 source. Healing power. Problems for scientists.



 1. Work bench                                           Frontispiece

 2. Top of magnet-winding reel                                     14
 3. Side of magnet-winding reel                                    14
 4. Journal block                                                  15
 5. Plain magnet bar                                               19
 6. Severed magnet                                                 20
 7. Reversed magnets                                               21
 8. Horseshoe magnet                                               22
 9. Earth's magnetic lines                                         23
 10. Two permanent magnets                                         24
 11. Magnets in earth's magnetic field                             24
 12. Armatures for magnets                                         25
 13. Magnetized field                                              26
 14. Magnetized bar                                                26
 15. Direction of current                                          27
 16. Direction of induction current                                28
 17. Frictional-electricity machine                                30
 18. Leyden jar                                                    32
 19. Galvanic electricity. Crown of cups                           33
 20. Voltaic electricity                                           34
 21. Primary battery                                               36
 22. Dynamo field and pole piece                                   39
 23. Base and fields assembled                                     41
 24. Details of the armature, core                                 42
 25. Details of the armature, body                                 42
 26. Armature Journals                                             43
 27. Commutator                                                    43
 28. End view of armature, mounted                                 44
 29. Top view of armature on base                                  45
 30. Field winding                                                 47
 31. Series-wound                                                  47
 32. Shunt-wound                                                   48
 33. Compound-wound                                                48
 34. Compass magnet, swing to the right                            50
 35. Magnetic compass                                              50
 36. Magnet, swing to the left                                     50
 37. Indicating direction of current                               51
 38. The bridge of the detector                                    52
 39. Details of detector                                           53
 40. Cross-section of detector                                     54
 41. Acid voltameter                                               56
 42. Copper voltameter                                             56
 43. Two-pole switch                                               66
 44. Double-pole switch                                            66
 45. Sliding switch                                                67
 46. Rheostat form of switch                                       68
 47. Reversing switch                                              69
 48. Push button                                                   70
 49. Electric bell                                                 71
 50. Armature of electric bell                                     72
 51. Vertical section of annunciator                               72
 52. Front view of annunciator                                     72
 53. Horizontal section of annunciator                             72
 54. Front plate of annunciator                                    72
 55. Alarm switch on window                                        76
 56. Burglar alarm on window                                       76
 57. Burglar alarm contact                                         77
 58. Neutral position of contact                                   78
 59. Circuiting for electric bell                                  79
 60. Annunciators in circuit                                       80
 61. Wiring system for a house                                     80
 62. Accumulator grids                                             83
 63. Assemblage of accumulator grids                               85
 64. Connecting up storage battery in series                       87
 65. Parallel series                                               88
 66. Charging circuit                                              88
 67. Telegraph sending key                                         91
 68. Telegraph sounder                                             92
 69. A telegraph circuit                                           94
 70. Induction coil and circuit                                    99
 71. Illustrating elasticity                                      100
 72. Condenser                                                    101
 73. High-tension circuit                                         102
 74. Current interrupter                                          103
 75. Wireless-telegraphy coherer                                  105
 76. Wireless sending-apparatus                                   107
 77. Wireless receiving-apparatus                                 108
 78. Acoustic telephone                                           111
 79. Illustrating vibrations                                      111
 80. The magnetic field                                           112
 81. Section of telephone receiver                                114
 82. The magnet and receiver head                                 115
 83. Simple telephone connection                                  116
 84. Telephone stations in circuit                                117
 85. Illustrating light contact points                            118
 86. The microphone                                               119
 87. The transmitter                                              119
 88. Complete telephone circuit                                   121
 89. Device for making hydrogen and oxygen                        124
 90. Electric-water purifier                                      127
 91. Portable electric purifier                                   129
 92. Section of positive plate                                    130
 93. Section of negative plate                                    130
 94. Positive and negative in position                            130
 95. Form of the insulator                                        130
 96. Simple electric heater                                       137
 97. Side view of resistance device                               139
 98. Top view of resistance device                                139
 99. Plan view of electric iron                                   140
100. Section of electric iron                                     141
101. Thermo-electric couple                                       143
102. Cutting a magnetic field                                     146
103. Alternations, first position                                 148
104. Alternations, second position                                148
105. Alternations, third position                                 148
106. Alternations, fourth position                                148
107. Increasing alternations, first view                          149
108. Increasing alternations, second view                         149
109. Connection of alternating dynamo armature                    150
110. Direct current dynamo                                        151
111. Circuit wires in direct current dynamo                       152
112. Alternating polarity lines                                   154
113. Alternating current dynamo                                   155
114. Choking coil                                                 157
115. A transformer                                                158
116. Parallel carbons                                             164
117. Arc-lighting circuit                                         165
118. Interrupted conductor                                        166
119. Incandescent circuit                                         167
120. Magnetic action in dynamo, 1st                               177
121. Magnetic action in dynamo, 2d                                177
122. Magnetic action in dynamo, 3d                                178
123. Magnetic action in dynamo, 4th                               178
124. Magnetic action in motor, 1st                                179
125. Magnetic action in motor, 2d                                 179
126. Magnetic action in motor, 3d                                 180
127. Magnetic action in motor, 4th                                180


Electricity, like every science, presents two phases to the student, one
belonging to a theoretical knowledge, and the other which pertains to
the practical application of that knowledge. The boy is directly
interested in the practical use which he can make of this wonderful
phenomenon in nature.

It is, in reality, the most successful avenue by which he may obtain the
theory, for he learns the abstract more readily from concrete examples.

It is an art in which shop practice is a greater educator than can be
possible with books. Boys are not, generally, inclined to speculate or
theorize on phenomena apart from the work itself; but once put them into
contact with the mechanism itself, let them become a living part of it,
and they will commence to reason and think for themselves.

It would be a dry, dull and uninteresting thing to tell a boy that
electricity can be generated by riveting together two pieces of
dissimilar metals, and applying heat to the juncture. But put into his
hands the metals, and set him to perform the actual work of riveting the
metals together, then wiring up the ends of the metals, heating them,
and, with a galvanometer, watching for results, it will at once make him
see something in the experiment which never occurred when the abstract
theory was propounded.

He will inquire first what metals should be used to get the best
results, and finally, he will speculate as to the reasons for the
phenomena. When he learns that all metals are positive-negative or
negative-positive to each other, he has grasped a new idea in the realm
of knowledge, which he unconsciously traces back still further, only to
learn that he has entered a field which relates to the constitution of
matter itself. As he follows the subject through its various channels he
will learn that there is a common source of all things; a manifestation
common to all matter, and that all substances in nature are linked
together in a most wonderful way.

An impulse must be given to a boy's training. The time is past for the
rule-and-rote method. The rule can be learned better by a manual
application than by committing a sentence to memory.

In the preparation of this book, therefore, I have made practice and
work the predominating factors. It has been my aim to suggest the best
form in which to do the things in a practical way, and from that work,
as the boy carries it out, to deduce certain laws and develop the
principles which underlie them. Wherever it is deemed possible to do so,
it is planned to have the boy make these discoveries for himself, so as
to encourage him to become a thinker and a reasoner instead of a mere

A boy does not develop into a philosopher or a scientist through being
told he must learn the principles of this teaching, or the fundamentals
of that school of reasoning. He will unconsciously imbibe the spirit and
the willingness if we but place before him the tools by which he may
build even the simple machinery that displays the various electrical



There is no study so profound as electricity. It is a marvel to the
scientist as well as to the novice. It is simple in its manifestations,
but most complex in its organization and in its ramifications. It has
been shown that light, heat, magnetism and electricity are the same, but
that they differ merely in their modes of motion.

FIRST HISTORICAL ACCOUNT.--The first historical account of electricity
dates back to 600 years B. C. Thales of Miletus was the first to
describe the properties of amber, which, when rubbed, attracted and
repelled light bodies. The ancients also described what was probably
tourmaline, a mineral which has the same qualities. The torpedo, a fish
which has the power of emitting electric impulses, was known in very
early times.

From that period down to about the year 1600 no accounts of any
historical value have been given. Dr. Gilbert, of England, made a number
of researches at that time, principally with amber and other materials,
and Boyle, in 1650, made numerous experiments with frictional

Sir Isaac Newton also took up the subject at about the same period. In
1705 Hawksbee made numerous experiments; also Gray, in 1720, and a
Welshman, Dufay, at about the same time. The Germans, from 1740 to 1780,
made many experiments. In 1740, at Leyden, was discovered the jar which
bears that name. Before that time, all experiments began and ended with
frictional electricity.

The first attempt to "bottle" electricity was attempted by
Muschenbr[oe]ck, at Leyden, who conceived the idea that electricity in
materials might be retained by surrounding them with bodies which did
not conduct the current. He electrified some water in a jar, and
communication having been established between the water and the prime
conductor, his assistant, who was holding the bottle, on trying to
disengage the communicating wire, received a sudden shock.

In 1747 Sir William Watson fired gunpowder by an electric spark, and,
later on, a party from the Royal Society, in conjunction with Watson,
conducted a series of experiments to determine the velocity of the
electric fluid, as it was then termed.

Benjamin Franklin, in 1750, showed that lightning was electricity, and
later on made his interesting experiments with the kite and the key.

DISCOVERING GALVANIC ELECTRICITY.--The great discovery of Galvani, in
1790, led to the recognition of a new element in electricity, called
galvanic or voltaic (named after the experimenter, Volta), and now known
to be identical with frictional electricity. In 1805 Poisson was the
first to analyze electricity; and when [OE]rsted of Copenhagen, in 1820,
discovered the magnetic action of electricity, it offered a great
stimulus to the science, and paved the way for investigation in a new
direction. Ampere was the first to develop the idea that a motor or a
dynamo could be made operative by means of the electro-magnetic current;
and Faraday, about 1830, discovered electro-magnetic rotation.

ELECTRO-MAGNETIC FORCE.--From this time on the knowledge of electricity
grew with amazing rapidity. Ohm's definition of electro-motive force,
current strength and resistance eventuated into Ohm's law. Thomson
greatly simplified the galvanometer, and Wheatstone invented the
rheostat, a means of measuring resistance, about 1850. Then primary
batteries were brought forward by Daniels, Grove, Bunsen and Thomson,
and electrolysis by Faraday. Then came the instruments of precision--the
electrometer, the resistance bridge, the ammeter, the voltmeter--all of
the utmost value in the science.

MEASURING INSTRUMENTS.--The perfection of measuring instruments did more
to advance electricity than almost any other field of endeavor; so that
after 1875 the inventors took up the subject, and by their energy
developed and put into practical operation a most wonderful array of
mechanism, which has become valuable in the service of man in almost
every field of human activity.

RAPIDITY OF MODERN PROGRESS.--This brief history is given merely to show
what wonders have been accomplished in a few years. The art is really
less than fifty years old, and yet so rapidly has it gone forward that
it is not at all surprising to hear the remark, that the end of the
wonders has been reached. Less than twenty-five years ago a high
official of the United States Patent Office stated that it was probable
the end of electrical research had been reached. The most wonderful
developments have been made since that time; and now, as in the past,
one discovery is but the prelude to another still more remarkable. We
are beginning to learn that we are only on the threshold of that
storehouse in which nature has locked her secrets, and that there is no
limit to human ingenuity.

HOW TO ACQUIRE THE VAST KNOWLEDGE.--As the boy, with his limited vision,
surveys this vast accumulation of tools, instruments and machinery, and
sees what has been and is now being accomplished, it is not to be
wondered at that he should enter the field with timidity. In his mind
the great question is, how to acquire the knowledge. There is so much to
learn. How can it be accomplished?

The answer to this is, that the student of to-day has the advantage of
the knowledge of all who have gone before; and now the pertinent thing
is to acquire that knowledge.

THE MEANS EMPLOYED.--This brings us definitely down to an examination of
the means that we shall employ to instil this knowledge, so that it may
become a permanent asset to the student's store of information.

The most significant thing in the history of electrical development is
the knowledge that of all the great scientists not one of them ever
added any knowledge to the science on purely speculative reasoning. All
of them were experimenters. They practically applied and developed their
theories in the laboratory or the workshop. The natural inference is,
therefore, that the boy who starts out to acquire a knowledge of
electricity, must not only theorize, but that he shall, primarily,
conduct the experiments, and thereby acquire the information in a
practical way, one example of which will make a more lasting impression
than pages of dry text.

Throughout these pages, therefore, I shall, as briefly as possible,
point out the theories involved, as a foundation for the work, and then
illustrate the structural types or samples; and the work is so arranged
that what is done to-day is merely a prelude or stepping-stone to the
next phase of the art. In reality, we shall travel, to a considerable
extent, the course which the great investigators followed when they were
groping for the facts and discovering the great manifestations in



PREPARING THE WORKSHOP.--Before commencing actual experiments we should
prepare the workshop and tools. Since we are going into this work as
pioneers, we shall have to be dependent upon our own efforts for the
production of the electrical apparatus, so as to be able, with our
home-made factory, to provide the power, the heat and the electricity.
Then, finding we are successful in these enterprises, we may look
forward for "more worlds to conquer."

By this time our neighbors will become interested in and solicit work
from us.

USES OF OUR WORKSHOPS.--They may want us to test batteries, and it then
becomes necessary to construct mechanism to detect and measure
electricity; to install new and improved apparatus; and to put in and
connect up electric bells in their houses, as well as burglar alarms. To
meet the requirements, we put in a telegraph line, having learned, as
well as we are able, how they are made and operated. But we find the
telegraph too slow and altogether unsuited for our purposes, as well as
for the uses of the neighborhood, so we conclude to put in a telephone

WHAT TO BUILD.--It is necessary, therefore, to commence right at the
bottom to build a telephone, a transmitter, a receiver and a
switch-board for our system. From the telephone we soon see the
desirability of getting into touch with the great outside world, and
wireless telegraphy absorbs our time and energies.

But as we learn more and more of the wonderful things electricity will
do, we are brought into contact with problems which directly interest
the home. Sanitation attracts our attention. Why cannot electricity act
as an agent to purify our drinking water, to sterilize sewage and to
arrest offensive odors? We must, therefore, learn something about the
subject of electrolysis.

WHAT TO LEARN.--The decomposition of water is not the only thing that we
shall describe pertaining to this subject. We go a step further, and
find that we can decompose metals as well as liquids, and that we can
make a pure metal out of an impure one, as well as make the foulest
water pure. But we shall also, in the course of our experiments, find
that a cheap metal can be coated with a costly one by means of
electricity--that we can electroplate by electrolysis.

USES OF THE ELECTRICAL DEVICES.--While all this is progressing and our
factory is turning out an amazing variety of useful articles, we are led
to inquire into the uses to which we may devote our surplus electricity.
The current may be diverted for boiling water; for welding metals; for
heating sad-irons, as well as for other purposes which are daily

TOOLS.--To do these things tools are necessary, and for the present they
should not be expensive. A small, rigidly built bench is the first
requirement. This may be made, as shown in Fig. 1, of three 2-inch
planks, each 10 inches wide and 6 feet long, mounted on legs 36 inches
in height. In the front part are three drawers for your material, or the
small odds and ends, as well as for such little tools as you may
accumulate. Then you will need a small vise, say, with a 2-inch jaw, and
you will also require a hand reel for winding magnets. This will be
fully described hereafter.

You can also, probably, get a small, cheap anvil, which will be of the
greatest service in your work. It should be mounted close up to the work
bench. Two small hammers, one with an A-shaped peon, and the other with
a round peon, should be selected, and also a plane and a small wood saw
with fine teeth. A bit stock, or a ratchet drill, if you can afford it,
with a variety of small drills; two wood chisels, say of 3/8-inch and
3/4-inch widths; small cold chisels; hack saw, 10-inch blade; small
iron square; pair of dividers; tin shears; wire cutters; 2 pairs of
pliers, one flat and the other round-nosed; 2 awls, centering punch,
wire cutters, and, finally, soldering tools.

[Illustration: _Fig. 2. Top View_ MAGNET-WINDING REEL]

[Illustration: _Fig. 3. Side View_ MAGNET-WINDING REEL]

If a gas stove is not available, a brazing torch is an essential tool.
Numerous small torches are being made, which are cheap and easily
operated. A small soldering iron, with pointed end, should be provided;
also metal shears and a small square; an awl and several sizes of
gimlets; a screwdriver; pair of pliers and wire cutters.

From the foregoing it will be seen that the cost of tools is not a very
expensive item.

This entire outfit, not including the anvil and vise, may be purchased
new for about $20.00, so we have not been extravagant.

MAGNET-WINDING REEL.--Some little preparation must be made, so we may be
enabled to handle our work by the construction of mechanical aids.

[Illustration: _Fig. 4. Journal Block._]

First of these is the magnet-winding reel, a plan view of which is shown
in Fig. 2. This, for our present work, will be made wholly of wood.

Select a plank 1-1/2 inches thick and 8 inches wide, and from this cut
off two pieces (A), each 7 inches long, and then trim off the corners
(B, B), as shown in Fig. 4. To serve as the mandrel (C, Fig. 2), select
a piece of broomstick 9 inches long. Bore a hole (D) in each block (A) a
half inch below the upper margin of the block, this hole being of such
diameter that the broomstick mandrel will fit and easily turn therein.

Place a crank (E), 5 inches long, on the outer end of the mandrel, as in
Fig. 3. Then mount one block on the end of the bench and the other block
3 inches away. Affix them to the bench by nails or screws, preferably
the latter.

On the inner end of the mandrel put a block (F) of hard wood. This is
done by boring a hole 1 inch deep in the center of the block, into which
the mandrel is driven. On the outer face of the block is a square hole
large enough to receive the head of a 3/8-inch bolt, and into the
depression thus formed a screw (G) is driven through the block and into
the end of the mandrel, so as to hold the block (F) and mandrel firmly
together. When these parts are properly put together, the inner side of
the block will rest and turn against the inner journal block (A).

The tailpiece is made of a 2" × 4" scantling (H), 10 inches long, one
end of it being nailed to a transverse block (I) 2" × 2" × 4". The inner
face of this block has a depression in which is placed a V-shaped cup
(J), to receive the end of the magnet core (K) or bolt, which is to be
used for this purpose. The tailpiece (H) has a longitudinal slot (L) 5
inches long adapted to receive a 1/2-inch bolt (M), which passes down
through the bench, and is, therefore, adjustable, so it may be moved to
and from the journal bearing (A), thereby providing a place for the
bolts to be put in. These bolts are the magnet cores (K), 6 inches long,
but they may be even longer, if you bore several holes (N) through the
bench so you may set over the tailpiece.

With a single tool made substantially like this, over a thousand of the
finest magnets have been wound. Its value will be appreciated after you
have had the experience of winding a few magnets.

ORDER IN THE WORKSHOP.--Select a place for each tool on the rear upright
of the bench, and make it a rule to put each tool back into its place
after using. This, if persisted in, will soon become a habit, and will
save you hours of time. Hunting for tools is the unprofitable part of
any work.



THE TWO KINDS OF MAGNET.--Generally speaking, magnets are of two kinds,
namely, permanent and electro-magnetic.

PERMANENT MAGNETS.--A permanent magnet is a piece of steel in which an
electric force is exerted at all times. An electro-magnet is a piece of
iron which is magnetized by a winding of wire, and the magnet is
energized only while a current of electricity is passing through the

ELECTRO-MAGNET.--The electro-magnet, therefore, is the more useful,
because the pull of the magnet can be controlled by the current which
actuates it.

The electro-magnet is the most essential of all contrivances in the
operation and use of electricity. It is the piece of mechanism which
does the physical work of almost every electrical apparatus or machine.
It is the device which has the power to convert the unseen electric
current into motion which may be observed by the human eye. Without it
electricity would be a useless agent to man.

While the electro-magnet is, therefore, the form of device which is
almost wholly used, it is necessary, first, to understand the principles
of the permanent magnet.

MAGNETISM.--The curious force exerted by a magnet is called magnetism,
but its origin has never been explained. We know its manifestations
only, and laws have been formulated to explain its various phases; how
to make it more or less intense; how to make its pull more effective;
the shape and form of the magnet and the material most useful in its

[Illustration: _Fig 5._ PLAIN MAGNET BAR]

MATERIALS FOR MAGNETS.--Iron and steel are the best materials for
magnets. Some metals are non-magnetic, this applying to iron if combined
with manganese. Others, like sulphur, zinc, bismuth, antimony, gold,
silver and copper, not only are non-magnetic, but they are actually
repelled by magnetism. They are called the diamagnetics.

NON-MAGNETIC MATERIALS.--Any non-magnetic body in the path of a magnetic
force does not screen or diminish its action, whereas a magnetic
substance will.

In Fig. 5 we show the simplest form of magnet, merely a bar of steel (A)
with the magnetic lines of force passing from end to end. It will be
understood that these lines extend out on all sides, and not only along
two sides, as shown in the drawing. The object is to explain clearly how
the lines run.

[Illustration: _Fig. 6._ SEVERED MAGNET]

ACTION OF A SEVERED MAGNET.--Now, let us suppose that we sever this bar
in the middle, as in Fig. 6, or at any other point between the ends. In
this case each part becomes a perfect magnet, and a new north pole (N)
and a new south pole (S) are made, so that the movement of the magnetic
lines of force are still in the same direction in each--that is, the
current flows from the north pole to the south pole.

WHAT NORTH AND SOUTH POLES MEAN.--If these two parts are placed close
together they will attract each other. But if, on the other hand, one of
the pieces is reversed, as in Fig. 7, they will repel each other. From
this comes the statement that likes repel and unlikes attract each

REPULSION AND ATTRACTION.--This physical act of repulsion and attraction
is made use of in motors, as we shall see hereinafter.

It will be well to bear in mind that in treating of electricity the
north pole is always associated with the plus sign (+) and the south
pole with the minus sign (-). Or the N sign is positive and the S sign
negative electricity.

[Illustration: _Fig. 7._ REVERSED MAGNETS]

POSITIVES AND NEGATIVES.--There is really no difference between positive
and negative electricity, so called, but the foregoing method merely
serves as a means of identifying or classifying the opposite ends of a
magnet or of a wire.

MAGNETIC LINES OF FORCE.--It will be noticed that the magnetic lines of
force pass through the bar and then go from end to end through the
atmosphere. Air is a poor conductor of electricity, so that if we can
find a shorter way to conduct the current from the north pole to the
south pole, the efficiency of the magnet is increased.

This is accomplished by means of the well-known horseshoe magnet, where
the two ends (N, S) are brought close together, as in Fig. 8.

THE EARTH AS A MAGNET.--The earth is a huge magnet and the magnetic
lines run from the north pole to the south pole around all sides of the

[Illustration: _Fig. 8._ HORSESHOE MAGNET]

The north magnetic pole does not coincide with the true north pole or
the pivotal point of the earth's rotation, but it is sufficiently near
for all practical purposes. Fig. 9 shows the magnetic lines running from
the north to the south pole.

WHY THE COMPASS POINTS NORTH AND SOUTH.--Now, let us try to ascertain
why the compass points north and south.

Let us assume that we have a large magnet (A, Fig. 10), and suspend a
small magnet (B) above it, so that it is within the magnetic field of
the large magnet. This may be done by means of a short pin (C), which is
located in the middle of the magnet (B), the upper end of this pin
having thereon a loop to which a thread (D) is attached. The pin also
carries thereon a pointer (E), which is directed toward the north pole
of the bar (B).

[Illustration: _Fig. 9._ EARTH'S MAGNETIC LINES]

You will now take note of the interior magnetic lines (X), and the
exterior magnetic lines (Z) of the large magnet (A), and compare the
direction of their flow with the similar lines in the small magnet (B).

The small magnet has both its exterior and its interior lines within the
exterior lines (Z) of the large magnet (A), so that as the small magnet
(B) is capable of swinging around, the N pole of the bar (B) will point
toward the S pole of the larger bar (A). The small bar, therefore, is
influenced by the exterior magnetic field (Z).

[Illustration: _Fig. 10._ TWO PERMANENT MAGNETS]


Let us now take the outline represented by the earth's surface (Fig.
11), and suspend a magnet (A) at any point, like the needle of a
compass, and it will be seen that the needle will arrange itself north
and south, within the magnetic field which flows from the north to the
south pole.

PECULIARITY OF A MAGNET.--One characteristic of a magnet is that, while
apparently the magnetic field flows out at one end of the magnet, and
moves inwardly at the other end, the power of attraction is just the
same at both ends.

In Fig. 12 are shown a bar (A) and a horseshoe magnet (B). The bar (A)
has metal blocks (C) at each end, and each of these blocks is attracted
to and held in contact with the ends by magnetic influence, just the
same as the bar (D) is attracted by and held against the two ends of the
horseshoe magnet. These blocks (C) or the bar (D) are called armatures.
Through them is represented the visible motion produced by the magnetic

[Illustration: _Fig. 12._ ARMATURES FOR MAGNETS]

ACTION OF THE ELECTRO-MAGNET.--The electro-magnet exerts its force in
the same manner as a permanent magnet, so far as attraction and
repulsion are concerned, and it has a north and a south pole, as in the
case with the permanent magnet. An electro-magnet is simply a bar of
iron with a coil or coils of wire around it; when a current of
electricity flows through the wire, the bar is magnetized. The moment
the current is cut off, the bar is demagnetized. The question that now
arises is, why an electric current flowing through a wire, under those
conditions, magnetizes the bar, or _core_, as it is called.

[Illustration: _Fig. 13._ MAGNETIZED FIELD]

[Illustration: _Fig. 14._ MAGNETIZED BAR]

In Fig. 13 is shown a piece of wire (A). Let us assume that a current of
electricity is flowing through this wire in the direction of the darts.
What actually takes place is that the electricity extends out beyond the
surface of the wire in the form of the closed rings (B). If, now, this
wire (A) is wound around an iron core (C, Fig. 14), you will observe
that this electric field, as it is called, entirely surrounds the core,
or rather, that the core is within the magnetic field or influence of
the current flowing through the wire, and the core (C) thereby becomes
magnetized, but it is magnetized only when the current passes through
the wire coil (A).

[Illustration: _Fig. 15._ DIRECTION OF CURRENT]

From the foregoing, it will be understood that a wire carrying a current
of electricity not only is affected within its body, but that it also
has a sphere of influence exteriorly to the body of the wire, at all
points; and advantage is taken of this phenomenon in constructing
motors, dynamos, electrical measuring devices and almost every kind of
electrical mechanism in existence.

mind that the wire coil (A, Fig. 14) does not come into contact with the
core (C). It is insulated from the core, either by air or by rubber or
other insulating substance, and a current passing from A to C under
those conditions is a current of _induction_. On the other hand, the
current flowing through the wire (A) from end to end is called a
_conduction_ current. Remember these terms.

In this connection there is also another thing which you will do well to
bear in mind. In Fig. 15 you will notice a core (C) and an insulated
wire coil (B) wound around it. The current, through the wire (B), as
shown by the darts (D), moves in one direction, and the induced current
in the core (C) travels in the opposite direction, as shown by the darts


PARALLEL WIRES.--In like manner, if two wires (A, B, Fig. 16) are
parallel with each other, and a current of electricity passes along the
wire (A) in one direction, the induced current in the wire (B) will move
in the opposite direction.

These fundamental principles should be thoroughly understood and



THREE ELECTRICAL SOURCES.--It has been found that there are three kinds
of electricity, or, to be more accurate, there are three ways to
generate it. These will now be described.

When man first began experimenting, he produced a current by frictional
means, and collected the electricity in a bottle or jar. Electricity, so
stored, could be drawn from the jar, by attaching thereto suitable
connection. This could be effected only in one way, and that was by
discharging the entire accumulation instantaneously. At that time they
knew of no means whereby the current could be made to flow from the jar
as from a battery or cell.

FRICTIONAL ELECTRICITY.--With a view of explaining the principles
involved, we show in Fig. 17 a machine for producing electricity by


This is made up as follows: A represents the base, having thereon a flat
member (B), on which is mounted a pair of parallel posts or standards
(C, C), which are connected at the top by a cross piece (D). Between
these two posts is a glass disc (E), mounted upon a shaft (F), which
passes through the posts, this shaft having at one end a crank (G). Two
leather collecting surfaces (H, H), which are in contact with the glass
disc (E), are held in position by arms (I, J), the arm (I) being
supported by the cross piece (D), and the arm (J) held by the base piece
(B). A rod (K), U-shaped in form, passes over the structure here thus
described, its ends being secured to the base (B). The arms (I, J) are
both electrically connected with this rod, or conductor (K), joined to a
main conductor (L), which has a terminating knob (M). On each side and
close to the terminal end of each leather collector (H) is a fork-shaped
collector (N). These two collectors are also connected electrically with
the conductor (K). When the disc is turned electricity is generated by
the leather flaps and accumulated by the collectors (N), after which it
is ready to be discharged at the knob (M).

In order to collect the electricity thus generated a vessel called a
Leyden jar is used.

LEYDEN JAR.--This is shown in Fig. 18. The jar (A) is of glass coated
exteriorly at its lower end with tinfoil (B), which extends up a little
more than halfway from the bottom. This jar has a wooden cover or top
(C), provided centrally with a hole (D). The jar is designed to receive
within it a tripod and standard (E) of lead. Within this lead standard
is fitted a metal rod (F), which projects upwardly through the hole (D),
its upper end having thereon a terminal knob (G). A sliding cork (H) on
the rod (F) serves as a means to close the jar when not in use. When in
use this cork is raised so the rod may not come into contact,
electrically, with the cover (C).

The jar is half filled with sulphuric acid (I), after which, in order
to charge the jar, the knob (G) is brought into contact with the knob
(M) of the friction generator (Fig. 17).

VOLTAIC OR GALVANIC ELECTRICITY.--The second method of generating
electricity is by chemical means, so called, because a liquid is used as
one of the agents.

[Illustration: _Fig. 18._ LEYDEN JAR]

Galvani, in 1790, made the experiments which led to the generation of
electricity by means of liquids and metals. The first battery was called
the "crown of cups," shown in Fig. 19, and consisting of a row of glass
cups (A), containing salt water. These cups were electrically connected
by means of bent metal strips (B), each strip having at one end a copper
plate (C), and at the other end a zinc plate (D). The first plate in the
cup at one end is connected with the last plate in the cup at the other
end by a conductor (E) to make a complete circuit.


THE CELL AND BATTERY.--From the foregoing it will be seen that within
each cup the current flows from the zinc to the copper plates, and
exteriorly from the copper to the zinc plates through the conductors (B
and E).

A few years afterwards Volta devised what is known as the voltaic pile
(Fig. 20).

VOLTAIC PILE--HOW MADE.--This is made of alternate discs of copper and
zinc with a piece of cardboard of corresponding size between each zinc
and copper plate. The cardboard discs are moistened with acidulated
water. The bottom disc of copper has a strip which connects with a cup
of acid, and one wire terminal (A) runs therefrom. The upper disc, which
is of zinc, is also connected, by a strip, with a cup of acid from which
extends the other terminal wire (B).

[Illustration: _Fig. 20._ VOLTAIC ELECTRICITY]

_Plus and Minus Signs._--It will be noted that the positive or copper
disc has the plus sign (+) while the zinc disc has the minus (-) sign.
These signs denote the positive and the negative sides of the current.

The liquid in the cells, or in the moistened paper, is called the
_electrolyte_ and the plates or discs are called _electrodes_. To define
them more clearly, the positive plate is the _anode_, and the negative
plate the _cathode_.

The current, upon entering the zinc plate, decomposes the water in the
electrolyte, thereby forming oxygen. The hydrogen in the water, which
has also been formed by the decomposition, is carried to the copper
plate, so that the plate finally is so coated with hydrogen that it is
difficult for the current to pass through. This condition is called
"polarization," and to prevent it has been the aim of all inventors. To
it also we may attribute the great variety of primary batteries, each
having some distinctive claim of merit.

THE COMMON PRIMARY CELL.--The most common form of primary cell contains
sulphuric acid, or a sulphuric acid solution, as the electrolyte, with
zinc for the _anode_, and carbon, instead of copper, for the _cathode_.

The ends of the zinc and copper plates are called _terminals_, and while
the zinc is the anode or positive element, its _terminal_ is designated
as the positive pole. In like manner, the carbon is the negative
element or cathode, and its terminal is designated as negative pole.

Fig. 21 will show the relative arrangement of the parts. It is customary
to term that end or element from which the current flows as positive. A
cell is regarded as a whole, and as the current passes out of the cell
from the copper element, the copper terminal becomes positive.

[Illustration: _Fig. 21._ PRIMARY BATTERY]

carefully memorized:

A cell has reference to a single vessel. When two or more cells are
coupled together they form a _battery_.

_Resistance_ is opposition to the movement of the current. If it is
offered by the electrolyte, it is designated "Internal Resistance." If,
on the other hand, the opposition takes place, for instance, through the
wire, it is then called "External Resistance."

The electrolyte must be either acid, or alkaline, or saline, and the
electrodes must be of dissimilar metals, so the electrolyte will attack
one of them.

The current is measured in amperes, and the force with which it is
caused to flow is measured in volts. In practice the word "current" is
used to designate ampere flow; and electromotive force, or E. M. F., is
used instead of voltage.

ELECTRO-MAGNETIC ELECTRICITY.--The third method of generating
electricity is by electro-magnets. The value and use of induction will
now be seen, and you will be enabled to utilize the lesson concerning
magnetic action referred to in the previous chapter.

MAGNETIC RADIATION.--You will remember that every piece of metal which
is within the path of an electric current has a space all about its
surface from end to end which is electrified. This electrified field
extends out a certain distance from the metal, and is supposed to
maintain a movement around it. If, now, another piece of metal is
brought within range of this electric or magnetic zone and moved across
it, so as to cut through this field, a current will be generated
thereby, or rather added to the current already exerted, so that if we
start with a feeble current, it can be increased by rapidly "cutting the
lines of force," as it is called.

DIFFERENT KINDS OF DYNAMO.--While there are many kinds of dynamo, they
all, without exception, are constructed in accordance with this
principle. There are also many varieties of current. For instance, a
dynamo may be made to produce a high voltage and a low amperage; another
with high amperage and low voltage; another which gives a direct current
for lighting, heating, power, and electroplating; still another which
generates an alternating current for high tension power, or
transmission, arc-lighting, etc., all of which will be explained

In this place, however, a full description of a direct-current dynamo
will explain the principle involved in all dynamos--that to generate a
current of electricity makes it necessary for us to move a field of
force, like an armature, rapidly and continuously through another field
of force, like a magnetic field.

DIRECT-CURRENT DYNAMO.--We shall now make the simplest form of dynamo,
using for this purpose a pair of permanent magnets.

[Illustration: _Fig. 22._ DYNAMO FIELD AND POLE PIECE]

SIMPLE MAGNET CONSTRUCTION.--A simple way to make a pair of magnets for
this purpose is shown in Fig. 22. A piece of round 3/4-inch steel core
(A), 5-1/2 inches long, is threaded at both ends to receive at one end a
nut (B), which is screwed on a sufficient distance so that the end of
the core (A) projects a half inch beyond the nut. The other end of the
steel core has a pole piece of iron (C) 2" × 2" × 4", with a hole
midway between the ends, threaded entirely through, and provided along
one side with a concave channel, within which the armature is to turn.
Now, before the pole piece (C) is put on, we will slip on a disc (E),
made of hard rubber, then a thin rubber tube (F), and finally a rubber
disc (G), so as to provide a positive insulation for the wire coil which
is wound on the bobbin thus made.

HOW TO WIND.--In practice, and as you go further along in this work, you
will learn the value, first, of winding one layer of insulated wire on
the spool, coating it with shellac, and then putting on the next layer,
and so on; when completely wound, the two wire terminals may be brought
out at one end; but for our present purpose, and to render the
explanation clearer, the wire terminals are at the opposite ends of the
spool (H, H').

THE DYNAMO FIELDS.--Two of these spools are so made and they are called
the _fields_ of the dynamo.

We will next prepare an iron bar (I), 5 inches long and 1/2 inch thick
and 1-1/2 inches wide, then bore two holes through it so the distance
measures 3 inches from center to center. These holes are to be threaded
for the 3/4-inch cores (A). This bar holds together the upper ends of
the cores, as shown in Fig. 23.

[Illustration: _Fig. 23._ BASE AND FIELDS ASSEMBLED]

We then prepare a base (J) of any hard wood, 2 inches thick, 8 inches
long and 8 inches wide, and bore two 3/4-inch holes 3 inches apart on a
middle line, to receive a pair of 3/4-inch cap screws (K), which pass
upwardly through the holes in the base and screw into the pole pieces
(C). A wooden bar (L), 1-1/2" × 1-1/2", 8 inches long, is placed under
each pole piece, which is also provided with holes for the cap screws
(K). The lower side of the base (J) should be countersunk, as at M, so
the head of the nut will not project. The fields of the dynamo are now
secured in position to the base.

[Illustration: _Fig. 24._ DETAILS OF THE ARMATURE, CORE


THE ARMATURE.--A bar of iron (Fig. 24), 1" × 1" and 2-1/4 inches long,
is next provided. Through this bar (1) are then bored two 5/16-inch
holes 1-3/4 inches apart, and on the opposite sides of this bar are two
half-rounded plates of iron (3) (Fig. 25).

ARMATURE WINDING.--Each plate is 1/2 inch thick, 1-3/4 inches wide and 4
inches long, each plate having holes (4) to coincide with the holes (2)
of the bar (1), so that when the two plates are applied to opposite
sides of the bar, and riveted together, a cylindrical member is formed,
with two channels running longitudinally, and transversely at the ends;
and in these channels the insulated wires are wound from end to end
around the central block (1).

MOUNTING THE ARMATURE.--It is now necessary to provide a means for
revolving this armature. To this end a brass disc (5, Fig. 26) is made,
2 inches in diameter, 1/8 inch thick. Centrally, at one side, is a
projecting stem (6) of round brass, which projects out 2 inches, and the
outer end is turned down, as at 7, to form a small bearing surface.

[Illustration: _Fig. 26._ JOURNALS _Fig. 27._ COMMUTATOR,

The other end of the armature has a similar disc (8), with a central
stem (9), 1-1/2 inches long, turned down to 1/4-inch diameter up to
within 1/4 inch of the disc (7), so as to form a shoulder.

THE COMMUTATOR.--In Fig. 27 is shown, at 10, a wooden cylinder, 1 inch
long and 1-1/4 inches in diameter, with a hole (11) bored through
axially, so that it will fit tightly on the stem (6) of the disc (5). On
this wooden cylinder is driven a brass or copper tube (12), which has
holes (13) opposite each other. Screws are used to hold the tube to the
wooden cylinder, and after they are properly secured together, the tube
(12) is cut by a saw, as at 14, so as to form two independent tubular

[Illustration: _Fig. 28._ END VIEW ARMATURE, MOUNTED]

These tubular sections are called the commutator plates.

[Illustration: _Fig. 29._ TOP VIEW OF ARMATURE ON BASE]

In order to mount this armature, two bearings are provided, each
comprising a bar of brass (15, Fig. 28), each 1/4 inch thick, 1/2 inch
wide and 4-1/2 inches long. Two holes, 3 inches apart, are formed
through this bar, to receive round-headed wood screws (16), these screws
being 3 inches long, so they will pass through the wooden pieces (I)
and enter the base (J). Midway between the ends, each bar (15) has an
iron bearing block (17), 3/4" × 1/2" and 1-1/2 inches high, the 1/4-inch
hole for the journal (7) being midway between its ends.

COMMUTATOR BRUSHES.--Fig. 28 shows the base, armature and commutator
assembled in position, and to these parts have been added the commutator
brushes. The brush holder (18) is a horizontal bar made of hard rubber
loosely mounted upon the journal pin (7), which is 2-1/2 inches long. At
each end is a right-angled metal arm (19) secured to the bar (18) by
screws (20). To these arms the brushes (21) are attached, so that their
spring ends engage with the commutator (12). An adjusting screw (22) in
the bearing post (17), with the head thereof bearing against the
brush-holder (18), serves as a means for revolubly adjusting the brushes
with relation to the commutator.

DYNAMO WINDINGS.--There are several ways to wind the dynamos. These
can be shown better by the following diagrams (Figs. 30, 31, 32, 33):

THE FIELD.--If the field (A, Fig. 30) is not a permanent magnet, it must
be excited by a cell or battery, and the wires (B, B') are connected up
with a battery, while the wires (C, C') may be connected up to run a
motor. This would, therefore, be what is called a "separately excited"
dynamo. In this case the battery excites the field and the armature
(D), cutting the lines of force at the pole pieces (E), so that the
armature gathers the current for the wires (C, C').

[Illustration: _Fig. 30._ FIELD WINDING]

[Illustration: _Fig. 31._ SERIES-WOUND]

SERIES-WOUND FIELD.--Fig. 31 shows a "series-wound" dynamo. The wires of
the fields (A) are connected up in series with the brushes of the
armature (D), and the wires (G, G') are led out and connected up with a
lamp, motor or other mechanism. In this case, as well as in Figs. 32 and
33, both the field and the armature are made of soft gray iron. With
this winding and means of connecting the wires, the field is constantly
excited by the current passing through the wires.

SHUNT-WOUND FIELD.--Fig. 32 represents what is known as a "shunt-wound"
dynamo. Here the field wires (H, H) connect with the opposite brushes
of the armature, and the wires (I, I') are also connected with the
brushes, these two wires being provided to perform the work required.
This is a more useful form of winding for electroplating purposes.

[Illustration: _Fig. 32._ SHUNT-WOUND _Fig. 32._ COMPOUND-WOUND]

COMPOUND-WOUND FIELD.--Fig. 33 is a diagram of a "compound-wound"
dynamo. The regular field winding (J) has its opposite ends connected
directly with the armature brushes. There is also a winding, of a
comparatively few turns, of a thicker wire, one terminal (K) of which is
connected with one of the brushes and the other terminal (K') forms one
side of the lighting circuit. A wire (L) connects with the other
armature brush to form a complete lighting circuit.



MEASURING INSTRUMENTS.--The production of an electric current would not
be of much value unless we had some way by which we might detect and
measure it. The pound weight, the foot rule and the quart measure are
very simple devices, but without them very little business could be
done. There must be a standard of measurement in electricity as well as
in dealing with iron or vegetables or fabrics.

As electricity cannot be seen by the human eye, some mechanism must be
made which will reveal its movements.

THE DETECTOR.--It has been shown in the preceding chapter that a current
of electricity passing through a wire will cause a current to pass
through a parallel wire, if the two wires are placed close together, but
not actually in contact with each other. An instrument which reveals
this condition is called a _galvanometer_. It not only detects the
presence of a current, but it shows the direction of its flow. We shall
now see how this is done.

For example, the wire (A, Fig. 35) is connected up in an electric
circuit with a permanent magnet (B) suspended by a fine wire (C), so
that the magnet (B) may freely revolve.

[Illustration: _Fig. 34._     _Fig. 35._      _Fig. 36._

For convenience, the magnetic field is shown flowing in the direction of
the darts, in which the dart (D) represents the current within the
magnet (B) flowing toward the north pole, and the darts (E) showing the
exterior current flowing toward the south pole. Now, if the wire (A) is
brought up close to the magnet (B), and a current passed through A, the
magnet (B) will be affected. Fig. 35 shows the normal condition of the
magnetized bar (B) parallel with the wire (A) when a current is not
passing through the latter.

DIRECTION OF CURRENT.--If the current should go through the wire (A)
from right to left, as shown in Fig. 34, the magnet (B) would swing in
the direction taken by the hands of a clock and assume the position
shown in Fig. 34. If, on the other hand, the current in the wire (A)
should be reversed or flow from left to right, the magnet (B) would
swing counter-clock-wise, and assume the position shown in Fig. 36. The
little pointer (G) would, in either case, point in the direction of the
flow of the current through the wire (A).


SIMPLE CURRENT DETECTOR.--A simple current detector may be made as

Prepare a base 3' × 4' in size and 1 inch thick. At each corner of one
end fix a binding post, as at A, A', Fig. 37. Then select 20 feet of No.
28 cotton-insulated wire, and make a coil (B) 2 inches in diameter,
leaving the ends free, so they may be affixed to the binding posts (A,
A'). Now glue or nail six blocks (C) to the base, each block being 1" ×
1" × 2", and lay the coil on these blocks. Then drive an L-shaped nail
(D) down into each block, on the inside of the coil, as shown, so as to
hold the latter in place.

[Illustration: _Fig. 38._ THE BRIDGE]

Now make a bridge (E, Fig. 38) of a strip of brass 1/2 inch wide, 1/16
inch thick and long enough to span the coil, and bend the ends down, as
at F, so as to form legs. A screw hole (G) is formed in each foot, so it
may be screwed to the base.

Midway between the ends this bridge has a transverse slot (H) in one
edge, to receive therein the pivot pin of the swinging magnet. In order
to hold the pivot pin in place, cut out an H-shaped piece of sheet brass
(I), which, when laid on the bridge, has its ends bent around the
latter, as shown at J, and the crossbar of the H-shaped piece then will
prevent the pivot pin from coming out of the slot (H).

[Illustration: _Fig. 39._ DETAILS OF DETECTOR]

The magnet is made of a bar of steel (K, Fig. 39) 1-1/2 inches long, 3/8
inch wide and 1/16 inch thick, a piece of a clock spring being very
serviceable for this purpose. The pivot pin is made of an ordinary pin
(L), and as it is difficult to solder the steel magnet (K) to the pin,
solder only a small disc (M) to the pin (L). Then bore a hole (N)
through the middle of the magnet (K), larger in diameter than the pin
(L), and, after putting the pin in the hole, pour sealing wax into the
hole, and thereby secure the two parts together. Near the upper end of
the pin (L) solder the end of a pointer (O), this pointer being at right
angles to the armature (K). It is better to have a metal socket for the
lower end of the pin. When these parts are put together, as shown in
Fig. 37, a removable glass top, or cover, should be provided.

This is shown in Fig. 40, in which a square, wooden frame (P) is used,
and a glass (Q) fitted into the frame, the glass being so arranged that
when the cover is in position it will be in close proximity to the upper
projecting end of the pivot pin (L), and thus prevent the magnet from
becoming misplaced.

[Illustration: _Fig. 40._ CROSS SECTION OF DETECTOR]

HOW TO PLACE THE DETECTOR.--If the detector is placed north and south,
as shown by the two markings, N and S (Fig. 37), the magnet bar will
point north and south, being affected by the earth's magnetism; but when
a current of electricity flows through the coil (B), the magnet will be
deflected to the right or to the left, so that the pointer (O) will then
show the direction in which the current is flowing through the wire (R)
which you are testing.

The next step of importance is to _measure_ the current, that is, to
determine its strength or intensity, as well as the flow or quantity.

measure the properties of a current, which may be defined as follows:

1. THE SULPHURIC ACID VOLTAMETER.--By means of an electrolytic action,
whereby the current decomposes an acidulated solution--that is, water
which has in it a small amount of sulphuric acid--and then measuring the
gas generated by the current.

2. THE COPPER VOLTAMETER.--By electro-chemical means, in which the
current passes through plates immersed in a solution of copper sulphate.

3. THE GALVANOSCOPE.--By having a coil of insulated wire, with a magnet
suspended so as to turn freely within the coil, forming what is called a

4. ELECTRO-MAGNETIC METHOD.--By using a pair of magnets and sending a
current through the coils, and then measuring the pull on the armature.

5. THE POWER OR SPEED METHOD.--By using an electric fan, and noting the
revolutions produced by the current.

6. THE CALORIMETER.--By using a coil of bare wire, immersed in paraffine
oil, and then measuring the temperature by means of a thermometer.

[Illustration: _Fig. 41._ ACID VOLTAMETER]

[Illustration: _Fig. 42._ COPPER VOLTAMETER]

7. THE LIGHT METHOD.--Lastly, by means of an electric light, which
shows, by its brightness, a greater or less current.

THE PREFERRED METHODS.--It has been found that the first and second
methods are the only ones which will accurately register current
strength, and these methods have this advantage--that the chemical
effect produced is not dependent upon the size or shape of the apparatus
or the plates used.

HOW TO MAKE A SULPHURIC ACID VOLTAMETER.--In Fig. 41 is shown a simple
form of sulphuric acid voltameter, to illustrate the first method. A is
a jar, tightly closed by a cover (B). Within is a pair of platinum
plates (C, C), each having a wire (D) through the cover. The cover has a
vertical glass tube (E) through it, which extends down to the bottom of
the jar, the electrolyte therein being a weak solution of sulphuric
acid. When a current passes through the wires (D), the solution is
partially decomposed--that is, converted into gas, which passes up into
the vacant space (F) above the liquid, and, as it cannot escape, it
presses the liquid downwardly, and causes the latter to flow upwardly
into the tube (E). It is then an easy matter, after the current is on
for a certain time, to determine its strength by the height of the
liquid in the tube.

HOW TO MAKE A COPPER VOLTAMETER.--The second, or copper voltameter, is
shown in Fig. 42. The glass jar (A) contains a solution of copper
sulphate, known in commerce as blue vitriol. A pair of copper plates
(B, B') are placed in this solution, each being provided with a
connecting wire (C). When a current passes through the wires (C), one
copper plate (B) is eaten away and deposited on the other plate (B'). It
is then an easy matter to take out the plates and find out how much in
weight B' has gained, or how much B has lost.

In this way, in comparing the strength of, say, two separate currents,
one should have each current pass through the voltameter the same length
of time as the other, so as to obtain comparative results.

It is not necessary, in the first and second methods, to consider the
shapes, the sizes of the plates or the distances between them. In the
first method the gas produced, within a given time, will be the same,
and in the second method the amount deposited or eaten away will be the
same under all conditions.

DISADVANTAGES OF THE GALVANOSCOPE.--With the third method (using the
galvanoscope) it is necessary, in order to get a positively correct
reading instrument, to follow an absolutely accurate plan in
constructing each part, in every detail, and great care must be
exercised, particularly in winding. It is necessary also to be very
careful in selecting the sizes of wire used and in the number of turns
made in the coils.

This is equally true of the fourth method, using the electro-magnet,
because the magnetic pull is dependent upon the size of wire from which
the coils are made and the number of turns of wire.

OBJECTIONS TO THE CALORIMETER.--The calorimeter, or sixth method, has
the same objection. The galvanoscope and electro-magnet do not respond
equally to all currents, and this is also true, even to a greater
extent, with the calorimeter.



UNDERSTANDING TERMS.--We must now try to ascertain the meaning of some
of the terms so frequently used in connection with electricity. If you
intended to sell or measure produce or goods of any kind, it would be
essential to know how many pints or quarts are contained in a gallon, or
in a bushel, or how many inches there are in a yard, and you also ought
to know just what the quantity term _bushel_ or the measurement _yard_

INTENSITY AND QUANTITY.--Electricity, while it has no weight, is capable
of being measured by means of its intensity, or by its quantity. Light
may be measured or tested by its brilliancy. If one light is of less
intensity than another and both of them receive their impulses from the
same source, there must be something which interferes with that light
which shows the least brilliancy. Electricity can also be interfered
with, and this interference is called _resistance_.

VOLTAGE.--Water may be made to flow with greater or less force, or
velocity, through a pipe, the degree of same depending upon the height
of the water which supplies the pipe. So with electricity. It may pass
over a wire with greater or less force under one condition than another.
This force is called voltage. If we have a large pipe, a much greater
quantity of water will flow through it than will pass through a small
pipe, providing the pressure in each case is alike. This quantity in
electricity is called _amperage_.

In the case of water, a column 1" × 1", 28 inches in height, weighs 1
pound; so that if a pipe 1 inch square draws water from the bottom it
flows with a pressure of 1 pound. If the pipe has a measurement of 2
square inches, double the quantity of water will flow therefrom, at the
same pressure.

AMPERAGE.--If, on the other hand, we have a pipe 1 inch square, and
there is a depth of 56 inches of water in the reservoir, we shall get as
much water from the reservoir as though we had a pipe of 2 square inches
drawing water from a reservoir which is 28 inches deep.

MEANING OF WATTS.--It is obvious, therefore, that if we multiply the
height of the water in inches with the area of the pipe, we shall obtain
a factor which will show how much water is flowing.

Here are two examples:

1. 28 inches = height of the water in the reservoir.

2 square inches = size of the pipe.
Multiply 28 × 2 = 56.

2. 56 = height of the water in the reservoir.
1 square inch = size of the pipe.
Multiply 56 × 1 = 56.

Thus the two problems are equal.

A KILOWATT.--Now, in electricity, remembering that the height of the
water corresponds with _voltage_ in electricity, and the size of the
pipe with _amperage_, if we multiply volts by amperes, or amperes by
volts, we get a result which is indicated by the term _watts_. One
thousand of these watts make a kilowatt, and the latter is the standard
of measurement by which a dynamo or motor is judged or rated.

Thus, if we have 5 amperes and 110 volts, the result of multiplying them
would be 550 watts, or 5 volts and 110 amperes would produce 550 watts.

A STANDARD OF MEASUREMENT.--But with all this we must have some
standard. A bushel measure is of a certain size, and a foot has a
definite length, so in electricity there is a recognized force and
quantity which are determined as follows:

THE AMPERE STANDARD.--It is necessary, first, to determine what an
ampere is. For this purpose a standard solution of nitrate of silver is
used, and a current of electricity is passed through this solution. In
doing so the current deposits silver at the rate of 0.001118 grains per
second for each ampere.

THE VOLTAGE STANDARD.--In order to determine the voltage we must know
something of _resistance_. Different metals do not transmit a current
with equal ease. The size of a conductor, also, is an important factor
in the passage of a current. A large conductor will transmit a current
much better than a small conductor. We must therefore have a standard
for the _ohm_, which is the measure of resistance.

THE OHM.--It is calculated in this way: There are several standards, but
the one most generally employed is the _International Ohm_. To determine
it, by this system, a column of pure mercury, 106.3 millimeters long and
weighing 14.4521 grams, is used. This would make a square tube about 94
inches long, and a little over 1/25 of an inch in diameter. The
resistance to a current flow in such a column would be equal to 1 ohm.

CALCULATING THE VOLTAGE.--In order to arrive at the voltage we must use
a conductor, which, with a resistance of 1 ohm, will produce 1 ampere.
It must be remembered that the volt is the practical unit of
electro-motive force.

While it would be difficult for the boy to conduct these experiments in
the absence of suitable apparatus, still, it is well to understand
thoroughly how and why these standards are made and used.



SIMPLE SWITCHES.--We have now gone over the simpler or elementary
outlines of electrical phenomena, and we may commence to do some of the
practical work in the art. We need certain apparatus to make
connections, which will be constructed first.

A TWO-POLE SWITCH.--A simple two-pole switch for a single line is made
as follows:

A base block (A, Fig. 43) 3 inches long, 2 inches wide and 3/4 inch
thick, has on it, at one end, a binding screw (B), which holds a pair of
fingers (C) of brass or copper, these fingers being bent upwardly and so
arranged as to serve as fingers to hold a switch bar (D) between them.
This bar is also of copper or brass and is pivoted to the fingers. Near
the other end of the base is a similar binding screw (E) and fingers (F)
to receive the blade of the switch bar. The bar has a handle (G) of
wood. The wires are attached to the respective binding screws (B, E).

DOUBLE-POLE SWITCH.--A double-pole switch or a switch for a double line
is shown in Fig. 44. This is made similar in all respects to the one
shown in Fig. 43, excepting that there are two switch blades (A, A)
connected by a cross bar (B) of insulating material, and this bar
carries the handle (C).

[Illustration: _Fig. 43._ TWO-POLE SWITCH]

[Illustration: _Fig. 44._ DOUBLE-POLE SWITCH]

Other types of switch will be found very useful. In Fig. 45 is a simple
sliding switch in which the base block has, at one end, a pair of copper
plates (A, B), each held at one end to the base by a binding screw (C),
and having a bearing or contact surface (D) at its other end. At the
other end of the base is a copper plate (E) held by a binding screw (F),
to the inner end of which plate is hinged a swinging switch blade (G),
the free end of which is adapted to engage with the plates (A, B).

[Illustration: _Fig. 45._ SLIDING SWITCH]

SLIDING SWITCH.--This sliding switch form may have the contact plates
(A, B and C, Fig. 46) circularly arranged and any number may be located
on the base, so they may be engaged by a single switching lever (H). It
is the form usually adopted for rheostats.

REVERSING SWITCH.--A reversing switch is shown in Fig. 47. The base has
two plates (A, B) at one end, to which the parallel switch bars (C, D)
are hinged. The other end of the base has three contact plates (E, F, G)
to engage the swinging switch bars, these latter being at such distance
apart that they will engage with the middle and one of the outer plates.
The inlet wires, positive and negative, are attached to the plates (A,
B, respectively), and one of the outlet wires (H) is attached to the
middle contact plate (F), while the other wire is connected up with both
of the outside plates. When the switch bars (C, D) are thrown to the
left so as to be in contact with E, F, the outside plate (E) and the
middle plate (F) will be positive and negative, respectively; but when
the switch is thrown to the right, as shown in the figure, plate F
becomes positive and plate E negative, as shown.

[Illustration: _Fig. 46._ RHEOSTAT FORM OF SWITCH]

PUSH BUTTONS.--A push button is but a modified structure of a switch,
and they are serviceable because they are operating, or the circuit is
formed only while the finger is on the button.

[Illustration: _Fig. 47._ REVERSING SWITCH]

In its simplest form (Fig. 48) the push button has merely a circular
base (A) of insulating material, and near one margin, on the flat side,
is a rectangular plate (B), intended to serve as a contact plate as well
as a means for attaching one of the wires thereto. In line with this
plate is a spring finger (C), bent upwardly so that it is normally out
of contact with the plate (B), its end being held by a binding screw
(D). To effect contact, the spring end of the finger (C) is pressed
against the bar (B), as at E. This is enclosed in a suitable casing,
such as will readily suggest itself to the novice.

ELECTRIC BELL.--One of the first things the boy wants to make, and one
which is also an interesting piece of work, is an electric bell.

To make this he will be brought, experimentally, in touch with several
important features in electrical work. He must make a battery for the
production of current, a pair of electro-magnets to be acted upon by the
current, a switch to control it, and, finally, he must learn how to
connect it up so that it may be operated not only from one, but from two
or more push buttons.

[Illustration: _Fig. 48._ PUSH BUTTON]

HOW MADE.--In Fig. 49 is shown an electric bell, as usually constructed,
so modified as to show the structure at a glance, with its connections.
A is the base, B, B' the binding posts for the wires, C, C the
electro-magnets, C' the bracket for holding the magnets, D the armature,
E the thin spring which connects the armature with the post F, G the
clapper arm, H the bell, I the adjusting screw on the post J, K the wire
lead from the binding post B to the first magnet, L the wire which
connects the two magnets, M the wire which runs from the second magnet
to the post J, and N a wire leading from the armature post to the
binding post B'.

[Illustration: _Fig. 49._ ELECTRIC BELL]

The principle of the electric bell is this: In looking at Fig. 49, you
will note that the armature bar D is held against the end of the
adjusting screw by the small spring E. When a current is turned on, it
passes through the connections and conduits as follows: Wire K to the
magnets, wire M to the binding post J, and set screw I, then through the
armature to the post F, and from post F to the binding post B'.

[Illustration: _Fig. 50._ ARMATURE OF ELECTRIC BELL]

ELECTRIC BELL--HOW OPERATED.--The moment a current passes through the
magnets (C, C), the core is magnetized, and the result is that the
armature (D) is attracted to the magnets, as shown by the dotted lines
(O), when the clapper strikes the bell. But when the armature moves over
to the magnet, the connection is broken between the screw (I) and
armature (D), so that the cores of the magnets are demagnetized and lose
their pull, and the spring (E) succeeds in drawing back the armature.
This operation of vibrating the armature is repeated with great
rapidity, alternately breaking and re-establishing the circuit, by the
action of the current.

In making the bell, you must observe one thing, the binding posts (B,
B') must be insulated from each other, and the post J, or the post F,
should also be insulated from the base. For convenience we show the post
F insulated, so as to necessitate the use of wire (N) from post (F) to
binding post (B').

The foregoing assumes that you have used a cast metal base, as most
bells are now made; but if you use a wooden base, the binding posts (B,
B') and the posts (F, J) are insulated from each other, and the
construction is much simplified.

It is better, in practice, to have a small spring (P, Fig. 50) between
the armature (D) and the end of the adjusting screw (I), so as to give a
return impetus to the clapper. The object of the adjusting screw is to
push and hold the armature close up to the ends of the magnets, if it
seems necessary.

If two bells are placed on the base with the clapper mounted between
them, both bells will be struck by the swinging motion of the armature.

An easily removable cap or cover is usually placed over the coils and
armature, to keep out dust.

A very simple annunciator may be attached to the bell, as shown in the
following figures:

[Illustration: _Figs. 51-54._ ANNUNCIATOR]

ANNUNCIATORS.--Make a box of wood, with a base (A) 4" × 5" and 1/2 inch
thick. On this you can permanently mount the two side pieces (B) and two
top and bottom pieces (C), respectively, so they project outwardly
4-1/2 inches from the base. On the open front place a wood or metal
plate (D), provided with a square opening (D), as in Fig. 54, near its
lower end. This plate is held to the box by screws (E).

Within is a magnet (F), screwed into the base (A), as shown in Fig. 51;
and pivoted to the bottom of the box is a vertical armature (G), which
extends upwardly and contacts with the core of the magnet. The upper end
of the armature has a shoulder (H), which is in such position that it
serves as a rest for a V-shaped stirrup (I), which is hinged at J to the
base (C). This stirrup carries the number plate (K), and when it is
raised to its highest point it is held on the shoulder (H), unless the
electro-magnet draws the armature out of range of the stirrup. A spring
(L) bearing against the inner side of the armature keeps its upper end
normally away from the magnet core. When the magnet draws the armature
inwardly, the number plate drops and exposes the numeral through the
opening in the front of the box. In order to return the number plate to
its original position, as shown in Fig. 51, a vertical trigger (M)
passes up through the bottom, its upper end being within range of one of
the limbs of the stirrup.

This is easily made by the ingenious boy, and will be quite an
acquisition to his stock of instruments. In practice, the annunciator
may be located in any convenient place and wires run to that point.

[Illustration: _Fig. 55._ ALARM SWITCH ON WINDOW]


BURGLAR ALARM.--In order to make a burglar alarm connection with a bell,
push buttons or switches may be put in circuit to connect with the
windows and doors, and by means of the annunciators you may locate the
door or window which has been opened. The simplest form of switch for a
window is shown in the following figures:

The base piece (A), which may be of hard rubber or fiber, is 1/4 inch
thick and 1" × 1-1/2" in size.

[Illustration: _Fig. 57._ BURGLAR ALARM CONTACT]

At one end is a brass plate (B), with a hole for a wood screw (C), this
screw being designed to pass through the plate and also into the
window-frame, so as to serve as a means of attaching one of the wires
thereto. The inner end of the plate has a hole for a round-headed screw
(C') that also goes through the base and into the window-frame. It also
passes through the lower end of the heart-shaped metal switch-piece

The upper end of the base has a brass plate (E), also secured to the
base and window by a screw (F) at its upper end. The heart-shaped switch
is of such length and width at its upper end that when it is swung to
the right with one of the lobes projecting past the edge of the
window-frame, the other lobe will be out of contact with the plate (E).

[Illustration: _Fig. 58._ NEUTRAL POSITION OF CONTACT]

The window sash (G) has a removable pin (H), which, when the sash moves
upwardly, is in the path of the lobe of the heart-shaped switch, as
shown in Fig. 56, and in this manner the pin (H) moves the upper end of
the switch (D) inwardly, so that the other lobe contacts with the plate
(E), and establishes an electric circuit, as shown in Fig. 57. During
the daytime the pin (H) may be removed, and in order to protect the
switch the heart-shaped piece (D) is swung inwardly, as shown in Fig.
58, so that neither of the lobes is in contact with the plate (E).

WIRE CIRCUITING.--For the purpose of understanding fully the circuiting,
diagrams will be shown of the simple electric bell with two push
buttons; next in order, the circuiting with an annunciator and then the
circuiting necessary for a series of windows and doors, with annunciator

[Illustration: _Fig. 59._ CIRCUITING FOR ELECTRIC BELL]

simple circuiting system which has two push buttons, although any number
may be used, so that the bell will ring when the circuit is closed by
either button.

buttons and an annunciator for each button. These three circuits are
indicated by A, B and C, so that when either button makes contact, a
complete circuit is formed through the corresponding annunciator.

[Illustration: _Fig. 60._ _Annunciators_]

[Illustration: _Fig. 61._ WIRING SYSTEM FOR A HOUSE]

WIRING UP A HOUSE.--The system of wiring up a house so that all doors
and windows will be connected to form a burglar alarm outfit, is shown
in Fig. 61. It will be understood that, in practice, the bell is mounted
on or at the annunciator, and that, for convenience, the annunciator
box has also a receptacle for the battery. The circuiting is shown
diagramatically, as it is called, so as fully to explain how the lines
are run. Two windows and a door are connected up with an annunciator
having three drops, or numbers 1, 2, 3. The circuit runs from one pole
of the battery to the bell and then to one post of the annunciator. From
the other post a wire runs to one terminal of the switch at the door or
window. The other switch terminal has a wire running to the other pole
of the battery.

A, B, C represent the circuit wires from the terminals of the window and
door switches, to the annunciators.

It is entirely immaterial which side of the battery is connected up with
the bell.

From the foregoing it will readily be understood how to connect up any
ordinary apparatus, remembering that in all cases the magnet must be
brought into the electric circuit.



STORING UP ELECTRICITY.--In the foregoing chapters we have seen that,
originally, electricity was confined in a bottle, called the Leyden jar,
from which it was wholly discharged at a single impulse, as soon as it
was connected up by external means. Later the primary battery and the
dynamo were invented to generate a constant current, and after these
came the second form of storing electricity, called the storage or
secondary battery, and later still recognized as accumulators.

THE ACCUMULATOR.--The term _accumulator_ is, strictly speaking, the more
nearly correct, as electricity is, in reality, "_stored_" in an
accumulator. But when an accumulator is charged by a current of
electricity, a chemical change is gradually produced in the active
element of which the accumulator is made. This change or decomposition
continues so long as the charging current is on. When the accumulator is
disconnected from the charging battery or dynamo, and its terminals are
connected up with a lighting system, or with a motor, for instance, a
reverse process is set up, or the particles re-form themselves into
their original compositions, which causes a current to flow in a
direction opposite to that of the charging current.

It is immaterial to the purposes of this chapter, as to the charging
source, whether it be by batteries or dynamos; the same principles will
apply in either case.

[Illustration: _Fig. 62._ ACCUMULATOR GRIDS]

ACCUMULATOR PLATES.--The elements used for accumulator plates are red
lead for the positive plates, and precipitated lead, or the well-known
litharge, for the negative plates. Experience has shown that the best
way to hold this material is by means of lead grids.

Fig. 62 shows the typical form of one of these grids. It is made of
lead, cast or molded in one piece, usually square, as at A, with a wing
or projection (B), at one margin, extending upwardly and provided with a
hole (C). The grid is about a quarter of an inch thick.

THE GRID.--The open space, called the grid, proper, comprises cross
bars, integral with the plate, made in a variety of shapes. Fig. 62
shows three forms of constructing these bars or ribs, the object being
to provide a form which will hold in the lead paste, which is pressed in
so as to make a solid-looking plate when completed.

THE POSITIVE PLATE.--The positive plate is made in the following manner:
Make a stiff paste of red lead and sulphuric acid; using a solution,
say, of one part of acid to two parts of water. The grid is laid on a
flat surface and the paste forced into the perforations with a stiff
knife or spatula. Turn over the grid so as to get the paste in evenly on
both sides.

The grid is then stood on its edge, from 18 to 20 hours, to dry, and
afterwards immersed in a concentrated solution of chloride of lime, so
as to convert it into lead peroxide. When the action is complete it is
thoroughly rinsed in cold water, and is ready to use.

THE NEGATIVE PLATE.--The negative plate is filled, in like manner, with
precipitated lead. This lead is made by putting a strip of zinc into a
standard solution of acetate of lead, and crystals will then form on the
zinc. These will be very thin, and will adhere together, firmly, forming
a porous mass. This, when saturated and kept under water for a short
time, may be put into the openings of the negative plate.


CONNECTING UP THE PLATES.--The next step is to put these plates in
position to form a battery. In Fig. 63 is shown a collection of plates
connected together.

For simplicity in illustrating, the cell is made up of glass, porcelain,
or hard rubber, with five plates (A), A, A representing the negative and
B, B the positive plates. A base of grooved strips (C, C) is placed in
the batteries of the cell to receive the lower ends of the plates. The
positive plates are held apart by means of a short section of tubing
(D), which is clamped and held within the plates by a bolt (E), this
bolt also being designed to hold the terminal strip (F).

In like manner, the negative plates are held apart by the two tubular
sections (G), each of which is of the same length as the section D of
the positives. The bolt (H) holds the negatives together as well as the
terminal (I). The terminals should be lead strips, and it would be well,
owing to the acid fumes which are formed, to coat all brass work,
screws, etc., with paraffine wax.

The electrolyte or acid used in the cell, for working purposes, is a
pure sulphuric acid, which should be diluted with about four times its
weight in water. Remember, you should always add the strong acid to the
water, and never pour the water into the acid, as the latter method
causes a dangerous ebullition, and does not produce a good mixture.

Put enough of this solution into the cell to cover the tops of the
plates, and the cell is ready.


CHARGING THE CELLS.--The charge of the current must never be less than
2.5 volts. Each cell has an output, in voltage, of about 2 volts, hence
if we have, say, 10 cells, we must have at least 25 volts charging
capacity. We may arrange these in one line, or in series, as it is
called, so far as the connections are concerned, and charge them with a
dynamo, or other electrical source, which shows a pressure of 25 volts,
as illustrated in Fig. 64, or, instead of this, we may put them into two
parallel sets of 5 cells each, as shown in Fig. 65, and use 12.5 volts
to charge with. In this case it will take double the time because we are
charging with only one-half the voltage used in the first case.

The positive pole of the dynamo should be connected with the positive
pole of the accumulator cell, and negative with negative. When this has
been done run up the machine until it slightly exceeds the voltage of
the cells. Thus, if we have 50 cells in parallel, like in Fig. 64, at
least 125 volts will be required, and the excess necessary should bring
up the voltage in the dynamo to 135 or 140 volts.

[Illustration: _Fig. 65._ PARALLEL SERIES]

[Illustration: _Fig. 66._ CHARGING CIRCUIT]

THE INITIAL CHARGE.--It is usual initially to charge the battery from
periods ranging from 36 to 40 hours, and to let it stand for 12 or 15
hours, after which to re-charge, until the positive plates have turned
to a chocolate color, and the negative plates to a slate or gray color,
and both plates give off large bubbles of gas.

In charging, the temperature of the electrolyte should not exceed 100°

When using the accumulators they should never be fully discharged.

THE CHARGING CIRCUIT.--The diagram (Fig. 66) shows how a charging
circuit is formed. The lamps are connected up in parallel, as
illustrated. Each 16-candle-power 105-volt lamp will carry 1/2 ampere,
so that, supposing we have a dynamo which gives 110 volts, and we want
to charge a 4-volt accumulator, there will be 5-volt surplus to go to
the accumulator. If, for instance, you want the cell to have a charge of
2 amperes, four of these lamps should be connected up in parallel. If 3
amperes are required, use 6 lamps, and so on.



The telegraph is a very simple instrument. The key is nothing more or
less than a switch which turns the current on and off alternately.

The signals sent over the wires are simply the audible sounds made by
the armature, as it moves to and from the magnets.

MECHANISM IN TELEGRAPH CIRCUITS.--A telegraph circuit requires three
pieces of mechanism at each station, namely, a key used by the sender, a
sounder for the receiver, and a battery.

THE SENDING KEY.--The base of the sending instrument is six inches long,
four inches wide, and three-quarters of an inch thick, made of wood, or
any suitable non-conducting material. The key (A) is a piece of brass
three-eighths by one-half inch in thickness and six inches long. Midway
between its ends is a cross hole, to receive the pivot pin (B), which
also passes through a pair of metal brackets (C, D), the bracket C
having a screw to hold one of the line wires, and the other bracket
having a metal switch (E) hinged thereto. This switch bar, like the
brackets, is made of brass, one-half inch wide by one-sixteenth of an
inch thick.

Below the forward end of the key (A) is a cross bar of brass (F),
screwed to the base by a screw at one end, to receive the other line
wire. Directly below the key (A) is a screw (G), so that the key will
strike it when moved downwardly. The other end of the bar (F) contacts
with the forward end of the switch bar (E) when the latter is moved

[Illustration: _Fig. 67._ TELEGRAPH SENDING KEY]

The forward end of the key (A) has a knob (H) for the fingers, and the
rear end has an elastic (I) attached thereto which is secured to the end
of the base, so that, normally, the rear end is held against the base
and away from the screw head (G). The head (J) of a screw projects from
the base at its rear end. Key A contacts with it.

When the key A contacts with the screw heads G, J, a click is produced,
one when the key is pressed down and the other when the key is released.

You will notice that the two plates C, F are connected up in circuit
with the battery, so that, as the switch E is thrown, so as to be out of
contact, the circuit is open, and may be closed either by the key A or
the switch E. The use of the switch will be illustrated in connection
with the sounder.

[Illustration: _Fig. 68._ TELEGRAPH SOUNDER]

When the key A is depressed, the circuit of course goes through plate C,
key A and plate F to the station signalled.

THE SOUNDER.--The sounder is the instrument which carries the

In Fig. 68 this is shown in perspective. The base is six inches long and
four inches wide, being made, preferably, of wood. Near the forward end
is mounted a pair of electro-magnets (A, A), with their terminal wires
connected up with plates B, B', to which the line wires are attached.

Midway between the magnets and the rear end of the base is a pair of
upwardly projecting brackets (C). Between these are pivoted a bar (D),
the forward end of which rests between the magnets and carries, thereon,
a cross bar (E) which is directly above the magnets, and serves as the

The rear end of the base has a screw (F) directly beneath the bar D of
such height that when the rear end of the bar D is in contact therewith
the armature E will be out of contact with the magnet cores (A, A). A
spiral spring (G) secured to the rear ends of the arm and to the base,
respectively, serves to keep the rear end of the key normally in contact
with the screw F.

CONNECTING UP THE KEY AND SOUNDER.--Having made these two instruments,
we must next connect them up in the circuit, or circuits, formed for
them, as there must be a battery, a key, and a sounder at each end of
the line.

In Fig. 69 you will note two groups of those instruments. Now observe
how the wires connect them together. There are two line wires, one (A)
which connects up the two batteries, the wire being attached so that
one end connects with the positive terminal of the battery, and the
other end with the negative terminal.

[Illustration: _Fig. 69._ A TELEGRAPH CIRCUIT]

The other line wire (B), between the two stations, has its opposite ends
connected with the terminals of the electro-magnet C of the sounders.
The other terminals of each electro-magnet are connected up with one
terminal of each key by a wire (D), and to complete the circuit at each
station, the other terminal of the key has a wire (E) to its own

TWO STATIONS IN CIRCUIT.--The illustration shows station 2 telegraphing
to station 1. This is indicated by the fact that the switch F' of that
instrument is open, and the switch F of station 1 closed. When,
therefore, the key of station 2 is depressed, a complete circuit is
formed which transmits the current through wire E' and battery, through
line A, then through the battery of station 1, through wire E to the
key, and from the key, through wire D, to the sounder, and finally from
the sounder over line wire B back to the sounder of station 2,
completing the circuit at the key through wire D'.

When the operator at station 2 closes the switch F', and the operator at
station 1 opens the switch F, the reverse operation takes place. In both
cases, however, the sounder is in at both ends of the line, and only the
circuit through the key is cut out by the switch F, or F'.

THE DOUBLE CLICK.--The importance of the double click of the sounder
will be understood when it is realized that the receiving operator must
have some means of determining if the sounder has transmitted a dot or a
dash. Whether he depresses the key for a dot or a dash, there must be
one click when the key is pressed down on the screw head G (Fig. 62),
and also another click, of a different kind, when the key is raised up
so that its rear end strikes the screw head J. This action of the key is
instantly duplicated by the bar D (Fig. 68) of the sounder, so that the
sounder as well as the receiver knows the time between the first and the
second click, and by that means he learns that a dot or a dash is made.

ILLUSTRATING THE DOT AND THE DASH.--To illustrate: Let us suppose, for
convenience, that the downward movement of the lever in the key, and the
bar in the sounder, make a sharp click, and the return of the lever and
bar make a dull click. In this case the ear, after a little practice,
can learn readily how to distinguish the number of downward impulses
that have been given to the key.

_The Morse Telegraph Code_

A . -        N - .       & . ...
B - ...      O ..        1 . - - .
C .. .       P .....     2 .. - ..
D - . .      Q .. - .    3 ... - .
E .          R . ..      4 .... -
F . - .      S ...       5 - - -
G - - .      T -         6 ......
H ....       U .. -      7 - - ..
I ..         V ... -     8 - ....
J - . - .    W . - -     9 - .. -
K - . -      X . - ..    0 ---- ------
L --         Y .. ..
M - -        Z ... .

EXAMPLE IN USE.--Let us take an example in the word "electrical."

E    L    E    C    T    R    I    C    A    L
.   --   .   .. .   -  . ..  ..  .. .  . -  --

The operator first makes a dot, which means a sharp and a dull click
close together; there is then a brief interval, then a lapse, after
which there is a sharp click, followed, after a comparatively longer
interval, with the dull click. Now a dash by itself may be an L, a T, or
the figure 0, dependent upon its length. The short dash is T, and the
longest dash the figure 0. The operator will soon learn whether it is
either of these or the letter L, which is intermediate in length.

In time the sender as well as receiver will give a uniform length to the
dash impulse, so that it may be readily distinguished. In the same way,
we find that R, which is indicated by a dot, is followed, after a short
interval, by two dots. This might readily be mistaken for the single dot
for E and the two dots for I, were it not that the time element in R is
not as long between the first and second dots, as it ordinarily is
between the single dot of E when followed by the two dots of I.



INDUCTION.--One of the most remarkable things in electricity is the
action of induction--that property of an electric current which enables
it to pass from one conductor to another conductor through the air.
Another singular and interesting thing is that the current so
transmitted across spaces changes its direction of flow, and,
furthermore, the tension of such a current may be changed by
transmitting it from one conductor to another.

LOW AND HIGH TENSION.--In order to effect this latter change--that is,
to convert it from a low tension to a high tension--coils are used, one
coil being wound upon the other; one of these coils is called the
primary and the other the secondary. The primary coil receives the
current from the battery, or source of electrical power, and the
secondary coil receives charges, and transmits the current.

For an illustration of this examine Fig. 70, in which you will note a
coil of heavy wire (A), around which is wound a coil of fine wire (B).
If, for instance, the primary coil has a low voltage, the secondary
coil will have a high voltage, or tension. Advantage is taken of this
phase to use a few cells, as a primary battery, and then, by a set of
_Induction Coils_, as they are called, to build up a high-tension
electro-motive force, so that the spark will jump across a gap, as shown
at C, for the purpose of igniting the charges of gas in a gasoline
motor; or the current may be used for medical batteries, and for other

[Illustration: _Fig. 70._ INDUCTION COIL AND CIRCUIT]

The current passes, by induction, from the primary to the secondary
coil. It passes from a large conductor to a small conductor, the small
conductor having a much greater resistance than the large one.

ELASTIC PROPERTY OF ELECTRICITY.--While electricity has no resiliency,
like a spring, for instance, still it acts in the manner of a cushion
under certain conditions. It may be likened to an oscillating spring
acted upon by a bar.

Referring to Fig. 71, we will assume that the bar A in falling down upon
the spring B compresses the latter, so that at the time of greatest
compression the bar goes down as far as the dotted line C. It is obvious
that the spring B will throw the bar upwardly. Now, electricity appears
to have a kind of elasticity, which characteristic is taken advantage of
in order to increase the efficiency of the induction in the coil.

[Illustration: _Fig. 71._ ILLUSTRATING ELASTICITY]

THE CONDENSER.--To make a condenser, prepare two pine boards like A,
say, eight by ten inches and a half inch thick, and shellac thoroughly
on all sides. Then prepare sheets of tinfoil (B), six by eight inches in
size, and also sheets of paraffined paper (C), seven by nine inches in
dimensions. Also cut out from the waste pieces of tinfoil strips (D),
one inch by two inches. To build up the condenser, lay down a sheet of
paraffined paper (C), then a sheet of tinfoil (B), and before putting
on the next sheet of paraffined paper lay down one of the small strips
(D) of tinfoil, as shown in the illustration, so that its end projects
over one end of the board A; then on the second sheet of paraffine paper
lay another sheet of tinfoil, and on this, at the opposite end, place
one of the small strips (D), and so on, using from 50 to 100 of the
tinfoil sheets. When the last paraffine sheet is laid on, the other
board is placed on top, and the whole bound together, either by wrapping
cords around the same or by clamping them together with bolts.

[Illustration: _Fig. 72._ CONDENSER]

You may now make a hole through the projecting ends of the strips, and
you will have two sets of tinfoil sheets, alternately connected together
at opposite ends of the condenser.

Care should be exercised to leave the paraffine sheets perfect or
without holes. You can make these sheets yourself by soaking them in
melted paraffine wax.

CONNECTING UP A CONDENSER.--When completed, one end of the condenser is
connected up with one terminal of the secondary coil, and the other end
of the condenser with the other secondary terminal.

[Illustration: _Fig. 73._ HIGH-TENSION CIRCUIT]

In Fig. 73 a high-tension circuit is shown. Two coils, side by side, are
always used to show an induction coil, and a condenser is generally
shown, as illustrated, by means of a pair of forks, one resting within
the other.

THE INTERRUPTER.--One other piece of mechanism is necessary, and that is
an _Interrupter_, for the purpose of getting the effect of the
pulsations given out by the secondary coil.

A simple current interrupter is made as follows: Prepare a wooden base
(A), one inch thick, six inches wide, and twelve inches long. Upon this
mount a toothed wheel (B), six inches in diameter, of thin sheet metal,
or a brass gear wheel will answer the purpose. The standard (C), which
supports the wheel, may be of metal bent up to form two posts, between
which the crankshaft (D) is journaled. The base of the posts has an
extension plate (E), with a binding post for a wire. At the front end of
the base is an L-shaped strip (F), with a binding post for a wire
connection, and the upwardly projecting part of the strip contacts with
the toothed wheel. When the wheel B is rotated the spring finger (F)
snaps from one tooth to the next, so that, momentarily, the current is
broken, and the frequency is dependent upon the speed imparted to the

[Illustration: _Fig. 74._ CURRENT INTERRUPTER]

USES OF HIGH-TENSION COILS.--This high-tension coil is made use of, and
is the essential apparatus in wireless telegraphy, as we shall see in
the chapter treating upon that subject.



TELEGRAPHING WITHOUT WIRES.--Wireless telegraphy is an outgrowth of the
ordinary telegraph system. When Maxwell, and, later on, Hertz,
discovered that electricity, magnetism, and light were transmitted
through the ether, and that they differed only in their wave lengths,
they laid the foundations for wireless telegraphy. Ether is a substance
which is millions and millions of times lighter than air, and it
pervades all space. It is so unstable that it is constantly in motion,
and this phase led some one to suggest that if a proper electrical
apparatus could be made, the ether would thereby be disturbed
sufficiently so that its impulses would extend out a distance
proportioned to the intensity of the electrical agitation thereby

electricity is sent through a wire, hundreds of miles in length, the
current surges back and forth on the wire many thousands of times a
second. Light comes to us from the sun, over 90,000,000 of miles,
through the ether. It is as reasonable to suppose, or infer, that the
ether can, therefore, convey an electrical impulse as readily as does a

It is on this principle that impulses are sent for thousands of miles,
and no doubt they extend even farther, if the proper mechanism could be
devised to detect movement of the waves so propagated.

THE COHERER.--The instrument for detecting these impulses, or
disturbances, in the ether is generally called a _coherer_, although
detector is the term which is most satisfactory. The name coherer comes
from the first practical instrument made for this purpose.

[Illustration: _Fig. 75._ WIRELESS TELEGRAPHY COHERER]

HOW MADE.--The coherer is simply a tube, say, of glass, within which is
placed iron filings. When the oscillations surge through the secondary
coil the pressure or potentiality of the current finally causes it to
leap across the small space separating the filings and, as it were, it
welds together their edges so that a current freely passes. The
bringing together of the particles, under these conditions, is called

Fig. 75 shows the simplest form of coherer. The posts (A) are firmly
affixed to the base (B), each post having an adjusting screw (C) in its
upper end, and these screw downwardly against and serve to bind a pair
of horizontal rods (D), the inner ends of which closely approach each
other. These may be adjusted so as to be as near together or as far
apart as desired. E is a glass tube in which the ends of the rods (D)
rest, and between the separated ends of the rods (D) the iron filings
(F) are placed.

THE DECOHERERS.--For the purpose of causing the metal filings to fall
apart, or decohere, the tube is tapped lightly, and this is done by a
little object like the clapper of an electric bell.

In practice, the coils and the parts directly connected with it are put
together on one base.

THE SENDING APPARATUS.--Fig. 76 shows a section of a coil with its
connection in the sending station. The spark gap rods (A) may be swung
so as to bring them closer together or farther apart, but they must not
at any time contact with each other.

The induction coil has one terminal of the primary coil connected up by
a wire (B) with one post of a telegraph key, and the other post of the
key has a wire connection (C), with one side of a storage battery. The
other side of the battery has a wire (D) running to the other terminal
of the primary.

[Illustration: _Fig. 76._ WIRELESS SENDING APPARATUS]

The secondary coil has one of its terminals connected with a binding
post (E). This binding post has an adjustable rod with a knob (F) on its
end, and the other binding post (G), which is connected up with the
other terminal of the secondary coil, carries a similar adjusting rod
with a knob (H).

From the post (E) is a wire (I), which extends upwardly, and is called
the aerial wire, or wire for the antennæ, and this wire also connects
with one side of the condenser by a conductor (J). The ground wire (K)
connects with the other binding post (G), and a branch wire (L) also
connects the ground wire (K) with one end of the condenser.


THE RECEIVING APPARATUS.--The receiving station, on the other hand, has
neither condenser, induction coil, nor key. When the apparatus is in
operation, the coherer switch is closed, and the instant a current
passes through the coherer and operates the telegraph sounder, the
galvanometer indicates the current.

Of course, when the coherer switch is closed, the battery operates the

HOW THE CIRCUITS ARE FORMED.--By referring again to Fig. 76, it will be
seen that when the key is depressed, a circuit is formed from the
battery through wire B to the primary coil, and back again to the
battery through wire D. The secondary coil is thereby energized, and,
when the full potential is reached, the current leaps across the gap
formed between the two knobs (F, H), thereby setting up a disturbance in
the ether which is transmitted through space in all directions.

It is this impulse, or disturbance, which is received by the coherer at
the receiving station, and which is indicated by the telegraph sounder.



VIBRATIONS.--Every manifestation in nature is by way of vibration. The
beating of the heart, the action of the legs in walking, the winking of
the eyelid; the impulses from the sun, which we call light; sound, taste
and color appeal to our senses by vibratory means, and, as we have
hereinbefore stated, the manifestations of electricity and magnetism are
merely vibrations of different wave lengths.

THE ACOUSTIC TELEPHONE.--That sound is merely a product of vibrations
may be proven in many ways. One of the earliest forms of telephones was
simply a "sound" telephone, called the _Acoustic Telephone_. The
principle of this may be illustrated as follows:

Take two cups (A, B), as in Fig. 78, punch a small hole through the
bottom of each, and run a string or wire (C) from the hole of one cup to
that of the other, and secure it at both ends so it may be drawn taut.
Now, by talking into the cup (A) the bottom of it will vibrate to and
fro, as shown by the dotted lines and thereby cause the bottom of the
other cup (B) to vibrate in like manner, and in so vibrating it will
receive not only the same amplitude, but also the same character of
vibrations as the cup (A) gave forth.

[Illustration: _Fig. 78._ ACOUSTIC TELEPHONE]

[Illustration: _Fig. 79._ ILLUSTRATING VIBRATIONS]

SOUND WAVES.--Sound waves are long and short; the long waves giving
sounds which are low in the musical scale, and the short waves high
musical tones. You may easily determine this by the following

Stretch a wire, as at B (Fig. 79), fairly tight, and then vibrate it.
The amplitude of the vibration will be as indicated by dotted line A.
Now, stretch it very tight, as at C, so that the amplitude of vibration
will be as shown at E. By putting your ear close to the string you will
find that while A has a low pitch, C is very much higher. This is the
principle on which stringed instruments are built. You will note that
the wave length, which represents the distance between the dotted lines
A is much greater than E.

HEARING ELECTRICITY.--In electricity, mechanism has been made to enable
man to note the action of the current. By means of the armature,
vibrating in front of a magnet, we can see its manifestations. It is now
but a step to devise some means whereby we may hear it. In this, as in
everything else electrically, the magnet comes into play.

[Illustration: _Fig. 80._ THE MAGNETIC FIELD]

In the chapter on magnetism, it was stated that the magnetic field
extended out beyond the magnet, so that if we were able to see the
magnetism, the end of a magnet would appear to us something like a
moving field, represented by the dotted lines in Fig. 80.

The magnetic field is shown in Fig. 80 at only one end, but its
manifestations are alike at both ends. It will be seen that the magnetic
field extends out to a considerable distance and has quite a radius of

THE DIAPHRAGM IN A MAGNETIC FIELD.--If, now, we put a diaphragm (A) in
this magnetic field, close up to the end of the magnet, but not so close
as to touch it, and then push it in and out, or talk into it so that the
sound waves strike it, the movement or the vibration of the diaphragm
(A) will disturb the magnetic field emanating from the magnet, and this
disturbance of the magnetic field at one end of the magnet also affects
the magnetic field at the other end in the same way, so that the
disturbance there will be of the same amplitude. It will also display
the same characteristics as did the magnetic field when the diaphragm
(A) disturbed it.

A SIMPLE TELEPHONE CIRCUIT.--From this simple fact grew the telephone.
If two magnets are connected up in the same circuit, so that the
magnetic fields of the two magnets have the same source of electric
power, the disturbance of one diaphragm will affect the other similarly,
just the same as the two magnetic fields of the single magnet are
disturbed in unison.

HOW TO MAKE A TELEPHONE.--For experimental and testing purposes two of
these telephones should be made at the same time. The case or holder
(A) may be made either of hard wood or hard rubber, so that it is of
insulating material. The core (B) is of soft iron, 3/8 inch in diameter
and 5 inches long, bored and threaded at one end to receive a screw (C)
which passes through the end of the case (A).

The enlarged end of the case should be, exteriorly, 2-1/4 inches in
diameter, and the body of the case 1 inch in diameter.

[Illustration: _Fig. 81._ SECTION OF TELEPHONE RECEIVER]

Interiorly, the large end of the case is provided with a circular recess
1-3/4 inches in diameter and adapted to receive therein a spool which
is, diametrically, a little smaller than the recess. The spool fits
fairly tight upon the end of the core, and when in position rests
against an annular shoulder in the recess. A hollow space (F) is thus
provided behind the spool (D), so the two wires from the magnet may
have room where they emerge from the spool.

The spool is a little shorter than the distance between the shoulder (E)
and the end of the casing, at G, and the core projects only a short
distance beyond the end of the spool, so that when the diaphragm (H) is
put upon the end of the case, and held there by screws (I) it will not
touch the end of the core. A wooden or rubber mouthpiece (J) is then
turned up to fit over the end of the case.

[Illustration: _Fig. 82._ THE MAGNET AND RECEIVER HEAD]

The spool (D) is made of hard rubber, and is wound with No. 24
silk-covered wire, the windings to be well insulated from each other.
The two ends of the wire are brought out, and threaded through holes (K)
drilled longitudinally through the walls of the case, and affixed to the
end by means of screws (L), so that the two wires may be brought
together and connected with a duplex wire (M).

As the screw (C), which holds the core in place, has its head hidden
within a recess, which can be closed up by wax, the two terminals of the
wires are well separated so that short-circuiting cannot take place.

TELEPHONE CONNECTIONS.--The simplest form of telephone connection is
shown in Fig. 83. This has merely the two telephones (A and B), with a
single battery (C) to supply electricity for both. One line wire (D)
connects the two telephones directly, while the other line (E) has the
battery in its circuit.

[Illustration: _Fig. 83._ SIMPLE TELEPHONE CONNECTION]

COMPLETE INSTALLATION.--To install a more complete system requires, at
each end, a switch, a battery and an electro-magneto bell. You may use,
for this purpose, a bell, made as shown in the chapter on bells.

Fig. 84 shows such a circuit. We now dispense with one of the line
wires, because it has been found that the ground between the two
stations serves as a conductor, so that only one line wire (A) is
necessary to connect directly with the telephones of the two stations.
The telephones (B, B', respectively) have wires (C, C') running to the
pivots of double-throw switches (D, D'), one terminal of the switches
having wires (E, E'), which go to electric bells (F, F'), and from the
bells are other wires (G, G'), which go to the ground. The ground wires
also have wires (H, H'), which go to the other terminals of the switch
(D, D'). The double-throw switch (D, D'), in the two stations, is thrown
over so the current, if any should pass through, will go through the
bell to the ground, through the wires (E, G or E', G').

[Illustration: _Fig. 84._ TELEPHONE STATIONS IN CIRCUIT]

Now, supposing the switch (D'), in station 2, should be thrown over so
it contacts with the wire (H'). It is obvious that the current will then
flow from the battery (I') through wires (H', C') and line (A) to
station 1; then through wire C, switch D, wire E to the bell F, to the
ground through wire G. From wire G the current returns through the
ground to station 2, where it flows up wire G' to the battery, thereby
completing the circuit.


The operator at station 2, having given the signal, again throws his
switch (D') back to the position shown in Fig. 84, and the operator at
station 1 throws on his switch (D), so as to ring the bell in station 2,
thereby answering the signal, which means that both switches are again
to be thrown over so they contact with the battery wires (H and H'),
respectively. When both are thus thrown over, the bells (G, G') are cut
out of the circuit, and the batteries are both thrown in, so that the
telephones are now ready for talking purposes.

MICROPHONE.--Originally this form of telephone system was generally
employed, but it was found that for long distances a more sensitive
instrument was necessary.

LIGHT CONTACT POINTS.--In 1877 Professor Hughes discovered,
accidentally, that a light contact point in an electric circuit
augmented the sound in a telephone circuit. If, for instance, a light
pin, or a nail (A, Fig. 85) should be used to connect the severed ends
of a wire (B), the sounds in the telephone not only would be louder, but
they would be more distinct, and the first instrument made practically,
to demonstrate this, is shown in Fig. 86.

[Illustration: _Fig. 86._ MICROPHONE]

[Illustration: _Fig. 87._ TRANSMITTER]

HOW TO MAKE A MICROPHONE.--This instrument has simply a base (A) of
wood, and near one end is a perpendicular sounding-board (B) of wood, to
one side of which is attached, by wax or otherwise, a pair of carbon
blocks (C, D). The lower carbon block (C) has a cup-shaped depression in
its upper side, and the upper block has a similar depression in its
lower side. A carbon pencil (E) is lightly held within these cups, so
that the lightest contact of the upper end of the pencil with the
carbon block, makes the instrument so sensitive that a fly, walking upon
the sounding-board, may be distinctly heard through the telephone which
is in the circuit.

greatly modified, and is now used as a transmitter, the latter thereby
taking the place of the pin (A), shown in Fig. 85.

AUTOMATIC CUT-OUTS FOR TELEPHONES.--In the operation of the telephone,
the great drawback originally was in inducing users of the lines to
replace or adjust their instruments carefully. When switches were used,
they would forget to throw them back, and all sorts of trouble resulted.

It was found necessary to provide an automatic means for throwing in and
cutting out an instrument, this being done by hanging the telephone on
the hook, so that the act merely of leaving the telephone made it
necessary, in replacing the instrument, to cut out the apparatus.

Before describing the circuiting required for these improvements, we
show, in Fig. 87, a section of a transmitter.

A cup-shaped case (A) is provided, made of some insulating material,
which has a diaphragm (B) secured at its open side. This diaphragm
carries the carbon pencil (C) on one side and from the blocks which
support the carbon pencil the wires run to binding posts on the case.
Of course the carbon supporting posts must be insulated from each other,
so the current will go through the carbon pencil (C).

COMPLETE CIRCUITING WITH TRANSMITTER.--In showing the circuiting (Fig.
88) it will not be possible to illustrate the boxes, or casings, which
receive the various instruments. For instance, the hook which carries
the telephone or the receiver, is hinged within the transmitter box. The
circuiting is all that it is intended to show.

[Illustration: _Fig. 88._ COMPLETE TELEPHONIC CIRCUIT]

The batteries of the two stations are connected up by a wire (A), unless
a ground circuit is used. The other side of each battery has a wire
connection (B, B') with one terminal of the transmitter, and the other
terminal of the transmitter has a wire (C, C') which goes to the
receiver. From the other terminal of the receiver is a wire (D, D')
which leads to the upper stop contact (E, E') of the telephone hook. A
wire (F, F') from the lower stop contact (G, G') of the hook goes to one
terminal of the bell, and from the other terminal of the bell is a wire
(H, H') which makes connection with the line wire (A). In order to make
a complete circuit between the two stations, a line wire (I) is run from
the pivot of the hook in station 1 to the pivot of the hook in station

In the diagram, it is assumed that the receivers are on the hooks, and
that both hooks are, therefore, in circuit with the lower contacts (G,
G'), so that the transmitter and receiver are both out of circuit with
the batteries, and the bell in circuit; but the moment the receiver, for
instance, in station 1 is taken off the hook, the latter springs up so
that it contacts with the stop (E), thus establishing a circuit through
the line wire (I) to the hook of station 2, and from the hook through
line (F') to the bell. From the bell, the line (A) carries the current
back to the battery of station (A), thence through the wire (B) to the
transmitter wire (C) to receiver and wire (D) to the post (E), thereby
completing the circuit.

When, at station 2, the receiver is taken off the hook, and the latter
contacts with the post (E'), the transmitter and receiver of both
stations are in circuit with each other, but both bells are cut out.



DECOMPOSING LIQUIDS.--During the earlier experiments in the field of
electricity, after the battery or cell was discovered, it was noted that
when a current was formed in the cell, the electrolyte was charged and
gases evolved from it. A similar action takes place when a current of
electricity passes through a liquid, with the result that the liquid is
decomposed--that is, the liquid is broken up into its original
compounds. Thus, water is composed of two parts, by bulk, of hydrogen
and of oxygen, so that if two electrodes are placed in water, and a
current is sent through the electrodes in either direction, all the
water will finally disappear in the form of hydrogen and oxygen gases.

MAKING HYDROGEN AND OXYGEN.--During this electrical action, the hydrogen
is set free at the negative pole and the oxygen at the positive pole. A
simple apparatus, which any boy can make, to generate pure oxygen and
pure hydrogen, is shown in Fig. 89.

It is constructed of a glass or earthen jar (A), preferably square, to
which is fitted a wooden top (B), this top being provided with a
packing ring (C), so as to make it air-tight. Within is a vertical
partition (D), the edges of which, below the cap, fit tightly against
the inner walls of the jar. This partition extends down into the jar a
sufficient distance so it will terminate below the water level. A pipe
is fitted through the top on each side of the partition, and each pipe
has a valve. An electrode, of any convenient metal, is secured at its
upper end to the top of the cap, on each side of the partition. These
electrodes extend down to the bottom of the jar, and an electric wire
connects with each of them at the top.


If a current of electricity is passed through the wires and the
electrodes, in the direction shown by the darts, hydrogen will form at
the negative pole, and oxygen at the positive pole. These gases will
escape upwardly, so that they will be trapped in their respective
compartments, and may be drawn off by means of the pipes.

PURIFYING WATER.--Advantage is taken of this electrolytic action, to
purify water. Oxygen is the most wonderful chemical in nature. It is
called the acid-maker of the universe. The name is derived from two
words, _oxy_ and _gen_; one denoting oxydation, and the other that it
generates. In other words, it is the _generator of oxides_. It is the
element which, when united with any other element, produces an acid, an
alkali or a neutral compound.

RUST.--For instance, iron is largely composed of ferric acid. When
oxygen, in a free or gaseous state, comes into contact with iron, it
produces ferrous oxide, which is recognized as rust.

OXYGEN AS A PURIFIER.--But oxygen is also a purifier. All low forms of
animal life, like bacteria or germs in water, succumb to free oxygen. By
_free oxygen_ is meant oxygen in the form of gas.

COMPOSITION OF WATER.--Now, water, in which harmful germs live, is
one-third oxygen. Nevertheless, the germs thrive in water, because the
oxygen is in a compound state, and, therefore, not an active agent. But
if oxygen, in the form of gas, can be forced through water, it will
attack the germs, and destroy them.

COMMON AIR NOT A GOOD PURIFIER.--Water may be purified, to a certain
extent, by forcing common air through it, and the foulest water, if run
over rocks, will be purified, in a measure, because air is intermingled
with it. But common air is composed of four-fifths nitrogen, and only
one-fifth oxygen, and, as nitrogen is the staple article of food for
bacteria, the purifying method by air is not effectual.

PURE OXYGEN.--When, however, oxygen is generated from water, by means of
electrolysis, it is pure; hence is more active and is not tainted by a
life-giving substance for germs, such as nitrogen.

The mechanism usually employed for purifying water is shown in Fig. 90.

A WATER PURIFIER.--The case (A, Fig. 90) may be made of metal or of an
insulating material. If made of metal it must be insulated within with
slate, glass, marble or hard rubber, as shown at B. The case is provided
with exterior flanges (C, D), with upper and lower ends, and it is
mounted upon a base plate (E) and affixed thereto by bolts. The upper
end has a conically-formed cap (F) bolted to the flanges (C), and this
has an outlet to which a pipe (G) is attached. The water inlet pipe (H)
passes through the lower end of the case (A). The electrodes (I, J) are
secured, vertically, within the case, separated from each other
equidistant, each alternate electrode being connected up with one wire
(K), and the alternate electrodes with a wire (L).

[Illustration: _Fig. 90._ ELECTRIC WATER PURIFIER]

When the water passes upwardly, the decomposed or gaseous oxygen
percolates through the water and thus attacks the germs and destroys

THE USE OF HYDROGEN IN PURIFICATION.--On the other hand, the hydrogen
also plays an important part in purifying the water. This depends upon
the material of which the electrodes are made. Aluminum is by far the
best material, as it is one of nature's most active purifiers. All clay
contains aluminum, in what is known as the sulphate form, and water
passing through the clay of the earth thereby becomes purified, because
of this element.

ALUMINUM ELECTRODES.--When this material is used as the electrodes in
water, hydrate of aluminum is formed, or a compound of hydrogen and
oxygen with aluminum. The product of decomposition is a flocculent
matter which moves upwardly through the water, giving it a milky
appearance. This substance is like gelatine, so that it entangles or
enmeshes the germ life and prevents it from passing through a filter.

If no filter is used, this flocculent matter, as soon as it has given
off the gases, will settle to the bottom and carry with it all
decomposed matter, such as germs and other organic matter attacked by
the oxygen, which has become entangled in the aluminum hydrate.

ELECTRIC HAND PURIFIER.--An interesting and serviceable little purifier
may be made by any boy with the simplest tools, by cutting out three
pieces of sheet aluminum. Hard rolled is best for the purpose. It is
better to have one of the sheets (A), the middle one, thicker than the
two outer plates (B).

[Illustration: _Fig. 91._ PORTABLE ELECTRIC PURIFIER]

Let each sheet be 1-1/2 inches wide and 5-1/2 inches thick. One-half
inch from the upper ends of the two outside plates (B, B) bore bolt
holes (C), each of these holes being a quarter of an inch from the edge
of the plate. The inside plate (A) has two large holes (D) corresponding
with the small holes (C) in the outside plates. At the upper end of this
plate form a wing (E), 1/2 inch wide and 1/2 inch long, provided with a
small hole for a bolt. Next cut out two hard-rubber blocks (F), each
1-1/2 inches long, 1 inch wide and 3/8 inch thick, and then bore a hole
(G) through each, corresponding with the small holes (C) in the plates
(B). The machine is now ready to be assembled. If the inner plate is 1/8
inch thick and the outer plates each 1/16 inch thick, use two small
eighth-inch bolts 1-1/4 inches long, and clamp together the three
plates with these bolts. One of the bolts may be used to attach thereto
one of the electric wires (H), and the other wire (I) is attached by a
bolt to the wing (E).

[Illustration: _Figs. 92-95._ DETAILS OF PORTABLE PURIFIER]

Such a device will answer for a 110-volt circuit, in ordinary water. Now
fill a glass nearly full of water, and stand the purifier in the glass.
Within a few minutes the action of electrolysis will be apparent by the
formation of numerous bubbles on the plates, followed by the
decomposition of the organic matter in the water. At first the
flocculent decomposed matter will rise to the surface of the water, but
before many minutes it will settle to the bottom of the glass and leave
clear water above.

utilized in metallurgy for the purpose of producing pure metals, but it
is more largely used to separate copper from its base. In order to
utilize a current for this purpose, a high ampere flow and low voltage
are required. The sheets of copper, containing all of its impurities,
are placed within a tank, parallel with a thin copper sheet. The impure
sheet is connected with the positive pole of an electroplating dynamo,
and the thin sheet of copper is connected with the negative pole. The
electrolyte in the tank is a solution of sulphate of copper. The action
of the current will cause the pure copper in the impure sheet to
disintegrate and it is then carried over and deposited upon the thin
sheet, this action continuing until the impure sheet is entirely eaten
away. All the impurities which were in the sheet fall to the bottom of
the tank.

Other metals are treated in the same way, and this treatment has a very
wide range of usefulness.

ELECTROPLATING.--The next feature to be considered in electrolysis is a
most interesting and useful one, because a cheap or inferior metal may
be coated by a more expensive metal. Silver and nickel plating are
brought about by this action of a current passing through metals, which
are immersed in an electrolyte.

PLATING IRON WITH COPPER.--We have room in this chapter for only one
concrete example of this work, which, with suitable modifications, is an
example of the art as practiced commercially. Iron, to a considerable
extent, is now being coated with copper to preserve it from rust. To
carry out this work, however, an electroplating dynamo, of large
amperage, is required, the amperage, of course, depending upon the
surface to be treated at one time. The pressure should not exceed 5

The iron surface to be treated should first be thoroughly cleansed, and
then immediately put into a tank containing a cyanide of copper
solution. Two forms of copper solution are used, namely, the cyanide,
which is a salt solution of copper, and the sulphate, which is an acid
solution of copper. Cyanide is first used because it does not attack the
iron, as would be the case if the sulphate solution should first come
into contact with the iron.

A sheet of copper, termed the anode, is then placed within the tank,
parallel with the surface to be plated, known as the cathode, and so
mounted that it may be adjusted to or from the iron surface, or cathode.
A direct current of electricity is then caused to flow through the
copper plate and into the iron plate or surface, and the plating
proceeded with until the iron surface has a thin film of copper
deposited thereon. This is a slow process with the cyanide solution, so
it is discontinued as soon as possible, after the iron surface has been
completely covered with copper. This copper surface is thoroughly
cleaned off to remove therefrom the saline or alkaline solution, and it
is then immersed within a bath, containing a solution of sulphate of
copper. The current is then thrown on and allowed so to remain until it
has deposited the proper thickness of copper.

DIRECTION OF CURRENT.--If a copper and an iron plate are put into a
copper solution and connected up in circuit with each other, a primary
battery is thereby formed, which will generate electricity. In this
case, the iron will be positive and the copper negative, so that the
current within such a cell would flow from the iron (in this instance,
the anode) to the negative, or cathode.

The action of electroplating reverses this process and causes the
current to flow from the copper to the iron (in this instance, the



GENERATING HEAT IN A WIRE.--When a current of electricity passes through
a conductor, like a wire, more or less heat is developed in the
conductor. This heat may be so small that it cannot be measured, but it
is, nevertheless, present in a greater or less degree. Conductors offer
a resistance to the passage of a current, just the same as water finds a
resistance in pipes through which it passes. This resistance is measured
in ohms, as explained in a preceding chapter, and it is this resistance
which is utilized for electric heating.

RESISTANCE OF SUBSTANCES.--Silver offers less resistance to the passage
of a current than any other metal, the next in order is copper, while
iron is, comparatively, a poor conductor.

The following is a partial list of metals, showing their relative

Silver              1.
Copper              1.04 to 1.09
Gold                1.38 to 1.41
Aluminum            1.64
Zinc                3.79
Nickel              4.69
Iron                6.56
Tin                 8.9
Lead               13.2
German Silver      12.2 to 15

From this table it will be seen that, for instance, iron offers six and
a half times the resistance of silver, and that German silver has
fifteen times the resistance of silver.

This table is made up of strands of the different metals of the same
diameters and lengths, so as to obtain their relative values.

SIZES OF CONDUCTORS.--Another thing, however, must be understood. If two
conductors of the same metal, having different diameters, receive the
same current of electricity, the small conductor will offer a greater
resistance than the large conductor, hence will generate more heat. This
can be offset by increasing the diameter of the conductor. The metal
used is, therefore, of importance, on account of the cost involved.

COMPARISON OF METALS.--A conductor of aluminum, say, 10 feet long and of
the same weight as copper, has a diameter two and a quarter times
greater than copper; but as the resistance of aluminum is 50 per cent.
more than that of silver, it will be seen that, weight for weight,
copper is the cheaper, particularly as aluminum costs fully three times
as much as copper.

[Illustration: _Fig. 96._ SIMPLE ELECTRIC HEATER]

The table shows that German silver has the highest resistance. Of
course, there are other metals, like antimony, platinum and the like,
which have still higher resistance. German silver, however, is most
commonly used, although there are various alloys of metal made which
have high resistance and are cheaper.

The principle of all electric heaters is the same, namely, the
resistance of a conductor to the passage of a current, and an
illustration of a water heater will show the elementary principles in
all of these devices.

A SIMPLE ELECTRIC HEATER.--In Fig. 96 the illustration shows a cup or
holder (A) for the wire, made of hard rubber. This may be of such
diameter as to fit upon and form the cover for a glass (B). The rubber
should be 1/2 inch thick. Two holes are bored through the rubber cup,
and through them are screwed two round-headed screws (C, D), each screw
being 1-1/2 inches long, so they will project an inch below the cap.
Each screw should have a small hole in its lower end to receive a pin
(E) which will prevent the resistance wire from slipping off.

The resistance wire (F) is coiled for a suitable length, dependent upon
the current used, one end being fastened by wrapping it around the screw
(C). The other end of the wire is then brought upwardly through the
interior of the coil and secured in like manner to the other screw (D).

Caution must be used to prevent the different coils or turns from
touching each other. When completed, the coil may be immersed in water,
the current turned on, and left so until the water is sufficiently

[Illustration: _Figs. 97-98._ RESISTANCE DEVICE]

determine just the proper length the coil should be, or the sizes of the
wire, unless you know what kind of current you have. You may, however,
rig up your own apparatus for the purpose of making it fit your heater,
by preparing a base of wood (A) 8 inches long, 3 inches wide and 1 inch
thick. On this mount four electric lamp sockets (B). Then connect the
inlet wire (C) by means of short pieces of wire (D) with all the sockets
on one side. The outlet wire (E) should then be connected up with the
other sides of the sockets by the short wires (F). If, now, we have one
16-candlepower lamp in one of the sockets, there is a half ampere going
through the wires (C, F). If there are two lamps on the board you will
have 1 ampere, and so on. By this means you may readily determine how
much current you are using and it will also afford you a means of
finding out whether you have too much or too little wire in your coil to
do the work.

[Illustration: _Fig. 99._ PLAN VIEW OF ELECTRIC IRON]

AN ELECTRIC IRON.--An electric iron is made in the same way. The upper
side of a flatiron has a circular or oval depression (A) cast therein,
and a spool of slate (B) is made so it will fit into the depression and
the high resistance wire (C) is wound around this spool, and insulating
material, such as asbestos, must be used to pack around it. Centrally,
the slate spool has an upwardly projecting circular extension (D) which
passes through the cap or cover (E) of the iron. The wires of the
resistance coil are then brought through this circular extension and
are connected up with the source of electrical supply. Wires are now
sold for this purpose, which are adapted to withstand an intense heat.

[Illustration: _Fig. 100._ SECTION OF ELECTRIC IRON]

The foregoing example of the use of the current, through resistance
wires, has a very wide application, and any boy, with these examples
before him, can readily make these devices.

THERMO ELECTRICITY.--It has long been the dream of scientists to convert
heat directly into electricity. The present practice is to use a boiler
to generate steam, an engine to provide the motion, and a dynamo to
convert that motion into electricity. The result is that there is loss
in the process of converting the fuel heat into steam; loss to change
the steam into motion, and loss to make electricity out of the motion
of the engine. By using water-power there is less actual loss; but
water-power is not available everywhere.

directly into electricity without using a boiler, an engine or a dynamo,
but it has not been successful from a commercial standpoint. It is
interesting, however, to know and understand the subject, and for that
reason it is explained herein.

METALS; ELECTRIC POSITIVE-NEGATIVE.--To understand the principle, it may
be stated that all metals are electrically positive-negative to each
other. You will remember that it has hereinbefore been stated that if,
for instance, iron and copper are put into an acid solution, a current
will be created or generated thereby. So with zinc and copper, the usual
primary battery elements. In all such cases an electrolyte is used.

Thermo-electricity dispenses with the electrolyte, and nothing is used
but the metallic elements and heat. The word thermo means heat. If, now,
we can select two strips of different metals, and place them as far
apart as possible--that is, in their positive-negative relations with
each other, and unite the end of one with one end of other by means of a
rivet, and then heat the riveted ends, a current will be generated in
the strips. If, for instance, we use an iron in conjunction with a
copper strip, the current will flow from the copper to the iron, because
copper is positive to iron, and iron negative to copper. It is from this
that the term positive-negative is taken.

The two metals most available, which are thus farthest apart in the
scale of positive-negative relation, are bismuth and antimony.

[Illustration: _Fig. 101._ THERMO-ELECTRIC COUPLE]

In Fig. 101 is shown a thermo-electric couple (A, B) riveted together,
with thin outer ends connected by means of a wire (C) to form a circuit.
A galvanometer (D) or other current-testing means is placed in this
circuit. A lamp is placed below the joined ends.

THERMO-ELECTRIC COUPLES.--Any number of these couples may be put
together and joined at each end to a common wire and a fairly large flow
of current obtained thereby.

One thing must be observed: A current will be generated only so long as
there exists a difference in temperature between the inner and the outer
ends of the bars (A, B). This may be accomplished by water, or any other
cooling means which may suggest itself.



DIRECT CURRENT.--When a current of electricity is generated by a cell,
it is assumed to move along the wire in one direction, in a steady,
continuous flow, and is called a _direct_ current. This direct current
is a natural one if generated by a cell.

ALTERNATING CURRENT.--On the other hand, the natural current generated
by a dynamo is alternating in its character--that is, it is not a
direct, steady flow in one direction, but, instead, it flows for an
instant in one direction, then in the other direction, and so on.

A direct-current dynamo such as we have shown in Chapter IV, is much
easier to explain, hence it is illustrated to show the third method used
in generating an electric current.

It is a difficult matter to explain the principle and operation of
alternating current machines, without becoming, in a measure, too
technical for the purposes of this book, but it is important to know the
fundamentals involved, so that the operation and uses of certain
apparatus, like the choking coil, transformers, rectifiers and
converters, may be explained.

THE MAGNETIC FIELD.--It has been stated that when a wire passes through
the magnetic field of a magnet, so as to cut the lines of force flowing
out from the end of a magnet, the wire will receive a charge of

[Illustration: _Fig. 102._ CUTTING A MAGNETIC FIELD]

To explain this, study Fig. 102, in which is a bar magnet (A). If we
take a metal wire (B) and bend it in the form of a loop, as shown, and
mount the ends on journal-bearing blocks, the wire may be rotated so
that the loop will pass through the magnetic field. When this takes
place, the wire receives a charge of electricity, which moves, say, in
the direction of the darts, and will make a complete circuit if the ends
of the looped wire are joined, as shown by the conductor (D).

ACTION OF THE MAGNETIZED WIRE.--You will remember, also that we have
pointed out how, when a current passes over a wire, it has a magnetic
field extending out around it at all points, so that while it is passing
through the magnetic field of the magnet (A), it becomes, in a measure,
a magnet of its own and tries to set up in business for itself as a
generator of electricity. But when the loop leaves the magnetic field,
the magnetic or electrical impulse in the wire also leaves it.

directed, also, to another statement, heretofore made, namely, that when
a current from a charged wire passes by induction to a wire across
space, so as to charge it with an electric current, it moves along the
charged wire in a direction opposite to that of the current in the
charging wire.

Now, the darts show the direction in which the current moves while it is
approaching and passing through the magnetic field. But the moment the
loop is about to pass out of the magnetic field, the current in the loop
surges back in the opposite direction, and when the loop has made a
revolution and is again entering the magnetic field, it must again
change the direction of flow in the current, and thus produce
alternations in the flow thereof.

Let us illustrate this by showing the four positions of the revolving
loop. In Fig. 103 the loop (B) is in the middle of the magnetic field,
moving upwardly in the direction of the curved dart (A), and while in
that position the voltage, or the electrical impulse, is the most
intense. The current used flows in the direction of the darts (C) or to
the left.

In Fig. 104, the loop (A) has gone beyond the influence of the magnetic
field, and now the current in the loop tries to return, or reverse
itself, as shown by the dart (D). It is a reaction that causes the
current to die out, so that when the loop has reached the point farthest
from the magnet, as shown in Fig. 105, there is no current in the loop,
or, if there is any, it moves faintly in the direction of the dart (E).

[Illustration: _Figs. 103-106._ ILLUSTRATING ALTERNATIONS]

CURRENT REVERSING ITSELF.--When the loop reaches its lowest point (Fig.
106) it again comes within the magnetic field and the current commences
to flow back to its original direction, as shown by darts (C).

SELF-INDUCTION.--This tendency of a current to reverse itself, under the
conditions cited, is called self-induction, or inductance, and it would
be well to keep this in mind in pursuing the study of alternating

You will see from the foregoing, that the alternations, or the change of
direction of the current, depends upon the speed of rotation of the loop
past the end of the magnet.

[Illustration: _Figs. 107-108._ FORM FOR INCREASING ALTERNATIONS]

Instead, therefore, of using a single loop, we may make four loops (Fig.
107), which at the same speed as we had in the case of the single loop,
will give four alternations, instead of one, and still further, to
increase the periods of alternation, we may use the four loops and two
magnets, as in Fig. 108. By having a sufficient number of loops and of
magnets, there may be 40, 50, 60, 80, 100 or 120 such alternating
periods in each second. Time, therefore, is an element in the operation
of alternating currents.

Let us now illustrate the manner of connecting up and building the
dynamo, so as to derive the current from it. In Fig. 109, the loop (A)
shows, for convenience, a pair of bearings (B). A contact finger (C)
rests on each, and to these the circuit wire (D) is attached. Do not
confuse these contact fingers with the commutator brushes, shown in the
direct-current motor, as they are there merely for the purpose of making
contact between the revolving loop (A) and stationary wire (D).


BRUSHES IN A DIRECT-CURRENT DYNAMO.--The object of the brushes in the
direct-current dynamo, in connection with a commutator, is to convert
this _inductance_ of the wire, or this effort to reverse itself into a
current which will go in one direction all the time, and not in both
directions alternately.

To explain this more fully attention is directed to Figs. 110 and 111.
Let A represent the armature, with a pair of grooves (B) for the wires.
The commutator is made of a split tube, the parts so divided being
insulated from each other, and in Fig. 110, the upper one, we shall call
and designate the positive (+) and the lower one the negative (-). The
armature wire (C) has one end attached to the positive commutator
terminal and the other end of this wire is attached to the negative

[Illustration: _Fig. 110._ DIRECT CURRENT DYNAMO]

One brush (D) contacts with the positive terminal of the commutator and
the other brush (E) with the negative terminal. Let us assume that the
current impulse imparted to the wire (C) is in the direction of the dart
(F, Fig. 110). The current will then flow through the positive (+)
terminal of the commutator to the brush (D), and from the brush (D)
through the wire (G) to the brush (E), which contacts with the negative
(-) terminal of the commutator. This will continue to be the case, while
the wire (C) is passing the magnetic field, and while the brush (D) is
in contact with the positive (+) terminal. But when the armature makes a
half turn, or when it reaches that point where the brush (D) contacts
with the negative (-) terminal, and the brush (E) contacts with the
positive (+) terminal, a change in the direction of the current through
the wire (G) takes place, unless something has happened to change it
before it has reached the brushes (D, E).


Now, this change is just exactly what has happened in the wire (C), as
we have explained. The current attempts to reverse itself and start out
on business of its own, so to speak, with the result that when the
brushes (D and E) contact with the negative and positive terminals,
respectively, the surging current in the wire (C) is going in the
direction of the dart (H)--that is, while, in Fig. 110, the current
flows from the wire (C) into the positive terminal, and out of the
negative terminal into the wire (C), the conditions are exactly reversed
in Fig. 111. Here the current in wire C flows _into_ the negative (-)
terminal, and _from_ the positive (+) terminal into the wire C, so that
in either case the current will flow out of the brush D and into the
brush E, through the external circuit (G).

It will be seen, therefore, that in the direct-current motor, advantage
is taken of the surging, or back-and-forth movement, of the current to
pass it along in one direction, whereas in the alternating current no
such change in direction is attempted.

owing to this surging movement, makes the poles alternately positive and
negative. To express this more clearly, supposing we take a line (A,
Fig. 112), which is called the zero line, or line of no electricity. The
current may be represented by the zigzag line (B). The lines (B) above
zero (A) may be designated as positive, and those below the line as
negative. The polarity reverses at the line A, goes up to D, which is
the maximum intensity or voltage above zero, and, when the current falls
and crosses the line A, it goes in the opposite direction to E, which is
its maximum voltage in the other direction. In point of time, if it
takes one second for the current to go from C to F, on the down line,
then it takes only a half second to go from C to G, so that the line A
represents the time, and the line H the intensity, a complete cycle
being formed from C, D, F, then through F, E, C, and so on.

[Illustration: _Fig. 112._ ALTERNATING POLARITY LINES]

HOW AN ALTERNATING DYNAMO IS MADE.--It is now necessary to apply these
principles in the construction of an alternating-current machine. Fig.
113 is a diagram representing the various elements, and the circuiting.

[Illustration: _Fig. 113._ ALTERNATING CURRENT DYNAMO]

Let A represent the ring or frame containing the inwardly projecting
field magnet cores (B). C is the shaft on which the armature revolves,
and this carries the wheel (D), which has as many radially disposed
magnet cores (E) as there are of the field magnet cores (B).

The shaft (C) also carries two pulleys with rings thereon. One of these
rings (F) is for one end of the armature winding, and the other ring
(G) for the other end of the armature wire.

THE WINDINGS.--The winding is as follows: One wire, as at H, is first
coiled around one magnet core, the turnings being to the right. The
outlet terminal of this wire is then carried to the next magnet core and
wound around that, in the opposite direction, and so on, so that the
terminal of the wire is brought out, as at I, all of these wires being
connected to binding posts (J, J'), to which, also, the working circuits
are attached.

THE ARMATURE WIRES.--The armature wires, in like manner, run from the
ring (G) to one armature core, being wound from right to left, then to
the next core, which is wound to the right, afterward to the next core,
which is wound to the left, and so on, the final end of the wire being
connected up with the other ring (F). The north (N) and the south (S)
poles are indicated in the diagram.

CHOKING COIL.--The self-induction in a current of this kind is utilized
in transmitting electricity to great distances. Wires offer resistance,
or they impede the flow of a current, as hereinbefore stated, so that it
is not economical to transmit a direct current over long distances. This
can be done more efficiently by means of the alternating current, which
is subject to far less loss than is the case with the direct current.
It affords a means whereby the flow of a current may be checked or
reduced without depending upon the resistance offered by the wire over
which it is transmitted. This is done by means of what is called a
choking coil. It is merely a coil of wire, wound upon an iron core, and
the current to be choked passes through the coil. To illustrate this,
let us take an arc lamp designed to use a 50-volt current. If a current
is supplied to it carrying 100 volts, it is obvious that there are 50
volts more than are needed. We must take care of this excess of 50 volts
without losing it, as would happen were we to locate a resistance of
some kind in the circuit. This result we accomplish by the introduction
of the choking coil, which has the effect of absorbing the excessive 50
volts, the action being due to its quality of self-induction, referred
to in the foregoing.

[Illustration: _Fig. 114._ CHOKING COIL]

In Fig. 114, A is the choking coil and B an arc lamp, connected up, in
series, with the choking coil.

THE TRANSFORMER.--It is more economical to transmit 10,000 volts a long
distance than 1,000 volts, because the lower the pressure, or the
voltage, the larger must be the conductor to avoid loss. It is for this
reason that 500 volts, or more, are used on electric railways. For
electric light purposes, where the current goes into dwellings, even
this is too high, so a transformer is used to take a high-voltage
current from the main line and transform it into a low voltage. This is
done by means of two distinct coils of wire, wound upon an iron core.

[Illustration: _Fig. 115._ A TRANSFORMER]

In Fig. 115 the core is O-shaped, so that a primary winding (A), from
the electrical source, can be wound upon one limb, and the secondary
winding (B) wound around the other limb. The wires, to supply the
lamps, run from the secondary coil. There is no electrical connection
between the two coils, but the action from the primary to the secondary
coil is solely by induction. When a current passes through the primary
coil, the surging movement, heretofore explained, is transmitted to the
iron core, and the iron core, in turn, transmits this electrical energy
to the secondary coil.

HOW THE VOLTAGE IS DETERMINED.--The voltage produced by the secondary
coil will depend upon several things, namely, the strength of the
magnetism transmitted to it; the rapidity, or periodicity of the
current, and the number of turns of wire around the coil. The voltage is
dependent upon the length of the winding. But the voltage may also be
increased, as well as decreased. If the primary has, we will say, 100
turns of wire, and has 200 volts, and the secondary has 50 turns of
wire, the secondary will give forth only one-half as much as the
primary, or 100 volts.

If, on the other hand, 400 volts would be required, the secondary should
have 200 turns in the winding.

VOLTAGE AND AMPERAGE IN TRANSFORMERS.--It must not be understood that,
by increasing the voltage in this way, we are getting that much more
electricity. If the primary coil, with 100 turns, produces a current of
200 volts and 50 amperes, which would be 200 × 50 = 10,000 watts, and
the secondary coil has 50 turns, we shall have 100 volts and 100
amperes: 100 (V.) × 100 (A.) = 10,000 watts. Or, if, on the other hand,
our secondary winding is composed of 200 turns, we shall have 400 volts
and 25 amperes, 400 (volts) × 25 (amperes) also gives 10,000 watts.

Necessarily, there will be some loss, but the foregoing is offered as
the theoretical basis of calculation.



The most important step in the electric field, after the dynamo had been
brought to a fairly workable condition, was its utilization to make
light. It was long known prior to the discovery of practical electric
dynamos, that the electric current would produce an intense heat.

Ordinary fuels under certain favorable conditions will produce a
temperature of 4,500 degrees of heat; but by means of the electric arc,
as high as six, eight and ten thousand degrees are available.

The fact that when a conductor, in an electric current, is severed, a
spark will follow the drawing part of the broken ends, led many
scientists to believe, even before the dynamo was in a practical shape,
that electricity, sooner or later, would be employed as the great
lighting agent.

When the dynamo finally reached a stage in development where its
operation could be depended on, and was made reversible, the first
active steps were taken to not only produce, but to maintain an arc
between two electrodes.

It would be difficult and tedious to follow out the first experiments
in detail, and it might, also, be useless, as information, in view of
the present knowledge of the science. A few steps in the course of the
development are, however, necessary to a complete understanding of the

Reference has been made in a previous chapter to what is called the
_Electric Arc_, produced by slightly separated conductors, across which
the electric current jumps, producing the brilliantly lighted area.

This light is produced by the combustion of the carbon of which the
electrodes are composed. Thus, the illumination is the result of
directly burning a fuel. The current, in passing from one electrode to
the other, through the gap, produces such an intense heat that the fuel
through which the current passes is consumed.

Carbon in a comparatively pure state is difficult to ignite, owing to
its great resistance to heat. At about 7,000 degrees it will fuse, and
pass into a vapor which causes the intense illumination.

The earliest form of electric lighting was by means of the arc, in which
the light is maintained so long as the electrodes were kept a certain
distance apart.

To do this requires delicate mechanism, for the reason that when contact
is made, and the current flows through the two electrodes, which are
connected up directly with the coils of a magnet, the cores, or
armatures, will be magnetized. The result is that the electrode,
connected with the armature of the magnet, is drawn away from the other
electrode, and the arc is formed, between the separated ends.

As the current also passes through a resistance coil, the moment the
ends of the electrodes are separated too great a distance, the
resistance prevents a flow of the normal amount of current, and the
armature is compelled to reduce its pull. The effect is to cause the two
electrodes to again approach each other, and in doing so the arc becomes

It will be seen, therefore, that there is a constant fight between the
resistance coil and the magnet, the combined action of the two being
such, that, if properly arranged, and with powers in correct relation to
each other, the light may be maintained without undue flickering. Such
devices are now universally used, and they afford a steady and reliable
means of illumination.

Many improvements are made in this direction, as well as in the
ingredients of the electrodes. A very novel device for assuring a
perfect separation at all times between the electrodes, is by means of a
pair of parallel carbons, held apart by a non-conductor such as clay, or
some mixture of earth, a form of which is shown in Fig. 116.

The drawing shows two electrodes, separated by a non-conducting
material, which is of such a character that it will break down and
crumble away, as the ends of the electrodes burn away.

[Illustration: _Fig. 116. Parallel Carbons._]

This device is admirable where the alternating current is used, because
the current moves back and forth, and the two electrodes are thus burned
away at the same rate of speed.

In the direct or continuous current the movement is in one direction
only, and as a result the positive electrode is eaten away twice as fast
as the negative.

This is the arc form of lamp universally used for lighting large spaces
or areas, such as streets, railway stations, and the like. It is
important also as the means for utilizing searchlight illumination, and
frequently for locomotive headlights.

Arc lights are produced by what is called the _series current_. This
means that the lamps are all connected in a single line. This is
illustrated by reference to Fig. 117, in which A represents the wire
from the dynamo, and B, C the two electrodes, showing the current
passing through from one lamp to the next.

[Illustration: _Fig. 117. Arc-Lighting Circuit._]

A high voltage is necessary in order to cause the current to leap across
the gap made by the separation of the electrodes.

THE INCANDESCENT SYSTEM.--This method is entirely different from the arc
system. It has been stated that certain metals conduct electricity with
greater facility than others, and some have higher resistance than
others. If a certain amount of electricity is forced through some
metals, they will become heated. This is true, also, if metals, which,
ordinarily, will conduct a current freely, are made up into such small
conductors that it is difficult for the current to pass.

[Illustration: _Fig 118. Interrupted Conductor._]

In the arc method high voltage is essential; in the incandescent plan,
current is the important consideration. In the arc, the light is
produced by virtue of the break in the line of the conductor; in the
incandescent, the system is closed at all times.

Supposing we have a wire A, a quarter of an inch in diameter, carrying a
current of, say, 500 amperes, and at any point in the circuit the wire
is made very small, as shown at B, in Fig. 118, it is obvious that the
small wire would not be large enough to carry the current.

The result would be that the small connection B would heat up, and,
finally, be fused. While the large part of the wire would carry 500
amperes, the small wire could not possibly carry more than, say, 10
amperes. Now these little wires are the filaments in an electric bulb,
and originally the attempt was made to have them so connected up that
they could be illuminated by a single wire, as with the arc system above
explained, one following the other as shown in Fig. 117.

[Illustration: _Fig. 119. Incandescent Circuit._]

It was discovered, however, that the addition of each successive lamp,
so wired, would not give light in proportion to the addition, but at
only about one-fourth the illumination, and such a course would,
therefore, make electric lighting enormously expensive.

This knowledge resulted in an entirely new system of wiring up the lamps
in a circuit. This is explained in Fig. 119. In this figure A represents
the dynamo, B, B the brushes, C, D the two line wires, E the lamps, and
F the short-circuiting wires between the two main conductors C, D.

It will be observed that the wires C, D are larger than the cross wires
F. The object is to show that the main wires might carry a very heavy
amperage, while the small cross wires F require only a few amperes.

This is called the _multiple_ circuit, and it is obvious that the entire
amperage produced by the dynamo will not be required to pass through
each lamp, but, on the other hand, each lamp takes only enough necessary
to render the filament incandescent.

This invention at once solved the problem of the incandescent system and
was called the subdivision of the electric light. By this means the cost
was materially reduced, and the wiring up and installation of lights
materially simplified.

But the divisibility of the light did not, by any means, solve the great
problem that has occupied the attention of electricians and
experimenters ever since. The great question was and is to preserve the
little filament which is heated to incandescence, and from which we get
the light.

The effort of the current to pass through the small filament meets with
such a great resistance that the substance is heated up. If it is made
of metal there is a point at which it will fuse, and thus the lamp is

It was found that carbon, properly treated, would heat to a brilliant
white heat without fusing, or melting, so that this material was
employed. But now followed another difficulty. As this intense heat
consumed the particles of carbon, owing to the presence of oxygen, means
were sought to exclude the air.

This was finally accomplished by making a bulb of glass, from which the
air was exhausted, and as such a globe had no air to support combustion,
the filaments were finally made so that they would last a long time
before being finally disintegrated.

The quest now is, and has been, to find some material of a purely
metallic character, which will have a very high fusing point, and which
will, therefore, dispense with the cost of the exhausted bulb. Some
metals, as for instance, osmium, tantalum, thorium, and others, have
been used, and others, also, with great success, so that the march of
improvements is now going forward with rapid strides.

VAPOR LAMPS.--One of the directions in which considerable energy has
been directed in the past, was to produce light from vapors. The Cooper
Hewitt mercury vapor lamp is a tube filled with the vapor of mercury,
and a current is sent through the vapor which produces a greenish
light, and owing to that peculiar color, has not met with much success.

It is merely cited to show that there are other directions than the use
of metallic conductors and filaments which will produce light, and the
day is no doubt close at hand when we may expect some important
developments in the production of light by means of the Hertzian waves.

DIRECTIONS FOR IMPROVEMENTS.--Electricity, however, is not a cheap
method of illumination. The enormous heat developed is largely wasted.
The quest of the inventor is to find a means whereby light can be
produced without the generation of the immense heat necessary.

Man has not yet found a means whereby he can make a heat without
increasing the temperature, as nature does it in the glow worm, or in
the firefly. A certain electric energy will produce both light and heat,
but it is found that much more of this energy is used in the heat than
in the light.

What wonderful possibilities are in store for the inventor who can make
a heatless light! It is a direction for the exercise of ingenuity that
will well repay any efforts.

_Curious Superstitions Concerning Electricity_

Electricity, as exhibited in light, has been the great marvel of all
times. The word electricity itself comes from the thunderbolt of the
ancient God Zeus, which is known to be synonymous with the thunderbolt
and the lightning.

Magnetism, which we know to be only another form of electricity, was not
regarded the same as electricity by the ancients. Iron which had the
property to attract, was first found near the town of Magnesia, in
Lydia, and for that reason was called magnetism.

Later on, a glimmer of the truth seemed to dawn on the early scientists,
when they saw the resemblance between the actions of the amber and the
loadstone, as both attracted particles. And here another curious thing
resulted. Amber will attract particles other than metals. The magnet did
not; and from this imperfect observation and understanding, grew a
belief that electricity, or magnetism would attract all substances, even
human flesh, and many devices were made from magnets, and used as cures
for the gout, and to affect the brain, or to remove pain.

Even as early as 2,500 years before the birth of Christ the Chinese knew
of the properties of the magnet, and also discovered that a bar of the
permanent magnet would arrange itself north and south, like the
mariners' compass. There is no evidence, however, that it was used as a
mariner's compass until centuries afterwards.

But the matter connected with light, as an electrical development, which
interests us, is its manifestations to the ancients in the form of
lightning. The electricity of the earth concentrates itself on the tops
of mountains, or in sharp peaks, and accounts for the magnificent
electrical displays always found in mountainous regions.

Some years ago, a noted scientist, Dr. Siemens, while standing on the
top of the great pyramid of Cheops, in Egypt, during a storm, noted that
an electrical discharge flowed from his hand when extended toward the
heavens. The current manifested itself in such a manner that the hissing
noise was plainly perceptible.

The literature of all ages and of all countries shows that this
manifestation of electrical discharges was noted, and became the subject
of discussions among learned men.

All these displays were regarded as the bolts of an angry God, and
historians give many accounts of instances where, in His anger, He sent
down the lightning to destroy.

Among the Romans Jupiter thus hurled forth his wrath; and among many
ancient people, even down to the time of Charlemagne, any space struck
by lightning was considered sacred, and made consecrated ground.

From this grew the belief that it was sacrilegious to attempt to imitate
the lightning of the sky--that Deity would visit dire punishment on any
man who attempted to produce an electric light. Virgil relates accounts
where certain princes attempted to imitate the lightning, and were
struck by thunderbolts as punishments.

Less than a century ago Benjamin Franklin devised the lightning rod, in
order to prevent lightning from striking objects. The literature of that
day abounds with instances of protests made, on the part of those who
were as superstitions as the people in ancient times, who urged that it
was impious to attempt to ward off Heaven's lightnings. It was argued
that the lightning was one way in which the Creator manifested His
displeasure, and exercised His power to strike the wicked.

When such writers as Pliny will gravely set forth an explanation of the
causes of lightning, as follows in the paragraph below, we can
understand why it inculcated superstitious fears in the people of
ancient times. He says:

"Most men are ignorant of that secret, which, by close observation of
the heavens, deep scholars and principal men of learning have found
out, namely, that they are the fires of the uppermost planets, which,
falling to the earth, are called lightning; but those especially which
are seated in the middle, that is about Jupiter, perhaps because
participating in the excessive cold and moisture from the upper circle
of Saturn, and the immoderate heat of Mars, that is next beneath, by
this means he discharges his superfluity, and therefore it is commonly
said, 'That Jupiter shooteth and darteth lightning.' Therefore, like as
out of a burning piece of wood a coal flieth forth with a crack, even so
from a star is spit out, as it were, and voided forth this celestial
fire, carrying with it presages of future things; so that the heavens
showeth divine operations, even in these parcels and portions which are
rejected and cast away as superfluous."



It would be difficult to mention any direction in human activity where
electricity does not serve as an agent in some form or manner. Man has
learned that the Creator gave this great power into the hands of man to
use, and not to curse.

When the dynamo was first developed it did not appear possible that it
could generate electricity, and then use that electricity in order to
turn the dynamo in the opposite direction. It all seems so very natural
to us now, that such a thing should practically follow; but man had to
learn this.

Let us try to make the statement plain by a few simple illustrations. By
carefully going over the chapter on the making of the dynamo, it will be
evident that the basis of the generation of the current depends on the
changing of the direction of the flow of an electric current.

Look at the simple horse-shoe magnet. If two of them are gradually moved
toward each other, so that the north pole of one approaches the north
pole of the other, there is a sensible attempt for them to push away
from each other. If, however, one of them is turned, so that the north
pole of one is opposite the south pole of the other, they will draw

In this we have the foundation physical action of the dynamo and the
motor. When power is applied to an armature, and it moves through a
magnetic field, the action is just the same as in the case of the hand
drawing the north and the south pole of the two approaching magnets from
each other.

The influence of the electrical disturbance produced by that act
permeated the entire winding of the field and armature, and extended out
on the whole line with which the dynamo was connected. In this way a
current was established and transmitted, and with proper wires was sent
in the form of circuits and distributed so as to do work.

But an electric current, without suitable mechanism, is of no value. It
must have mechanism to use it, as well as to make it. In the case of
light, we have explained how the arc and the incandescent lamps utilize
it for that purpose.

But now, attempting to get something from it in the way of power, means
another piece of mechanism. This is done by the motor, and this motor is
simply a converter, or a device for reversing the action of the

Attention is called to Figs. 120 and 121. Let us assume that the field
magnets A, A are the positives, and the magnets B, B the negatives. The
revolving armature has also four magnet coils, two of them, C, C, being
positive, and the other two, D, D, negative, each of these magnet coils
being so connected up that they will reverse the polarities of the

[Illustration: _Figs. 120-121._ ACTION OF MAGNETS IN A DYNAMO]

Now in the particular position of the revolving armature, in Fig. 120,
the magnets of the armature have just passed the respective poles of the
field magnets, and the belt E is compelled to turn the armature past the
pole pieces by force in the direction of the arrow F. After the armature
magnets have gone to the positions in Fig. 121, the positives A try to
draw back the negatives D of the armature, and at the same time the
negatives B repel the negatives D, because they are of the same

This repulsion of the negatives A, B continues until the armature poles
C, D have slightly passed them, when the polarities of the magnets C, D
are changed; so that it will be seen, by reference to Fig. 122, that D
is now retreating from B, and C is going away from A--that is, being
forced away contrary to their natural attractive influences, and in Fig.
123, when the complete cycle is nearly finished, the positives are again
approaching each other and the negatives moving together.

[Illustration: _Figs. 122-123._ CYCLE ACTION IN DYNAMO]

In this manner, at every point, the sets of magnets are compelled to
move against their magnetic pull. This explains the dynamo.

Now take up the cycle of the motor, and note in Fig. 124 that the
negative magnets D of the armature are closely approaching the positive
and negative magnets, on one side; and the positive magnets C are
nearing the positive and negatives on the other side. The positives A,
therefore, attract the negatives D, and the negative B exert a pull on
the positives C at the same time. The result is that the armature is
caused to revolve, as shown by the dart G, in a direction opposite to
the dart in Fig. 120.

[Illustration: _Figs. 124-125._ ACTION OF MAGNETS IN MOTOR]

When the pole pieces of the magnets C, D are about to pass magnets A, B,
as shown in Fig. 125, it is necessary to change the polarities of the
armature magnets C, D; so that by reference to Fig. 126, it will be seen
that they are now indicated as C-, and D+, respectively, and have moved
to a point midway between the poles A, B (as in Fig. 125), where the
pull on one side, and the push on the other are again the same, and the
last Figure 127 shows the cycle nearly completed.

The shaft of the motor armature is now the element which turns the
mechanism which is to be operated. To convert electrical impulses into
power, as thus shown, results in great loss. The first step is to take
the steam boiler, which is the first stage in that source which is the
most common and universal, and by means of fuel, converting water into
steam. The second is to use the pressure of this steam to drive an
engine; the third is to drive the dynamo which generates the electrical
impulse; and the fourth is the conversion from the dynamo into a motor
shaft. Loss is met with at each step, and the great problem is to
eliminate this waste.

[Illustration: _Figs. 126-127._ POSITIONS OF MAGNETS IN MOTOR]

The great advantage of electrical power is not in utilizing it for
consumption at close ranges, but where it is desired to transmit it for
long distances. Such illustrations may be found in electric railways,
and where water power can be obtained as the primal source of energy,
the cost is not excessive. It is found, however, that even with the most
improved forms of mechanism, in electrical construction, the internal
combustion engines are far more economical.

_Transmission of Energy_

One of the great problems has been the transmission of the current to
great distances. By using a high voltage it may be sent hundreds of
miles, but to use a current of that character in the cars, or shops, or
homes, would be exceedingly dangerous.

To meet this requirement transformers have been devised, which will take
a current of very high voltage, and deliver a current of low tension,
and capable of being used anywhere with the ordinary motors.

THE TRANSFORMER.--This is an electrical device made up of a core or
cores of thin sheet metal, around which is wound sets of insulated
wires, one set being designed to receive the high voltage, and the other
set to put out the low voltage, as described in a former chapter.

These may be made where the original output is a very high voltage, so
that they will be stepped down, first from one voltage to a lower, and
then from that to the next lower stage. This is called the "Step down"
transformer, and is now used over the entire world, where large voltages
are generated.

ELECTRIC FURNACES.--The most important development of electricity in the
direction of heat is its use in furnaces. As before stated, an intense
heat is capable of being generated by the electric current, so that it
becomes the great agent to use for the treatment of refractory material.

In furnaces of this kind the electric arc is the mechanical form used to
produce the great heat, the only difference being in the size of the
apparatus. The electric furnace is simply an immense form of arc light,
capable of taking a high voltage, and such an arc is enclosed within a
suitable oven of refractory material, which still further conserves the

WELDING BY ELECTRICITY.--The next step is to use the high heat thus
capable of being produced, to fuse metals so that they may be welded
together. It is a difficult matter to unite two large pieces of metal by
the forging method, because the highest heat is required, owing to their
bulk, and in addition immense hammers, weighing tons, must be employed.

Electric welding offers a simple and easy method of accomplishing the
result, and in the doing of which it avoids the oxidizing action of the
forging heat. Instead of heating the pieces to be welded in a forge, as
is now done, the ends to be united are simply brought into contact, and
the current is sent through the ends until they are in a soft condition,
after which the parts are pressed together and united by the simple
merging of the plastic condition in which they are reduced by the high
electric heat.

This form of welding makes the most perfect joint, and requires no
hammering, as the mass of the metal flows from one part or end to the
other; the unity is a perfect one, and the advantage is that the metals
can be kept in a semi-fluid state for a considerable time, thus assuring
a perfect admixture of the two parts.

With the ordinary form of welding it is necessary to drive the heated
parts together without any delay, and at the least cooling must be
reheated, or the joint will not be perfect.

The smallest kinds of electric heating apparatus are now being made, so
that small articles, sheet metal, small rods, and like parts can be
united with the greatest facility.



The camera sees things invisible to the human eye. Its most effective
work is done with beams which are beyond human perception. The
photographer uses the _Actinic_ rays. Ordinary light is composed of the
seven primary colors, of which the lowest in the scale is the red, and
the highest to violet.

Those below the red are called the Infra-red, and they are the Hertzian
waves, or those used in wireless telegraphy. Those above the violet are
called Ultra-violet, and these are employed for X-ray work. The former
are produced by the high tension electric apparatus, which we have
described in the chapter relating to wireless telegraphy; and the
latter, called also the Roentgen rays, are generated by the Crookes'

This is a tube from which all the atmosphere has been extracted so that
it is a practical vacuum. Within this are placed electrodes so as to
divert the action of the electrical discharge in a particular direction,
and this light, when discharged, is of such a peculiar character that
its discovery made a sensation in the scientific world.

The reason for this great wonder was not in the fact that it projected a
light, but because of its character. Ordinary light, as we see it with
the eye, is capable of being reflected, as when we look into a mirror at
an angle. The X-ray will not reflect, but instead, pass directly through
the glass.

Then, ordinary light is capable of refraction. This is shown by a ray of
light bending as it passes through a glass of water, which is noticed
when the light is at an angle to the surface.

The X-ray will pass through the water without being changed from a
straight line. The foregoing being the case, it was but a simple step to
conclude that if it were possible to find a means whereby the human eye
could see within the ultra-violet beam, it would be possible to see
through opaque substances.

From the discovery so important and far reaching it was not long until
it was found that if the ultra-violet rays, thus propagated, were
transmitted through certain substances, their rates of vibration would
be brought down to the speeds which send forth the visible rays, and now
the eye is able to see, in a measure at least, what the actinic rays

This discovery was but the forerunner of a still more important
development, namely, the discovery of _radium_. The actual finding of
the metal was preceded by the knowledge that certain minerals, and
water, as well, possessed the property of radio-activity.

Radio-activity is a word used to express that quality in metals or other
material by means of which obscure rays are emitted, that have the
capacity of discharging electrified bodies, and the power to ionize
gases, as well as to actually affect photograph plates.

Certain metals had this property to a remarkable degree, particularly
uranium, thorium, polonium, actinium, and others, and in 1898 the
Curies, husband and wife, French chemists, isolated an element, very
ductile in its character, which was a white metal, and had a most
brilliant luster.

Pitchblende, the base metal from which this was extracted, was
discovered to be highly radio-active, and on making tests of the product
taken from it, they were surprised to find that it emitted a form of
energy that far exceeded in calculations any computations made on the
basis of radio-activity in the metals hitherto examined.

But this was not the most remarkable part of the developments. The
energy, whatever it was, had the power to change many other substances
if brought into close proximity. It darkens the color of diamonds,
quartz, mica, and glass. It changes some of the latter in color, some
kinds being turned to brown and others into violet or purple tinges.

Radium has the capacity to redden the skin, and affect the flesh of
persons, even at some considerable distance, and it is a most powerful
germicide, destroying bacteria, and has been found also to produce some
remarkable cures in diseases of a cancerous nature.

The remarkable similarity of the rays propagated by this substance, with
the X-rays, lead many to believe that they are electrical in their
character, and the whole scientific world is now striving to use this
substance, as well as the more familiar light waves of the Roentgen
tube, in the healing of diseases.

It is not at all remarkable that this use of it should first be
considered, as it has been the history of the electrical developments,
from the earliest times, that each successive stage should find
advocates who would urge its virtues to heal the sick.

It was so when the dynamo was invented, when the high tension current
was produced; and electrical therapeutics became a leading theme when
transmission by induction became recognized as a scientific fact.

It is not many years since the X-rays were discovered, and the first
announcement was concerning its wonderful healing powers.

This was particularly true in the case of radium, but for some reason,
after the first tests, all experimenters were thwarted in their
theories, because the science, like all others, required infinite
patience and experience. It was discovered, in the case of the X-ray,
that it must be used in a modified form, and accordingly, various
modifications of the waves were introduced, called the _m_ and the _n_
rays, as well as many others, each having some peculiar qualification.

In time, no doubt, the investigators will find the right quality for
each disease, and learn how to apply it. Thus, electricity, that most
alluring thing which, in itself, cannot be seen, and is of such a
character that it cannot even be defined in terms which will suit the
exact scientific mind, is daily bringing new wonders for our
investigation and use.

It is, indeed, a study which is so broad that it has no limitations, and
a field which never will be exhausted.



Acid.             Accumulator material is sulphuric acid, diluted
                    with water.

Active            That part of the material in accumulator plates
  Material.         which is acted upon by the electric current.

Accumulator.      A cell, generally known as a storage battery, which
                    while it initially receives a charge of electricity,
                    is nevertheless, of such a character, owing to the
                    active material of which it is made, that it
                    accumulates, or, as it were, generates electricity.

Aerial Wire,      The wire which, in wireless  telegraphy, is carried
  or Conductor.     up into the air to connect the antennæ with the
                    receiving and sending apparatus.

Alarm, Burglar.   A circulating system in a building, connected up with
                    a bell or other signaling means.

Alloy.            A mixture of two or more metals; as copper and zinc
                    to make brass; nickel and zinc to form German silver.

Alternating Current. A current which goes back and forth in opposite
                    directions, unlike a direct current which flows
                    continuously in one direction over a wire.

Alternation.      The term applied to a change in the direction of an
                    alternating current, the frequency of the alternations
                    ranging up to 20,000 or more vibrations per second.

Amber.            A resin, yellow in color, which when rubbed with a
                    cloth, becomes excited and gives forth negative

Ammeter.          An instrument for measuring the quantity or flow of

Ampere.           The unit of current; the term in which strength of
                    the current is measured. An ampere is an
                    electromotive force of one volt through a resistance
                    of one ohm.

Annunciator.      A device which indicates or signals a call given from
                    some distant point.

Anode.            The positive terminal in a conducting circuit, like
                    the terminal of the carbon plate in a battery. It is
                    a plate in an electroplating bath from which the
                    current goes over to the cathode or negative plate or

Arc.              A term employed to designate the gap, or the current
                    which flows across between the conductors, like the
                    space between the two carbons of an arc lamp, which
                    gives the light.

Armature.         A body of iron, or other suitable metal, which is in
                    the magnetic field of a magnet.

Armature Bar.     The piece which holds the armature. Also one of a
                    series of bars which form the conductors in armature

Armature Coil.    The winding around an armature, or around the core
                    of an armature.

Armature Core.    The part in a dynamo or motor which revolves,
                    and on which the wire coils are wound.

Astatic (Galvanometer). That which has no magnetic action to direct
                    or divert anything exterior to it.

Atom.             The ultimate particle of an elementary substance.

Attraction.       That property of matter which causes particles to
                    adhere, or cohere, to each other. It is known under
                    a variety of terms, such as gravitation, chemical
                    affinity, electro-magnetism and dynamic attraction.

Automatic Cut-out. A device which acts through the operation of the
                    mechanism with which it is connected. It is usually
                    applied to a device which cuts out a current when it
                    overcharges or overloads the wire.

Bath.             In electroplating, the vessel or tank which holds
                    the electroplating solution.

Battery.          A combination of two or more cells.

Battery, Dry.     A primary battery in which the electrolyte is made
                    in a solid form.

Battery, Galvanic. A battery which is better known by the name of the
                    Voltaic Pile, made up of zinc and copper plates
                    which alternate, and with a layer of acidulated paper
                    between each pair of plates.

Battery, Storage.  A battery which accumulates
                    electricity generated by a primary battery or a

Brush.            A term applied to the conducting medium that
                    bears against the cylindrical surface of a commutator.

Buzzer.           An electric call produced by a rapidly moving
                    armature of an electro-magnet.

Cable.            A number of wires or conductors assembled in one

Candle-power.     The amount of light given by the legal-standard
                    candle. This standard is a sperm candle, which burns
                    two grains a minute.

Capacity.         The carrying power of a wire or circuit, without
                    heating.  When heated there is an overload, or the
                    _capacity_ of the wire is overtaxed.

Capacity, Storage. The quantity of electricity in a secondary battery
                    when fully charged, usually reckoned in ampere hours.

Carbon.           A material, like coke, ground or crushed, and formed
                    into sticks or plates by molding or compression. It
                    requires a high heat to melt or burn, and is used as
                    electrodes for arc lamps and for battery elements. It
                    has poor conductivity, and for arc lamps is coated
                    with copper to increase its conductivity.

Cell, Electrolytic. A vessel containing an electrolyte for
                    electroplating purposes.

Charge.           The quantity of electricity on the surface of a body
                    or conductor.

Chemical Change.  When a current passes through electrodes in a
                    solution, a change takes place which is chemical
                    in its character. Adding sulphuric acid to water
                    produces heat. If electrodes of opposite polarity are
                    placed in such an acid solution, a chemical change is
                    produced, which is transformed into electricity.

Choking Coil.     An instrument in a circuit which by a form of
                    resistance regulates the flow of the current, or
                    returns part of it to the source of its generation.

Counter-electromotive Force. Cells which are inserted in opposition to
                    a battery to reduce high voltage.

Circuit, Astatic. A circuit in an instrument so wound that the earth's
                    magnetism will not affect it.

Circuit Breaker.  Any instrument in a circuit which cuts out or
                    interrupts the flow of a current.

Circuit, External. A current flows through a wire or conductor,
                  and also along the air outside of the conductor,
                  the latter being the _external circuit._

Circuit Indicator. An instrument, like a galvanometer, that shows
                    the direction in which a current is flowing through
                    a conductor.

Circuit, Return.  Usually the ground return, or the negative wire from
                    a battery.

Circuit, Short.   Any connection between the mains or parallel lines
                    of a circuit which does not go through the
                    apparatus for which the circuit is intended.

Coherer.          A tube, or other structure, containing normally
                    high resistance particles which form a path or bridge
                    between the opposite terminals of a circuit.

Coil.             A wire, usually insulated, wound around a spool.

Coil, Induction.  One of a pair of coils designed to change the
                    voltage of a current of electricity, from a higher
                    to a lower, or from a lower to a higher
                    electro-motive force.

Coil, Resistance. A coil so wound that it will offer a resistance
                    to a steady current, or reduce the flow of electricity.

Commutator.       A cylinder on the end of the armature of a dynamo
                    or motor and provided with a pair of contact plates
                    for each particular coil in the armature, in order
                    to change the direction of the current.

Compass.          An apparatus which indicates the direction or flow
                    of the earth's magnetism.

Condenser.        A device for storing up electro-static charges.

Conductance.      That quality of a conductor to carry a current of
                    electricity, dependent on its shape for the best

Conduction.       The transmission of a current through a rod, wire
                    or conductor.

Conductivity.     That quality which has reference to the capacity
                    to conduct a current.

Conductor.        Any body, such as a bar, rod, wire, or machine,
                    which will carry a current.

Connector.        A binding post, clamp, screw, or other means to
                    hold the end of a wire, or electric conductor.

Contact.          To unite any parts in an electric circuit.

Controller.       The handle of a switchboard, or other contact
                    making and breaking means in a circuit.

Converter.        An induction coil in an alternating circuit for
                    changing potential difference, such as high
                    alternating voltage into low direct current voltage.

Convolution.      To wind like a clock spring.

Core.             The inner portion of an electro-magnet. The inside
                    part of an armature wound with wire.

Core, Laminated.  When the core is built up of a number of separate
                    pieces of the same material, but not insulated from
                    each other.

Coulomb.          The unit of electrical quantity. It is the quantity
                    passed by a current of one ampere intensity in one
                    second of time.

Couple, Electric. Two or more electrodes in a liquid to produce an
                    electric force.

Current, Alternating. A natural current produced by the action of
                    electro-magnets. It is a succession of short impulses
                    in opposite directions.

Current, Constant. A current which is uniformly maintained in a steady

Current, Induced.  A current produced by electro-dynamic induction.

Current Meter.    An apparatus for indicating the strength of a current.
                    An ammeter.

Current, Oscillating. A current which periodically alternates.

Current, Periodic. A periodically varying current strength.

Current, Undulating. A current which has a constant direction,
                    but has a continuously varying strength.

Decomposition.    The separation of a liquid, such as an electrolyte,
                    into its prime elements, either electrically or

Deflection.       The change of movement of a magnetic needle out of
                    its regular direction of movement.

Demagnetization.  When a current passes through a coil wound on an
                    iron core, the core becomes magnetized. When the
                    current ceases the core is no longer a magnet. It
                    is then said to be _demagnetized_. It also has
                    reference to the process for making a watch
                    non-magnetic so that it will not be affected when
                    in a magnetic field.

Density.          The quantity of an electric charge in a
                    conductor or substance.

Depolarization.   The removal of magnetism from a permanent magnet,
                    or a horse-shoe magnet, for instance. It is generally
                    accomplished by applying heat.

Deposition,       The act of carrying metal from one pole of a cell to
  Electrolysis.     another pole, as in electroplating.

Detector.         Mechanism for indicating the presence of a current
                    in a circuit.

Diaphragm.        A plate in a telephone, which, in the receiver, is
                    in the magnetic field of a magnet, and in a
                    transmitter carries the light contact points.

Dielectric.       A non-conductor for an electric current, but through
                    which electro-static induction will take place.
                    For example: glass and rubber are dielectrics.

Discharge.        The current flowing from an accumulator.

Disintegration.   The breaking up of the plate or active material.

Disruptive.       A static discharge passing through a dielectric.

Duplex Wire.      A pair of wires usually twisted together and
                    insulated from each other to form the conducting
                    circuit of a system.

Dynamic Electricity. The term applied to a current flowing through
                    a wire.

Dynamo.           An apparatus, consisting of core and field magnets,
                    which, when the core is turned, will develop a
                    current of electricity.

Earth Returns.    Instead of using two wires to carry a circuit,
                    the earth is used for what is called the _return_

Efficiency.       The total electrical energy produced, in which that
                    wasted, as well as that used, is calculated.

Elasticity.       That property of any matter which, after a stress,
                    will cause the substance to return to its original
                    form or condition. Electricity has elasticity,
                    which is utilized in condensers, as an instance.

Electricity,      Lightning, and, in short, any current or electrical
  Atmospheric.      impulse, like wireless telegraphic waves, is called

Electricity,      Electricity with a low potentiality and large current
   Voltaic.         density.

Electrification.  The process of imparting a charge of electricity
                    to any body.

Electro-chemistry. The study of which treats of electric and chemical
                    forces, such as electric plating, electric fusing,
                    electrolysis, and the like.

Electrode.        The terminals of a battery, or of any circuit; as,
                    for instance, an arc light.

Electrolyte.      Any material which is capable of being decomposed
                    by an electric current.

Electro-magnetism. Magnetism which is created by an electric current.

Electrometer.     An instrument for measuring static electricity,
                    differing from a galvanometer, which measures a
                    current in a wire that acts on the magnetic needle
                    of the galvanometer.

Electro-motive    Voltage, which is the measure or unit of e. m. f.
  Force. (E. M. F.)

Electroscope.     A device for indicating not only the
                    presence of electricity, but whether it is positive
                    or negative.

Electro-static    Surfaces separated by a dielectric for opposite
  Accumulator.    charging of the surface.

Element.          In electricity a form of matter, as, for instance,
                    gold, or silver, that has no other matter or
                    compound. Original elements cannot be separated,
                    because they are not made up of two or more elements,
                    like brass, for instance.

Excessive Charge.  A storage battery charged at too high a rate.

Excessive Discharge. A storage battery discharged at too high a rate.

Excessive Overcharge. Charging for too long a time.

Exciter.          A generator, either a dynamo or a battery, for
                    exciting the field of a dynamo.

Exhaustive Discharge. An excessive over-discharge of an accumulator.

F.                The sign used to indicate the heat term Fahrenheit.

Fall of Voltage.  The difference between the initial and the final
                    voltage in a current.

Field.            The space or region near a magnet or charged wire.
                    Also the electro-magnets in a dynamo or motor.

Flow.             The volume of a current going through a conductor.

Force, Electro-magnetic. The pull developed by an electro-magnet.

Frictional        A current produced by rubbing dissimilar
  Electricity.      substances together.

Full Load.        The greatest load a battery, accumulator or dynamo
                    will sustain.

Galvanic.         Pertaining to the electro-chemical relations of
                    metals toward each other.

Galvanizing.      The art of coating one metal with another, such,
                    for instance, as immersing iron in molten zinc.

Galvanometry.     An instrument having a permanently magnetized needle,
                    which is influenced by a coil or a wire in close
                    proximity to it.

Galvanoscope.     An instrument, like a galvanometer, which determines
                    whether or not a current is present in a tested wire.

Generator.        A term used to generally indicate any device which
                    originates a current.

German Silver.    An alloy of copper, nickel and zinc.

Graphite.         One form of carbon. It is made artificially by the
                    electric current.

Grid.             The metallic frame of a plate used to hold the active
                    material of an accumulator.

Gravity.          The attraction of mass for mass. Weight. The
                    accelerating tendency of material to move toward the

Gutta Percha.     Caoutchouc, which has been treated with sulphur,
                    to harden it. It is produced from the sap of
                    tropical trees, and is a good insulator.

Harmonic Receiver. A vibrating reed acted on by an electro-magnet,
                    when tuned to its pitch.

High E. M. F.     A term to indicate currents which have a high
                    voltage, and usually low amperage.

Igniter.          Mechanism composed of a battery, induction coil and
                    a vibrator, for making a jump spark, to ignite gas,
                    powder, etc.

I. H. P.          Abbreviation, which means Indicated Horse Power.

Impulse.          A sudden motion of one body acting against another.
                    An electro-magnetic wave magnetizing soft iron,
                    and this iron attracting another piece of iron, as an

Incandescence,    A conductor heated up by a current so it will
  Electric.         glow.

Induced Current.  A current of electricity which sets up lines of
                    force at right angles to the body of the wire
                    through which the current is transmitted.

Induction, Magnetic. A body within a magnetic field which is excited
                    by the magnetism.

Installation.     Everything belonging to an equipment of a building,
                    or a circuiting system to do a certain thing.

Insulation.       A material or substance which resists the passage
                    of a current placed around a conductor.

Intensity.        The strength of a magnetic field, or of a current
                    flowing over a wire.

Internal Resistance. The current strength of electricity of a wire
                    to resist the passage.

Interrupter.      A device in a wire or circuit for checking a
                    current. It also refers to the vibrator of an
                    induction coil.

Joint.            The place where two or more conductors are united.

Joint Resistance. The combined resistance offered by two or more
                    substances or conductors.

Jump Spark.       A spark, disruptive in its character, between two
                    conducting points.

Initial Charge.   The charge required to start a battery.

Kathode, or Cathode. The negative plate or side of a battery. The
                    plate on which the electro deposit is made.

Key.              The arm of a telegraph sounder. A bar with a finger
                    piece, which is hinged and so arranged that it will
                    make and break contacts in an electric circuit.

Keyboard.         A switch-board; a board on which is mounted a number
                    of switches.

Kilowatt.         A unit, representing 1,000 watts. An electric current
                    measure, usually expressed thus: K.W.

Kilowatt Hour.    The computation of work equal to the exertion of one
                    kilowatt in one hour.

Knife Switch.     A bar of a blade-like form, adapted to move down
                    between two fingers, and thus establish metallic

Laminated.        Made up of thin plates of the same material, laid
                    together, but not insulated from each other.

Lamp Arc.         A voltaic arc lamp, using carbon electrodes, with
                    mechanism for feeding the electrodes regularly.

Lamp, Incandescent. A lamp with a filament heated up to a glow by the
                    action of an electric current. The filament is within
                    a vacuum in a glass globe.

Leak.             Loss of electrical energy through a fault in wiring,
                    or in using bare wires.

Load.             The ampere current delivered by a dynamo under certain

Low Frequency.    A current in which the vibrations are of
                    few alternations per second.

Magnet.           A metallic substance which has power to attract
                    iron and steel.

Magnet Bar.       A straight piece of metal.

Magnet Coil.      A coil of wire, insulated, surrounding a core of
                    iron, to receive a current of electricity.

Magnet Core.      A bar of iron adapted to receive a winding of wire.

Magnet, Field.    A magnet in a dynamo. A motor to produce electric

Magnet, Permanent. A short steel form, to hold magnetism for a long

Magnetic Adherence. The adherence of particles to the
                    poles of a magnet.

Magnetic          That quality of a metal which draws metals. Also
  Attraction and    the pulling action of unlike poles for each
  Repulsion.        other, and pushing away of like poles when brought

Magnetic Force.   The action exercised by a magnet of attracting
                  or repelling.

Magnetic Pole.    The earth has North and South magnetic poles.
                    The south pole of a magnetic needle is attracted
                    so it points to the north magnetic pole; and the north
                    pole of the needle is attracted to point to the south
                    magnetic pole.

Magneto-generator. A permanent magnet and a revolving armature for
                    generating a current.

Maximum Voltage.  The final voltage after charging.

Molecule.         Invisible particles made up of two or more atoms
                    of different matter. An atom is a particle of one
                    substance only.

Morse Sounder.    An electric instrument designed to make a clicking
                    sound, when the armature is drawn down by a

Motor-dynamo.     A motor and a dynamo having their armatures
                    connected together, whereby the motor is driven
                    by the dynamo, so as to change the current into a
                    different voltage and amperage.

Motor-transformer. A motor which delivers the current like a generator.

Needle.           A bar magnet horizontally poised on a vertical
                    pivot point, like the needle of a mariner's compass.

Negative          Amber, when rubbed, produces negative electricity.
  Electricity.      A battery has positive as well as negative

Negative Element. That plate in the solution of a battery
                    cell which is not disintegrated.

Normal.           The usual, or ordinary. The average. In a
                    current the regular force required to do the work.

North Pole,       The term applied to the force located near
  Electric.        the north pole of the globe, to which a permanent
                   magnet will point if allowed to swing freely.

O.                Abbreviation for Ohm.

Ohm.              The unit of resistance. Equal to the resistance of
                    a column of mercury one square millimeter in cross
                    section, and 106.24 centimeters in length.

Ohm's Law.        It is expressed as follows:
                  1. The current strength is equal to the electro-motive
                       force divided by its resistance.
                  2. The electro-motive force is equal to the current
                       strength multiplied by the resistance.
                  3. The resistance is equal to the electro-motive force
                       divided by the current strength.

Overload.         In a motor an excess of mechanical work which causes
                    the armature to turn too slowly and produces heat.

Phase.            One complete oscillation. The special form of a
                    wave at any instant, or at any interval of time.

Plate, Condenser. In a static machine it is usually a plate of glass
                    and revoluble.

Plate, Negative.  The plate in a battery, such as carbon, copper or
                    platinum, which is not attacked by the solution.

Plating, Electro-. The method of coating one metal with another by

Polarity.         The peculiarity, in a body, of arranging itself
                    with reference to magnetic influence.

Parallel.         When a number of cells are coupled so that their
                    similar poles are grouped together. That is to say,
                    as the carbon plates, for instance, are connected
                    with one terminal, and all the zinc plates with the
                    other terminal.

Polarization.     When the cell is deprived of its electro-motive
                    force, or any part of it, polarization is the result.
                    It is usually caused by coating of the plates.

Porosity.         Having small interstices or holes.

Positive Current. One which deflects a needle to the left.

Positive          Any current flowing from the active element,
  Electricity.     such as zinc, in a battery. The negative
                    electricity flows from the carbon to the zinc.

  Electric.       The power which performs work in a circuit.

Potential Energy. That form of force, which, when liberated, does or
                    performs work.

Power Unit.       The volt-amperes or watt.

Primary.          The induction coil in induction machines, or in
                    a transformer.

Push Button.      A thumb piece which serves as a switch to
                    close a circuit while being pressed inwardly.

Quantity.         Such arrangement of electrical connections
                    which give off the largest amount of current.

Receiver.         An instrument in telephony and telegraphy which
                    receives or takes in the sound or impulses.

Relay.            The device which opens or closes a circuit so as to
                    admit a new current which is sent to a more distant

Repulsion,        That tendency in bodies to repel each other when
  Electric.         similarly charged.

Resilience.       The springing back to its former condition or
                    position. Electricity has resilience.

Resistance.       The quality in all conductors to oppose the passage
                    of a current.

Resistance Coil.  A coil made up of wire which prevents the passage
                    of a current to a greater or less degree.

Resistance,       The counter force in an electrolyte which seeks
  Electrolytic.     to prevent a decomposing current to pass through it.

Resistance: Internal, The opposing force to the movement of a current
  External.         which is in the cell or generator. This is called the
                     _internal_. That opposite action outside of the cell
                    or generator is the _external_.

Resonator,        An open-circuited conductor for electrically
  Electric.         resounding or giving back a vibration, usually
                   exhibited by means of a spark.

Rheostat.         A device which has an adjustable resistance, so
                    arranged that while adjusting the same the circuit
                    will not be open.

Safety Fuse.      A piece of fusible metal of such resistance that
                    it breaks down at a certain current strength.

Saturated.        When a liquid has taken up a soluble material
                    to the fullest extent it is then completely saturated.

Secondary.        One of the two coils in a transformer, or induction

Secondary Plates. The brown or deep red plates in a storage battery
                    when charged.

Self-excited.     Producing electricity by its own current.

Series.           Arranged in regular order. From one to the other
                    directly. If lamps, for instance, should be arranged
                    in circuit on a single wire, they would be in series.

Series, Multiple. When lamps are grouped in sets in parallel,
                    and these sets are then connected up in series.

Series Windings.  A generator or motor wound in such a manner that
                    one of the commutator brush connections is joined
                    to the field magnet winding, and the other end of
                    the magnet winding joined to the outer circuit.

Shunt.            Going around.

Shunt Winding.    A dynamo in which the field winding is parallel with
                    the winding of the armature.

Snap Switch.      A switch so arranged that it will quickly make a

Sounder.          The apparatus at one end of a line actuated by a key
                    at the other end of the line.

Spark Coil.       A coil, to make a spark from a low electro-motive

Spark, Electric.  The flash caused by drawing apart the ends of a

Specific Gravity. The weight or density of a body.

Static Electricity. Generated by friction. Also lightning.
                    Any current generated by a high electro-motive force.

Strength of Current. The quantity of electricity in a circuit.

Synchronize.      Operating together; acting in unison.

Terminal.         The end of any electric circuit or of a body
                    or machine which has a current passing through it.

Thermostat, Electric. An electric thermometer. Usually made
                    with a metal coil which expands through the action
                    of the electricity passing through it, and, in
                    expanding, it makes a contact and closes a circuit.

Transformer.      The induction coil with a high initial E. M. F.
                    changes into a low electro-motive force.

Unit.             A standard of light, heat, electricity, or of
                    other phenomena.

Vacuum.           A space from which all matter has been exhausted.

Vibrator.         Mechanism for making and breaking circuits in
                    induction coils or other apparatus.

Volt.             The unit of electro-motive force.

Voltage.          Electro-motive force which is expressed in volts.

Voltaic.          A term applied to electric currents and devices.

Volt-meter.       An apparatus for showing the difference of
                    potential, or E.  M. F. in the term of volts.

Watt.             The unit of electrical activity. The product of
                    amperes multiplied by volts.

Watt Hour.        One watt maintained through one hour of time.

Waves, Electric   Waves in the ether caused by electro-magnetic
  Magnetic.         disturbances.

X-rays.           The radiation of invisible rays of light, which
                    penetrate or pass through opaque substances.

Yoke, or Bar.     A soft iron body across the ends of a
                    horseshoe magnet, to enable the magnet to retain its
                    magnetism an indefinite time.

Zinc Battery.     A battery which uses zinc for one of its elements.



Accumulated, 31.

Accumulation, 29.

Accumulator cell, 87.

Accumulators, 82, 88, 89.

Accumulators, plates, 83.

Acid, 34, 37, 125.

Acid maker, 125.

Acid, sulphuric, 31, 84.

Acidulated, 55.

Acidulated water, 34.

Acoustics, 110.

Actinic rays, 184, 185.

Actinium, 186.

Active element, 82.

Adjustable rod, 107.

Adjusting screw, 70, 71, 72, 73, 106.

Aerial wire, 108.

Agents, 13, 32.

Alarms, burglar, 11, 76, 80.

Alkali, 125.

Alkaline, 37.

Alternate, 127.

Alternating, 38, 149, 150, 153, 154, 155, 156.

Alternating current, 145.

Alternating periods, 149.

Alternations, 147.

Aluminum, 128, 129, 135, 137.

Aluminum hydrate, 129.

Amber, 5, 171.

Ammeter, 7, 88.

Amperage, 38, 61, 62, 132, 159, 160, 168.

Ampere, 7, 37, 60, 63, 139, 140, 167.

Amplitude, 111.

Annunciator, 65, 74, 76, 79, 80, 81.

Annunciator bells, 11.

Anode, 35, 133, 134.

Antennæ, 108.

Antimony 137, 143.

Anvil, 13, 14.

Apparatus, 11, 57, 106, 139, 145.

Arc, 163, 182.

Arc lighting, 38, 165.

Arc system, 166.

Armature, 18, 25, 38, 40, 42, 43, 45, 46, 47, 48, 53, 55, 70, 72, 73,
        74, 90, 93, 112, 151, 152, 155, 163, 176, 177, 178, 179, 180.

Armature brush, 48.

Armature post, 71.

Armature, vertical, 75.

Armature winding, 42, 43, 156.

Asbestos, 140.

Astatic galvanometer, 108.

Atmosphere, 184.

Attract, 30.

Attracted, 72.

Attraction, 21, 25.

Attractive, 178.

Automatic, 120.

Auxiliary, 44.

Awls, 14.


Bacteria, 126, 187.

Bar, cross, 66.

Bar, horizontal, 46.

Bar, parallel switch, 67.

Bar, switch, 65, 68.

Base block, 66.

Batteries, 11, 93, 122.

Battery, 29, 30, 32, 35, 36, 46, 47, 80, 81, 82, 83, 85, 86, 88, 92, 94,
          95, 107, 108, 116, 117, 118, 121, 134, 142.

Battery charging, 82.

Bearings, 45, 46.

Bells, 65, 73, 76, 122.

Bells, electric, 70.

Bench, 13, 15, 17.

Binding post, 52, 70, 71, 72, 103, 107, 108, 121.

Binding screw, 65, 66.

Bismuth, 18, 143.

Bit, 13.

Blue vitriol, 57.

Brass plate, 77, 78.

Brazing, 17, 65.

Bridge, 52.

Brush holder, 46.

Brushes, 48, 150, 151, 153, 167.

Burglar, 11.

Burglar alarm, 76, 80.

Buttons, contact, 80.

Buttons, push, 65, 68, 69, 70, 76, 79.


Calorimeter, 56.

Cancerous, 187.

Candle power, 89, 139.

Cap, removable, 73.

Cap screws, 42.

Carbon, 35, 119, 121, 162, 163, 169.

Carbon block, 120.

Carbon pencil, 119.

Cathode, 35, 36, 133, 134.

Cell, 29, 33.

Cell, accumulator, 87.

Cell, charging, 87.

Channel, 43.

Channel, concave, 40.

Charged, 120.

Charged battery, 82.

Charging circuit, 82, 89.

Charging source, 83.

Charged wire, 147.

Chemical, 57.

Chisels, 13.

Chloride of lime, 84.

Choked, 157.

Choking coils, 145, 146, 156, 158.

Circuit, 33, 69, 73, 76, 78, 80, 81, 90, 92, 93, 109, 113, 116, 121,
         122, 131, 134, 143, 156.

Circuit, primary, 99.

Circuit, secondary, 99.

Circuiting, 81, 155.

Circuiting system, 79.

Clapper arm, 70.

Closed rings, 26.

Coherer, 105, 108, 109.

Cohering, 106.

Coils, 18, 26, 52, 55, 74, 160.

Coils, choking, 145, 146, 156, 158.

Coils, induction, 99, 102.

Coils, primary, 109.

Coils, secondary, 102, 109.

Coincide, 42.

Cold, 14.

Collecting surfaces, 30.

Collector, 31.

Column, 61.

Combustion, 169.

Commutator, 44, 46, 151, 152.

Commutator brushes, 46.

Commutator plates, 45.

Compass, 22, 24, 172.

Composition, 83, 124.

Compound wound, 47.

Concave channel, 40.

Condenser, 98, 100, 101, 102, 108.

Conduct, 6, 108.

Conduction, 135, 136, 138, 166, 170.

Conduction current, 27.

Conductor, 21, 31, 33, 63, 98, 116, 161, 162.

Conduit, 72.

Conically formed, 126.

Conjunction, 143.

Connecting wire, 58.

Connection, 72, 76.

Construction, magnet, 39.

Consumption, 180.

Contact, 122, 123, 152, 162.

Contact finger, 150.

Contact plate, 67, 68, 79.

Contact screws, 93.

Contact surface, 66.

Continuous, 145.

Converter, 176.

Converting, 142, 145, 146.

Copper, 18, 34, 36, 65, 66, 132, 133, 134, 135, 136, 137, 142, 143.

Copper cyanide, 133.

Copper plate, 33, 35, 58, 67.

Copper sulphate, 57.

Copper voltameter, 55, 57.

Core, 27, 28, 36, 39, 40, 115.

Core, magnet, 75, 93.

Counter, clock-wise, 51.

Coupled, 36.

Crank, 30.

Crookes' tube, 184.

Cross bar, 52, 66.

Crown of cups, 32.

Crystal, 85.

Current, 6, 7, 13, 18, 26, 27, 28, 35, 36, 37, 38, 47, 50, 51, 52, 55,
  56, 57, 58, 59, 62, 63, 70, 72, 73, 90, 95, 98, 105, 108, 116, 133, 134,
  135, 136, 138, 139, 140, 141, 142, 143, 147, 148, 149, 150, 152, 153,
  157, 160, 161, 163, 165, 166, 170.

Current, alternating, 150.

Current changing, 82.

Current conduction, 27.

Current, continuous, 164.

Current, direct, 145, 150.

Current direction, 50.

Current, exterior, 50, 150.

Current, reversing, 148.

Current strength, 7, 57.

Current testing, 143.

Cut-out, 120.

Cutter, 14.

Cutting, lines of force, 38.

Cylinder, 44.

Cylindrical, 43.


Dash, 95, 97.

Decoherer, 106, 108.

Decomposed, 57, 128.

Decomposes, 55.

Decomposing, 123.

Decomposition, 12, 35, 82.

Deflected, 54.

Degree, 135, 162.

Demagnetized, 24, 72.

Deposited, 58, 133.

Depression, 15, 140.

Detecting current, 49.

Detector, 49, 52, 54, 105.

Devices, measuring, 27.

Diagrams, 46, 48, 79, 89.

Diagrammatically, 81.

Diamagnetic, 19.

Diametrically, 114.

Diaphragm, 112, 113, 116, 120, 122.

Diamonds, 186.

Diluted, 86.

Direct current, 38, 140.

Direction of current, 50.

Direction of flow, 98.

Discharge, 172.

Disintegrate, 132.

Disk, 43.

Dissimilar, 37.

Disturbance, 176.

Dividers, 14.

Divisibility, 168.

Dot, 96, 97.

Dot and dash, 96.

Double click, 95.

Double line, 65.

Double-pole switch, 65.

Double-throw switch, 117.

Drawing, 20.

Drill, ratchet, 13.

Drops, 81.

Ductile, 186.

Duplex wire, 115.

Dynamo, 7, 27, 38, 42, 46, 48, 62, 82, 83, 87, 89, 132, 141, 142, 145,
       150, 155, 161, 165, 167, 175, 176, 180, 187.

Dynamo fields, 40, 41.


Earth, 22.

Elasticity, 100, 142.

Electric, 6, 31, 49, 50, 76, 78, 81, 131, 142, 158, 162, 173, 176.

Electric arc, 63, 163.

Electric bell, 19, 69, 70, 71, 72, 106, 117.

Electric bulbs, 167.

Electric circuit, 118.

Electric fan, 55.

Electric field, 76.

Electric hand purifier, 129.

Electric heating, 135, 137, 161.

Electric iron, 130, 141.

Electric lamp socket, 139.

Electric light, 56, 66.

Electric lighting, 161.

Electric power, 113.

Electric welding, 183.

Electrical, 8, 11, 65, 96, 98, 104, 141, 159, 180, 184, 187.

Electrical impulses, 105, 147, 148.

Electrical manifestations, 175.

Electrically, 32, 70.

Electricity, 5, 6, 7, 8, 9, 12, 13, 18, 21, 26, 27, 28, 29, 38, 49, 54,
     60, 61, 62, 82, 97, 98, 100, 104, 110, 112, 116, 123, 124, 133, 134,
    136, 138, 145, 146, 147, 154, 156, 160, 166, 170, 171, 172, 175, 182,

Electricity measuring, 49.

Electricity, thermo-, 142.

Electrified, 37, 186.

Electro-chemical, 55.

Electrode, 35, 124, 127, 128, 161, 162, 163, 164, 165, 184.

Electrolysis, 7, 123, 126, 132.

Electrolyte, 33, 35, 36, 57, 86, 88, 123, 132, 142.

Electrolytic, 55, 123, 125.

Electro-magnet, 59, 78.

Electro-magnetic, 7, 24, 25, 29, 37, 55, 92, 93, 94.

Electro-magnetic force, 7.

Electro-magnetic rotation, 7.

Electro-magnetic switch, 116.

Electro-meter, 7.

Electro-motive force, 37, 63, 99.

Electroplate, 12, 38, 48, 123, 132, 134.

Electro-positive-negative, 142, 143.

Elements, 36, 83.

Engine energy, 170, 180.

Equidistant, 127.

Ether, 104.

Example, 61.

Excited, 47.

Extension plate, 103.

Exterior, 3.

Exterior magnetic, 27.

External, 37.

External circuit, 153.

External current, 50.

External resistance, 37.


Factor, 61.

Ferrous oxide, 125.

Field, 46, 47.

Field, dynamo, 40, 41.

Field magnet cores, 155.

Field, magnetic, 38.

Field of force, 33.

Field wire, 48.

Filament, 168, 169, 170.

Filter, 128.

Flat iron, 140.

Flocculent, 128.

Force, 50.

Formulated, 19.

Friction, 32.

Frictional, 6, 7, 29.

Fuse, 169.


Galvani, 7.

Galvanic, 7, 23, 30.

Galvanometer, 7, 49, 108, 143.

Galvanoscope, 55, 58, 59.

Gaseous, 128.

Gasoline, 99.

Gas stove, 17.

Gelatine, 128.

Generate, 29, 38, 134, 136, 145.

Generated, 55.

Generating, 32, 134.

Generation, 170.

Generator, 32, 125, 147.

German silver, 136, 137.

Germicide, 187.

Gimlets, 17.

Glass, 30, 86, 126, 186.

Gold, 135.

Grid, 84.

Ground circuit, 121.

Gunpowder, 6.


Hack-saw, 14.

Hammer, 13.

Heart-shaped switch, 77.

Heater, 136.

Heating, 13, 38.

Hertzian rays, 170.

Hertzian wave, 184.

High tension, 38, 102, 184.

High tension apparatus, 98.

High tension coils, 103.

High voltage, 158.

Horizontal bar, 46.

Horseshoe magnet, 22, 24, 175.

Hydrate of aluminum, 129.

Hydrogen, 35, 123, 125, 128.


Igniting, 99.

Illumination, 162, 163, 165, 167, 170.

Immersed, 133.

Impulses, 60, 62, 96, 104, 109, 152, 179.

Incandescent, 166, 168.

Induced, 28.

Inductance, 149, 150.

Induction, 27, 37, 98, 147.

Induction coils, 99, 102, 106.

Influences, 178.

Initial charge, 88.

Insulated, 27, 28, 40, 43, 52, 55, 73, 115, 151, 180.

Insulating, 66, 69, 120, 140, 164.

Insulating material, 114.

Insulation, 40, 116.

Instruments, 49, 94, 112, 118, 120.

Instruments, measuring, 8.

Intensity, 55, 60, 104, 154.

Interior, magnetic, 23.

Internal resistance, 37.

Interruption, 102, 103.

Installation, 168.

Ionize, 186.

Iron, 19, 132, 133, 136, 142, 171.

Isolated, 186.


Jar, 29, 31, 32.

Journal, 46.

Journal block, 16, 146.

Jump spark, 99.


Key, 90, 91, 95.

Key, sending, 90.

Knob, 32.

Knob, terminal, 31.


Laboratory, 9.

Lead, 31, 136.

Lead, precipitated, 83, 85.

Lead, red, 83, 84.

Lever switching, 67.

Light, 104.

Light method, 56.

Lighting, 9, 38.

Lighting circuit, 48.

Lighting system, 82.

Lightning, 6, 171, 172, 173.

Lightning rod, 173.

Lime, chloride of, 84.

Line of force, 146.

Line wire, 122.

Line, magnetic, 22, 23.

Liquid, 32.

Litharge, 83.

Loadstone, 17.

Locomotives, 165.

Low tension, 38, 98, 102, 179.


Magnet bar, 20.

Magnet core, 16, 75, 93.

Magnet, electro, 59, 78.

Magnet, horseshoe, 22, 25, 175.

Magnet lines, 22, 23.

Magnet, permanent, 25, 38, 46, 50, 172.

Magnet, reversed, 20.

Magnet, steel, 53.

Magnet, swinging, 53.

Magnetic, 7, 19, 20, 21, 22, 25, 113, 178.

Magnetic construction, 39.

Magnetic exterior, 27.

Magnetic field, 22, 24, 27, 38, 50, 112, 146, 148, 155.

Magnetic interior, 23.

Magnetic pull, 59.

Magnetic radiator, 37.

Magnetism, 19, 54, 104, 110, 159, 171.

Magnetized, 18, 25, 27, 50.

Magnetized wire, 146.

Magnets, 13, 14, 18, 19, 20, 21, 22, 23, 24, 25, 39, 51, 53, 54, 70, 71,
       73, 75, 81, 90, 93, 112, 113, 115, 147, 150, 163, 176, 177, 178.

Main conductor, 31.

Mandrel, 15, 16.

Manganese, 19.

Manifestations, 19.

Mariner, 172.

Material, non-conducting, 90.

Maximum, 154.

Measure, 55, 56, 60, 62.

Measurement, 62.

Measuring devices, 27.

Measuring instruments, 8.

Mechanism, 47, 180.

Medical batteries, 99.

Mercury, 63, 169.

Metal base, 73.

Mica, 186.

Microphone, 118, 119, 120.

Millimeter, 63.

Minus, 34.

Minus sign, 21.

Morse code, 76.

Motor, 7, 21, 27, 46, 47, 62, 82, 99, 150, 176, 180.

Mouthpiece, 115.

Mouthpiece rays, 188.

Moving field, 117.

Multiple, 168.

Musical scale, 111.


Negative, 21, 35, 36, 68, 83, 86, 87, 94, 125, 151, 152, 154, 165, 177,
    178, 179.

Neutral, 125.

Neutral plate, 84.

Nickel, 136.

Nickel plating, 132.

Nitrate of silver, 62.

Nitrogen, 126.

Non-conducting material, 90.

Non-conductor, 164.

Non-magnetic, 19.

North pole, 20, 21, 22, 23, 25, 50, 54, 156.

Number plate, 75.

N-ray, 188.


Ohms, 60, 63.

Ohms, international, 63.

Ohms law, 7.

Operator, 95, 118.

Oscillating, 99, 105.

Osmium, 169.

Oxides, 125.

Oxidizing, 183.

Oxygen, 35, 123, 125, 126, 128, 129, 169.


Packing ring, 124.

Paraffine, 56, 100, 101, 102.

Paraffine wax, 86.

Parallel, 87, 88, 89.

Parallel switch bar, 67.

Parallel wires, 28, 49.

Partition, 124.

Peon, 13.

Percolate, 128.

Periodicity, 159.

Periods of alternations, 149.

Permanent, 18, 19, 50.

Permanent magnet, 25, 38, 46, 50, 172.

Phase, 19.

Phenomenon, 27, 65.

Photograph, 186.

Physical, 21.

Pile, voltaic, 33.

Pipe, 61.

Pitchblende, 186.

Pivot pin, 53.

Pivotal, 22.

Plane, 13.

Plate, 57, 93.

Plate, contact, 67, 68, 79.

Plate, copper, 33, 35, 58, 67.

Plate, negative, 84.

Plate, number, 75.

Plate, positive, 84, 88.

Plate, zinc, 33.

Platinum, 13, 57, 137.

Pliers, 14.

Plus sign, 21, 24.

Pointer, 53.

Polarity, 154, 177, 178, 179.

Polarization, 35.

Pole, north, 20, 21, 22, 23, 25, 50, 54, 156.

Pole piece, 40, 42.

Pole, south, 20, 21, 22, 25, 50, 54, 156.

Poles, 177, 179.

Polonium, 186.

Porcelain, 86.

Porous, 85.

Positive, 4, 21, 25, 36, 40, 68, 83, 86, 87, 94, 123, 125, 151, 152,
   153, 155, 165.

Post, binding, 52, 71.

Potentiality, 105, 109.

Power, 38, 186.

Power, candle, 89, 139.

Precipitate of lead, 83, 85.

Precision, 7.

Pressure, 87.

Primary, 35, 62, 98, 134, 142, 159, 184.

Primary battery, 7, 99.

Primary circuit, 99.

Primary coil, 106, 109.

Prime conductor, 6.

Projected, 185.

Propagated, 105, 185.

Properties, 55.

Purification, 123, 128.

Purifier, 126, 131.

Push button, 65, 68, 69, 70, 76, 79.


Quantity, 55, 60, 61, 138.

Quartz, 186.


Radio-activity, 186.

Radium, 184, 185, 187, 188.

Ratchet drill, 13.

Reaction, 148.

Receiver, 12, 90, 97, 121, 122.

Receiving station, 109.

Rectangular, 69.

Rectifiers, 146.

Red lead, 83, 84.

Reel, 13.

Reflected, 185.

Refraction, 185.

Refractory, 182.

Register, 57.

Removable, 54.

Removable cap, 73.

Repel, 20.

Repulsion, 21, 128.

Reservoir, 61, 62.

Resiliency, 99.

Resistance, 7, 36, 37, 60, 63, 99, 135, 136, 137, 138, 140, 141, 156,
   157, 163, 166, 168.

Resistance bridge, 7.

Resistance, external, 37.

Resistance, internal, 37.

Rheostat, 7.

Reversed, 20, 50, 153.

Reversible, 163.

Reversing, 176.

Reversing switch, 67.

Revolubly, 46.

Revolve, 179.

Revolving, 177.

Roentgen rays, 184.

Roentgen tube, 187.

Rotation, 149.

Rubber, 40, 46, 77, 115, 126, 130, 138.


Sad-irons, 13.

Saline, 133.

Sanitation, 12.

Saturated, 85.

Screw, 15.

Screw, binding, 65, 66.

Screw-driver, 14.

Screw, set, 72.

Sealing wax, 53.

Secondary, 62, 98, 105, 158, 159, 160.

Secondary circuit, 99.

Secondary coil, 107, 108.

Self-induction, 149, 156.

Sender, 90, 97.

Sending apparatus, 106.

Sending key, 90.

Separately excited, 46.

Series-wound, 47.

Severed magnet, 20.

Sewage, 12.

Shaft, 30.

Shears, 14, 17.

Shellac, 40.

Shunt-wound, 47.

Signal, 118.

Silver, 19, 63, 125.

Silver nitrate, 62.

Socket, 54, 139.

Soldering, 14.

Soldering iron, 17.

Solution, 55, 57, 62, 63, 84, 86, 133, 134, 142.

Sounder, 90, 92, 95, 96.

Sounding board, 119.

Source, charging, 83.

South pole, 20, 21, 22, 25, 50, 54, 156.

Spark gap, 102, 106.

Spark jump, 99.

Spring finger, 69.

Square, 14, 17.

Standard, 62, 63.

Station, 94, 95, 117, 122.

Steel, 18, 19.

Steel magnet, 53.

Sterilized, 12.

Stirrup, 75.

Stock bit, 13.

Stock contact, 121.

Storage, 82.

Storage battery, 107.

Storing, 82.

Substances, 135.

Sulphate, 55, 128, 133.

Sulphur, 19.

Sulphuric acid, 31, 84.

Sulphuric acid voltameter, 55, 57.

Superstition, 171, 173.

Surging, 153, 154.

Swinging magnet, 53.

Swinging switch blade, 67.

Switch blades, 66.

Switches, 65, 66, 70, 77, 78, 90, 117.

Switches, bar, 65, 68, 90, 91.

Switches, bar, parallel, 67.

Switches, heart-shaped, 78.

Switches, piece, 77.

Switches, reversing, 67.

Switches, sliding, 67, 80.

Switches, terminal, 8.

Switches, two-pole, 65.

System, circuiting, 79.


Tail-piece, 16.

Tantalum, 169.

Telegraph, 11, 90, 96.

Telegraph key, 106.

Telegraph sounder, 108, 109.

Telegraphing, 94.

Telephone, 12, 110, 113, 117, 118, 119, 120.

Telephone circuit, 118.

Telephone connections, 116.

Telephone hook, 122.

Temperature, 56, 88, 134, 161, 170.

Tension, high, 38, 102, 184.

Tension, low, 38, 98, 102, 179.

Terminal, 31, 34, 35, 40, 48, 82, 86, 93, 95, 107, 116, 121, 122, 151,
    152, 153, 154, 156.

Terminal knob, 31.

Terminal, secondary, 102.

Terminal switch, 81.

Theoretical, 160.

Therapeutics, 187.

Thermo-electric couples, 146.

Thermo-electricity, 135.

Thermometer, 56.

Thorium, 169, 186.

Thunderbolt, 171, 173.

Tin, 136.

Tinfoil, 31, 101.

Tools, 11, 13, 17.

Torch, brazing, 17.

Transformer, 145, 146, 158, 159, 180, 182.

Transformer, step-down, 182.

Transmission, 38, 187.

Transmit, 63, 95, 157.

Transmitter, 12, 120, 121, 122, 123.

Transverse, 16, 52.

Transversely, 43.

Trigger, 75.

Tripod, 31.

Tubular, 44, 45.

Two-pole switch, 65.


Ultra-violet, 185.

Uranium, 186.


Vacuum, 184.

Vapor lamps, 169.

Velocity, 60, 73.

Vertical armature, 75.

Vibration, 110, 111, 113.

Vibratory, 110.

Vise, 13.

Voltage, 37, 38, 60, 61, 62, 63, 87, 88, 99, 147, 154, 165, 180, 182.

Voltage, high, 158.

Voltaic, 29, 32.

Voltaic pile, 33.

Voltameter, 7, 58, 88.

Voltameter, sulphuric, acid, 55, 57.

Volts, 60, 62, 87, 89, 132, 158, 159.


Water, 123, 138, 144.

Water power, 142.

Watts, 60, 61, 160.

Wave lengths, 104, 110.

Weight, 49.

Welding, 13, 182.

Winding, 18, 40, 47, 58, 159, 196.

Winding reel, 14.

Window connection, 76.

Window frame, 78.

Wire, 6, 18, 21, 26, 28, 156.

Wire, circuiting, 79.

Wire coil, 40.

Wire lead, 70.

Wire, parallel, 28, 49.

Wireless, 12.

Wireless telegraphy, 103, 104, 184.

Wiring, 80.

Wiring, window, 77.

Workshop, 11, 17.

Wound, compound, 48.

Wound-series, 47.

Wound-shunt, 47.


X-ray, 184, 185, 187, 188.


Zinc, 17, 34, 35, 85, 135.

Zinc plates, 33.



A book which treats, in a most practical and fascinating manner all
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tools; drawing; designing, and the laying out of work; the principles
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complete glossary of the technical terms used in the art. The most
comprehensive volume on this subject ever published for boys.


The author has adopted the unique plan of setting forth the fundamental
principles in each phase of the science, and practically applying the
work in the successive stages. It shows how the knowledge has been
developed, and the reasons for the various phenomena, without using
technical words so as to bring it within the compass of every boy. It
has a complete glossary of terms, and is illustrated with two hundred
original drawings.


This book takes the beginner through a comprehensive series of practical
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_Price 60 cents per volume_


 | Transcriber's Note.                                             |
 |                                                                 |
 | Every effort has been made to replicate this text as faithfully |
 | as possible, including obsolete and variant spellings and other |
 | inconsistencies.                                                |
 |                                                                 |
 | Minor punctuation and printing errors have been corrected.      |
 |                                                                 |
 | The first page of the original book is an advertisement. The    |
 | page was moved to the end of the text.                          |
 |                                                                 |
 | Some hyphenation inconsistencies in the text were retained:     |
 |    16-candle-power and 16-candlepower,                          |
 |    Electromotive and electro-motive,                            |
 |    Electro-meter and Electrometer,                              |
 |    Horseshoe and horse-shoe,                                    |
 |    Switchboard and switch-board,                                |
 |                                                                 |
 |  Two occurrences of 'Colorimeter' for 'Calorimeter' repaired.   |

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