Title: A History of Science — Volume 3
Author: Williams, Henry Smith, 1863-1943, Williams, Edward Huntington, 1868-1944
Language: English
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A HISTORY OF SCIENCE


MODERN DEVELOPMENT OF THE PHYSICAL SCIENCES



By Henry Smith Williams, M.D., Ll.D.

Assisted By Edward H. Williams, M.D.

In Five Volumes

Volume III.



CONTENTS

  BOOK III

  CHAPTER I. THE SUCCESSORS OF NEWTON IN ASTRONOMY

  The work of Johannes Hevelius--Halley and Hevelius--Halley's observation
  of the transit of Mercury, and his method of determining the parallax of
  the planets--Halley's observation of meteors--His inability to
  explain these bodies--The important work of James Bradley--Lacaille's
  measurement of the arc of the meridian--The determination of the
  question as to the exact shape of the earth--D'Alembert and his
  influence upon science--Delambre's History of Astronomy--The
  astronomical work of Euler.

  CHAPTER II. THE PROGRESS OF MODERN ASTRONOMY

  The work of William Herschel--His discovery of Uranus--His discovery
  that the stars are suns--His conception of the universe--His deduction
  that gravitation has caused the grouping of the heavenly bodies--The
  nebula, hypothesis,--Immanuel Kant's conception of the formation of the
  world--Defects in Kant's conception--Laplace's final solution of the
  problem--His explanation in detail--Change in the mental attitude of the
  world since Bruno--Asteroids and satellites--Discoveries of Olbersl--The
  mathematical calculations of Adams and Leverrier--The discovery of the
  inner ring of Saturn--Clerk Maxwell's paper on the stability of Saturn's
  rings--Helmholtz's conception of the action of tidal friction--Professor
  G. H. Darwin's estimate of the consequences of tidal action--Comets
  and meteors--Bredichin's cometary theory--The final solution of the
  structure of comets--Newcomb's estimate of the amount of cometary dust
  swept up daily by the earth--The fixed stars--John Herschel's studies
  of double stars--Fraunhofer's perfection of the refracting
  telescope--Bessel's measurement of the parallax of a star,--Henderson's
  measurements--Kirchhoff and Bunsen's perfection of the
  spectroscope--Wonderful revelations of the spectroscope--Lord Kelvin's
  estimate of the time that will be required for the earth to become
  completely cooled--Alvan Clark's discovery of the companion star of
  Sirius--The advent of the photographic film in astronomy--Dr. Huggins's
  studies of nebulae--Sir Norman Lockyer's "cosmogonic guess,"--Croll's
  pre-nebular theory.

  CHAPTER III. THE NEW SCIENCE OF PALEONTOLOGY

  William Smith and fossil shells--His discovery that fossil rocks are
  arranged in regular systems--Smith's inquiries taken up by Cuvier--His
  Ossements Fossiles containing the first description of hairy
  elephant--His contention that fossils represent extinct species
  only--Dr. Buckland's studies of English fossil-beds--Charles Lyell
  combats catastrophism,--Elaboration of his ideas with reference to
  the rotation of species--The establishment of the doctrine of
  uniformitarianism,--Darwin's Origin of Species--Fossil man--Dr.
  Falconer's visit to the fossil-beds in the valley of the
  Somme--Investigations of Prestwich and Sir John Evans--Discovery of the
  Neanderthal skull,--Cuvier's rejection of human fossils--The finding
  of prehistoric carving on ivory--The fossil-beds of America--Professor
  Marsh's paper on the fossil horses in America--The Warren mastodon,--The
  Java fossil, Pithecanthropus Erectus.

  CHAPTER IV. THE ORIGIN AND DEVELOPMENT OF MODERN GEOLOGY

  James Hutton and the study of the rocks--His theory of the earth--His
  belief in volcanic cataclysms in raising and forming the continents--His
  famous paper before the Royal Society of Edinburgh, 1781---His
  conclusions that all strata of the earth have their origin at the bottom
  of the sea---His deduction that heated and expanded matter caused the
  elevation of land above the sea-level--Indifference at first shown this
  remarkable paper--Neptunists versus Plutonists--Scrope's classical work
  on volcanoes--Final acceptance of Hutton's explanation of the origin
  of granites--Lyell and uniformitarianism--Observations on the gradual
  elevation of the coast-lines of Sweden and Patagonia--Observations on
  the enormous amount of land erosion constantly taking place,--Agassiz
  and the glacial theory--Perraudin the chamois-hunter, and his
  explanation of perched bowlders--De Charpentier's acceptance of
  Perraudin's explanation--Agassiz's paper on his Alpine studies--His
  conclusion that the Alps were once covered with an ice-sheet--Final
  acceptance of the glacial theory--The geological ages--The work of
  Murchison and Sedgwick--Formation of the American continents--Past,
  present, and future.

  CHAPTER V. THE NEW SCIENCE OF METEOROLOGY

  Biot's investigations of meteors--The observations of Brandes and
  Benzenberg on the velocity of falling stars--Professor Olmstead's
  observations on the meteoric shower of 1833--Confirmation of Chladni's
  hypothesis of 1794--The aurora borealis--Franklin's suggestion that
  it is of electrical origin--Its close association with terrestrial
  magnetism--Evaporation, cloud-formation, and dew--Dalton's demonstration
  that water exists in the air as an independent gas--Hutton's theory of
  rain--Luke Howard's paper on clouds--Observations on dew, by Professor
  Wilson and Mr. Six--Dr. Wells's essay on dew--His observations
  on several appearances connected with dew--Isotherms and ocean
  currents--Humboldt and the-science of comparative climatology--His
  studies of ocean currents--Maury's theory that gravity is the cause
  of ocean currents--Dr. Croll on Climate and Time--Cyclones and
  anti-cyclones,--Dove's studies in climatology--Professor Ferrel's
  mathematical law of the deflection of winds--Tyndall's estimate of
  the amount of heat given off by the liberation of a pound of
  vapor--Meteorological observations and weather predictions.

  CHAPTER VI. MODERN THEORIES OF HEAT AND LIGHT

  Josiah Wedgwood and the clay pyrometer--Count Rumford and the vibratory
  theory of heat--His experiments with boring cannon to determine the
  nature of heat--Causing water to boil by the friction of the borer--His
  final determination that heat is a form of motion--Thomas Young and the
  wave theory of light--His paper on the theory of light and colors--His
  exposition of the colors of thin plates--Of the colors of thick
  plates, and of striated surfaces,--Arago and Fresnel champion the wave
  theory--opposition to the theory by Biot--The French Academy's tacit
  acceptance of the correctness of the theory by its admission of Fresnel
  as a member.

  CHAPTER VII. THE MODERN DEVELOPMENT OF ELECTRICITY AND MAGNETISM

  Galvani and the beginning of modern electricity--The construction of
  the voltaic pile--Nicholson's and Carlisle's discovery that the galvanic
  current decomposes water--Decomposition of various substances by Sir
  Humphry Davy--His construction of an arc-light--The deflection of the
  magnetic needle by electricity demonstrated by Oersted--Effect of
  this important discovery--Ampere creates the science of
  electro-dynamics--Joseph Henry's studies of electromagnets--Michael
  Faraday begins his studies of electromagnetic induction--His famous
  paper before the Royal Society, in 1831, in which he demonstrates
  electro-magnetic induction--His explanation of Arago's
  rotating disk--The search for a satisfactory method of storing
  electricity--Roentgen rays, or X-rays.

  CHAPTER VIII. THE CONSERVATION OF ENERGY

  Faraday narrowly misses the discovery of the doctrine of
  conservation--Carnot's belief that a definite quantity of work can be
  transformed into a definite quantity of heat--The work of James Prescott
  Joule--Investigations begun by Dr. Mayer--Mayer's paper of 1842--His
  statement of the law of the conservation of energy--Mayer and
  Helmholtz--Joule's paper of 1843--Joule or Mayer--Lord Kelvin and the
  dissipation of energy-The final unification.


  CHAPTER IX. THE ETHER AND PONDERABLE MATTER

  James Clerk-Maxwell's conception of ether--Thomas Young and
  "Luminiferous ether,"--Young's and Fresnel's conception of transverse
  luminiferous undulations--Faraday's experiments pointing to the
  existence of ether--Professor Lodge's suggestion of two ethers--Lord
  Kelvin's calculation of the probable density of ether--The vortex theory
  of atoms--Helmholtz's calculations in vortex motions--Professor
  Tait's apparatus for creating vortex rings in the air---The ultimate
  constitution of matter as conceived by Boscovich--Davy's speculations
  as to the changes that occur in the substance of matter at different
  temperatures--Clausius's and Maxwell's investigations of the
  kinetic theory of gases--Lord Kelvin's estimate of the size of the
  molecule--Studies of the potential energy of molecules--Action of gases
  at low temperatures.

  APPENDIX



A HISTORY OF SCIENCE



BOOK III. MODERN DEVELOPMENT OF THE PHYSICAL SCIENCES

With the present book we enter the field of the distinctively modern.
There is no precise date at which we take up each of the successive
stories, but the main sweep of development has to do in each case with
the nineteenth century. We shall see at once that this is a time both
of rapid progress and of great differentiation. We have heard almost
nothing hitherto of such sciences as paleontology, geology, and
meteorology, each of which now demands full attention. Meantime,
astronomy and what the workers of the elder day called natural
philosophy become wonderfully diversified and present numerous
phases that would have been startling enough to the star-gazers and
philosophers of the earlier epoch.

Thus, for example, in the field of astronomy, Herschel is able, thanks
to his perfected telescope, to discover a new planet and then to reach
out into the depths of space and gain such knowledge of stars and
nebulae as hitherto no one had more than dreamed of. Then, in rapid
sequence, a whole coterie of hitherto unsuspected minor planets is
discovered, stellar distances are measured, some members of the starry
galaxy are timed in their flight, the direction of movement of the solar
system itself is investigated, the spectroscope reveals the chemical
composition even of suns that are unthinkably distant, and a tangible
theory is grasped of the universal cycle which includes the birth and
death of worlds.

Similarly the new studies of the earth's surface reveal secrets of
planetary formation hitherto quite inscrutable. It becomes known that
the strata of the earth's surface have been forming throughout untold
ages, and that successive populations differing utterly from one another
have peopled the earth in different geological epochs. The entire point
of view of thoughtful men becomes changed in contemplating the history
of the world in which we live--albeit the newest thought harks back to
some extent to those days when the inspired thinkers of early Greece
dreamed out the wonderful theories with which our earlier chapters have
made our readers familiar.

In the region of natural philosophy progress is no less pronounced and
no less striking. It suffices here, however, by way of anticipation,
simply to name the greatest generalization of the century in physical
science--the doctrine of the conservation of energy.



I. THE SUCCESSORS OF NEWTON IN ASTRONOMY


HEVELIUS AND HALLEY

STRANGELY enough, the decade immediately following Newton was one of
comparative barrenness in scientific progress, the early years of the
eighteenth century not being as productive of great astronomers as the
later years of the seventeenth, or, for that matter, as the later years
of the eighteenth century itself. Several of the prominent astronomers
of the later seventeenth century lived on into the opening years of the
following century, however, and the younger generation soon developed
a coterie of astronomers, among whom Euler, Lagrange, Laplace, and
Herschel, as we shall see, were to accomplish great things in this field
before the century closed.

One of the great seventeenth-century astronomers, who died just before
the close of the century, was Johannes Hevelius (1611-1687), of Dantzig,
who advanced astronomy by his accurate description of the face and
the spots of the moon. But he is remembered also for having retarded
progress by his influence in refusing to use telescopic sights in his
observations, preferring until his death the plain sights long before
discarded by most other astronomers. The advantages of these telescope
sights have been discussed under the article treating of Robert Hooke,
but no such advantages were ever recognized by Hevelius. So great was
Hevelius's reputation as an astronomer that his refusal to recognize the
advantage of the telescope sights caused many astronomers to hesitate
before accepting them as superior to the plain; and even the famous
Halley, of whom we shall speak further in a moment, was sufficiently
in doubt over the matter to pay the aged astronomer a visit to test his
skill in using the old-style sights. Side by side, Hevelius and Halley
made their observations, Hevelius with his old instrument and Halley
with the new. The results showed slightly in the younger man's favor,
but not enough to make it an entirely convincing demonstration. The
explanation of this, however, did not lie in the lack of superiority
of the telescopic instrument, but rather in the marvellous skill of the
aged Hevelius, whose dexterity almost compensated for the defect of his
instrument. What he might have accomplished could he have been induced
to adopt the telescope can only be surmised.

Halley himself was by no means a tyro in matters astronomical at that
time. As the only son of a wealthy soap-boiler living near London, he
had been given a liberal education, and even before leaving college
made such novel scientific observations as that of the change in the
variation of the compass. At nineteen years of age he discovered a new
method of determining the elements of the planetary orbits which was a
distinct improvement over the old. The year following he sailed for the
Island of St, Helena to make observations of the heavens in the southern
hemisphere.

It was while in St. Helena that Halley made his famous observation
of the transit of Mercury over the sun's disk, this observation being
connected, indirectly at least, with his discovery of a method of
determining the parallax of the planets. By parallax is meant the
apparent change in the position of an object, due really to a change in
the position of the observer. Thus, if we imagine two astronomers making
observations of the sun from opposite sides of the earth at the same
time, it is obvious that to these observers the sun will appear to be
at two different points in the sky. Half the angle measuring this
difference would be known as the sun's parallax. This would depend,
then, upon the distance of the earth from the sun and the length of
the earth's radius. Since the actual length of this radius has been
determined, the parallax of any heavenly body enables the astronomer to
determine its exact distance.

The parallaxes can be determined equally well, however, if two observers
are separated by exactly known distances, several hundreds or thousands
of miles apart. In the case of a transit of Venus across the sun's
disk, for example, an observer at New York notes the image of the planet
moving across the sun's disk, and notes also the exact time of this
observation. In the same manner an observer at London makes similar
observations. Knowing the distance between New York and London, and
the different time of the passage, it is thus possible to calculate the
difference of the parallaxes of the sun and a planet crossing its disk.
The idea of thus determining the parallax of the planets originated, or
at least was developed, by Halley, and from this phenomenon he thought
it possible to conclude the dimensions of all the planetary orbits. As
we shall see further on, his views were found to be correct by later
astronomers.

In 1721 Halley succeeded Flamsteed as astronomer royal at the Greenwich
Observatory. Although sixty-four years of age at that time his activity
in astronomy continued unabated for another score of years. At Greenwich
he undertook some tedious observations of the moon, and during those
observations was first to detect the acceleration of mean motion. He
was unable to explain this, however, and it remained for Laplace in the
closing years of the century to do so, as we shall see later.

Halley's book, the Synopsis Astronomiae Cometicae, is one of the most
valuable additions to astronomical literature since the time of Kepler.
He was first to attempt the calculation of the orbit of a comet, having
revived the ancient opinion that comets belong to the solar system,
moving in eccentric orbits round the sun, and his calculation of the
orbit of the comet of 1682 led him to predict correctly the return of
that comet in 1758. Halley's Study of Meteors.

Like other astronomers of his time he was greatly puzzled over the
well-known phenomena of shooting-stars, or meteors, making many
observations himself, and examining carefully the observations of other
astronomers. In 1714 he gave his views as to the origin and composition
of these mysterious visitors in the earth's atmosphere. As this
subject will be again referred to in a later chapter, Halley's views,
representing the most advanced views of his age, are of interest.

"The theory of the air seemeth at present," he says, "to be perfectly
well understood, and the differing densities thereof at all altitudes;
for supposing the same air to occupy spaces reciprocally proportional to
the quantity of the superior or incumbent air, I have elsewhere proved
that at forty miles high the air is rarer than at the surface of
the earth at three thousand times; and that the utmost height of the
atmosphere, which reflects light in the Crepusculum, is not fully
forty-five miles, notwithstanding which 'tis still manifest that some
sort of vapors, and those in no small quantity, arise nearly to that
height. An instance of this may be given in the great light the society
had an account of (vide Transact. Sep., 1676) from Dr. Wallis, which was
seen in very distant counties almost over all the south part of England.
Of which though the doctor could not get so particular a relation as was
requisite to determine the height thereof, yet from the distant places
it was seen in, it could not but be very many miles high.

"So likewise that meteor which was seen in 1708, on the 31st of July,
between nine and ten o'clock at night, was evidently between forty and
fifty miles perpendicularly high, and as near as I can gather, over
Shereness and the buoy on the Nore. For it was seen at London moving
horizontally from east by north to east by south at least fifty degrees
high, and at Redgrove, in Suffolk, on the Yarmouth road, about twenty
miles from the east coast of England, and at least forty miles to the
eastward of London, it appeared a little to the westward of the south,
suppose south by west, and was seen about thirty degrees high, sliding
obliquely downward. I was shown in both places the situation thereof,
which was as described, but could wish some person skilled in
astronomical matters bad seen it, that we might pronounce concerning its
height with more certainty. Yet, as it is, we may securely conclude
that it was not many more miles westerly than Redgrove, which, as I
said before, is about forty miles more easterly than London. Suppose it,
therefore, where perpendicular, to have been thirty-five miles east
from London, and by the altitude it appeared at in London--viz., fifty
degrees, its tangent will be forty-two miles, for the height of the
meteor above the surface of the earth; which also is rather of the
least, because the altitude of the place shown me is rather more than
less than fifty degrees; and the like may be concluded from the altitude
it appeared in at Redgrove, near seventy miles distant. Though at this
very great distance, it appeared to move with an incredible velocity,
darting, in a very few seconds of time, for about twelve degrees of
a great circle from north to south, being very bright at its first
appearance; and it died away at the east of its course, leaving for some
time a pale whiteness in the place, with some remains of it in the track
where it had gone; but no hissing sound as it passed, or bounce of an
explosion were heard.

"It may deserve the honorable society's thoughts, how so great a
quantity of vapor should be raised to the top of the atmosphere, and
there collected, so as upon its ascension or otherwise illumination, to
give a light to a circle of above one hundred miles diameter, not much
inferior to the light of the moon; so as one might see to take a pin
from the ground in the otherwise dark night. 'Tis hard to conceive what
sort of exhalations should rise from the earth, either by the action
of the sun or subterranean heat, so as to surmount the extreme cold
and rareness of the air in those upper regions: but the fact is
indisputable, and therefore requires a solution."

From this much of the paper it appears that there was a general belief
that this burning mass was heated vapor thrown off from the earth in
some mysterious manner, yet this is unsatisfactory to Halley, for after
citing various other meteors that have appeared within his knowledge, he
goes on to say:

"What sort of substance it must be, that could be so impelled and
ignited at the same time; there being no Vulcano or other Spiraculum of
subterraneous fire in the northeast parts of the world, that we ever yet
heard of, from whence it might be projected.

"I have much considered this appearance, and think it one of the hardest
things to account for that I have yet met with in the phenomena of
meteors, and I am induced to think that it must be some collection of
matter formed in the aether, as it were, by some fortuitous concourse
of atoms, and that the earth met with it as it passed along in its orb,
then but newly formed, and before it had conceived any great impetus of
descent towards the sun. For the direction of it was exactly opposite to
that of the earth, which made an angle with the meridian at that time
of sixty-seven gr., that is, its course was from west southwest to east
northeast, wherefore the meteor seemed to move the contrary way. And
besides falling into the power of the earth's gravity, and losing its
motion from the opposition of the medium, it seems that it descended
towards the earth, and was extinguished in the Tyrrhene Sea, to the
west southwest of Leghorn. The great blow being heard upon its first
immersion into the water, and the rattling like the driving of a cart
over stones being what succeeded upon its quenching; something like this
is always heard upon quenching a very hot iron in water. These facts
being past dispute, I would be glad to have the opinion of the learned
thereon, and what objection can be reasonably made against the above
hypothesis, which I humbly submit to their censure."(1)

These few paragraphs, coming as they do from a leading
eighteenth-century astronomer, convey more clearly than any comment the
actual state of the meteorological learning at that time. That this ball
of fire, rushing "at a greater velocity than the swiftest cannon-ball,"
was simply a mass of heated rock passing through our atmosphere, did not
occur to him, or at least was not credited. Nor is this surprising when
we reflect that at that time universal gravitation had been but recently
discovered; heat had not as yet been recognized as simply a form of
motion; and thunder and lightning were unexplained mysteries, not to
be explained for another three-quarters of a century. In the chapter on
meteorology we shall see how the solution of this mystery that puzzled
Halley and his associates all their lives was finally attained.


BRADLEY AND THE ABERRATION OF LIGHT

Halley was succeeded as astronomer royal by a man whose useful additions
to the science were not to be recognized or appreciated fully until
brought to light by the Prussian astronomer Bessel early in the
nineteenth century. This was Dr. James Bradley, an ecclesiastic, who
ranks as one of the most eminent astronomers of the eighteenth century.
His most remarkable discovery was the explanation of a peculiar motion
of the pole-star, first observed, but not explained, by Picard a
century before. For many years a satisfactory explanation was sought
unsuccessfully by Bradley and his fellow-astronomers, but at last he was
able to demonstrate that the stary Draconis, on which he was making his
observations, described, or appeared to describe, a small ellipse.
If this observation was correct, it afforded a means of computing the
aberration of any star at all times. The explanation of the physical
cause of this aberration, as Bradley thought, and afterwards
demonstrated, was the result of the combination of the motion of light
with the annual motion of the earth. Bradley first formulated this
theory in 1728, but it was not until 1748--twenty years of continuous
struggle and observation by him--that he was prepared to communicate the
results of his efforts to the Royal Society. This remarkable paper is
thought by the Frenchman, Delambre, to entitle its author to a place in
science beside such astronomers as Hipparcbus and Kepler.

Bradley's studies led him to discover also the libratory motion of the
earth's axis. "As this appearance of Draconis indicated a diminution
of the inclination of the earth's axis to the plane of the ecliptic,"
he says; "and as several astronomers have supposed THAT inclination to
diminish regularly; if this phenomenon depended upon such a cause, and
amounted to 18" in nine years, the obliquity of the ecliptic would, at
that rate, alter a whole minute in thirty years; which is much
faster than any observations, before made, would allow. I had reason,
therefore, to think that some part of this motion at the least, if not
the whole, was owing to the moon's action upon the equatorial parts of
the earth; which, I conceived, might cause a libratory motion of
the earth's axis. But as I was unable to judge, from only nine years
observations, whether the axis would entirely recover the same position
that it had in the year 1727, I found it necessary to continue my
observations through a whole period of the moon's nodes; at the end of
which I had the satisfaction to see, that the stars, returned into the
same position again; as if there had been no alteration at all in the
inclination of the earth's axis; which fully convinced me that I had
guessed rightly as to the cause of the phenomena. This circumstance
proves likewise, that if there be a gradual diminution of the obliquity
of the ecliptic, it does not arise only from an alteration in the
position of the earth's axis, but rather from some change in the plane
of the ecliptic itself; because the stars, at the end of the period
of the moon's nodes, appeared in the same places, with respect to the
equator, as they ought to have done, if the earth's axis had retained
the same inclination to an invariable plane."(2)


FRENCH ASTRONOMERS

Meanwhile, astronomers across the channel were by no means idle. In
France several successful observers were making many additions to the
already long list of observations of the first astronomer of the Royal
Observatory of Paris, Dominic Cassini (1625-1712), whose reputation
among his contemporaries was much greater than among succeeding
generations of astronomers. Perhaps the most deserving of these
successors was Nicolas Louis de Lacaille (1713-1762), a theologian who
had been educated at the expense of the Duke of Bourbon, and who, soon
after completing his clerical studies, came under the patronage of
Cassini, whose attention had been called to the young man's interest in
the sciences. One of Lacaille's first under-takings was the remeasuring
of the French are of the meridian, which had been incorrectly measured
by his patron in 1684. This was begun in 1739, and occupied him for
two years before successfully completed. As a reward, however, he was
admitted to the academy and appointed mathematical professor in Mazarin
College.

In 1751 he went to the Cape of Good Hope for the purpose of determining
the sun's parallax by observations of the parallaxes of Mars and Venus,
and incidentally to make observations on the other southern hemisphere
stars. The results of this undertaking were most successful, and were
given in his Coelum australe stelligerum, etc., published in 1763. In
this he shows that in the course of a single year he had observed some
ten thousand stars, and computed the places of one thousand nine hundred
and forty-two of them, measured a degree of the meridian, and made
many observations of the moon--productive industry seldom equalled in
a single year in any field. These observations were of great service to
the astronomers, as they afforded the opportunity of comparing the stars
of the southern hemisphere with those of the northern, which were being
observed simultaneously by Lelande at Berlin.

Lacaille's observations followed closely upon the determination of an
absorbing question which occupied the attention of the astronomers in
the early part of the century. This question was as to the shape of the
earth--whether it was actually flattened at the poles. To settle this
question once for all the Academy of Sciences decided to make the
actual measurement of the length of two degrees, one as near the pole
as possible, the other at the equator. Accordingly, three astronomers,
Godin, Bouguer, and La Condamine, made the journey to a spot on the
equator in Peru, while four astronomers, Camus, Clairaut, Maupertuis,
and Lemonnier, made a voyage to a place selected in Lapland. The result
of these expeditions was the determination that the globe is oblately
spheroidal.

A great contemporary and fellow-countryman of Lacaille was Jean Le Rond
d'Alembert (1717-1783), who, although not primarily an astronomer, did
so much with his mathematical calculations to aid that science that
his name is closely connected with its progress during the eighteenth
century. D'Alembert, who became one of the best-known men of science of
his day, and whose services were eagerly sought by the rulers of Europe,
began life as a foundling, having been exposed in one of the markets of
Paris. The sickly infant was adopted and cared for in the family of a
poor glazier, and treated as a member of the family. In later years,
however, after the foundling had become famous throughout Europe, his
mother, Madame Tencin, sent for him, and acknowledged her relationship.
It is more than likely that the great philosopher believed her story,
but if so he did not allow her the satisfaction of knowing his belief,
declaring always that Madame Tencin could "not be nearer than a
step-mother to him, since his mother was the wife of the glazier."

D'Alembert did much for the cause of science by his example as well
as by his discoveries. By living a plain but honest life, declining
magnificent offers of positions from royal patrons, at the same time
refusing to grovel before nobility, he set a worthy example to other
philosophers whose cringing and pusillanimous attitude towards persons
of wealth or position had hitherto earned them the contempt of the upper
classes.

His direct additions to astronomy are several, among others the
determination of the mutation of the axis of the earth. He also
determined the ratio of the attractive forces of the sun and moon,
which he found to be about as seven to three. From this he reached the
conclusion that the earth must be seventy times greater than the moon.
The first two volumes of his Researches on the Systems of the World,
published in 1754, are largely devoted to mathematical and astronomical
problems, many of them of little importance now, but of great interest
to astronomers at that time.

Another great contemporary of D'Alembert, whose name is closely
associated and frequently confounded with his, was Jean Baptiste Joseph
Delambre (1749-1822). More fortunate in birth as also in his educational
advantages, Delambre as a youth began his studies under the celebrated
poet Delille. Later he was obliged to struggle against poverty,
supporting himself for a time by making translations from Latin, Greek,
Italian, and English, and acting as tutor in private families. The
turning-point of his fortune came when the attention of Lalande was
called to the young man by his remarkable memory, and Lalande soon
showed his admiration by giving Delambre certain difficult astronomical
problems to solve. By performing these tasks successfully his future as
an astronomer became assured. At that time the planet Uranus had just
been discovered by Herschel, and the Academy of Sciences offered as the
subject for one of its prizes the determination of the planet's orbit.
Delambre made this determination and won the prize--a feat that brought
him at once into prominence.

By his writings he probably did as much towards perfecting modern
astronomy as any one man. His History of Astronomy is not merely a
narrative of progress of astronomy but a complete abstract of all the
celebrated works written on the subject. Thus he became famous as an
historian as well as an astronomer.


LEONARD EULER

Still another contemporary of D'Alembert and Delambre, and somewhat
older than either of them, was Leonard Euler (1707-1783), of Basel,
whose fame as a philosopher equals that of either of the great
Frenchmen. He is of particular interest here in his capacity of
astronomer, but astronomy was only one of the many fields of science in
which he shone. Surely something out of the ordinary was to be expected
of the man who could "repeat the AEneid of Virgil from the beginning
to the end without hesitation, and indicate the first and last line of
every page of the edition which he used." Something was expected, and he
fulfilled these expectations.

In early life he devoted himself to the study of theology and the
Oriental languages, at the request of his father, but his love of
mathematics proved too strong, and, with his father's consent, he
finally gave up his classical studies and turned to his favorite study,
geometry. In 1727 he was invited by Catharine I. to reside in St.
Petersburg, and on accepting this invitation he was made an associate
of the Academy of Sciences. A little later he was made professor of
physics, and in 1733 professor of mathematics. In 1735 he solved a
problem in three days which some of the eminent mathematicians would not
undertake under several months. In 1741 Frederick the Great invited him
to Berlin, where he soon became a member of the Academy of Sciences and
professor of mathematics; but in 1766 he returned to St. Petersburg.
Towards the close of his life he became virtually blind, being obliged
to dictate his thoughts, sometimes to persons entirely ignorant of the
subject in hand. Nevertheless, his remarkable memory, still further
heightened by his blindness, enabled him to carry out the elaborate
computations frequently involved.

Euler's first memoir, transmitted to the Academy of Sciences of Paris
in 1747, was on the planetary perturbations. This memoir carried off the
prize that had been offered for the analytical theory of the motions of
Jupiter and Saturn. Other memoirs followed, one in 1749 and another in
1750, with further expansions of the same subject. As some slight
errors were found in these, such as a mistake in some of the formulae
expressing the secular and periodic inequalities, the academy proposed
the same subject for the prize of 1752. Euler again competed, and won
this prize also. The contents of this memoir laid the foundation for
the subsequent demonstration of the permanent stability of the planetary
system by Laplace and Lagrange.

It was Euler also who demonstrated that within certain fixed limits
the eccentricities and places of the aphelia of Saturn and Jupiter are
subject to constant variation, and he calculated that after a lapse
of about thirty thousand years the elements of the orbits of these two
planets recover their original values.



II. THE PROGRESS OF MODERN ASTRONOMY


A NEW epoch in astronomy begins with the work of William Herschel, the
Hanoverian, whom England made hers by adoption. He was a man with a
positive genius for sidereal discovery. At first a mere amateur in
astronomy, he snatched time from his duties as music-teacher to grind
him a telescopic mirror, and began gazing at the stars. Not content with
his first telescope, he made another and another, and he had such genius
for the work that he soon possessed a better instrument than was ever
made before. His patience in grinding the curved reflective surface was
monumental. Sometimes for sixteen hours together he must walk steadily
about the mirror, polishing it, without once removing his hands.
Meantime his sister, always his chief lieutenant, cheered him with her
presence, and from time to time put food into his mouth. The telescope
completed, the astronomer turned night into day, and from sunset to
sunrise, year in and year out, swept the heavens unceasingly, unless
prevented by clouds or the brightness of the moon. His sister sat always
at his side, recording his observations. They were in the open air,
perched high at the mouth of the reflector, and sometimes it was so cold
that the ink froze in the bottle in Caroline Herschel's hand; but the
two enthusiasts hardly noticed a thing so common-place as terrestrial
weather. They were living in distant worlds.

The results? What could they be? Such enthusiasm would move mountains.
But, after all, the moving of mountains seems a liliputian task compared
with what Herschel really did with those wonderful telescopes. He moved
worlds, stars, a universe--even, if you please, a galaxy of universes;
at least he proved that they move, which seems scarcely less wonderful;
and he expanded the cosmos, as man conceives it, to thousands of times
the dimensions it had before. As a mere beginning, he doubled the
diameter of the solar system by observing the great outlying planet
which we now call Uranus, but which he christened Georgium Sidus,
in honor of his sovereign, and which his French contemporaries, not
relishing that name, preferred to call Herschel.

This discovery was but a trifle compared with what Herschel did later
on, but it gave him world-wide reputation none the less. Comets and
moons aside, this was the first addition to the solar system that had
been made within historic times, and it created a veritable furor of
popular interest and enthusiasm. Incidentally King George was flattered
at having a world named after him, and he smiled on the astronomer, and
came with his court to have a look at his namesake. The inspection
was highly satisfactory; and presently the royal favor enabled the
astronomer to escape the thraldom of teaching music and to devote his
entire time to the more congenial task of star-gazing.

Thus relieved from the burden of mundane embarrassments, he turned with
fresh enthusiasm to the skies, and his discoveries followed one another
in bewildering profusion. He found various hitherto unseen moons of our
sister planets; he made special studies of Saturn, and proved that this
planet, with its rings, revolves on its axis; he scanned the spots on
the sun, and suggested that they influence the weather of our earth; in
short, he extended the entire field of solar astronomy. But very soon
this field became too small for him, and his most important researches
carried him out into the regions of space compared with which the span
of our solar system is a mere point. With his perfected telescopes he
entered abysmal vistas which no human eve ever penetrated before, which
no human mind had hitherto more than vaguely imagined. He tells us that
his forty-foot reflector will bring him light from a distance of "at
least eleven and three-fourths millions of millions of millions of
miles"--light which left its source two million years ago. The smallest
stars visible to the unaided eye are those of the sixth magnitude; this
telescope, he thinks, has power to reveal stars of the 1342d magnitude.

But what did Herschel learn regarding these awful depths of space and
the stars that people them? That was what the world wished to know.
Copernicus, Galileo, Kepler, had given us a solar system, but the stars
had been a mystery. What says the great reflector--are the stars points
of light, as the ancients taught, and as more than one philosopher of
the eighteenth century has still contended, or are they suns, as others
hold? Herschel answers, they are suns, each and every one of all the
millions--suns, many of them, larger than the one that is the centre of
our tiny system. Not only so, but they are moving suns. Instead of
being fixed in space, as has been thought, they are whirling in gigantic
orbits about some common centre. Is our sun that centre? Far from it.
Our sun is only a star like all the rest, circling on with its attendant
satellites--our giant sun a star, no different from myriad other stars,
not even so large as some; a mere insignificant spark of matter in an
infinite shower of sparks.

Nor is this all. Looking beyond the few thousand stars that are visible
to the naked eye, Herschel sees series after series of more distant
stars, marshalled in galaxies of millions; but at last he reaches a
distance beyond which the galaxies no longer increase. And yet--so he
thinks--he has not reached the limits of his vision. What then? He has
come to the bounds of the sidereal system--seen to the confines of the
universe. He believes that he can outline this system, this universe,
and prove that it has the shape of an irregular globe, oblately
flattened to almost disklike proportions, and divided at one edge--a
bifurcation that is revealed even to the naked eye in the forking of the
Milky Way.

This, then, is our universe as Herschel conceives it--a vast galaxy
of suns, held to one centre, revolving, poised in space. But even
here those marvellous telescopes do not pause. Far, far out beyond the
confines of our universe, so far that the awful span of our own system
might serve as a unit of measure, are revealed other systems, other
universes, like our own, each composed, as he thinks, of myriads of
suns, clustered like our galaxy into an isolated system--mere islands of
matter in an infinite ocean of space. So distant from our universe are
these now universes of Herschel's discovery that their light reaches
us only as a dim, nebulous glow, in most cases invisible to the unaided
eye. About a hundred of these nebulae were known when Herschel began
his studies. Before the close of the century he had discovered about
two thousand more of them, and many of these had been resolved by his
largest telescopes into clusters of stars. He believed that the farthest
of these nebulae that he could see was at least three hundred thousand
times as distant from us as the nearest fixed star. Yet that nearest
star--so more recent studies prove--is so remote that its light,
travelling one hundred and eighty thousand miles a second, requires
three and one-half years to reach our planet.

As if to give the finishing touches to this novel scheme of cosmology,
Herschel, though in the main very little given to unsustained
theorizing, allows himself the privilege of one belief that he cannot
call upon his telescope to substantiate. He thinks that all the myriad
suns of his numberless systems are instinct with life in the human
sense. Giordano Bruno and a long line of his followers had held that
some of our sister planets may be inhabited, but Herschel extends
the thought to include the moon, the sun, the stars--all the heavenly
bodies. He believes that he can demonstrate the habitability of our own
sun, and, reasoning from analogy, he is firmly convinced that all the
suns of all the systems are "well supplied with inhabitants." In this,
as in some other inferences, Herschel is misled by the faulty physics
of his time. Future generations, working with perfected instruments, may
not sustain him all along the line of his observations, even, let alone
his inferences. But how one's egotism shrivels and shrinks as one grasps
the import of his sweeping thoughts!

Continuing his observations of the innumerable nebulae, Herschel is led
presently to another curious speculative inference. He notes that some
star groups are much more thickly clustered than others, and he is
led to infer that such varied clustering tells of varying ages of the
different nebulae. He thinks that at first all space may have been
evenly sprinkled with the stars and that the grouping has resulted from
the action of gravitation.

"That the Milky Way is a most extensive stratum of stars of various
sizes admits no longer of lasting doubt," he declares, "and that our sun
is actually one of the heavenly bodies belonging to it is as evident. I
have now viewed and gauged this shining zone in almost every direction
and find it composed of stars whose number... constantly increases and
decreases in proportion to its apparent brightness to the naked eye.

"Let us suppose numberless stars of various sizes, scattered over an
indefinite portion of space in such a manner as to be almost equally
distributed throughout the whole. The laws of attraction which no doubt
extend to the remotest regions of the fixed stars will operate in such a
manner as most probably to produce the following effects:

"In the first case, since we have supposed the stars to be of various
sizes, it will happen that a star, being considerably larger than its
neighboring ones, will attract them more than they will be attracted by
others that are immediately around them; by which means they will be,
in time, as it were, condensed about a centre, or, in other words, form
themselves into a cluster of stars of almost a globular figure, more
or less regular according to the size and distance of the surrounding
stars....

"The next case, which will also happen almost as frequently as the
former, is where a few stars, though not superior in size to the rest,
may chance to be rather nearer one another than the surrounding ones,...
and this construction admits of the utmost variety of shapes....

"From the composition and repeated conjunction of both the foregoing
formations, a third may be derived when many large stars, or combined
small ones, are spread in long, extended, regular, or crooked rows,
streaks, or branches; for they will also draw the surrounding stars, so
as to produce figures of condensed stars curiously similar to the former
which gave rise to these condensations.

"We may likewise admit still more extensive combinations; when, at the
same time that a cluster of stars is forming at the one part of
space, there may be another collection in a different but perhaps not
far-distant quarter, which may occasion a mutual approach towards their
own centre of gravity.

"In the last place, as a natural conclusion of the former cases, there
will be formed great cavities or vacancies by the retreating of the
stars towards the various centres which attract them."(1)


Looking forward, it appears that the time must come when all the suns
of a system will be drawn together and destroyed by impact at a common
centre. Already, it seems to Herschel, the thickest clusters have
"outlived their usefulness" and are verging towards their doom.

But again, other nebulae present an appearance suggestive of an opposite
condition. They are not resolvable into stars, but present an almost
uniform appearance throughout, and are hence believed to be composed of
a shining fluid, which in some instances is seen to be condensed at the
centre into a glowing mass. In such a nebula Herschel thinks he sees a
sun in process of formation.


THE NEBULAR HYPOTHESIS OF KANT

Taken together, these two conceptions outline a majestic cycle of world
formation and world destruction--a broad scheme of cosmogony, such as
had been vaguely adumbrated two centuries before by Kepler and in
more recent times by Wright and Swedenborg. This so-called "nebular
hypothesis" assumes that in the beginning all space was uniformly filled
with cosmic matter in a state of nebular or "fire-mist" diffusion,
"formless and void." It pictures the condensation--coagulation, if
you will--of portions of this mass to form segregated masses, and the
ultimate development out of these masses of the sidereal bodies that we
see.

Perhaps the first elaborate exposition of this idea was that given by
the great German philosopher Immanuel Kant (born at Konigsberg in 1724,
died in 1804), known to every one as the author of the Critique of Pure
Reason. Let us learn from his own words how the imaginative philosopher
conceived the world to have come into existence.

"I assume," says Kant, "that all the material of which the globes
belonging to our solar system--all the planets and comets--consist, at
the beginning of all things was decomposed into its primary elements,
and filled the whole space of the universe in which the bodies formed
out of it now revolve. This state of nature, when viewed in and by
itself without any reference to a system, seems to be the very simplest
that can follow upon nothing. At that time nothing has yet been formed.
The construction of heavenly bodies at a distance from one another,
their distances regulated by their attraction, their form arising out of
the equilibrium of their collected matter, exhibit a later state.... In
a region of space filled in this manner, a universal repose could last
only a moment. The elements have essential forces with which to put
each other in motion, and thus are themselves a source of life. Matter
immediately begins to strive to fashion itself. The scattered elements
of a denser kind, by means of their attraction, gather from a sphere
around them all the matter of less specific gravity; again, these
elements themselves, together with the material which they have united
with them, collect in those points where the particles of a still denser
kind are found; these in like manner join still denser particles, and
so on. If we follow in imagination this process by which nature fashions
itself into form through the whole extent of chaos, we easily perceive
that all the results of the process would consist in the formation of
divers masses which, when their formation was complete, would by the
equality of their attraction be at rest and be forever unmoved.

"But nature has other forces in store which are specially exerted when
matter is decomposed into fine particles. They are those forces by which
these particles repel one another, and which, by their conflict with
attractions, bring forth that movement which is, as it were, the lasting
life of nature. This force of repulsion is manifested in the elasticity
of vapors, the effluences of strong-smelling bodies, and the diffusion
of all spirituous matters. This force is an uncontestable phenomenon of
matter. It is by it that the elements, which may be falling to the point
attracting them, are turned sideways promiscuously from their movement
in a straight line; and their perpendicular fall thereby issues in
circular movements, which encompass the centre towards which they were
falling. In order to make the formation of the world more distinctly
conceivable, we will limit our view by withdrawing it from the infinite
universe of nature and directing it to a particular system, as the
one which belongs to our sun. Having considered the generation of this
system, we shall be able to advance to a similar consideration of the
origin of the great world-systems, and thus to embrace the infinitude of
the whole creation in one conception.

"From what has been said, it will appear that if a point is situated in
a very large space where the attraction of the elements there situated
acts more strongly than elsewhere, then the matter of the elementary
particles scattered throughout the whole region will fall to that point.
The first effect of this general fall is the formation of a body at this
centre of attraction, which, so to speak, grows from an infinitely
small nucleus by rapid strides; and in the proportion in which this mass
increases, it also draws with greater force the surrounding particles
to unite with it. When the mass of this central body has grown so great
that the velocity with which it draws the particles to itself with great
distances is bent sideways by the feeble degree of repulsion with which
they impede one another, and when it issues in lateral movements which
are capable by means of the centrifugal force of encompassing the
central body in an orbit, then there are produced whirls or vortices
of particles, each of which by itself describes a curved line by the
composition of the attracting force and the force of revolution that had
been bent sideways. These kinds of orbits all intersect one another,
for which their great dispersion in this space gives place. Yet these
movements are in many ways in conflict with one another, and they
naturally tend to bring one another to a uniformity--that is, into a
state in which one movement is as little obstructive to the other as
possible. This happens in two ways: first by the particles limiting
one another's movement till they all advance in one direction; and,
secondly, in this way, that the particles limit their vertical movements
in virtue of which they are approaching the centre of attraction, till
they all move horizontally--i. e., in parallel circles round the sun as
their centre, no longer intercept one another, and by the centrifugal
force becoming equal with the falling force they keep themselves
constantly in free circular orbits at the distance at which they move.
The result, finally, is that only those particles continue to move in
this region of space which have acquired by their fall a velocity, and
through the resistance of the other particles a direction, by which they
can continue to maintain a FREE CIRCULAR MOVEMENT....

"The view of the formation of the planets in this system has the
advantage over every other possible theory in holding that the origin
of the movements, and the position of the orbits in arising at that same
point of time--nay, more, in showing that even the deviations from the
greatest possible exactness in their determinations, as well as the
accordances themselves, become clear at a glance. The planets are formed
out of particles which, at the distance at which they move, have exact
movements in circular orbits; and therefore the masses composed out of
them will continue the same movements and at the same rate and in the
same direction."(2)


It must be admitted that this explanation leaves a good deal to be
desired. It is the explanation of a metaphysician rather than that of
an experimental scientist. Such phrases as "matter immediately begins to
strive to fashion itself," for example, have no place in the reasoning
of inductive science. Nevertheless, the hypothesis of Kant is a
remarkable conception; it attempts to explain along rational lines
something which hitherto had for the most part been considered
altogether inexplicable.

But there are various questions that at once suggest themselves which
the Kantian theory leaves unanswered. How happens it, for example, that
the cosmic mass which gave birth to our solar system was divided into
several planetary bodies instead of remaining a single mass? Were the
planets struck from the sun by the chance impact of comets, as Buffon
has suggested? or thrown out by explosive volcanic action, in accordance
with the theory of Dr. Darwin? or do they owe their origin to some
unknown law? In any event, how chanced it that all were projected in
nearly the same plane as we now find them?


LAPLACE AND THE NEBULAR HYPOTHESIS

It remained for a mathematical astronomer to solve these puzzles. The
man of all others competent to take the subject in hand was the French
astronomer Laplace. For a quarter of a century he had devoted his
transcendent mathematical abilities to the solution of problems of
motion of the heavenly bodies. Working in friendly rivalry with his
countryman Lagrange, his only peer among the mathematicians of the age,
he had taken up and solved one by one the problems that Newton left
obscure. Largely through the efforts of these two men the last lingering
doubts as to the solidarity of the Newtonian hypothesis of universal
gravitation had been removed. The share of Lagrange was hardly less than
that of his co-worker; but Laplace will longer be remembered, because
he ultimately brought his completed labors into a system, and,
incorporating with them the labors of his contemporaries, produced
in the Mecanique Celeste the undisputed mathematical monument of the
century, a fitting complement to the Principia of Newton, which it
supplements and in a sense completes.

In the closing years of the eighteenth century Laplace took up the
nebular hypothesis of cosmogony, to which we have just referred, and
gave it definite proportions; in fact, made it so thoroughly his own
that posterity will always link it with his name. Discarding the crude
notions of cometary impact and volcanic eruption, Laplace filled up the
gaps in the hypothesis with the aid of well-known laws of gravitation
and motion. He assumed that the primitive mass of cosmic matter which
was destined to form our solar system was revolving on its axis even at
a time when it was still nebular in character, and filled all space to
a distance far beyond the present limits of the system. As this vaporous
mass contracted through loss of heat, it revolved more and more swiftly,
and from time to time, through balance of forces at its periphery, rings
of its substance were whirled off and left revolving there, subsequently
to become condensed into planets, and in their turn whirl off minor
rings that became moons. The main body of the original mass remains in
the present as the still contracting and rotating body which we call the
sun.

Let us allow Laplace to explain all this in detail:

"In order to explain the prime movements of the planetary system,"
he says, "there are the five following phenomena: The movement of the
planets in the same direction and very nearly in the same plane; the
movement of the satellites in the same direction as that of the planets;
the rotation of these different bodies and the sun in the same
direction as their revolution, and in nearly the same plane; the slight
eccentricity of the orbits of the planets and of the satellites; and,
finally, the great eccentricity of the orbits of the comets, as if their
inclinations had been left to chance.

"Buffon is the only man I know who, since the discovery of the true
system of the world, has endeavored to show the origin of the planets
and their satellites. He supposes that a comet, in falling into the sun,
drove from it a mass of matter which was reassembled at a distance in
the form of various globes more or less large, and more or less removed
from the sun, and that these globes, becoming opaque and solid, are now
the planets and their satellites.

"This hypothesis satisfies the first of the five preceding phenomena;
for it is clear that all the bodies thus formed would move very nearly
in the plane which passed through the centre of the sun, and in the
direction of the torrent of matter which was produced; but the four
other phenomena appear to be inexplicable to me by this means. Indeed,
the absolute movement of the molecules of a planet ought then to be in
the direction of the movement of its centre of gravity; but it does not
at all follow that the motion of the rotation of the planets should be
in the same direction. Thus the earth should rotate from east to west,
but nevertheless the absolute movement of its molecules should be
from east to west; and this ought also to apply to the movement of the
revolution of the satellites, in which the direction, according to the
hypothesis which he offers, is not necessarily the same as that of the
progressive movement of the planets.

"A phenomenon not only very difficult to explain under this hypothesis,
but one which is even contrary to it, is the slight eccentricity of the
planetary orbits. We know, by the theory of central forces, that if
a body moves in a closed orbit around the sun and touches it, it also
always comes back to that point at every revolution; whence it follows
that if the planets were originally detached from the sun, they would
touch it at each return towards it, and their orbits, far from being
circular, would be very eccentric. It is true that a mass of matter
driven from the sun cannot be exactly compared to a globe which touches
its surface, for the impulse which the particles of this mass receive
from one another and the reciprocal attractions which they exert among
themselves, could, in changing the direction of their movements, remove
their perihelions from the sun; but their orbits would be always most
eccentric, or at least they would not have slight eccentricities except
by the most extraordinary chance. Thus we cannot see, according to
the hypothesis of Buffon, why the orbits of more than a hundred comets
already observed are so elliptical. This hypothesis is therefore
very far from satisfying the preceding phenomena. Let us see if it is
possible to trace them back to their true cause.

"Whatever may be its ultimate nature, seeing that it has caused or
modified the movements of the planets, it is necessary that this cause
should embrace every body, and, in view of the enormous distances which
separate them, it could only have been a fluid of immense extent.
In order to have given them an almost circular movement in the same
direction around the sun, it is necessary that this fluid should
have enveloped the sun as in an atmosphere. The consideration of the
planetary movements leads us then to think that, on account of excessive
heat, the atmosphere of the sun originally extended beyond the orbits of
all the planets, and that it was successively contracted to its present
limits.

"In the primitive condition in which we suppose the sun to have been, it
resembled a nebula such as the telescope shows is composed of a nucleus
more or less brilliant, surrounded by a nebulosity which, on condensing
itself towards the centre, forms a star. If it is conceived by analogy
that all the stars were formed in this manner, it is possible to imagine
their previous condition of nebulosity, itself preceded by other states
in which the nebulous matter was still more diffused, the nucleus being
less and less luminous. By going back as far as possible, we thus
arrive at a nebulosity so diffused that its existence could hardly be
suspected.

"For a long time the peculiar disposition of certain stars, visible
to the unaided eye, has struck philosophical observers. Mitchell
has already remarked how little probable it is that the stars in the
Pleiades, for example, could have been contracted into the small
space which encloses them by the fortuity of chance alone, and he has
concluded that this group of stars, and similar groups which the skies
present to us, are the necessary result of the condensation of a nebula,
with several nuclei, and it is evident that a nebula, by continually
contracting, towards these various nuclei, at length would form a group
of stars similar to the Pleiades. The condensation of a nebula with two
nuclei would form a system of stars close together, turning one upon
the other, such as those double stars of which we already know the
respective movements.

"But how did the solar atmosphere determine the movements of the
rotation and revolution of the planets and satellites? If these bodies
had penetrated very deeply into this atmosphere, its resistance would
have caused them to fall into the sun. We can therefore conjecture that
the planets were formed at their successive limits by the condensation
of a zone of vapors which the sun, on cooling, left behind, in the plane
of his equator.

"Let us recall the results which we have given in a preceding chapter.
The atmosphere of the sun could not have extended indefinitely. Its
limit was the point where the centrifugal force due to its movement
of rotation balanced its weight. But in proportion as the cooling
contracted the atmosphere, and those molecules which were near to them
condensed upon the surface of the body, the movement of the rotation
increased; for, on account of the Law of Areas, the sum of the areas
described by the vector of each molecule of the sun and its atmosphere
and projected in the plane of the equator being always the same, the
rotation should increase when these molecules approach the centre of the
sun. The centrifugal force due to this movement becoming thus larger,
the point where the weight is equal to it is nearer the sun. Supposing,
then, as it is natural to admit, that the atmosphere extended at some
period to its very limits, it should, on cooling, leave molecules behind
at this limit and at limits successively occasioned by the increased
rotation of the sun. The abandoned molecules would continue to revolve
around this body, since their centrifugal force was balanced by their
weight. But this equilibrium not arising in regard to the atmospheric
molecules parallel to the solar equator, the latter, on account of their
weight, approached the atmosphere as they condensed, and did not cease
to belong to it until by this motion they came upon the equator.

"Let us consider now the zones of vapor successively left behind. These
zones ought, according to appearance, by the condensation and mutual
attraction of their molecules, to form various concentric rings of vapor
revolving around the sun. The mutual gravitational friction of each ring
would accelerate some and retard others, until they had all acquired the
same angular velocity. Thus the actual velocity of the molecules most
removed from the sun would be the greatest. The following cause would
also operate to bring about this difference of speed. The molecules
farthest from the sun, and which by the effects of cooling and
condensation approached one another to form the outer part of the ring,
would have always described areas proportional to the time since the
central force by which they were controlled has been constantly directed
towards this body. But this constancy of areas necessitates an increase
of velocity proportional to the distance. It is thus seen that the same
cause would diminish the velocity of the molecules which form the inner
part of the ring.

"If all the molecules of the ring of vapor continued to condense without
disuniting, they would at length form a ring either solid or fluid. But
this formation would necessitate such a regularity in every part of the
ring, and in its cooling, that this phenomenon is extremely rare; and
the solar system affords us, indeed, but one example--namely, in the
ring of Saturn. In nearly every case the ring of vapor was broken into
several masses, each moving at similar velocities, and continuing to
rotate at the same distance around the sun. These masses would take
a spheroid form with a rotatory movement in the direction of the
revolution, because their inner molecules had less velocity than the
outer. Thus were formed so many planets in a condition of vapor. But
if one of them were powerful enough to reunite successively by its
attraction all the others around its centre of gravity, the ring of
vapor would be thus transformed into a single spheroidical mass of
vapor revolving around the sun with a rotation in the direction of its
revolution. The latter case has been that which is the most common, but
nevertheless the solar system affords us an instance of the first case
in the four small planets which move between Jupiter and Mars; at least,
if we do not suppose, as does M. Olbers, that they originally formed a
single planet which a mighty explosion broke up into several portions
each moving at different velocities.

"According to our hypothesis, the comets are strangers to our planetary
system. In considering them, as we have done, as minute nebulosities,
wandering from solar system to solar system, and formed by the
condensation of the nebulous matter everywhere existent in profusion in
the universe, we see that when they come into that part of the heavens
where the sun is all-powerful, he forces them to describe orbits either
elliptical or hyperbolic, their paths being equally possible in all
directions, and at all inclinations of the ecliptic, conformably to what
has been observed. Thus the condensation of nebulous matter, by which
we have at first explained the motions of the rotation and revolution
of the planets and their satellites in the same direction, and in nearly
approximate planes, explains also why the movements of the comets escape
this general law."(3)


The nebular hypothesis thus given detailed completion by Laplace is a
worthy complement of the grand cosmologic scheme of Herschel. Whether
true or false, the two conceptions stand as the final contributions
of the eighteenth century to the history of man's ceaseless efforts to
solve the mysteries of cosmic origin and cosmic structure. The world
listened eagerly and without prejudice to the new doctrines; and that
attitude tells of a marvellous intellectual growth of our race. Mark the
transition. In the year 1600, Bruno was burned at the stake for teaching
that our earth is not the centre of the universe. In 1700, Newton was
pronounced "impious and heretical" by a large school of philosophers
for declaring that the force which holds the planets in their orbits
is universal gravitation. In 1800, Laplace and Herschel are honored for
teaching that gravitation built up the system which it still controls;
that our universe is but a minor nebula, our sun but a minor star, our
earth a mere atom of matter, our race only one of myriad races peopling
an infinity of worlds. Doctrines which but the span of two human lives
before would have brought their enunciators to the stake were now
pronounced not impious, but sublime.


ASTEROIDS AND SATELLITES

The first day of the nineteenth century was fittingly signalized by the
discovery of a new world. On the evening of January 1, 1801, an Italian
astronomer, Piazzi, observed an apparent star of about the eighth
magnitude (hence, of course, quite invisible to the unaided eye), which
later on was seen to have moved, and was thus shown to be vastly nearer
the earth than any true star. He at first supposed, as Herschel had
done when he first saw Uranus, that the unfamiliar body was a comet; but
later observation proved it a tiny planet, occupying a position in space
between Mars and Jupiter. It was christened Ceres, after the tutelary
goddess of Sicily.

Though unpremeditated, this discovery was not unexpected, for
astronomers had long surmised the existence of a planet in the wide
gap between Mars and Jupiter. Indeed, they were even preparing to make
concerted search for it, despite the protests of philosophers, who
argued that the planets could not possibly exceed the magic number
seven, when Piazzi forestalled their efforts. But a surprise came
with the sequel; for the very next year Dr. Olbers, the wonderful
physician-astronomer of Bremen, while following up the course of Ceres,
happened on another tiny moving star, similarly located, which soon
revealed itself as planetary. Thus two planets were found where only one
was expected.

The existence of the supernumerary was a puzzle, but Olbers solved it
for the moment by suggesting that Ceres and Pallas, as he called his
captive, might be fragments of a quondam planet, shattered by internal
explosion or by the impact of a comet. Other similar fragments, he
ventured to predict, would be found when searched for. William Herschel
sanctioned this theory, and suggested the name asteroids for the tiny
planets. The explosion theory was supported by the discovery of another
asteroid, by Harding, of Lilienthal, in 1804, and it seemed clinched
when Olbers himself found a fourth in 1807. The new-comers were named
Juno and Vesta respectively.

There the case rested till 1845, when a Prussian amateur astronomer
named Hencke found another asteroid, after long searching, and opened a
new epoch of discovery. From then on the finding of asteroids became a
commonplace. Latterly, with the aid of photography, the list has been
extended to above four hundred, and as yet there seems no dearth in the
supply, though doubtless all the larger members have been revealed. Even
these are but a few hundreds of miles in diameter, while the smaller
ones are too tiny for measurement. The combined bulk of these minor
planets is believed to be but a fraction of that of the earth.

Olbers's explosion theory, long accepted by astronomers, has been
proven open to fatal objections. The minor planets are now believed to
represent a ring of cosmical matter, cast off from the solar nebula
like the rings that went to form the major planets, but prevented
from becoming aggregated into a single body by the perturbing mass of
Jupiter.


The Discovery of Neptune

As we have seen, the discovery of the first asteroid confirmed a
conjecture; the other important planetary discovery of the nineteenth
century fulfilled a prediction. Neptune was found through scientific
prophecy. No one suspected the existence of a trans-Uranian planet till
Uranus itself, by hair-breadth departures from its predicted orbit, gave
out the secret. No one saw the disturbing planet till the pencil of the
mathematician, with almost occult divination, had pointed out its place
in the heavens. The general predication of a trans-Uranian planet was
made by Bessel, the great Konigsberg astronomer, in 1840; the analysis
that revealed its exact location was undertaken, half a decade later,
by two independent workers--John Couch Adams, just graduated senior
wrangler at Cambridge, England, and U. J. J. Leverrier, the leading
French mathematician of his generation.

Adams's calculation was first begun and first completed. But it had one
radical defect--it was the work of a young and untried man. So it found
lodgment in a pigeon-hole of the desk of England's Astronomer Royal, and
an opportunity was lost which English astronomers have never ceased to
mourn. Had the search been made, an actual planet would have been seen
shining there, close to the spot where the pencil of the mathematician
had placed its hypothetical counterpart. But the search was not made,
and while the prophecy of Adams gathered dust in that regrettable
pigeon-hole, Leverrier's calculation was coming on, his tentative
results meeting full encouragement from Arago and other French savants.
At last the laborious calculations proved satisfactory, and, confident
of the result, Leverrier sent to the Berlin observatory, requesting that
search be made for the disturber of Uranus in a particular spot of the
heavens. Dr. Galle received the request September 23, 1846. That very
night he turned his telescope to the indicated region, and there, within
a single degree of the suggested spot, he saw a seeming star, invisible
to the unaided eye, which proved to be the long-sought planet,
henceforth to be known as Neptune. To the average mind, which finds
something altogether mystifying about abstract mathematics, this was a
feat savoring of the miraculous.

Stimulated by this success, Leverrier calculated an orbit for an
interior planet from perturbations of Mercury, but though prematurely
christened Vulcan, this hypothetical nursling of the sun still haunts
the realm of the undiscovered, along with certain equally hypothetical
trans-Neptunian planets whose existence has been suggested by "residual
perturbations" of Uranus, and by the movements of comets. No other
veritable additions of the sun's planetary family have been made in our
century, beyond the finding of seven small moons, which chiefly attest
the advance in telescopic powers. Of these, the tiny attendants of our
Martian neighbor, discovered by Professor Hall with the great Washington
refractor, are of greatest interest, because of their small size and
extremely rapid flight. One of them is poised only six thousand
miles from Mars, and whirls about him almost four times as fast as he
revolves, seeming thus, as viewed by the Martian, to rise in the west
and set in the east, and making the month only one-fourth as long as the
day.


The Rings of Saturn

The discovery of the inner or crape ring of Saturn, made simultaneously
in 1850 by William C. Bond, at the Harvard observatory, in America,
and the Rev. W. R. Dawes in England, was another interesting optical
achievement; but our most important advances in knowledge of Saturn's
unique system are due to the mathematician. Laplace, like his
predecessors, supposed these rings to be solid, and explained their
stability as due to certain irregularities of contour which Herschel
bad pointed out. But about 1851 Professor Peirce, of Harvard, showed
the untenability of this conclusion, proving that were the rings such as
Laplace thought them they must fall of their own weight. Then Professor
J. Clerk-Maxwell, of Cambridge, took the matter in hand, and his
analysis reduced the puzzling rings to a cloud of meteoric particles--a
"shower of brickbats"--each fragment of which circulates exactly as if
it were an independent planet, though of course perturbed and jostled
more or less by its fellows. Mutual perturbations, and the disturbing
pulls of Saturn's orthodox satellites, as investigated by Maxwell,
explain nearly all the phenomena of the rings in a manner highly
satisfactory.

After elaborate mathematical calculations covering many pages of his
paper entitled "On the Stability of Saturn's Rings," he summarizes his
deductions as follows:

"Let us now gather together the conclusions we have been able to draw
from the mathematical theory of various kinds of conceivable rings.

"We found that the stability of the motion of a solid ring depended
on so delicate an adjustment, and at the same time so unsymmetrical a
distribution of mass, that even if the exact conditions were fulfilled,
it could scarcely last long, and, if it did, the immense preponderance
of one side of the ring would be easily observed, contrary to
experience. These considerations, with others derived from the
mechanical structure of so vast a body, compel us to abandon any theory
of solid rings.

"We next examined the motion of a ring of equal satellites, and found
that if the mass of the planet is sufficient, any disturbances produced
in the arrangement of the ring will be propagated around it in the form
of waves, and will not introduce dangerous confusion. If the satellites
are unequal, the propagations of the waves will no longer be regular,
but disturbances of the ring will in this, as in the former case,
produce only waves, and not growing confusion. Supposing the ring to
consist, not of a single row of large satellites, but a cloud of evenly
distributed unconnected particles, we found that such a cloud must
have a very small density in order to be permanent, and that this is
inconsistent with its outer and inner parts moving with the same angular
velocity. Supposing the ring to be fluid and continuous, we found that
it will be necessarily broken up into small portions.

"We conclude, therefore, that the rings must consist of disconnected
particles; these must be either solid or liquid, but they must be
independent. The entire system of rings must, therefore, consist either
of a series of many concentric rings each moving with its own velocity
and having its own system of waves, or else of a confused multitude of
revolving particles not arranged in rings and continually coming into
collision with one another.

"Taking the first case, we found that in an indefinite number of
possible cases the mutual perturbations of two rings, stable in
themselves, might mount up in time to a destructive magnitude, and that
such cases must continually occur in an extensive system like that of
Saturn, the only retarding cause being the irregularity of the rings.

"The result of long-continued disturbance was found to be the
spreading-out of the rings in breadth, the outer rings pressing outward,
while the inner rings press inward.

"The final result, therefore, of the mechanical theory is that the only
system of rings which can exist is one composed of an indefinite number
of unconnected particles, revolving around the planet with different
velocities, according to their respective distances. These particles
may be arranged in series of narrow rings, or they may move through one
another irregularly. In the first case the destruction of the system
will be very slow, in the second case it will be more rapid, but there
may be a tendency towards arrangement in narrow rings which may retard
the process.

"We are not able to ascertain by observation the constitution of the two
outer divisions of the system of rings, but the inner ring is certainly
transparent, for the limb of Saturn has been observed through it. It is
also certain that though the space occupied by the ring is transparent,
it is not through the material parts of it that the limb of Saturn is
seen, for his limb was observed without distortion; which shows that
there was no refraction, and, therefore, that the rays did not pass
through a medium at all, but between the solar or liquid particles of
which the ring is composed. Here, then, we have an optical argument
in favor of the theory of independent particles as the material of
the rings. The two outer rings may be of the same nature, but not
so exceedingly rare that a ray of light can pass through their whole
thickness without encountering one of the particles.

"Finally, the two outer rings have been observed for two hundred years,
and it appears, from the careful analysis of all the observations of M.
Struve, that the second ring is broader than when first observed, and
that its inner edge is nearer the planet than formerly. The inner ring
also is suspected to be approaching the planet ever since its discovery
in 1850. These appearances seem to indicate the same slow progress of
the rings towards separation which we found to be the result of theory,
and the remark that the inner edge of the inner ring is more distinct
seems to indicate that the approach towards the planet is less rapid
near the edge, as we had reason to conjecture. As to the apparent
unchangeableness of the exterior diameter of the outer ring, we must
remember that the outer rings are certainly far more dense than the
inner one, and that a small change in the outer rings must balance a
great change in the inner one. It is possible, however, that some of the
observed changes may be due to the existence of a resisting medium.
If the changes already suspected should be confirmed by repeated
observations with the same instruments, it will be worth while to
investigate more carefully whether Saturn's rings are permanent or
transitory elements of the solar system, and whether in that part of
the heavens we see celestial immutability or terrestrial corruption
and generation, and the old order giving place to the new before our
eyes."(4)


Studies of the Moon

But perhaps the most interesting accomplishments of mathematical
astronomy--from a mundane standpoint, at any rate--are those that refer
to the earth's own satellite. That seemingly staid body was long ago
discovered to have a propensity to gain a little on the earth, appearing
at eclipses an infinitesimal moment ahead of time. Astronomers were
sorely puzzled by this act of insubordination; but at last Laplace and
Lagrange explained it as due to an oscillatory change in the earth's
orbit, thus fully exonerating the moon, and seeming to demonstrate the
absolute stability of our planetary system, which the moon's misbehavior
had appeared to threaten.

This highly satisfactory conclusion was an orthodox belief of celestial
mechanics until 1853, when Professor Adams of Neptunian fame, with whom
complex analyses were a pastime, reviewed Laplace's calculation, and
discovered an error which, when corrected, left about half the moon's
acceleration unaccounted for. This was a momentous discrepancy, which at
first no one could explain. But presently Professor Helmholtz, the great
German physicist, suggested that a key might be found in tidal friction,
which, acting as a perpetual brake on the earth's rotation, and
affecting not merely the waters but the entire substance of our planet,
must in the long sweep of time have changed its rate of rotation. Thus
the seeming acceleration of the moon might be accounted for as actual
retardation of the earth's rotation--a lengthening of the day instead of
a shortening of the month.

Again the earth was shown to be at fault, but this time the moon could
not be exonerated, while the estimated stability of our system, instead
of being re-established, was quite upset. For the tidal retardation is
not an oscillatory change which will presently correct itself, like the
orbital wobble, but a perpetual change, acting always in one direction.
Unless fully counteracted by some opposing reaction, therefore (as
it seems not to be), the effect must be cumulative, the ultimate
consequences disastrous. The exact character of these consequences was
first estimated by Professor G. H. Darwin in 1879. He showed that tidal
friction, in retarding the earth, must also push the moon out from the
parent planet on a spiral orbit. Plainly, then, the moon must formerly
have been nearer the earth than at present. At some very remote period
it must have actually touched the earth; must, in other words, have been
thrown off from the then plastic mass of the earth, as a polyp buds out
from its parent polyp. At that time the earth was spinning about in a
day of from two to four hours.

Now the day has been lengthened to twenty-four hours, and the moon has
been thrust out to a distance of a quarter-million miles; but the end is
not yet. The same progress of events must continue, till, at some remote
period in the future, the day has come to equal the month, lunar tidal
action has ceased, and one face of the earth looks out always at the
moon with that same fixed stare which even now the moon has been brought
to assume towards her parent orb. Should we choose to take even greater
liberties with the future, it may be made to appear (though some
astronomers dissent from this prediction) that, as solar tidal action
still continues, the day must finally exceed the month, and lengthen out
little by little towards coincidence with the year; and that the moon
meantime must pause in its outward flight, and come swinging back on a
descending spiral, until finally, after the lapse of untold aeons, it
ploughs and ricochets along the surface of the earth, and plunges to
catastrophic destruction.

But even though imagination pause far short of this direful culmination,
it still is clear that modern calculations, based on inexorable tidal
friction, suffice to revolutionize the views formerly current as to the
stability of the planetary system. The eighteenth-century mathematician
looked upon this system as a vast celestial machine which had been in
existence about six thousand years, and which was destined to run on
forever. The analyst of to-day computes both the past and the future of
this system in millions instead of thousands of years, yet feels well
assured that the solar system offers no contradiction to those laws of
growth and decay which seem everywhere to represent the immutable order
of nature.


COMETS AND METEORS

Until the mathematician ferreted out the secret, it surely never could
have been suspected by any one that the earth's serene attendant,

     "That orbed maiden, with white fire laden,
     Whom mortals call the moon,"

could be plotting injury to her parent orb. But there is another
inhabitant of the skies whose purposes have not been similarly free from
popular suspicion. Needless to say I refer to the black sheep of the
sidereal family, that "celestial vagabond" the comet.

Time out of mind these wanderers have been supposed to presage war,
famine, pestilence, perhaps the destruction of the world. And little
wonder. Here is a body which comes flashing out of boundless space into
our system, shooting out a pyrotechnic tail some hundreds of millions of
miles in length; whirling, perhaps, through the very atmosphere of the
sun at a speed of three or four hundred miles a second; then darting off
on a hyperbolic orbit that forbids it ever to return, or an elliptical
one that cannot be closed for hundreds or thousands of years; the tail
meantime pointing always away from the sun, and fading to nothingness as
the weird voyager recedes into the spatial void whence it came. Not many
times need the advent of such an apparition coincide with the outbreak
of a pestilence or the death of a Caesar to stamp the race of comets as
an ominous clan in the minds of all superstitious generations.

It is true, a hard blow was struck at the prestige of these alleged
supernatural agents when Newton proved that the great comet of 1680
obeyed Kepler's laws in its flight about the sun; and an even harder
one when the same visitant came back in 1758, obedient to Halley's
prediction, after its three-quarters of a century of voyaging but in
the abyss of space. Proved thus to bow to natural law, the celestial
messenger could no longer fully, sustain its role. But long-standing
notoriety cannot be lived down in a day, and the comet, though proved a
"natural" object, was still regarded as a very menacing one for
another hundred years or so. It remained for the nineteenth century to
completely unmask the pretender and show how egregiously our forebears
had been deceived.

The unmasking began early in the century, when Dr. Olbers, then the
highest authority on the subject, expressed the opinion that
the spectacular tail, which had all along been the comet's chief
stock-in-trade as an earth-threatener, is in reality composed of
the most filmy vapors, repelled from the cometary body by the sun,
presumably through electrical action, with a velocity comparable to that
of light. This luminous suggestion was held more or less in abeyance for
half a century. Then it was elaborated by Zollner, and particularly by
Bredichin, of the Moscow observatory, into what has since been regarded
as the most plausible of cometary theories. It is held that comets
and the sun are similarly electrified, and hence mutually repulsive.
Gravitation vastly outmatches this repulsion in the body of the comet,
but yields to it in the case of gases, because electrical force varies
with the surface, while gravitation varies only with the mass. From
study of atomic weights and estimates of the velocity of thrust of
cometary tails, Bredichin concluded that the chief components of the
various kinds of tails are hydrogen, hydrocarbons, and the vapor of
iron; and spectroscopic analysis goes far towards sustaining these
assumptions.

But, theories aside, the unsubstantialness of the comet's tail has been
put to a conclusive test. Twice during the nineteenth century the
earth has actually plunged directly through one of these threatening
appendages--in 1819, and again in 1861, once being immersed to a depth
of some three hundred thousand miles in its substance. Yet nothing
dreadful happened to us. There was a peculiar glow in the atmosphere,
so the more imaginative observers thought, and that was all. After such
fiascos the cometary train could never again pose as a world-destroyer.

But the full measure of the comet's humiliation is not yet told. The
pyrotechnic tail, composed as it is of portions of the comet's actual
substance, is tribute paid the sun, and can never be recovered. Should
the obeisance to the sun be many times repeated, the train-forming
material will be exhausted, and the comet's chiefest glory will have
departed. Such a fate has actually befallen a multitude of comets which
Jupiter and the other outlying planets have dragged into our system and
helped the sun to hold captive here. Many of these tailless comets were
known to the eighteenth-century astronomers, but no one at that time
suspected the true meaning of their condition. It was not even known how
closely some of them are enchained until the German astronomer Encke,
in 1822, showed that one which he had rediscovered, and which has
since borne his name, was moving in an orbit so contracted that it must
complete its circuit in about three and a half years. Shortly afterwards
another comet, revolving in a period of about six years, was discovered
by Biela, and given his name. Only two more of these short-period comets
were discovered during the first half of last century, but latterly they
have been shown to be a numerous family. Nearly twenty are known
which the giant Jupiter holds so close that the utmost reach of their
elliptical tether does not let them go beyond the orbit of Saturn. These
aforetime wanderers have adapted themselves wonderfully to planetary
customs, for all of them revolve in the same direction with the planets,
and in planes not wide of the ecliptic.

Checked in their proud hyperbolic sweep, made captive in a planetary
net, deprived of their trains, these quondam free-lances of the heavens
are now mere shadows of their former selves. Considered as to mere
bulk, they are very substantial shadows, their extent being measured in
hundreds of thousands of miles; but their actual mass is so slight that
they are quite at the mercy of the gravitation pulls of their captors.
And worse is in store for them. So persistently do sun and planets tug
at them that they are doomed presently to be torn into shreds.

Such a fate has already overtaken one of them, under the very eyes of
the astronomers, within the relatively short period during which these
ill-fated comets have been observed. In 1832 Biela's comet passed quite
near the earth, as astronomers measure distance, and in doing so created
a panic on our planet. It did no greater harm than that, of course, and
passed on its way as usual. The very next time it came within telescopic
hail it was seen to have broken into two fragments. Six years later
these fragments were separated by many millions of miles; and in 1852,
when the comet was due again, astronomers looked for it in vain. It had
been completely shattered.

What had become of the fragments? At that time no one positively knew.
But the question was to be answered presently. It chanced that just at
this period astronomers were paying much attention to a class of bodies
which they had hitherto somewhat neglected, the familiar shooting-stars,
or meteors. The studies of Professor Newton, of Yale, and Professor
Adams, of Cambridge, with particular reference to the great
meteor-shower of November, 1866, which Professor Newton had predicted
and shown to be recurrent at intervals of thirty-three years, showed
that meteors are not mere sporadic swarms of matter flying at random,
but exist in isolated swarms, and sweep about the sun in regular
elliptical orbits.

Presently it was shown by the Italian astronomer Schiaparelli that
one of these meteor swarms moves in the orbit of a previously observed
comet, and other coincidences of the kind were soon forthcoming. The
conviction grew that meteor swarms are really the debris of comets; and
this conviction became a practical certainty when, in November, 1872,
the earth crossed the orbit of the ill-starred Biela, and a shower of
meteors came whizzing into our atmosphere in lieu of the lost comet.

And so at last the full secret was out. The awe-inspiring comet, instead
of being the planetary body it had all along been regarded, is really
nothing more nor less than a great aggregation of meteoric particles,
which have become clustered together out in space somewhere, and which
by jostling one another or through electrical action become luminous. So
widely are the individual particles separated that the cometary body as
a whole has been estimated to be thousands of times less dense than the
earth's atmosphere at sea-level. Hence the ease with which the comet may
be dismembered and its particles strung out into streaming swarms.

So thickly is the space we traverse strewn with this cometary dust
that the earth sweeps up, according to Professor Newcomb's estimate, a
million tons of it each day. Each individual particle, perhaps no larger
than a millet seed, becomes a shooting-star, or meteor, as it burns to
vapor in the earth's upper atmosphere. And if one tiny planet sweeps
up such masses of this cosmic matter, the amount of it in the entire
stretch of our system must be beyond all estimate. What a story it tells
of the myriads of cometary victims that have fallen prey to the sun
since first he stretched his planetary net across the heavens!


THE FIXED STARS

When Biela's comet gave the inhabitants of the earth such a fright in
1832, it really did not come within fifty millions of miles of us. Even
the great comet through whose filmy tail the earth passed in 1861 was
itself fourteen millions of miles away. The ordinary mind, schooled to
measure space by the tiny stretches of a pygmy planet, cannot grasp the
import of such distances; yet these are mere units of measure compared
with the vast stretches of sidereal space. Were the comet which hurtles
past us at a speed of, say, a hundred miles a second to continue its
mad flight unchecked straight into the void of space, it must fly on its
frigid way eight thousand years before it could reach the very nearest
of our neighbor stars; and even then it would have penetrated but a
mere arm's-length into the vistas where lie the dozen or so of sidereal
residents that are next beyond. Even to the trained mind such distances
are only vaguely imaginable. Yet the astronomer of our century has
reached out across this unthinkable void and brought back many a secret
which our predecessors thought forever beyond human grasp.

A tentative assault upon this stronghold of the stars was being made
by Herschel at the beginning of the century. In 1802 that greatest of
observing astronomers announced to the Royal Society his discovery that
certain double stars had changed their relative positions towards one
another since he first carefully charted them twenty years before.
Hitherto it had been supposed that double stars were mere optical
effects. Now it became clear that some of them, at any rate, are
true "binary systems," linked together presumably by gravitation and
revolving about one another. Halley had shown, three-quarters of a
century before, that the stars have an actual or "proper" motion in
space; Herschel himself had proved that the sun shares this motion
with the other stars. Here was another shift of place, hitherto quite
unsuspected, to be reckoned with by the astronomer in fathoming sidereal
secrets.


Double Stars

When John Herschel, the only son and the worthy successor of the great
astronomer, began star-gazing in earnest, after graduating senior
wrangler at Cambridge, and making two or three tentative professional
starts in other directions to which his versatile genius impelled him,
his first extended work was the observation of his father's double
stars. His studies, in which at first he had the collaboration of Mr.
James South, brought to light scores of hitherto unrecognized pairs, and
gave fresh data for the calculation of the orbits of those longer
known. So also did the independent researches of F. G. W. Struve,
the enthusiastic observer of the famous Russian observatory at the
university of Dorpat, and subsequently at Pulkowa. Utilizing data
gathered by these observers, M. Savary, of Paris, showed, in 1827, that
the observed elliptical orbits of the double stars are explicable by
the ordinary laws of gravitation, thus confirming the assumption that
Newton's laws apply to these sidereal bodies. Henceforth there could be
no reason to doubt that the same force which holds terrestrial objects
on our globe pulls at each and every particle of matter throughout the
visible universe.

The pioneer explorers of the double stars early found that the systems
into which the stars are linked are by no means confined to single
pairs. Often three or four stars are found thus closely connected into
gravitation systems; indeed, there are all gradations between binary
systems and great clusters containing hundreds or even thousands of
members. It is known, for example, that the familiar cluster of the
Pleiades is not merely an optical grouping, as was formerly supposed,
but an actual federation of associated stars, some two thousand five
hundred in number, only a few of which are visible to the unaided eve.
And the more carefully the motions of the stars are studied, the more
evident it becomes that widely separated stars are linked together into
infinitely complex systems, as yet but little understood. At the same
time, all instrumental advances tend to resolve more and more seemingly
single stars into close pairs and minor clusters. The two Herschels
between them discovered some thousands of these close multiple systems;
Struve and others increased the list to above ten thousand; and Mr.
S. W. Burnham, of late years the most enthusiastic and successful of
double-star pursuers, added a thousand new discoveries while he was
still an amateur in astronomy, and by profession the stenographer of a
Chicago court. Clearly the actual number of multiple stars is beyond all
present estimate.

The elder Herschel's early studies of double stars were undertaken in
the hope that these objects might aid him in ascertaining the actual
distance of a star, through measurement of its annual parallax--that
is to say, of the angle which the diameter of the earth's orbit would
subtend as seen from the star. The expectation was not fulfilled. The
apparent shift of position of a star as viewed from opposite sides of
the earth's orbit, from which the parallax might be estimated, is so
extremely minute that it proved utterly inappreciable, even to the
almost preternaturally acute vision of Herschel, with the aid of any
instrumental means then at command. So the problem of star distance
allured and eluded him to the end, and he died in 1822 without seeing
it even in prospect of solution. His estimate of the minimum distance of
the nearest star, based though it was on the fallacious test of apparent
brilliancy, was a singularly sagacious one, but it was at best a
scientific guess, not a scientific measurement.


The Distance of the Stars

Just about this time, however, a great optician came to the aid of the
astronomers. Joseph Fraunhofer perfected the refracting telescope,
as Herschel had perfected the reflector, and invented a wonderfully
accurate "heliometer," or sun-measurer. With the aid of these
instruments the old and almost infinitely difficult problem of star
distance was solved. In 1838 Bessel announced from the Konigsberg
observatory that he had succeeded, after months of effort, in detecting
and measuring the parallax of a star. Similar claims had been made often
enough before, always to prove fallacious when put to further test; but
this time the announcement carried the authority of one of the greatest
astronomers of the age, and scepticism was silenced.

Nor did Bessel's achievement long await corroboration. Indeed, as so
often happens in fields of discovery, two other workers had almost
simultaneously solved the same problem--Struve at Pulkowa, where the
great Russian observatory, which so long held the palm over all others,
had now been established; and Thomas Henderson, then working at the
Cape of Good Hope, but afterwards the Astronomer Royal of Scotland.
Henderson's observations had actual precedence in point of time, but
Bessel's measurements were so much more numerous and authoritative that
he has been uniformly considered as deserving the chief credit of the
discovery, which priority of publication secured him.

By an odd chance, the star on which Henderson's observations were made,
and consequently the first star the parallax of which was ever measured,
is our nearest neighbor in sidereal space, being, indeed, some ten
billions of miles nearer than the one next beyond. Yet even this nearest
star is more than two hundred thousand times as remote from us as the
sun. The sun's light flashes to the earth in eight minutes, and to
Neptune in about three and a half hours, but it requires three and a
half years to signal Alpha Centauri. And as for the great majority of
the stars, had they been blotted out of existence before the Christian
era, we of to-day should still receive their light and seem to see them
just as we do. When we look up to the sky, we study ancient history;
we do not see the stars as they ARE, but as they WERE years, centuries,
even millennia ago.

The information derived from the parallax of a star by no means halts
with the disclosure of the distance of that body. Distance known, the
proper motion of the star, hitherto only to be reckoned as so many
seconds of arc, may readily be translated into actual speed of progress;
relative brightness becomes absolute lustre, as compared with the sun;
and in the case of the double stars the absolute mass of the components
may be computed from the laws of gravitation. It is found that stars
differ enormously among themselves in all these regards. As to speed,
some, like our sun, barely creep through space--compassing ten or twenty
miles a second, it is true, yet even at that rate only passing through
the equivalent of their own diameter in a day. At the other extreme,
among measured stars, is one that moves two hundred miles a second; yet
even this "flying star," as seen from the earth, seems to change its
place by only about three and a half lunar diameters in a thousand
years. In brightness, some stars yield to the sun, while others surpass
him as the arc-light surpasses a candle. Arcturus, the brightest
measured star, shines like two hundred suns; and even this giant orb is
dim beside those other stars which are so distant that their parallax
cannot be measured, yet which greet our eyes at first magnitude. As to
actual bulk, of which apparent lustre furnishes no adequate test, some
stars are smaller than the sun, while others exceed him hundreds or
perhaps thousands of times. Yet one and all, so distant are they, remain
mere disklike points of light before the utmost powers of the modern
telescope.


Revelations of the Spectroscope

All this seems wonderful enough, but even greater things were in store.
In 1859 the spectroscope came upon the scene, perfected by Kirchhoff
and Bunsen, along lines pointed out by Fraunhofer almost half a century
before. That marvellous instrument, by revealing the telltale lines
sprinkled across a prismatic spectrum, discloses the chemical nature
and physical condition of any substance whose light is submitted to it,
telling its story equally well, provided the light be strong enough,
whether the luminous substance be near or far--in the same room or at
the confines of space. Clearly such an instrument must prove a veritable
magic wand in the hands of the astronomer.

Very soon eager astronomers all over the world were putting the
spectroscope to the test. Kirchhoff himself led the way, and Donati and
Father Secchi in Italy, Huggins and Miller in England, and Rutherfurd in
America, were the chief of his immediate followers. The results exceeded
the dreams of the most visionary. At the very outset, in 1860, it was
shown that such common terrestrial substances as sodium, iron, calcium,
magnesium, nickel, barium, copper, and zinc exist in the form of glowing
vapors in the sun, and very soon the stars gave up a corresponding
secret. Since then the work of solar and sidereal analysis has gone on
steadily in the hands of a multitude of workers (prominent among whom,
in this country, are Professor Young of Princeton, Professor Langley of
Washington, and Professor Pickering of Harvard), and more than half
the known terrestrial elements have been definitely located in the sun,
while fresh discoveries are in prospect.

It is true the sun also contains some seeming elements that are unknown
on the earth, but this is no matter for surprise. The modern chemist
makes no claim for his elements except that they have thus far resisted
all human efforts to dissociate them; it would be nothing strange if
some of them, when subjected to the crucible of the sun, which is seen
to vaporize iron, nickel, silicon, should fail to withstand the test.
But again, chemistry has by no means exhausted the resources of the
earth's supply of raw material, and the substance which sends its
message from a star may exist undiscovered in the dust we tread or in
the air we breathe. In the year 1895 two new terrestrial elements were
discovered; but one of these had for years been known to the astronomer
as a solar and suspected as a stellar element, and named helium because
of its abundance in the sun. The spectroscope had reached out millions
of miles into space and brought back this new element, and it took the
chemist a score of years to discover that he had all along had samples
of the same substance unrecognized in his sublunary laboratory. There
is hardly a more picturesque fact than that in the entire history of
science.

But the identity in substance of earth and sun and stars was not more
clearly shown than the diversity of their existing physical conditions.
It was seen that sun and stars, far from being the cool, earthlike,
habitable bodies that Herschel thought them (surrounded by glowing
clouds, and protected from undue heat by other clouds), are in truth
seething caldrons of fiery liquid, or gas made viscid by condensation,
with lurid envelopes of belching flames. It was soon made clear, also,
particularly by the studies of Rutherfurd and of Secchi, that stars
differ among themselves in exact constitution or condition. There are
white or Sirian stars, whose spectrum revels in the lines of hydrogen;
yellow or solar stars (our sun being the type), showing various metallic
vapors; and sundry red stars, with banded spectra indicative of carbon
compounds; besides the purely gaseous stars of more recent discovery,
which Professor Pickering had specially studied. Zollner's famous
interpretation of these diversities, as indicative of varying stages
of cooling, has been called in question as to the exact sequence it
postulates, but the general proposition that stars exist under widely
varying conditions of temperature is hardly in dispute.

The assumption that different star types mark varying stages of cooling
has the further support of modern physics, which has been unable to
demonstrate any way in which the sun's radiated energy may be restored,
or otherwise made perpetual, since meteoric impact has been shown to
be--under existing conditions, at any rate--inadequate. In accordance
with the theory of Helmholtz, the chief supply of solar energy is held
to be contraction of the solar mass itself; and plainly this must
have its limits. Therefore, unless some means as yet unrecognized is
restoring the lost energy to the stellar bodies, each of them must
gradually lose its lustre, and come to a condition of solidification,
seeming sterility, and frigid darkness. In the case of our own
particular star, according to the estimate of Lord Kelvin, such a
culmination appears likely to occur within a period of five or six
million years.


The Astronomy of the Invisible

But by far the strongest support of such a forecast as this is furnished
by those stellar bodies which even now appear to have cooled to the
final stage of star development and ceased to shine. Of this class
examples in miniature are furnished by the earth and the smaller of its
companion planets. But there are larger bodies of the same type out
in stellar space--veritable "dark stars"--invisible, of course, yet
nowadays clearly recognized.

The opening up of this "astronomy of the invisible" is another of the
great achievements of the nineteenth century, and again it is Bessel
to whom the honor of discovery is due. While testing his stars
for parallax; that astute observer was led to infer, from certain
unexplained aberrations of motion, that various stars, Sirius himself
among the number, are accompanied by invisible companions, and in
1840 he definitely predicated the existence of such "dark stars." The
correctness of the inference was shown twenty years later, when Alvan
Clark, Jr., the American optician, while testing a new lens, discovered
the companion of Sirius, which proved thus to be faintly luminous. Since
then the existence of other and quite invisible star companions has been
proved incontestably, not merely by renewed telescopic observations, but
by the curious testimony of the ubiquitous spectroscope.

One of the most surprising accomplishments of that instrument is the
power to record the flight of a luminous object directly in the line of
vision. If the luminous body approaches swiftly, its Fraunhofer lines
are shifted from their normal position towards the violet end of the
spectrum; if it recedes, the lines shift in the opposite direction. The
actual motion of stars whose distance is unknown may be measured in this
way. But in certain cases the light lines are seen to oscillate on the
spectrum at regular intervals. Obviously the star sending such light
is alternately approaching and receding, and the inference that it is
revolving about a companion is unavoidable. From this extraordinary test
the orbital distance, relative mass, and actual speed of revolution of
the absolutely invisible body may be determined. Thus the spectroscope,
which deals only with light, makes paradoxical excursions into the
realm of the invisible. What secrets may the stars hope to conceal when
questioned by an instrument of such necromantic power?

But the spectroscope is not alone in this audacious assault upon the
strongholds of nature. It has a worthy companion and assistant in
the photographic film, whose efficient aid has been invoked by the
astronomer even more recently. Pioneer work in celestial photography
was, indeed, done by Arago in France and by the elder Draper in America
in 1839, but the results then achieved were only tentative, and it was
not till forty years later that the method assumed really important
proportions. In 1880, Dr. Henry Draper, at Hastings-on-the-Hudson, made
the first successful photograph of a nebula. Soon after, Dr. David
Gill, at the Cape observatory, made fine photographs of a comet, and the
flecks of starlight on his plates first suggested the possibilities of
this method in charting the heavens.

Since then star-charting with the film has come virtually to supersede
the old method. A concerted effort is being made by astronomers in
various parts of the world to make a complete chart of the heavens, and
before the close of our century this work will be accomplished, some
fifty or sixty millions of visible stars being placed on record with a
degree of accuracy hitherto unapproachable. Moreover, other millions of
stars are brought to light by the negative, which are too distant or
dim to be visible with any telescopic powers yet attained--a fact
which wholly discredits all previous inferences as to the limits of
our sidereal system. Hence, notwithstanding the wonderful instrumental
advances of the nineteenth century, knowledge of the exact form and
extent of our universe seems more unattainable than it seemed a century
ago.


The Structure of Nebulae

Yet the new instruments, while leaving so much untold, have revealed
some vastly important secrets of cosmic structure. In particular, they
have set at rest the long-standing doubts as to the real structure and
position of the mysterious nebulae--those lazy masses, only two or
three of them visible to the unaided eye, which the telescope reveals
in almost limitless abundance, scattered everywhere among the stars,
but grouped in particular about the poles of the stellar stream or disk
which we call the Milky Way.

Herschel's later view, which held that some at least of the nebulae are
composed of a "shining fluid," in process of condensation to form stars,
was generally accepted for almost half a century. But in 1844, when
Lord Rosse's great six-foot reflector--the largest telescope ever yet
constructed--was turned on the nebulae, it made this hypothesis seem
very doubtful. Just as Galileo's first lens had resolved the Milky Way
into stars, just as Herschel had resolved nebulae that resisted all
instruments but his own, so Lord Rosse's even greater reflector resolved
others that would not yield to Herschel's largest mirror. It seemed
a fair inference that with sufficient power, perhaps some day to be
attained, all nebulae would yield, hence that all are in reality what
Herschel had at first thought them--vastly distant "island universes,"
composed of aggregations of stars, comparable to our own galactic
system.

But the inference was wrong; for when the spectroscope was first applied
to a nebula in 1864, by Dr. Huggins, it clearly showed the spectrum not
of discrete stars, but of a great mass of glowing gases, hydrogen among
others. More extended studies showed, it is true, that some nebulae give
the continuous spectrum of solids or liquids, but the different types
intermingle and grade into one another. Also, the closest affinity
is shown between nebulae and stars. Some nebulae are found to contain
stars, singly or in groups, in their actual midst; certain condensed
"planetary" nebulae are scarcely to be distinguished from stars of the
gaseous type; and recently the photographic film has shown the presence
of nebulous matter about stars that to telescopic vision differ in no
respect from the generality of their fellows in the galaxy. The familiar
stars of the Pleiades cluster, for example, appear on the negative
immersed in a hazy blur of light. All in all, the accumulated
impressions of the photographic film reveal a prodigality of nebulous
matter in the stellar system not hitherto even conjectured.

And so, of course, all question of "island universes" vanishes, and the
nebulae are relegated to their true position as component parts of the
one stellar system--the one universe--that is open to present human
inspection. And these vast clouds of world-stuff have been found by
Professor Keeler, of the Lick observatory, to be floating through space
at the starlike speed of from ten to thirty-eight miles per second.

The linking of nebulae with stars, so clearly evidenced by all these
modern observations, is, after all, only the scientific corroboration of
what the elder Herschel's later theories affirmed. But the nebulae have
other affinities not until recently suspected; for the spectra of some
of them are practically identical with the spectra of certain comets.
The conclusion seems warranted that comets are in point of fact minor
nebulae that are drawn into our system; or, putting it otherwise, that
the telescopic nebulae are simply gigantic distant comets.


Lockyer's Meteoric Hypothesis

Following up the surprising clews thus suggested, Sir Norman Lockyer,
of London, has in recent years elaborated what is perhaps the most
comprehensive cosmogonic guess that has ever been attempted. His theory,
known as the "meteoric hypothesis," probably bears the same relation
to the speculative thought of our time that the nebular hypothesis of
Laplace bore to that of the eighteenth century. Outlined in a few words,
it is an attempt to explain all the major phenomena of the universe
as due, directly or indirectly, to the gravitational impact of such
meteoric particles, or specks of cosmic dust, as comets are composed
of. Nebulae are vast cometary clouds, with particles more or less widely
separated, giving off gases through meteoric collisions, internal or
external, and perhaps glowing also with electrical or phosphorescent
light. Gravity eventually brings the nebular particles into closer
aggregations, and increased collisions finally vaporize the entire mass,
forming planetary nebulae and gaseous stars. Continued condensation
may make the stellar mass hotter and more luminous for a time, but
eventually leads to its liquefaction, and ultimate consolidation--the
aforetime nebulae becoming in the end a dark or planetary star.

The exact correlation which Lockyer attempts to point out between
successive stages of meteoric condensation and the various types of
observed stellar bodies does not meet with unanimous acceptance. Mr.
Ranyard, for example, suggests that the visible nebulae may not be
nascent stars, but emanations from stars, and that the true pre-stellar
nebulae are invisible until condensed to stellar proportions. But such
details aside, the broad general hypothesis that all the bodies of the
universe are, so to speak, of a single species--that nebulae (including
comets), stars of all types, and planets, are but varying stages in the
life history of a single race or type of cosmic organisms--is accepted
by the dominant thought of our time as having the highest warrant of
scientific probability.

All this, clearly, is but an amplification of that nebular hypothesis
which, long before the spectroscope gave us warrant to accurately judge
our sidereal neighbors, had boldly imagined the development of stars out
of nebulae and of planets out of stars. But Lockyer's hypothesis does
not stop with this. Having traced the developmental process from the
nebular to the dark star, it sees no cause to abandon this dark star to
its fate by assuming, as the original speculation assumed, that this is
a culminating and final stage of cosmic existence. For the dark star,
though its molecular activities have come to relative stability and
impotence, still retains the enormous potentialities of molar motion;
and clearly, where motion is, stasis is not. Sooner or later, in its
ceaseless flight through space, the dark star must collide with some
other stellar body, as Dr. Croll imagines of the dark bodies which his
"pre-nebular theory" postulates. Such collision may be long delayed; the
dark star may be drawn in comet-like circuit about thousands of other
stellar masses, and be hurtled on thousands of diverse parabolic or
elliptical orbits, before it chances to collide--but that matters not:
"billions are the units in the arithmetic of eternity," and sooner
or later, we can hardly doubt, a collision must occur. Then without
question the mutual impact must shatter both colliding bodies into
vapor, or vapor combined with meteoric fragments; in short, into a
veritable nebula, the matrix of future worlds. Thus the dark star, which
is the last term of one series of cosmic changes, becomes the first term
of another series--at once a post-nebular and a pre-nebular condition;
and the nebular hypothesis, thus amplified, ceases to be a mere linear
scale, and is rounded out to connote an unending series of cosmic
cycles, more nearly satisfying the imagination.

In this extended view, nebulae and luminous stars are but the infantile
and adolescent stages of the life history of the cosmic individual; the
dark star, its adult stage, or time of true virility. Or we may think of
the shrunken dark star as the germ-cell, the pollen-grain, of the cosmic
organism. Reduced in size, as becomes a germ-cell, to a mere fraction
of the nebular body from which it sprang, it yet retains within
its seemingly non-vital body all the potentialities of the original
organism, and requires only to blend with a fellow-cell to bring a new
generation into being. Thus may the cosmic race, whose aggregate census
makes up the stellar universe, be perpetuated--individual solar systems,
such as ours, being born, and growing old, and dying to live again in
their descendants, while the universe as a whole maintains its unified
integrity throughout all these internal mutations--passing on, it may
be, by infinitesimal stages, to a culmination hopelessly beyond human
comprehension.



III. THE NEW SCIENCE OF PALEONTOLOGY


WILLIAM SMITH AND FOSSIL SHELLS

Ever since Leonardo da Vinci first recognized the true character of
fossils, there had been here and there a man who realized that the
earth's rocky crust is one gigantic mausoleum. Here and there a
dilettante had filled his cabinets with relics from this monster crypt;
here and there a philosopher had pondered over them--questioning whether
perchance they had once been alive, or whether they were not mere
abortive souvenirs of that time when the fertile matrix of the earth was
supposed to have

              "teemed at a birth
     Innumerous living creatures, perfect forms,
     Limbed and full grown."

Some few of these philosophers--as Robert Hooke and Steno in the
seventeenth century, and Moro, Leibnitz, Buffon, Whitehurst, Werner,
Hutton, and others in the eighteenth--had vaguely conceived the
importance of fossils as records of the earth's ancient history, but the
wisest of them no more suspected the full import of the story written
in the rocks than the average stroller in a modern museum suspects the
meaning of the hieroglyphs on the case of a mummy.

It was not that the rudiments of this story are so very hard to
decipher--though in truth they are hard enough--but rather that the
men who made the attempt had all along viewed the subject through an
atmosphere of preconception, which gave a distorted image. Before this
image could be corrected it was necessary that a man should appear who
could see without prejudice, and apply sound common-sense to what he
saw. And such a man did appear towards the close of the century, in the
person of William Smith, the English surveyor. He was a self-taught man,
and perhaps the more independent for that, and he had the gift, besides
his sharp eyes and receptive mind, of a most tenacious memory. By
exercising these faculties, rare as they are homely, he led the way to
a science which was destined, in its later developments, to shake the
structure of established thought to its foundations.

Little enough did William Smith suspect, however, that any such dire
consequences were to come of his act when he first began noticing the
fossil shells that here and there are to be found in the stratified
rocks and soils of the regions over which his surveyor's duties led him.
Nor, indeed, was there anything of such apparent revolutionary character
in the facts which he unearthed; yet in their implications these facts
were the most disconcerting of any that had been revealed since the days
of Copernicus and Galileo. In its bald essence, Smith's discovery was
simply this: that the fossils in the rocks, instead of being scattered
haphazard, are arranged in regular systems, so that any given stratum
of rock is labelled by its fossil population; and that the order of
succession of such groups of fossils is always the same in any vertical
series of strata in which they occur. That is to say, if fossil A
underlies fossil B in any given region, it never overlies it in any
other series; though a kind of fossils found in one set of strata may
be quite omitted in another. Moreover, a fossil once having disappeared
never reappears in any later stratum.

From these novel facts Smith drew the commonsense inference that the
earth had had successive populations of creatures, each of which in
its turn had become extinct. He partially verified this inference by
comparing the fossil shells with existing species of similar orders,
and found that such as occur in older strata of the rocks had no
counterparts among living species. But, on the whole, being eminently
a practical man, Smith troubled himself but little about the inferences
that might be drawn from his facts. He was chiefly concerned in using
the key he had discovered as an aid to the construction of the first
geological map of England ever attempted, and he left to others the
untangling of any snarls of thought that might seem to arise from his
discovery of the succession of varying forms of life on the globe.

He disseminated his views far and wide, however, in the course of his
journeyings--quite disregarding the fact that peripatetics went out of
fashion when the printing-press came in--and by the beginning of the
nineteenth century he had begun to have a following among the geologists
of England. It must not for a moment be supposed, however, that his
contention regarding the succession of strata met with immediate or
general acceptance. On the contrary, it was most bitterly antagonized.
For a long generation after the discovery was made, the generality of
men, prone as always to strain at gnats and swallow camels, preferred to
believe that the fossils, instead of being deposited in successive ages,
had been swept all at once into their present positions by the current
of a mighty flood--and that flood, needless to say, the Noachian deluge.
Just how the numberless successive strata could have been laid down
in orderly sequence to the depth of several miles in one such fell
cataclysm was indeed puzzling, especially after it came to be admitted
that the heaviest fossils were not found always at the bottom; but to
doubt that this had been done in some way was rank heresy in the early
days of the nineteenth century.


CUVIER AND FOSSIL VERTEBRATES

But once discovered, William Smith's unique facts as to the succession
of forms in the rocks would not down. There was one most vital point,
however, regarding which the inferences that seem to follow from
these facts needed verification--the question, namely, whether the
disappearance of a fauna from the register in the rocks really implies
the extinction of that fauna. Everything really depended upon the answer
to that question, and none but an accomplished naturalist could answer
it with authority. Fortunately, the most authoritative naturalist of the
time, George Cuvier, took the question in hand--not, indeed, with the
idea of verifying any suggestion of Smith's, but in the course of his
own original studies--at the very beginning of the century, when Smith's
views were attracting general attention.

Cuvier and Smith were exact contemporaries, both men having been born in
1769, that "fertile year" which gave the world also Chateaubriand, Von
Humboldt, Wellington, and Napoleon. But the French naturalist was of
very different antecedents from the English surveyor. He was brilliantly
educated, had early gained recognition as a scientist, and while yet a
young man had come to be known as the foremost comparative anatomist of
his time. It was the anatomical studies that led him into the realm of
fossils. Some bones dug out of the rocks by workmen in a quarry were
brought to his notice, and at once his trained eye told him that they
were different from anything he had seen before. Hitherto such bones,
when not entirely ignored, had been for the most part ascribed to
giants of former days, or even to fallen angels. Cuvier soon showed
that neither giants nor angels were in question, but elephants of an
unrecognized species. Continuing his studies, particularly with material
gathered from gypsum beds near Paris, he had accumulated, by the
beginning of the nineteenth century, bones of about twenty-five species
of animals that he believed to be different from any now living on the
globe.

The fame of these studies went abroad, and presently fossil bones poured
in from all sides, and Cuvier's conviction that extinct forms of animals
are represented among the fossils was sustained by the evidence of many
strange and anomalous forms, some of them of gigantic size. In 1816
the famous Ossements Fossiles, describing these novel objects, was
published, and vertebrate paleontology became a science. Among
other things of great popular interest the book contained the first
authoritative description of the hairy elephant, named by Cuvier the
mammoth, the remains of which bad been found embedded in a mass of
ice in Siberia in 1802, so wonderfully preserved that the dogs of the
Tungusian fishermen actually ate its flesh. Bones of the same species
had been found in Siberia several years before by the naturalist Pallas,
who had also found the carcass of a rhinoceros there, frozen in a
mud-bank; but no one then suspected that these were members of an
extinct population--they were supposed to be merely transported relics
of the flood.

Cuvier, on the other hand, asserted that these and the other creatures
he described had lived and died in the region where their remains were
found, and that most of them have no living representatives upon the
globe. This, to be sure, was nothing more than William Smith had tried
all along to establish regarding lower forms of life; but flesh and
blood monsters appeal to the imagination in a way quite beyond the power
of mere shells; so the announcement of Cuvier's discoveries aroused the
interest of the entire world, and the Ossements Fossiles was accorded a
popular reception seldom given a work of technical science--a reception
in which the enthusiastic approval of progressive geologists was mingled
with the bitter protests of the conservatives.


"Naturalists certainly have neither explored all the continents," said
Cuvier, "nor do they as yet even know all the quadrupeds of those parts
which have been explored. New species of this class are discovered from
time to time; and those who have not examined with attention all the
circumstances belonging to these discoveries may allege also that the
unknown quadrupeds, whose fossil bones have been found in the strata
of the earth, have hitherto remained concealed in some islands not yet
discovered by navigators, or in some of the vast deserts which occupy
the middle of Africa, Asia, the two Americas, and New Holland.

"But if we carefully attend to the kind of quadrupeds that have been
recently discovered, and to the circumstances of their discovery, we
shall easily perceive that there is very little chance indeed of our
ever finding alive those which have only been seen in a fossil state.

"Islands of moderate size, and at a considerable distance from the large
continents, have very few quadrupeds. These must have been carried
to them from other countries. Cook and Bougainville found no other
quadrupeds besides hogs and dogs in the South Sea Islands; and the
largest quadruped of the West India Islands, when first discovered, was
the agouti, a species of the cavy, an animal apparently between the rat
and the rabbit.

"It is true that the great continents, as Asia, Africa, the two
Americas, and New Holland, have large quadrupeds, and, generally
speaking, contain species common to each; insomuch, that upon
discovering countries which are isolated from the rest of the world,
the animals they contain of the class of quadruped were found entirely
different from those which existed in other countries. Thus, when the
Spaniards first penetrated into South America, they did not find it to
contain a single quadruped exactly the same with those of Europe, Asia,
and Africa. The puma, the jaguar, the tapir, the capybara, the llama,
or glama, and vicuna, and the whole tribe of sapajous, were to them
entirely new animals, of which they had not the smallest idea....

"If there still remained any great continent to be discovered, we
might perhaps expect to be made acquainted with new species of large
quadrupeds, among which some might be found more or less similar to
those of which we find the exuviae in the bowels of the earth. But it
is merely sufficient to glance the eye over the maps of the world and
observe the innumerable directions in which navigators have traversed
the ocean, in order to be satisfied that there does not remain any large
land to be discovered, unless it may be situated towards the Antarctic
Pole, where eternal ice necessarily forbids the existence of animal
life."(1)

Cuvier then points out that the ancients were well acquainted with
practically all the animals on the continents of Europe, Asia, and
Africa now known to scientists. He finds little grounds, therefore, for
belief in the theory that at one time there were monstrous animals on
the earth which it was necessary to destroy in order that the present
fauna and men might flourish. After reviewing these theories and beliefs
in detail, he takes up his Inquiry Respecting the Fabulous Animals
of the Ancients. "It is easy," he says, "to reply to the foregoing
objections, by examining the descriptions that are left us by the
ancients of those unknown animals, and by inquiring into their origins.
Now that the greater number of these animals have an origin, the
descriptions given of them bear the most unequivocal marks; as in almost
all of them we see merely the different parts of known animals united by
an unbridled imagination, and in contradiction to every established law
of nature."(2)

Having shown how the fabulous monsters of ancient times and of foreign
nations, such as the Chinese, were simply products of the imagination,
having no prototypes in nature, Cuvier takes up the consideration of the
difficulty of distinguishing the fossil bones of quadrupeds.

We shall have occasion to revert to this part of Cuvier's paper in
another connection. Here it suffices to pass at once to the final
conclusion that the fossil bones in question are the remains of an
extinct fauna, the like of which has no present-day representation on
the earth. Whatever its implications, this conclusion now seemed to
Cuvier to be fully established.

In England the interest thus aroused was sent to fever-heat in 1821 by
the discovery of abundant beds of fossil bones in the stalagmite-covered
floor of a cave at Kirkdale, Yorkshire which went to show that England,
too, had once had her share of gigantic beasts. Dr. Buckland, the
incumbent of the chair of geology at Oxford, and the most authoritative
English geologist of his day, took these finds in hand and showed that
the bones belonged to a number of species, including such alien forms as
elephants, rhinoceroses, hippopotami, and hyenas. He maintained that all
of these creatures had actually lived in Britain, and that the caves in
which their bones were found had been the dens of hyenas.

The claim was hotly disputed, as a matter of course. As late as 1827
books were published denouncing Buckland, doctor of divinity though he
was, as one who had joined in an "unhallowed cause," and reiterating the
old cry that the fossils were only remains of tropical species washed
thither by the deluge. That they were found in solid rocks or in caves
offered no difficulty, at least not to the fertile imagination of
Granville Penn, the leader of the conservatives, who clung to the old
idea of Woodward and Cattcut that the deluge had dissolved the entire
crust of the earth to a paste, into which the relics now called fossils
had settled. The caves, said Mr. Penn, are merely the result of gases
given off by the carcasses during decomposition--great air-bubbles, so
to speak, in the pasty mass, becoming caverns when the waters receded
and the paste hardened to rocky consistency.

But these and such-like fanciful views were doomed even in the day of
their utterance. Already in 1823 other gigantic creatures, christened
ichthyosaurus and plesiosaurus by Conybeare, had been found in deeper
strata of British rocks; and these, as well as other monsters whose
remains were unearthed in various parts of the world, bore such strange
forms that even the most sceptical could scarcely hope to find their
counterparts among living creatures. Cuvier's contention that all the
larger vertebrates of the existing age are known to naturalists was
borne out by recent explorations, and there seemed no refuge from the
conclusion that the fossil records tell of populations actually extinct.
But if this were admitted, then Smith's view that there have been
successive rotations of population could no longer be denied. Nor could
it be in doubt that the successive faunas, whose individual remains have
been preserved in myriads, representing extinct species by thousands
and tens of thousands, must have required vast periods of time for the
production and growth of their countless generations.

As these facts came to be generally known, and as it came to be
understood in addition that the very matrix of the rock in which fossils
are imbedded is in many cases one gigantic fossil, composed of the
remains of microscopic forms of life, common-sense, which, after all,
is the final tribunal, came to the aid of belabored science. It was
conceded that the only tenable interpretation of the record in the rocks
is that numerous populations of creatures, distinct from one another and
from present forms, have risen and passed away; and that the geologic
ages in which these creatures lived were of inconceivable length. The
rank and file came thus, with the aid of fossil records, to realize
the import of an idea which James Hutton, and here and there another
thinker, had conceived with the swift intuition of genius long
before the science of paleontology came into existence. The Huttonian
proposition that time is long had been abundantly established, and by
about the close of the first third of the last century geologists had
begun to speak of "ages" and "untold aeons of time" with a familiarity
which their predecessors had reserved for days and decades.


CHARLES LYELL COMBATS CATASTROPHISM

And now a new question pressed for solution. If the earth has been
inhabited by successive populations of beings now extinct, how have
all these creatures been destroyed? That question, however, seemed to
present no difficulties. It was answered out of hand by the application
of an old idea. All down the centuries, whatever their varying phases of
cosmogonic thought, there had been ever present the idea that past times
were not as recent times; that in remote epochs the earth had been the
scene of awful catastrophes that have no parallel in "these degenerate
days." Naturally enough, this thought, embalmed in every cosmogonic
speculation of whatever origin, was appealed to in explanation of the
destruction of these hitherto unimagined hosts, which now, thanks to
science, rose from their abysmal slumber as incontestable, but also as
silent and as thought-provocative, as Sphinx or pyramid. These ancient
hosts, it was said, have been exterminated at intervals of odd millions
of years by the recurrence of catastrophes of which the Mosaic deluge is
the latest, but perhaps not the last.

This explanation had fullest warrant of scientific authority. Cuvier had
prefaced his classical work with a speculative disquisition whose
very title (Discours sur les Revolutions du Globe) is ominous of
catastrophism, and whose text fully sustains the augury. And Buckland,
Cuvier's foremost follower across the Channel, had gone even beyond
the master, naming the work in which he described the Kirkdale fossils,
Reliquiae Diluvianae, or Proofs of a Universal Deluge.

Both these authorities supposed the creatures whose remains they studied
to have perished suddenly in the mighty flood whose awful current, as
they supposed, gouged out the modern valleys and hurled great blocks of
granite broadcast over the land. And they invoked similar floods for the
extermination of previous populations.

It is true these scientific citations had met with only qualified
approval at the time of their utterance, because then the conservative
majority of mankind did not concede that there had been a plurality of
populations or revolutions; but now that the belief in past geologic
ages had ceased to be a heresy, the recurring catastrophes of the great
paleontologists were accepted with acclaim. For the moment science and
tradition were at one, and there was a truce to controversy, except
indeed in those outlying skirmish-lines of thought whither news from
headquarters does not permeate till it has become ancient history at its
source.

The truce, however, was not for long. Hardly had contemporary
thought begun to adjust itself to the conception of past ages of
incomprehensible extent, each terminated by a catastrophe of the
Noachian type, when a man appeared who made the utterly bewildering
assertion that the geological record, instead of proving numerous
catastrophic revolutions in the earth's past history, gives no warrant
to the pretensions of any universal catastrophe whatever, near or
remote.

This iconoclast was Charles Lyell, the Scotchman, who was soon to be
famous as the greatest geologist of his time. As a young man he had
become imbued with the force of the Huttonian proposition, that present
causes are one with those that produced the past changes of the
globe, and he carried that idea to what he conceived to be its logical
conclusion. To his mind this excluded the thought of catastrophic
changes in either inorganic or organic worlds.

But to deny catastrophism was to suggest a revolution in current
thought. Needless to say, such revolution could not be effected without
a long contest. For a score of years the matter was argued pro and con.,
often with most unscientific ardor. A mere outline of the controversy
would fill a volume; yet the essential facts with which Lyell at last
established his proposition, in its bearings on the organic world, may
be epitomized in a few words. The evidence which seems to tell of past
revolutions is the apparently sudden change of fossils from one stratum
to another of the rocks. But Lyell showed that this change is not always
complete. Some species live on from one alleged epoch into the next. By
no means all the contemporaries of the mammoth are extinct, and numerous
marine forms vastly more ancient still have living representatives.

Moreover, the blanks between strata in any particular vertical series
are amply filled in with records in the form of thick strata in some
geographically distant series. For example, in some regions Silurian
rocks are directly overlaid by the coal measures; but elsewhere this
sudden break is filled in with the Devonian rocks that tell of a great
"age of fishes." So commonly are breaks in the strata in one region
filled up in another that we are forced to conclude that the
record shown by any single vertical series is of but local
significance--telling, perhaps, of a time when that particular sea-bed
oscillated above the water-line, and so ceased to receive sediment until
some future age when it had oscillated back again. But if this be
the real significance of the seemingly sudden change from stratum to
stratum, then the whole case for catastrophism is hopelessly lost; for
such breaks in the strata furnish the only suggestion geology can offer
of sudden and catastrophic changes of wide extent.

Let us see how Lyell elaborates these ideas, particularly with reference
to the rotation of species.(2)

"I have deduced as a corollary," he says, "that the species existing at
any particular period must, in the course of ages, become extinct, one
after the other. 'They must die out,' to borrow an emphatic expression
from Buffon, 'because Time fights against them.' If the views which I
have taken are just, there will be no difficulty in explaining why
the habitations of so many species are now restrained within exceeding
narrow limits. Every local revolution tends to circumscribe the range
of some species, while it enlarges that of others; and if we are led
to infer that new species originate in one spot only, each must require
time to diffuse itself over a wide area. It will follow, therefore, from
the adoption of our hypothesis that the recent origin of some species
and the high antiquity of others are equally consistent with the general
fact of their limited distribution, some being local because they have
not existed long enough to admit of their wide dissemination; others,
because circumstances in the animate or inanimate world have occurred to
restrict the range within which they may once have obtained....

"If the reader should infer, from the facts laid before him, that the
successive extinction of animals and plants may be part of the constant
and regular course of nature, he will naturally inquire whether there
are any means provided for the repair of these losses? Is it possible as
a part of the economy of our system that the habitable globe should to a
certain extent become depopulated, both in the ocean and on the land, or
that the variety of species should diminish until some new era arrives
when a new and extraordinary effort of creative energy is to be
displayed? Or is it possible that new species can be called into being
from time to time, and yet that so astonishing a phenomenon can escape
the naturalist?

"In the first place, it is obviously more easy to prove that a species
once numerously represented in a given district has ceased to be
than that some other which did not pre-exist had made its
appearance--assuming always, for reasons before stated, that single
stocks only of each animal and plant are originally created, and that
individuals of new species did not suddenly start up in many different
places at once.

"So imperfect has the science of natural history remained down to our
own times that, within the memory of persons now living, the numbers
of known animals and plants have doubled, or even quadrupled, in many
classes. New and often conspicuous species are annually discovered in
parts of the old continent long inhabited by the most civilized nations.
Conscious, therefore, of the limited extent of our information, we
always infer, when such discoveries are made, that the beings in
question bad previously eluded our research, or had at least existed
elsewhere, and only migrated at a recent period into the territories
where we now find them.

"What kind of proofs, therefore, could we reasonably expect to find of
the origin at a particular period of a new species?

"Perhaps, it may be said in reply, that within the last two or three
centuries some forest tree or new quadruped might have been observed to
appear suddenly in those parts of England or France which had been most
thoroughly investigated--that naturalists might have been able to show
that no such being inhabited any other region of the globe, and that
there was no tradition of anything similar having been observed in the
district where it had made its appearance.

"Now, although this objection may seem plausible, yet its force will be
found to depend entirely on the rate of fluctuation which we suppose
to prevail in the animal world, and on the proportions which such
conspicuous subjects of the animal and vegetable kingdoms bear to those
which are less known and escape our observation. There are perhaps
more than a million species of plants and animals, exclusive of the
microscopic and infusory animalcules, now inhabiting the terraqueous
globe, so that if only one of these were to become extinct annually, and
one new one were to be every year called into being, much more than a
million of years might be required to bring about a complete revolution
of organic life.

"I am not hazarding at present any hypothesis as to the probable rate
of change, but none will deny that when the annual birth and the annual
death of one species on the globe is proposed as a mere speculation,
this, at least, is to imagine no slight degree of instability in the
animate creation. If we divide the surface of the earth into twenty
regions of equal area, one of these might comprehend a space of land and
water about equal in dimensions to Europe, and might contain a twentieth
part of the million of species which may be assumed to exist in the
animal kingdom. In this region one species only could, according to the
rate of mortality before assumed, perish in twenty years, or only five
out of fifty thousand in the course of a century. But as a considerable
portion of the whole world belongs to the aquatic classes, with which
we have a very imperfect acquaintance, we must exclude them from our
consideration, and, if they constitute half of the entire number, then
one species only might be lost in forty years among the terrestrial
tribes. Now the mammalia, whether terrestrial or aquatic, bear so small
a proportion to other classes of animals, forming less, perhaps, than
a thousandth part of a whole, that, if the longevity of species in the
different orders were equal, a vast period must elapse before it would
come to the turn of this conspicuous class to lose one of their number.
If one species only of the whole animal kingdom died out in forty years,
no more than one mammifer might disappear in forty thousand years, in a
region of the dimensions of Europe.

"It is easy, therefore, to see that in a small portion of such an area,
in countries, for example, of the size of England and France, periods
of much greater duration must elapse before it would be possible
to authenticate the first appearance of one of the larger plants or
animals, assuming the annual birth and death of one species to be the
rate of vicissitude in the animal creation throughout the world."(3)


In a word, then, said Lyell, it becomes clear that the numberless
species that have been exterminated in the past have died out one by
one, just as individuals of a species die, not in vast shoals; if
whole populations have passed away, it has been not by instantaneous
extermination, but by the elimination of a species now here, now there,
much as one generation succeeds another in the life history of any
single species. The causes which have brought about such gradual
exterminations, and in the long lapse of ages have resulted in rotations
of population, are the same natural causes that are still in operation.
Species have died out in the past as they are dying out in the present,
under influence of changed surroundings, such as altered climate, or
the migration into their territory of more masterful species. Past and
present causes are one--natural law is changeless and eternal.

Such was the essence of the Huttonian doctrine, which Lyell adopted and
extended, and with which his name will always be associated. Largely
through his efforts, though of course not without the aid of many other
workers after a time, this idea--the doctrine of uniformitarianism, it
came to be called--became the accepted dogma of the geologic world not
long after the middle of the nineteenth century. The catastrophists,
after clinging madly to their phantom for a generation, at last
capitulated without terms: the old heresy became the new orthodoxy, and
the way was paved for a fresh controversy.


THE ORIGIN OF SPECIES

The fresh controversy followed quite as a matter of course. For the idea
of catastrophism had not concerned the destruction of species merely,
but their introduction as well. If whole faunas had been extirpated
suddenly, new faunas had presumably been introduced with equal
suddenness by special creation; but if species die out gradually,
the introduction of new species may be presumed to be correspondingly
gradual. Then may not the new species of a later geological epoch be
the modified lineal descendants of the extinct population of an earlier
epoch?

The idea that such might be the case was not new. It had been suggested
when fossils first began to attract conspicuous attention; and such
sagacious thinkers as Buffon and Kant and Goethe and Erasmus Darwin
had been disposed to accept it in the closing days of the eighteenth
century. Then, in 1809, it had been contended for by one of the early
workers in systematic paleontology--Jean Baptiste Lamarck, who
had studied the fossil shells about Paris while Cuvier studied the
vertebrates, and who had been led by these studies to conclude that
there had been not merely a rotation but a progression of life on the
globe. He found the fossil shells--the fossils of invertebrates, as he
himself had christened them--in deeper strata than Cuvier's vertebrates;
and he believed that there had been long ages when no higher forms than
these were in existence, and that in successive ages fishes, and then
reptiles, had been the highest of animate creatures, before mammals,
including man, appeared. Looking beyond the pale of his bare facts,
as genius sometimes will, he had insisted that these progressive
populations had developed one from another, under influence of changed
surroundings, in unbroken series.

Of course such a thought as this was hopelessly misplaced in a
generation that doubted the existence of extinct species, and hardly
less so in the generation that accepted catastrophism; but it had been
kept alive by here and there an advocate like Geoffrey Saint-Hilaire,
and now the banishment of catastrophism opened the way for its more
respectful consideration. Respectful consideration was given it by Lyell
in each recurring edition of his Principles, but such consideration led
to its unqualified rejection. In its place Lyell put forward a modified
hypothesis of special creation. He assumed that from time to time,
as the extirpation of a species had left room, so to speak, for a new
species, such new species had been created de novo; and he supposed that
such intermittent, spasmodic impulses of creation manifest themselves
nowadays quite as frequently as at any time in the past. He did not say
in so many words that no one need be surprised to-day were he to see a
new species of deer, for example, come up out of the ground before him,
"pawing to get free," like Milton's lion, but his theory implied as
much. And that theory, let it be noted, was not the theory of Lyell
alone, but of nearly all his associates in the geologic world. There is
perhaps no other fact that will bring home to one so vividly the advance
in thought of our own generation as the recollection that so crude, so
almost unthinkable a conception could have been the current doctrine of
science less than half a century ago.

This theory of special creation, moreover, excluded the current doctrine
of uniformitarianism as night excludes day, though most thinkers of the
time did not seem to be aware of the incompatibility of the two ideas.
It may be doubted whether even Lyell himself fully realized it. If he
did, he saw no escape from the dilemma, for it seemed to him that
the record in the rocks clearly disproved the alternative Lamarckian
hypothesis. And almost with one accord the paleontologists of the
time sustained the verdict. Owen, Agassiz, Falconer, Barrande, Pictet,
Forbes, repudiated the idea as unqualifiedly as their great predecessor
Cuvier had done in the earlier generation. Some of them did, indeed,
come to believe that there is evidence of a progressive development of
life in the successive ages, but no such graded series of fossils had
been discovered as would give countenance to the idea that one species
had ever been transformed into another. And to nearly every one this
objection seemed insuperable.

But in 1859 appeared a book which, though not dealing primarily with
paleontology, yet contained a chapter that revealed the geological
record in an altogether new light. The book was Charles Darwin's Origin
of Species, the chapter that wonderful citation of the "Imperfections of
the Geological Record." In this epoch-making chapter Darwin shows what
conditions must prevail in any given place in order that fossils shall
be formed, how unusual such conditions are, and how probable it is that
fossils once imbedded in sediment of a sea-bed will be destroyed by
metamorphosis of the rocks, or by denudation when the strata are raised
above the water-level. Add to this the fact that only small territories
of the earth have been explored geologically, he says, and it becomes
clear that the paleontological record as we now possess it shows but
a mere fragment of the past history of organisms on the earth. It is
a history "imperfectly kept and written in a changing dialect. Of this
history we possess the last volume alone, relating only to two or three
countries. Of this volume only here and there a short chapter has been
preserved, and of each page only here and there a few lines." For a
paleontologist to dogmatize from such a record would be as rash, he
thinks, as "for a naturalist to land for five minutes on a barren point
of Australia and then discuss the number and range of its productions."

This citation of observations, which when once pointed out seemed almost
self-evident, came as a revelation to the geological world. In the
clarified view now possible old facts took on a new meaning. It was
recalled that Cuvier had been obliged to establish a new order for some
of the first fossil creatures he examined, and that Buckland had noted
that the nondescript forms were intermediate in structure between
allied existing orders. More recently such intermediate forms had been
discovered over and over; so that, to name but one example, Owen had
been able, with the aid of extinct species, to "dissolve by gradations
the apparently wide interval between the pig and the camel." Owen,
moreover, had been led to speak repeatedly of the "generalized forms"
of extinct animals, and Agassiz had called them "synthetic or prophetic
types," these terms clearly implying "that such forms are in fact
intermediate or connecting links." Darwin himself had shown some years
before that the fossil animals of any continent are closely related to
the existing animals of that continent--edentates predominating, for
example, in South America, and marsupials in Australia. Many observers
had noted that recent strata everywhere show a fossil fauna more nearly
like the existing one than do more ancient strata; and that fossils from
any two consecutive strata are far more closely related to each other
than are the fossils of two remote formations, the fauna of each
geological formation being, indeed, in a wide view, intermediate between
preceding and succeeding faunas.

So suggestive were all these observations that Lyell, the admitted
leader of the geological world, after reading Darwin's citations, felt
able to drop his own crass explanation of the introduction of species
and adopt the transmutation hypothesis, thus rounding out the doctrine
of uniformitarianism to the full proportions in which Lamarck had
conceived it half a century before. Not all paleontologists could follow
him at once, of course; the proof was not yet sufficiently demonstrative
for that; but all were shaken in the seeming security of their former
position, which is always a necessary stage in the progress of thought.
And popular interest in the matter was raised to white heat in a
twinkling.

So, for the third time in this first century of its existence,
paleontology was called upon to play a leading role in a controversy
whose interest extended far beyond the bounds of staid truth-seeking
science. And the controversy waged over the age of the earth had not
been more bitter, that over catastrophism not more acrimonious, than
that which now raged over the question of the transmutation of species.
The question had implications far beyond the bounds of paleontology, of
course. The main evidence yet presented had been drawn from quite other
fields, but by common consent the record in the rocks might furnish a
crucial test of the truth or falsity of the hypothesis. "He who rejects
this view of the imperfections of the geological record," said Darwin,
"will rightly reject the whole theory."

With something more than mere scientific zeal, therefore,
paleontologists turned anew to the records in the rocks, to inquire what
evidence in proof or refutation might be found in unread pages of the
"great stone book." And, as might have been expected, many minds being
thus prepared to receive new evidence, such evidence was not long
withheld.


FOSSIL MAN

Indeed, at the moment of Darwin's writing a new and very instructive
chapter of the geologic record was being presented to the public--a
chapter which for the first time brought man into the story. In 1859
Dr. Falconer, the distinguished British paleontologist, made a visit
to Abbeville, in the valley of the Somme, incited by reports that for
a decade before bad been sent out from there by M. Boucher de Perthes.
These reports had to do with the alleged finding of flint implements,
clearly the work of man, in undisturbed gravel-beds, in the midst of
fossil remains of the mammoth and other extinct animals. What Falconer
saw there and what came of his visit may best be told in his own words:

"In September of 1856 I made the acquaintance of my distinguished friend
M. Boucher de Perthes," wrote Dr. Falconer, "on the introduction of M.
Desnoyers at Paris, when he presented to me the earlier volume of his
Antiquites celtiques, etc., with which I thus became acquainted for the
first time. I was then fresh from the examination of the Indian fossil
remains of the valley of the Jumna; and the antiquity of the human race
being a subject of interest to both, we conversed freely about it,
each from a different point of view. M. de Perthes invited me to visit
Abbeville, in order to examine his antediluvian collection, fossil and
geological, gleaned from the valley of the Somme. This I was unable to
accomplish then, but I reserved it for a future occasion.

"In October, 1856, having determined to proceed to Sicily, I arranged
by correspondence with M. Boucher de Perthes to visit Abbeville on my
journey through France. I was at the time in constant communication
with Mr. Prestwich about the proofs of the antiquity of the human race
yielded by the Broxham Cave, in which he took a lively interest; and
I engaged to communicate to him the opinions at which I should arrive,
after my examination of the Abbeville collection. M. de Perthes gave me
the freest access to his materials, with unreserved explanations of all
the facts of the case that had come under his observation; and having
considered his Menchecourt Section, taken with such scrupulous care, and
identified the molars of elephas primigenius, which he had exhumed with
his own hands deep in that section, along with flint weapons, presenting
the same character as some of those found in the Broxham Cave, I arrived
at the conviction that they were of contemporaneous age, although I
was not prepared to go along with M. de Perthes in all his inferences
regarding the hieroglyphics and in an industrial interpretation of the
various other objects which he had met with."(4)


That Dr. Falconer was much impressed by the collection of M. de
Perthes is shown in a communication which he sent at once to his friend
Prestwich:

"I have been richly rewarded," he exclaims. "His collection of wrought
flint implements, and of the objects of every description associated
with them, far exceeds everything I expected to have seen, especially
from a single locality. He has made great additions, since the
publication of his first volume, in the second, which I now have by
me. He showed me flint hatchets which HE HAD DUG UP with his own hands,
mixed INDISCRIMINATELY with molars of elephas primigenius. I examined
and identified plates of the molars and the flint objects which were
got along with them. Abbeville is an out-of-the-way place, very little
visited; and the French savants who meet him in Paris laugh at Monsieur
de Perthes and his researches. But after devoting the greater part of
a day to his vast collection, I am perfectly satisfied that there is
a great deal of fair presumptive evidence in favor of many of his
speculations regarding the remote antiquity of these industrial objects
and their association with animals now extinct. M. Boucher's hotel
is, from the ground floor to garret, a continued museum, filled with
pictures, mediaeval art, and Gaulish antiquities, including antediluvian
flint-knives, fossil-bones, etc. If, during next summer, you should
happen to be paying a visit to France, let me strongly recommend you to
come to Abbeville. I am sure you would be richly rewarded."(5)


This letter aroused the interest of the English geologists, and in the
spring of 1859 Prestwich and Mr. (afterwards Sir John) Evans made a
visit to Abbeville to see the specimens and examine at first hand the
evidences as pointed out by Dr. Falconer. "The evidence yielded by the
valley of the Somme," continues Falconer, in speaking of this visit,
"was gone into with the scrupulous care and severe and exhaustive
analysis which are characteristic of Mr. Prestwich's researches. The
conclusions to which he was conducted were communicated to the Royal
Society on May 12, 1859, in his celebrated memoir, read on May 26th and
published in the Philosophical Transactions of 1860, which, in addition
to researches made in the valley of the Somme, contained an account of
similar phenomena presented by the valley of the Waveney, near Hoxne, in
Suffolk. Mr. Evans communicated to the Society of Antiquaries a memoir
on the character and geological position of the 'Flint Implements in the
Drift,' which appeared in the Archaeologia for 1860. The results arrived
at by Mr. Prestwich were expressed as follows:

"First. That the flint implements are the result of design and the work
of man.

"Second. That they are found in beds of gravel, sand, and clay, which
have never been artificially disturbed.

"Third. That they occur associated with the remains of land,
fresh-water, and marine testacea, of species now living, and most of
them still common in the same neighborhood, and also with the remains of
various mammalia--a few species now living, but more of extinct forms.

"Fourth. That the period at which their entombment took place was
subsequent to the bowlder-clay period, and to that extent post-glacial;
and also that it was among the latest in geological time--one apparently
anterior to the surface assuming its present form, so far as it regards
some of the minor features."(6)


These reports brought the subject of the very significant human fossils
at Abbeville prominently before the public; whereas the publications of
the original discoverer, Boucher de Perthes, bearing date of 1847, had
been altogether ignored. A new aspect was thus given to the current
controversy.

As Dr. Falconer remarked, geology was now passing through the same
ordeal that astronomy passed in the age of Galileo. But the times were
changed since the day when the author of the Dialogues was humbled
before the Congregation of the Index, and now no Index Librorum
Prohibitorum could avail to hide from eager human eyes such pages of
the geologic story as Nature herself had spared. Eager searchers were
turning the leaves with renewed zeal everywhere, and with no small
measure of success. In particular, interest attached just at this
time to a human skull which Dr. Fuhlrott had discovered in a cave at
Neanderthal two or three years before--a cranium which has ever since
been famous as the Neanderthal skull, the type specimen of what modern
zoologists are disposed to regard as a distinct species of man, Homo
neanderthalensis. Like others of the same type since discovered at Spy,
it is singularly simian in character--low-arched, with receding forehead
and enormous, protuberant eyebrows. When it was first exhibited to the
scientists at Berlin by Dr. Fuhlrott, in 1857, its human character was
doubted by some of the witnesses; of that, however, there is no present
question.

This interesting find served to recall with fresh significance some
observations that had been made in France and Belgium a long generation
earlier, but whose bearings had hitherto been ignored. In 1826 MM.
Tournal and Christol had made independent discoveries of what they
believed to be human fossils in the caves of the south of France; and
in 1827 Dr. Schmerling had found in the cave of Engis, in Westphalia,
fossil bones of even greater significance. Schmerling's explorations
had been made with the utmost care, and patience. At Engis he had
found human bones, including skulls, intermingled with those of extinct
mammals of the mammoth period in a way that left no doubt in his mind
that all dated from the same geological epoch. He bad published a full
account of his discoveries in an elaborate monograph issued in 1833.

But at that time, as it chanced, human fossils were under a ban as
effectual as any ever pronounced by canonical index, though of far
different origin. The oracular voice of Cuvier had declared against the
authenticity of all human fossils. Some of the bones brought him for
examination the great anatomist had pettishly pitched out of the window,
declaring them fit only for a cemetery, and that had settled the matter
for a generation: the evidence gathered by lesser workers could avail
nothing against the decision rendered at the Delphi of Science. But no
ban, scientific or canonical, can longer resist the germinative power of
a fact, and so now, after three decades of suppression, the truth which
Cuvier had buried beneath the weight of his ridicule burst its bonds,
and fossil man stood revealed, if not as a flesh-and-blood, at least as
a skeletal entity.

The reception now accorded our prehistoric ancestor by the progressive
portion of the scientific world amounted to an ovation; but the
unscientific masses, on the other hand, notwithstanding their usual
fondness for tracing remote genealogies, still gave the men of Engis
and Neanderthal the cold shoulder. Nor were all of the geologists quite
agreed that the contemporaneity of these human fossils with the animals
whose remains had been mingled with them had been fully established. The
bare possibility that the bones of man and of animals that long preceded
him had been swept together into the eaves in successive ages, and
in some mysterious way intermingled there, was clung to by the
conservatives as a last refuge. But even this small measure of security
was soon to be denied them, for in 1865 two associated workers,
M. Edouard Lartet and Mr. Henry Christy, in exploring the caves of
Dordogne, unearthed a bit of evidence against which no such objection
could be urged. This momentous exhibit was a bit of ivory, a fragment
of the tusk of a mammoth, on which was scratched a rude but unmistakable
outline portrait of the mammoth itself. If all the evidence as to man's
antiquity before presented was suggestive merely, here at last was
demonstration; for the cave-dwelling man could not well have drawn the
picture of the mammoth unless he had seen that animal, and to admit that
man and the mammoth had been contemporaries was to concede the entire
case. So soon, therefore, as the full import of this most instructive
work of art came to be realized, scepticism as to man's antiquity was
silenced for all time to come.

In the generation that has elapsed since the first drawing of the
cave-dweller artist was discovered, evidences of the wide-spread
existence of man in an early epoch have multiplied indefinitely, and
to-day the paleontologist traces the history of our race back beyond the
iron and bronze ages, through a neolithic or polished-stone age, to
a paleolithic or rough-stone age, with confidence born of unequivocal
knowledge. And he looks confidently to the future explorer of the
earth's fossil records to extend the history back into vastly more
remote epochs, for it is little doubted that paleolithic man, the most
ancient of our recognized progenitors, is a modern compared to those
generations that represented the real childhood of our race.


THE FOSSIL-BEDS OF AMERICA

Coincidently with the discovery of these highly suggestive pages of the
geologic story, other still more instructive chapters were being brought
to light in America. It was found that in the Rocky Mountain region, in
strata found in ancient lake beds, records of the tertiary period, or
age of mammals, had been made and preserved with fulness not approached
in any other region hitherto geologically explored. These records were
made known mainly by Professors Joseph Leidy, O. C. Marsh, and E. D.
Cope, working independently, and more recently by numerous younger
paleontologists.

The profusion of vertebrate remains thus brought to light quite beggars
all previous exhibits in point of mere numbers. Professor Marsh, for
example, who was first in the field, found three hundred new tertiary
species between the years 1870 and 1876. Meanwhile, in cretaceous
strata, he unearthed remains of about two hundred birds with teeth, six
hundred pterodactyls, or flying dragons, some with a spread of wings
of twenty-five feet, and one thousand five hundred mosasaurs of the
sea-serpent type, some of them sixty feet or more in length. In a single
bed of Jurassic rock, not larger than a good-sized lecture-room, he
found the remains of one hundred and sixty individuals of mammals,
representing twenty species and nine genera; while beds of the same age
have yielded three hundred reptiles, varying from the size of a rabbit
to sixty or eighty feet in length.

But the chief interest of these fossils from the West is not their
number but their nature; for among them are numerous illustrations of
just such intermediate types of organisms as must have existed in the
past if the succession of life on the globe has been an unbroken lineal
succession. Here are reptiles with bat-like wings, and others with
bird-like pelves and legs adapted for bipedal locomotion. Here are
birds with teeth, and other reptilian characters. In short, what with
reptilian birds and birdlike reptiles, the gap between modern reptiles
and birds is quite bridged over. In a similar way, various diverse
mammalian forms, as the tapir, the rhinoceros, and the horse, are linked
together by fossil progenitors. And, most important of all, Professor
Marsh has discovered a series of mammalian remains, occurring in
successive geological epochs, which are held to represent beyond cavil
the actual line of descent of the modern horse; tracing the lineage
of our one-toed species back through two and three toed forms, to an
ancestor in the eocene or early tertiary that had four functional toes
and the rudiment of a fifth. This discovery is too interesting and too
important not to be detailed at length in the words of the discoverer.


Marsh Describes the Fossil Horse

"It is a well-known fact," says Professor Marsh, "that the Spanish
discoverers of America discovered no horses on this continent, and that
the modern horse (Equus caballus, Linn.) was subsequently introduced
from the Old World. It is, however, not so generally known that these
animals had formerly been abundant here, and that long before, in
tertiary time, near relatives of the horse, and probably his ancestors,
existed in the far West in countless numbers and in a marvellous variety
of forms. The remains of equine mammals, now known from the tertiary and
quaternary deposits of this country, already represent more than double
the number of genera and species hitherto found in the strata of the
eastern hemisphere, and hence afford most important aid in tracing out
the genealogy of the horses still existing.

"The animals of this group which lived in America during the three
diversions of the tertiary period were especially numerous in the Rocky
Mountain regions, and their remains are well preserved in the old lake
basins which then covered so much of that country. The most ancient
of these lakes--which extended over a considerable part of the present
territories of Wyoming and Utah--remained so long in eocene times that
the mud and sand, slowly deposited in it, accumulated to more than a
mile in vertical thickness. In these deposits vast numbers of tropical
animals were entombed, and here the oldest equine remains occur,
four species of which have been described. These belong to the genus
Orohippus (Marsh), and are all of a diminutive size, hardly bigger than
a fox. The skeletons of these animals resemble that of the horse in many
respects, much more indeed than any other existing species, but, instead
of the single toe on each foot, so characteristic of all modern equines,
the various species of Orohippus had four toes before and three behind,
all of which reached the ground. The skull, too, was proportionately
shorter, and the orbit was not enclosed behind by a bridge of bone.
There were fifty four teeth in all, and the premolars were larger than
the molars. The crowns of these teeth were very short. The canine teeth
were developed in both sexes, and the incisors did not have the "mark"
which indicates the age of the modern horse. The radius and ulna were
separate, and the latter was entire through the whole length. The tibia
and fibula were distinct. In the forefoot all the digits except the
pollex, or first, were well developed. The third digit is the largest,
and its close resemblance to that of the horse is clearly marked. The
terminal phalanx, or coffin-bone, has a shallow median bone in front,
as in many species of this group in the later tertiary. The fourth digit
exceeds the second in size, and the second is much the shortest of all.
Its metacarpal bone is considerably curved outward. In the hind-foot
of this genus there are but three digits. The fourth metatarsal is much
larger than the second.

"The larger number of equine mammals now known from the tertiary
deposits of this country, and their regular distributions through the
subdivisions of this formation, afford a good opportunity to ascertain
the probable descent of the modern horse. The American representative of
the latter is the extinct Equus fraternus (Leidy), a species almost, if
not wholly, identical with the Old World Equus caballus (Linnaeus), to
which our recent horse belongs. Huxley has traced successfully the later
genealogy of the horse through European extinct forms, but the line in
America was probably a more direct one, and the record is more complete.
Taking, then, as the extreme of a series, Orohippus agilis (Marsh),
from the eocene, and Equus fraternus (Leidy), from the quaternary,
intermediate forms may be intercalated with considerable certainty
from thirty or more well-marked species that lived in the intervening
periods. The natural line of descent would seem to be through the
following genera: Orohippus, of the eocene; Miohippus and Anchitherium,
of the miocene; Anchippus, Hipparion, Protohippus, Phohippus, of the
pliocene; and Equus, quaternary and recent.

"The most marked changes undergone by the successive equine genera are
as follows: First, increase in size; second, increase in speed, through
concentration of limb bones; third, elongation of head and neck, and
modifications of skull. The eocene Orohippus was the size of a fox.
Miohippus and Anchitherium, from the miocene, were about as large as a
sheep. Hipparion and Pliohippus, of the pliocene, equalled the ass in
height; while the size of the quaternary Equus was fully up to that of a
modern horse.

"The increase of speed was equally well marked, and was a direct
result of the gradual formation of the limbs. The latter were slowly
concentrated by the reduction of their lateral elements and enlargement
of the axial bone, until the force exerted by each limb came to act
directly through its axis in the line of motion. This concentration is
well seen--e.g., in the fore-limb. There was, first, a change in the
scapula and humerus, especially in the latter, which facilitated motion
in one line only; second, an expansion of the radius and reduction of
the ulna, until the former alone remained entire and effective; third,
a shortening of all the carpal bones and enlargement of the median ones,
insuring a firmer wrist; fourth, an increase of size of the third digit,
at the expense of those of each side, until the former alone supported
the limb.

"Such is, in brief, a general outline of the more marked changes that
seemed to have produced in America the highly specialized modern Equus
from his diminutive four-toed predecessor, the eocene Orohippus. The
line of descent appears to have been direct, and the remains now known
supply every important intermediate form. It is, of course, impossible
to say with certainty through which of the three-toed genera of the
pliocene that lived together the succession came. It is not impossible
that the latter species, which appear generically identical, are the
descendants of more distinct pliocene types, as the persistent tendency
in all the earlier forms was in the same direction. Considering the
remarkable development of the group through the tertiary period, and
its existence even later, it seems very strange that none of the species
should have survived, and that we are indebted for our present horse to
the Old World."(7)


PALEONTOLOGY OF EVOLUTION

These and such-like revelations have come to light in our own time--are,
indeed, still being disclosed. Needless to say, no index of any sort now
attempts to conceal them; yet something has been accomplished towards
the same end by the publication of the discoveries in Smithsonian
bulletins and in technical memoirs of government surveys. Fortunately,
however, the results have been rescued from that partial oblivion by
such interpreters as Professors Huxley and Cope, so the unscientific
public has been allowed to gain at least an inkling of the wonderful
progress of paleontology in our generation.

The writings of Huxley in particular epitomize the record. In 1862 he
admitted candidly that the paleontological record as then known, so far
as it bears on the doctrine of progressive development, negatives
that doctrine. In 1870 he was able to "soften somewhat the Brutus-like
severity" of his former verdict, and to assert that the results of
recent researches seem "to leave a clear balance in favor of the
doctrine of the evolution of living forms one from another." Six years
later, when reviewing the work of Marsh in America and of Gaudry
in Pikermi, he declared that, "on the evidence of paleontology, the
evolution of many existing forms of animal life from their predecessors
is no longer an hypothesis, but an historical fact." In 1881 he
asserted that the evidence gathered in the previous decade had been so
unequivocal that, had the transmutation hypothesis not existed, "the
paleontologist would have had to invent it."

Since then the delvers after fossils have piled proof on proof in
bewildering profusion. The fossil-beds in the "bad lands" of western
America seem inexhaustible. And in the Connecticut River Valley near
relatives of the great reptiles which Professor Marsh and others
have found in such profusion in the West left their tracks on the
mud-flats--since turned to sandstone; and a few skeletons also have been
found. The bodies of a race of great reptiles that were the lords of
creation of their day have been dissipated to their elements, while the
chance indentations of their feet as they raced along the shores, mere
footprints on the sands, have been preserved among the most imperishable
of the memory-tablets of the world.

Of the other vertebrate fossils that have been found in the eastern
portions of America, among the most abundant and interesting are the
skeletons of mastodons. Of these one of the largest and most complete is
that which was unearthed in the bed of a drained lake near Newburg, New
York, in 1845. This specimen was larger than the existing elephants,
and had tusks eleven feet in length. It was mounted and described by Dr.
John C. Warren, of Boston, and has been famous for half a century as the
"Warren mastodon."

But to the student of racial development as recorded by the fossils all
these sporadic finds have but incidental interest as compared with the
rich Western fossil-beds to which we have already referred. From records
here unearthed, the racial evolution of many mammals has in the past few
years been made out in greater or less detail. Professor Cope has traced
the ancestry of the camels (which, like the rhinoceroses, hippopotami,
and sundry other forms now spoken of as "Old World," seem to have had
their origin here) with much completeness.

A lemuroid form of mammal, believed to be of the type from which man
has descended, has also been found in these beds. It is thought that the
descendants of this creature, and of the other "Old-World" forms
above referred to, found their way to Asia, probably, as suggested by
Professor Marsh, across a bridge at Bering Strait, to continue their
evolution on the other hemisphere, becoming extinct in the land of their
nativity. The ape-man fossil found in the tertiary strata of the island
of Java in 1891 by the Dutch surgeon Dr. Eugene Dubois, and named
Pithecanthropus erectus, may have been a direct descendant of the
American tribe of primitive lemurs, though this is only a conjecture.

Not all the strange beasts which have left their remains in our "bad
lands" are represented by living descendants. The titanotheres, or
brontotheridae, for example, a gigantic tribe, offshoots of the
same stock which produced the horse and rhinoceros, represented the
culmination of a line of descent. They developed rapidly in a geological
sense, and flourished about the middle of the tertiary period; then,
to use Agassiz's phrase," time fought against them." The story of their
evolution has been worked out by Professors Leidy, Marsh, Cope, and H.
F. Osborne.

A recent bit of paleontological evidence bearing on the question of
the introduction of species is that presented by Dr. J. L. Wortman in
connection with the fossil lineage of the edentates. It was suggested by
Marsh, in 1877, that these creatures, whose modern representatives are
all South American, originated in North America long before the two
continents had any land connection. The stages of degeneration by which
these animals gradually lost the enamel from their teeth, coming finally
to the unique condition of their modern descendants of the sloth tribe,
are illustrated by strikingly graded specimens now preserved in the
American Museum of Natural History, as shown by Dr. Wortman.

All these and a multitude of other recent observations that cannot be
even outlined here tell the same story. With one accord paleontologists
of our time regard the question of the introduction of new species as
solved. As Professor Marsh has said, "to doubt evolution today is to
doubt science; and science is only another name for truth."

Thus the third great battle over the meaning of the fossil records has
come to a conclusion. Again there is a truce to controversy, and it may
seem to the casual observer that the present stand of the science of
fossils is final and impregnable. But does this really mean that a full
synopsis of the story of paleontology has been told? Or do we only await
the coming of the twentieth-century Lamarck or Darwin, who shall
attack the fortified knowledge of to-day with the batteries of a new
generalization?



IV. THE ORIGIN AND DEVELOPMENT OF MODERN GEOLOGY


JAMES HUTTON

One might naturally suppose that the science of the earth which lies at
man's feet would at least have kept pace with the science of the distant
stars. But perhaps the very obviousness of the phenomena delayed the
study of the crust of the earth. It is the unattainable that allures and
mystifies and enchants the developing mind. The proverbial child spurns
its toys and cries for the moon.

So in those closing days of the eighteenth century, when astronomers had
gone so far towards explaining the mysteries of the distant portions
of the universe, we find a chaos of opinion regarding the structure
and formation of the earth. Guesses were not wanting to explain the
formation of the world, it is true, but, with one or two exceptions,
these are bizarre indeed. One theory supposed the earth to have been at
first a solid mass of ice, which became animated only after a comet had
dashed against it. Other theories conceived the original globe as a mass
of water, over which floated vapors containing the solid elements, which
in due time were precipitated as a crust upon the waters. In a word, the
various schemes supposed the original mass to have been ice, or water,
or a conglomerate of water and solids, according to the random fancies
of the theorists; and the final separation into land and water was
conceived to have taken place in all the ways which fancy, quite
unchecked by any tenable data, could invent.

Whatever important changes in the general character of the surface of
the globe were conceived to have taken place since its creation were
generally associated with the Mosaic: deluge, and the theories which
attempted to explain this catastrophe were quite on a par with
those which dealt with a remoter period of the earth's history. Some
speculators, holding that the interior of the globe is a great abyss
of waters, conceived that the crust had dropped into this chasm and had
thus been inundated. Others held that the earth had originally revolved
on a vertical axis, and that the sudden change to its present position
bad caused the catastrophic shifting of its oceans. But perhaps the
favorite theory was that which supposed a comet to have wandered near
the earth, and in whirling about it to have carried the waters, through
gravitation, in a vast tide over the continents.

Thus blindly groped the majority of eighteenth-century philosophers in
their attempts to study what we now term geology. Deluded by the old
deductive methods, they founded not a science, but the ghost of a
science, as immaterial and as unlike anything in nature as any other
phantom that could be conjured from the depths of the speculative
imagination. And all the while the beckoning earth lay beneath the feet
of these visionaries; but their eyes were fixed in air.

At last, however, there came a man who had the penetration to see that
the phantom science of geology needed before all else a body corporeal,
and who took to himself the task of supplying it. This was Dr.
James Hutton, of Edinburgh, physician, farmer, and manufacturing
chemist--patient, enthusiastic, level-headed devotee of science.
Inspired by his love of chemistry to study the character of rocks and
soils, Hutton had not gone far before the earth stood revealed to him
in a new light. He saw, what generations of predecessors had blindly
refused to see, that the face of nature everywhere, instead of being
rigid and immutable, is perennially plastic, and year by year is
undergoing metamorphic changes. The solidest rocks are day by day
disintegrated slowly, but none the less surely, by wind and rain and
frost, by mechanical attrition and chemical decomposition, to form the
pulverized earth and clay. This soil is being swept away by perennial
showers, and carried off to the oceans. The oceans themselves beat on
their shores, and eat insidiously into the structure of sands and rocks.
Everywhere, slowly but surely, the surface of the land is being worn
away; its substance is being carried to burial in the seas.

Should this denudation continue long enough, thinks Hutton, the entire
surface of the continents must be worn away. Should it be continued LONG
ENOUGH! And with that thought there flashes on his mind an inspiring
conception--the idea that solar time is long, indefinitely long. That
seems a simple enough thought--almost a truism--to the twentieth-century
mind; but it required genius to conceive it in the eighteenth. Hutton
pondered it, grasped its full import, and made it the basis of his
hypothesis, his "theory of the earth."


MODERN GEOLOGY

The hypothesis is this--that the observed changes of the surface of
the earth, continued through indefinite lapses of time, must result in
conveying all the land at last to the sea; in wearing continents away
till the oceans overflow them. What then? Why, as the continents wear
down, the oceans are filling up. Along their bottoms the detritus of
wasted continents is deposited in strata, together with the bodies of
marine animals and vegetables. Why might not this debris solidify to
form layers of rocks--the basis of new continents? Why not, indeed?

But have we any proof that such formation of rocks in an ocean-bed has,
in fact, occurred? To be sure we have. It is furnished by every bed
of limestone, every outcropping fragment of fossil-bearing rock, every
stratified cliff. How else than through such formation in an ocean-bed
came these rocks to be stratified? How else came they to contain the
shells of once living organisms imbedded in their depths? The ancients,
finding fossil shells imbedded in the rocks, explained them as mere
freaks of "nature and the stars." Less superstitious generations had
repudiated this explanation, but had failed to give a tenable solution
of the mystery. To Hutton it is a mystery no longer. To him it seems
clear that the basis of the present continents was laid in ancient
sea-beds, formed of the detritus of continents yet more ancient.

But two links are still wanting to complete the chain of Hutton's
hypothesis. Through what agency has the ooze of the ocean-bed been
transformed into solid rock? and through what agency has this rock been
lifted above the surface of the water to form new continents? Hutton
looks about him for a clew, and soon he finds it. Everywhere about us
there are outcropping rocks that are not stratified, but which give
evidence to the observant eye of having once been in a molten state.
Different minerals are mixed together; pebbles are scattered through
masses of rock like plums in a pudding; irregular crevices in otherwise
solid masses of rock--so-called veinings--are seen to be filled with
equally solid granite of a different variety, which can have gotten
there in no conceivable way, so Hutton thinks, but by running in while
molten, as liquid metal is run into the moulds of the founder. Even
the stratified rocks, though they seemingly have not been melted, give
evidence in some instances of having been subjected to the action of
heat. Marble, for example, is clearly nothing but calcined limestone.

With such evidence before him, Hutton is at no loss to complete his
hypothesis. The agency which has solidified the ocean-beds, he says,
is subterranean heat. The same agency, acting excessively, has produced
volcanic cataclysms, upheaving ocean-beds to form continents. The rugged
and uneven surfaces of mountains, the tilted and broken character
of stratified rocks everywhere, are the standing witnesses of these
gigantic upheavals.

And with this the imagined cycle is complete. The continents, worn away
and carried to the sea by the action of the elements, have been made
over into rocks again in the ocean-beds, and then raised once more into
continents. And this massive cycle, In Hutton's scheme, is supposed
to have occurred not once only, but over and over again, times without
number. In this unique view ours is indeed a world without beginning
and without end; its continents have been making and unmaking in endless
series since time began.

Hutton formulated his hypothesis while yet a young man, not long after
the middle of the century. He first gave it publicity in 1781, in a
paper before the Royal Society of Edinburgh:

"A solid body of land could not have answered the purpose of a habitable
world," said Hutton, "for a soil is necessary to the growth of plants,
and a soil is nothing but the material collected from the destruction of
the solid land. Therefore the surface of this land inhabited by man, and
covered by plants and animals, is made by nature to decay, in dissolving
from that hard and compact state in which it is found; and this soil
is necessarily washed away by the continual circulation of the water
running from the summits of the mountains towards the general receptacle
of that fluid.

"The heights of our land are thus levelled with our shores, our fertile
plains are formed from the ruins of the mountains; and those travelling
materials are still pursued by the moving water, and propelled along the
inclined surface of the earth. These movable materials, delivered into
the sea, cannot, for a long continuance, rest upon the shore, for by the
agitation of the winds, the tides, and the currents every movable thing
is carried farther and farther along the shelving bottom of the sea,
towards the unfathomable regions of the ocean.

"If the vegetable soil is thus constantly removed from the surface of
the land, and if its place is then to be supplied from the dissolution
of the solid earth as here represented, we may perceive an end to this
beautiful machine; an end arising from no error in its constitution as
a world, but from that destructibility of its land which is so necessary
in the system of the globe, in the economy of life and vegetation.

"The immense time necessarily required for the total destruction of
the land must not be opposed to that view of future events which is
indicated by the surest facts and most approved principles. Time, which
measures everything in our idea, and is often deficient to our schemes,
is to nature endless and as nothing; it cannot limit that by which alone
it has existence; and as the natural course of time, which to us seems
infinite, cannot be bounded by any operation that may have an end, the
progress of things upon this globe that in the course of nature cannot
be limited by time must proceed in a continual succession. We are,
therefore, to consider as inevitable the destruction of our land, so far
as effected by those operations which are necessary in the purpose of
the globe, considered as a habitable world, and so far as we have
not examined any other part of the economy of nature, in which other
operations and a different intention might appear.

"We have now considered the globe of this earth as a machine,
constructed upon chemical as well as mechanical principles, by which its
different parts are all adapted, in form, in quality, and quantity, to a
certain end--an end attained with certainty of success, and an end from
which we may perceive wisdom in contemplating the means employed.

"But is this world to be considered thus merely as a machine, to last no
longer than its parts retain their present position, their proper forms
and qualities? Or may it not be also considered as an organized body
such as has a constitution, in which the necessary decay of the machine
is naturally repaired in the exertion of those productive powers by
which it has been formed?

"This is the view in which we are now to examine the globe; to see if
there be, in the constitution of the world, a reproductive operation
by which a ruined constitution may be again repaired and a duration of
stability thus procured to the machine considered as a world containing
plants and animals.

"If no such reproductive power, or reforming operation, after due
inquiry, is to be found in the constitution of this world, we should
have reason to conclude that the system of this earth has either been
intentionally made imperfect or has not been the work of infinite power
and wisdom."(1)


This, then, was the important question to be answered--the question of
the constitution of the globe. To accomplish this, it was necessary,
first of all, to examine without prejudice the material already in hand,
adding such new discoveries from time to time as might be made, but
always applying to the whole unvarying scientific principles and
inductive methods of reasoning.

"If we are to take the written history of man for the rule by which we
should judge of the time when the species first began," said Hutton,
"that period would be but little removed from the present state of
things. The Mosaic history places this beginning of man at no great
distance; and there has not been found, in natural history, any document
by which high antiquity might be attributed to the human race. But
this is not the case with regard to the inferior species of animals,
particularly those which inhabit the ocean and its shores. We find
in natural history monuments which prove that those animals had long
existed; and we thus procure a measure for the computation of a period
of time extremely remote, though far from being precisely ascertained.

"In examining things present, we have data from which to reason with
regard to what has been; and from what actually has been we have
data for concluding with regard to that which is to happen hereafter.
Therefore, upon the supposition that the operations of nature are
equable and steady, we find, in natural appearances, means for
concluding a certain portion of time to have necessarily elapsed in the
production of those events of which we see the effects.

"It is thus that, in finding the relics of sea animals of every kind
in the solid body of our earth, a natural history of those animals
is formed, which includes a certain portion of time; and for the
ascertaining this portion of time we must again have recourse to the
regular operations of this world. We shall thus arrive at facts which
indicate a period to which no other species of chronology is able to
remount.

"We find the marks of marine animals in the most solid parts of the
earth, consequently those solid parts have been formed after the ocean
was inhabited by those animals which are proper to that fluid medium.
If, therefore, we knew the natural history of these solid parts, and
could trace the operations of the globe by which they have been formed,
we would have some means for computing the time through which those
species of animals have continued to live. But how shall we describe a
process which nobody has seen performed and of which no written history
gives any account? This is only to be investigated, first, in examining
the nature of those solid bodies the history of which we want to know;
and, secondly, in examining the natural operations of the globe, in
order to see if there now exist such operations as, from the nature of
the solid bodies, appear to have been necessary for their formation.

"There are few beds of marble or limestone in which may not be found
some of those objects which indicate the marine object of the mass. If,
for example, in a mass of marble taken from a quarry upon the top of the
Alps or Andes there shall be found one cockle-shell or piece of coral,
it must be concluded that this bed of stone has been originally formed
at the bottom of the sea, as much as another bed which is evidently
composed almost altogether of cockle-shells and coral. If one bed of
limestone is thus found to have been of marine origin, every concomitant
bed of the same kind must be also concluded to have been formed in the
same manner.

"In those calcareous strata, which are evidently of marine origin,
there are many parts which are of sparry structure--that is to say, the
original texture of those beds in such places has been dissolved, and a
new structure has been assumed which is peculiar to a certain state of
the calcareous earth. This change is produced by crystallization, in
consequence of a previous state of fluidity, which has so disposed
the concerting parts as to allow them to assume a regular shape and
structure proper to that substance. A body whose external form has
been modified by this process is called a CRYSTAL; one whose internal
arrangement of parts is determined by it is said to be of a SPARRY
STRUCTURE, and this is known from its fracture.

"There are, in all the regions of the earth, huge masses of calcareous
matter in that crystalline form or sparry state in which, perhaps, no
vestige can be found of any organized body, nor any indication that such
calcareous matter has belonged to animals; but as in other masses this
sparry structure or crystalline state is evidently assumed by the marine
calcareous substances in operations which are natural to the globe,
and which are necessary to the consolidation of the strata, it does not
appear that the sparry masses in which no figured body is formed
have been originally different from other masses, which, being only
crystallized in part, and in part still retaining their original form,
have ample evidence of their marine origin.

"We are led, in this manner, to conclude that all the strata of the
earth, not only those consisting of such calcareous masses, but others
superincumbent upon these, have had their origin at the bottom of the
sea.

"The general amount of our reasoning is this, that nine-tenths, perhaps,
or ninety-nine-hundredths, of this earth, so far as we see, have been
formed by natural operations of the globe in collecting loose materials
and depositing them at the bottom of the sea; consolidating those
collections in various degrees, and either elevating those consolidated
masses above the level on which they were formed or lowering the level
of that sea.

"Let us now consider how far the other proposition of strata being
elevated by the power of heat above the level of the sea may be
confirmed from the examination of natural appearances. The strata formed
at the bottom of the ocean are necessarily horizontal in their position,
or nearly so, and continuous in their horizontal direction or extent.
They may be changed and gradually assume the nature of each other, so
far as concerns the materials of which they are formed, but there cannot
be any sudden change, fracture, or displacement naturally in the body
of a stratum. But if the strata are cemented by the heat of fusion,
and erected with an expansive power acting below, we may expect to find
every species of fracture, dislocation, and contortion in those bodies
and every degree of departure from a horizontal towards a vertical
position.

"The strata of the globe are actually found in every possible position:
for from horizontal they are frequently found vertical; from continuous
they are broken and separated in every possible direction; and from a
plane they are bent and doubled. It is impossible that they could have
originally been formed, by the known laws of nature, in their present
state and position; and the power that has been necessarily required
for their change has not been inferior to that which might have been
required for their elevation from the place in which they have been
formed."(2)


From all this, therefore, Hutton reached the conclusion that the
elevation of the bodies of land above the water on the earth's surface
had been effected by the same force which had acted in consolidating the
strata and giving them stability. This force he conceived to be exerted
by the expansion of heated matter.

"We have," he said, "been now supposing that the beginning of our
present earth had been laid in the bottom of the ocean, at the
completion of the former land, but this was only for the sake of
distinctness. The just view is this, that when the former land of the
globe had been complete, so as to begin to waste and be impaired by
the encroachment of the sea, the present land began to appear above the
surface of the ocean. In this manner we suppose a due proportion to be
always preserved of land and water upon the surface of the globe, for
the purpose of a habitable world such as this which we possess. We
thus also allow time and opportunity for the translation of animals and
plants to occupy the earth.

"But if the earth on which we live began to appear in the ocean at
the time when the LAST began to be resolved, it could not be from the
materials of the continent immediately preceding this which we examine
that the present earth has been constructed; for the bottom of the ocean
must have been filled with materials before land could be made to appear
above its surface.

"Let us suppose that the continent which is to succeed our land is at
present beginning to appear above the water in the middle of the Pacific
Ocean; it must be evident that the materials of this great body, which
is formed and ready to be brought forth, must have been collected from
the destruction of an earth which does not now appear. Consequently,
in this true statement of the case there is necessarily required the
destruction of an animal and vegetable earth prior to the former land;
and the materials of that earth which is first in our account must have
been collected at the bottom of the ocean, and begun to be concocted for
the production of the present earth, when the land immediately preceding
the present had arrived at its full extent.

"We have now got to the end of our reasoning; we have no data further
to conclude immediately from that which actually is; but we have got
enough; we have the satisfaction to find that in nature there are
wisdom, system, and consistency. For having in the natural history of
the earth seen a succession of worlds, we may from this conclude that
there is a system in nature; in like manner as, from seeing revolutions
of the planets, it is concluded that there is a system by which they are
intended to continue those revolutions. But if the succession of worlds
is established in the system of nature, it is in vain to look for
anything higher in the origin of the earth. The result, therefore,
of our present inquiry is that we find no vestige of a beginning--no
prospect of an end."


Altogether remarkable as this paper seems in the light of later
knowledge, neither friend nor foe deigned to notice it at the moment.
It was not published in book form until the last decade of the century,
when Hutton had lived with and worked over his theory for almost fifty
years. Then it caught the eye of the world. A school of followers
expounded the Huttonian doctrines; a rival school under Werner in
Germany opposed some details of the hypothesis, and the educated world
as a whole viewed the disputants askance. The very novelty of the new
views forbade their immediate acceptance. Bitter attacks were made upon
the "heresies," and that was meant to be a soberly tempered judgment
which in 1800 pronounced Hutton's theories "not only hostile to sacred
history, but equally hostile to the principles of probability, to the
results of the ablest observations on the mineral kingdom, and to the
dictates of rational philosophy." And all this because Hutton's theory
presupposed the earth to have been in existence more than six thousand
years.

Thus it appears that though the thoughts of men had widened, in those
closing days of the eighteenth century, to include the stars, they had
not as yet expanded to receive the most patent records that are written
everywhere on the surface of the earth. Before Hutton's views could be
accepted, his pivotal conception that time is long must be established
by convincing proofs. The evidence was being gathered by William Smith,
Cuvier, and other devotees of the budding science of paleontology in
the last days of the century, but their labors were not brought to
completion till a subsequent epoch.


NEPTUNISTS VERSUS PLUTONISTS

In the mean time, James Hutton's theory that continents wear away and
are replaced by volcanic upheaval gained comparatively few adherents.
Even the lucid Illustrations of the Huttonian Theory, which Playfair,
the pupil and friend of the great Scotchman, published in 1802, did not
at once prove convincing. The world had become enamoured of the rival
theory of Hutton's famous contemporary, Werner of Saxony--the theory
which taught that "in the beginning" all the solids of the earth's
present crust were dissolved in the heated waters of a universal sea.
Werner affirmed that all rocks, of whatever character, had been formed
by precipitation from this sea as the waters cooled; that even veins
have originated in this way; and that mountains are gigantic crystals,
not upheaved masses. In a word, he practically ignored volcanic action,
and denied in toto the theory of metamorphosis of rocks through the
agency of heat.

The followers of Werner came to be known as Neptunists; the Huttonians
as Plutonists. The history of geology during the first quarter of the
nineteenth century is mainly a recital of the intemperate controversy
between these opposing schools; though it should not be forgotten that,
meantime, the members of the Geological Society of London were making
an effort to hunt for facts and avoid compromising theories. Fact and
theory, however, were too closely linked to be thus divorced.

The brunt of the controversy settled about the unstratified
rocks--granites and their allies--which the Plutonists claimed as of
igneous origin. This contention had the theoretical support of the
nebular hypothesis, then gaining ground, which supposed the earth to be
a cooling globe. The Plutonists laid great stress, too, on the observed
fact that the temperature of the earth increases at a pretty constant
ratio as descent towards its centre is made in mines. But in particular
they appealed to the phenomena of volcanoes.

The evidence from this source was gathered and elaborated by Mr. G.
Poulett Scrope, secretary of the Geological Society of England, who, in
1823, published a classical work on volcanoes in which he claimed that
volcanic mountains, including some of the highest-known peaks, are
merely accumulated masses of lava belched forth from a crevice in the
earth's crust.

"Supposing the globe to have had any irregular shape when detached from
the sun," said Scrope, "the vaporization of its surface, and, of course,
of its projecting angles, together with its rotatory motion on its axis
and the liquefaction of its outer envelope, would necessarily occasion
its actual figure of an oblate spheroid. As the process of expansion
proceeded in depth, the original granitic beds were first partially
disaggregated, next disintegrated, and more or less liquefied,
the crystals being merged in the elastic vehicle produced by the
vaporization of the water contained between the laminae.

"Where this fluid was produced in abundance by great dilatation--that
is, in the outer and highly disintegrated strata, the superior specific
gravity of the crystals forced it to ooze upward, and thus a great
quantity of aqueous vapor was produced on the surface of the globe. As
this elastic fluid rose into outer space, its continually increasing
expansion must have proportionately lowered its temperature; and, in
consequence, a part was recondensed into water and sank back towards the
more solid surface of the globe.

"And in this manner, for a certain time, a violent reciprocation of
atmospheric phenomena must have continued--torrents of vapor rising
outwardly, while equally tremendous torrents of condensed vapor, or
rain, fell towards the earth. The accumulation of the latter on the
yet unstable and unconsolidated surface of the globe constituted the
primeval ocean. The surface of this ocean was exposed to continued
vaporization owing to intense heat; but this process, abstracting
caloric from the stratum of the water below, by partially cooling it,
tended to preserve the remainder in a liquid form. The ocean will have
contained, both in solution and suspension, many of the matters carried
upward from the granitic bed in which the vapors from whose condensation
it proceeded were produced, and which they had traversed in their rise.
The dissolved matters will have been silex, carbonates, and sulphates
of lime, and those other mineral substances which water at an intense
temperature and under such circumstances was enabled to hold in
solution. The suspended substances will have been all the lighter and
finer particles of the upper beds where the disintegration had been
extreme; and particularly their mica, which, owing to the tenuity of its
plate-shaped crystals, would be most readily carried up by the ascending
fluid, and will have remained longest in suspension.

"But as the torrents of vapor, holding these various matters in
solution and suspension, were forced upward, the greater part of the
disintegrated crystals by degrees subsided; those of felspar and quartz
first, the mica being, as observed above, from the form of its plates,
of peculiar buoyancy, and therefore held longest in suspension.

"The crystals of felspar and quartz as they subsided, together with a
small proportion of mica, would naturally arrange themselves so as to
have their longest dimensions more or less parallel to the surface on
which they rest; and this parallelism would be subsequently increased,
as we shall see hereafter, by the pressure of these beds sustained
between the weight of the supported column of matter and the expansive
force beneath them. These beds I conceive, when consolidated, to
constitute the gneiss formation.

"The farther the process of expansion proceeded in depth, the more was
the column of liquid matter lengthened, which, gravitating towards
the centre of the globe, tended to check any further expansion. It is,
therefore, obvious that after the globe settled into its actual orbit,
and thenceforward lost little of its enveloping matter, the whole
of which began from that moment to gravitate towards its centre, the
progress of expansion inwardly would continually increase in rapidity;
and a moment must have at length arrived hen the forces of expansion and
repression had reached an equilibrium and the process was stopped from
progressing farther inwardly by the great pressure of the gravitating
column of liquid.

"This column may be considered as consisting of different strata, though
the passage from one extremity of complete solidity to the other of
complete expansion, in reality, must have been perfectly gradual. The
lowest stratum, immediately above the extreme limit of expansion, will
have been granite barely DISAGGREGATED, and rendered imperfectly liquid
by the partial vaporization of its contained water.

"The second stratum was granite DISINTEGRATED; aqueous vapor, having
been produced in such abundance as to be enabled to rise upward,
partially disintegrating the crystals of felspar and mica, and
superficially dissolving those of quartz. This mass would reconsolidate
into granite, though of a smaller grain than the preceding rock.

"The third stratum was so disintegrated that a greater part of the mica
had been carried up by the escaping vapor IN SUSPENSION, and that of
quartz in solution; the felspar crystals, with the remaining quartz and
mica, SUBSIDING by their specific gravity and arranging themselves in
horizontal planes.

"The consolidation of this stratum produced the gneiss formation.

"The fourth zone will have been composed of the ocean of turbid and
heated water, holding mica, etc., in suspension, and quartz, carbonate
of lime, etc., in solution, and continually traversed by reciprocating
bodies of heated water rising from below, and of cold fluid sinking from
the surface, by reason of their specific gravities.

"The disturbance thus occasioned will have long retarded the deposition
of the suspended particles. But this must by degrees have taken place,
the quartz grains and the larger and coarser plates of mica subsiding
first and the finest last.

"But the fragments of quartz and mica were not deposited alone; a great
proportion of the quartz held in SOLUTION must have been precipitated
at the same time as the water cooled, and therefore by degrees lost
its faculty of so much in solution. Thus was gradually produced the
formation of mica-schist, the mica imperfectly recrystallizing or being
merely aggregated together in horizontal plates, between which the
quartz either spread itself generally in minute grains or unified into
crystalline nuclei. On other spots, instead of silex, carbonate of lime
was precipitated, together with more or less of the nucaceous sediment,
and gave rise to saccharoidal limestones. At a later period, when the
ocean was yet further cooled down, rock-salt and sulphate of lime were
locally precipitated in a similar mode.

"The fifth stratum was aeriform, and consisted in great part of
aqueous vapors; the remainder being a compound of other elastic fluids
(permanent gases) which had been formed probably from the volatilization
of some of the substances contained in the primitive granite and carried
upward with the aqueous vapor from below. These gases will have
been either mixed together or otherwise disposed, according to their
different specific gravities or chemical affinities, and this stratum
constituted the atmosphere or aerial envelope of the globe.

"When, in this manner, the general and positive expansion of the globe,
occasioned by the sudden reduction of outward pressure, had ceased (in
consequence of the REPRESSIVE FORCE, consisting of the weight of its
fluid envelope, having reached an equilibrium with the EXPANSIVE FORCE,
consisting of the caloric of the heated nucleus), the rapid superficial
evaporation of the ocean continued; and, by gradually reducing its
temperature, occasioned the precipitation of a proportionate quantity
of the minerals it held in solution, particularly its silex. These
substances falling to the bottom, accompanied by a large proportion of
the matters held in solution, particularly the mica, in consequence of
the greater comparative tranquillity of the ocean, agglomerated these
into more or less compact beds of rock (the mica-schist formation),
producing the first crust or solid envelope of the globe. Upon this,
other stratified rocks, composed sometimes of a mixture, sometimes of
an alternation of precipitations, sediments, and occasionally of
conglomerates, were by degrees deposited, giving rise to the TRANSITION
formations.

"Beneath this crust a new process now commenced. The outer zones of
crystalline matter having been suddenly refrigerated by the rapid
vaporization and partial escape of the water they contained, abstracted
caloric from the intensely heated nucleus of the globe. These
crystalline zones were of unequal density, the expansion they had
suffered diminishing from above downward.

"Their expansive force was, however, equal at all points, their
temperature everywhere bearing an inverse ratio to their density. But
when by the accession of caloric from the inner and unliquefied nucleus
the temperature, and consequently the expansive force of the lower
strata of dilated crystalline matter, was augmented, it acted upon the
upper and more liquefied strata. These being prevented from yielding
OUTWARDLY by the tenacity and weight of the solid involucrum of
precipitated and sedimental deposits which overspread them, sustained
a pressure out of proportion to their expansive force, and were in
consequence proportionately condensed, and by the continuance of the
process, where the overlying strata were sufficiently resistant, finally
consolidated.

"This process of consolidation must have progressed from above downward,
with the increase of the expansive force in the lower strata, commencing
from the upper surface, which, its temperature being lowest, offered the
least resistance to the force of compression.

"By this process the upper zone of crystalline matter, which had
intumesced so far as to allow of the escape of its aqueous vapor and of
much of its mica and quartz, was resolidified, the component crystals
arranging themselves in planes perpendicular to the direction of the
pressure by which the mass was consolidated--that is, to the radius of
the globe. The gneiss formation, as already observed, was the result.

"The inferior zone of barely disintegrated granite, from which only
a part of the steam and quartz and none of the mica had escaped,
reconsolidated in a confused or granitoidal manner; but exhibits marks
of the process it had undergone in its broken crystals of felspar and
mica, its rounded and superficially dissolved grains of quartz, its
imbedded fragments (broken from the more solid parts of the mass, as it
rose, and enveloped by the softer parts), its concretionary nodules and
new minerals, etc.

"Beneath this, the granite which had been simply disintegrated was again
solidified, and returned in all respects to its former condition. The
temperature, however, and with it the expansive force of the inferior
zone, was continually on the increase, the caloric of the interior of
the globe still endeavoring to put itself in equilibrio by passing off
towards the less-intensely heated crust.

"This continually increasing expansive force must at length have
overcome the resistance opposed by the tenacity and weight of the
overlying consolidated strata. It is reasonable to suppose that this
result took place contemporaneously, or nearly so, on many spots,
wherever accidental circumstances in the texture or composition of the
oceanic deposits led them to yield more readily; and in this manner
were produced those original fissures in the primeval crust of the earth
through some of which (fissures of elevation) were intruded portions of
interior crystalline zones in a solid or nearly solid state, together
with more or less of the intumescent granite, in the manner
above described; while others (fissures of eruption) gave rise to
extravasations of the heated crystalline matter, in the form of
lavas--that is, still further liquefied by the greater comparative
reduction of the pressure they endured."(3)


The Neptunists stoutly contended for the aqueous origin of volcanic as
of other mountains. But the facts were with Scrope, and as time went
on it came to be admitted that not merely volcanoes, but many "trap"
formations not taking the form of craters, had been made by the
obtrusion of molten rock through fissures in overlying strata. Such,
for example, to cite familiar illustrations, are Mount Holyoke, in
Massachusetts, and the well-known formation of the Palisades along the
Hudson.

But to admit the "Plutonic" origin of such widespread formations was
practically to abandon the Neptunian hypothesis. So gradually the
Huttonian explanation of the origin of granites and other "igneous"
rocks, whether massed or in veins, came to be accepted. Most geologists
then came to think of the earth as a molten mass, on which the crust
rests as a mere film. Some, indeed, with Lyell, preferred to believe
that the molten areas exist only as lakes in a solid crust, heated to
melting, perhaps, by electrical or chemical action, as Davy suggested.
More recently a popular theory attempts to reconcile geological facts
with the claim of the physicists, that the earth's entire mass is at
least as rigid as steel, by supposing that a molten film rests between
the observed solid crust and the alleged solid nucleus. But be that
as it may, the theory that subterranean heat has been instrumental in
determining the condition of "primary" rocks, and in producing many
other phenomena of the earth's crust, has never been in dispute since
the long controversy between the Neptunists and the Plutonists led to
its establishment.


LYELL AND UNIFORMITARIANISM

If molten matter exists beneath the crust of the earth, it must contract
in cooling, and in so doing it must disturb the level of the portion of
the crust already solidified. So a plausible explanation of the upheaval
of continents and mountains was supplied by the Plutonian theory, as
Hutton had from the first alleged. But now an important difference
of opinion arose as to the exact rationale of such upheavals. Hutton
himself, and practically every one else who accepted his theory, had
supposed that there are long periods of relative repose, during which
the level of the crust is undisturbed, followed by short periods of
active stress, when continents are thrown up with volcanic suddenness,
as by the throes of a gigantic earthquake. But now came Charles Lyell
with his famous extension of the "uniformitarian" doctrine, claiming
that past changes of the earth's surface have been like present changes
in degree as well as in kind. The making of continents and mountains,
he said, is going on as rapidly to-day as at any time in the past. There
have been no gigantic cataclysmic upheavals at any time, but all
changes in level of the strata as a whole have been gradual, by slow
oscillation, or at most by repeated earthquake shocks such as are still
often experienced.

In support of this very startling contention Lyell gathered a mass
of evidence of the recent changes in level of continental areas. He
corroborated by personal inspection the claim which had been made by
Playfair in 1802, and by Von Buch in 1807, that the coast-line of Sweden
is rising at the rate of from a few inches to several feet in a
century. He cited Darwin's observations going to prove that Patagonia is
similarly rising, and Pingel's claim that Greenland is slowly sinking.
Proof as to sudden changes of level of several feet, over large areas,
due to earthquakes, was brought forward in abundance. Cumulative
evidence left it no longer open to question that such oscillatory
changes of level, either upward or downward, are quite the rule, and
it could not be denied that these observed changes, if continued long
enough in one direction, would produce the highest elevations. The
possibility that the making of even the highest ranges of mountains had
been accomplished without exaggerated catastrophic action came to be
freely admitted.

It became clear that the supposedly stable-land surfaces are in
reality much more variable than the surface of the "shifting sea"; that
continental masses, seemingly so fixed, are really rising and falling
in billows thousands of feet in height, ages instead of moments being
consumed in the sweep between crest and hollow.

These slow oscillations of land surfaces being understood, many
geological enigmas were made clear--such as the alternation of marine
and fresh-water formations in a vertical series, which Cuvier and
Brongniart had observed near Paris; or the sandwiching of layers of
coal, of subaerial formation, between layers of subaqueous clay or
sandstone, which may be observed everywhere in the coal measures. In
particular, the extreme thickness of the sedimentary strata as a whole,
many times exceeding the depth of the deepest known sea, was for the
first time explicable when it was understood that such strata had formed
in slowly sinking ocean-beds.

All doubt as to the mode of origin of stratified rocks being thus
removed, the way was opened for a more favorable consideration of
that other Huttonian doctrine of the extremely slow denudation of land
surfaces. The enormous amount of land erosion will be patent to any
one who uses his eyes intelligently in a mountain district. It will be
evident in any region where the strata are tilted--as, for example, the
Alleghanies--that great folds of strata which must once have risen miles
in height have in many cases been worn entirely away, so that now a
valley marks the location of the former eminence. Where the strata are
level, as in the case of the mountains of Sicily, the Scotch Highlands,
and the familiar Catskills, the evidence of denudation is, if possible,
even more marked; for here it is clear that elevation and valley have
been carved by the elements out of land that rose from the sea as level
plateaus.

But that this herculean labor of land-sculpturing could have been
accomplished by the slow action of wind and frost and shower was an
idea few men could grasp within the first half-century after Hutton
propounded it; nor did it begin to gain general currency until Lyell's
crusade against catastrophism, begun about 1830, had for a quarter of a
century accustomed geologists to the thought of slow, continuous changes
producing final results of colossal proportions. And even long after
that it was combated by such men as Murchison, Director-General of
the Geological Survey of Great Britain, then accounted the foremost
field-geologist of his time, who continued to believe that the existing
valleys owe their main features to subterranean forces of upheaval.
Even Murchison, however, made some recession from the belief of the
Continental authorities, Elie de Beaumont and Leopold von Buch,
who contended that the mountains had sprung up like veritable
jacks-in-the-box. Von Buch, whom his friend and fellow-pupil Von
Humboldt considered the foremost geologist of the time, died in 1853,
still firm in his early faith that the erratic bowlders found high on
the Jura had been hurled there, like cannon-balls, across the valley of
Geneva by the sudden upheaval of a neighboring mountain-range.


AGASSIZ AND THE GLACIAL THEORY

The bowlders whose presence on the crags of the Jura the old Gerinan
accounted for in a manner so theatrical had long been a source of
contention among geologists. They are found not merely on the Jura,
but on numberless other mountains in all north-temperate latitudes, and
often far out in the open country, as many a farmer who has broken his
plough against them might testify. The early geologists accounted for
them, as for nearly everything else, with their supposititious Deluge.
Brongniart and Cuvier and Buckland and their contemporaries appeared
to have no difficulty in conceiving that masses of granite weighing
hundreds of tons had been swept by this current scores or hundreds
of miles from their source. But, of course, the uniformitarian faith
permitted no such explanation, nor could it countenance the projection
idea; so Lyell was bound to find some other means of transportation for
the puzzling erratics.

The only available medium was ice, but, fortunately, this one seemed
quite sufficient. Icebergs, said Lyell, are observed to carry all manner
of debris, and deposit it in the sea-bottoms. Present land surfaces
have often been submerged beneath the sea. During the latest of these
submergences icebergs deposited the bowlders now scattered here
and there over the land. Nothing could be simpler or more clearly
uniformitarian. And even the catastrophists, though they met Lyell
amicably on almost no other theoretical ground, were inclined to admit
the plausibility of his theory of erratics. Indeed, of all Lyell's
nonconformist doctrines, this seemed the one most likely to meet with
general acceptance.

Yet, even as this iceberg theory loomed large and larger before the
geological world, observations were making in a different field that
were destined to show its fallacy. As early as 1815 a sharp-eyed
chamois-hunter of the Alps, Perraudin by name, had noted the existence
of the erratics, and, unlike most of his companion hunters, had puzzled
his head as to how the bowlders got where he saw them. He knew nothing
of submerged continents or of icebergs, still less of upheaving
mountains; and though he doubtless had heard of the Flood, he had no
experience of heavy rocks floating like corks in water. Moreover, he
had never observed stones rolling uphill and perching themselves on
mountain-tops, and he was a good enough uniformitarian (though he would
have been puzzled indeed had any one told him so) to disbelieve that
stones in past times had disported themselves differently in this regard
from stones of the present. Yet there the stones are. How did they get
there?

The mountaineer thought that he could answer that question. He saw about
him those gigantic serpent-like streams of ice called glaciers, "from
their far fountains slow rolling on," carrying with them blocks of
granite and other debris to form moraine deposits. If these glaciers had
once been much more extensive than they now are, they might have carried
the bowlders and left them where we find them. On the other hand, no
other natural agency within the sphere of the chamois-hunter's knowledge
could have accomplished this, ergo the glaciers must once have been more
extensive. Perraudin would probably have said that common-sense drove
him to this conclusion; but be that as it may, he had conceived one of
the few truly original and novel ideas of which the nineteenth century
can boast.

Perraudin announced his idea to the greatest scientist in his little
world--Jean de Charpentier, director of the mines at Bex, a skilled
geologist who had been a fellow-pupil of Von Buch and Von Humboldt
under Werner at the Freiberg School of Mines. Charpentier laughed at
the mountaineer's grotesque idea, and thought no more about it. And ten
years elapsed before Perraudin could find any one who treated his notion
with greater respect. Then he found a listener in M. Venetz, a civil
engineer, who read a paper on the novel glacial theory before a local
society in 1823. This brought the matter once more to the attention of
De Charpentier, who now felt that there might be something in it worth
investigation.

A survey of the field in the light of the new theory soon convinced
Charpentier that the chamois-hunter had all along been right. He became
an enthusiastic supporter of the idea that the Alps had once been
imbedded in a mass of ice, and in 1836 he brought the notion to the
attention of Louis Agassiz, who was spending the summer in the Alps.
Agassiz was sceptical at first, but soon became a convert.

In 1840 Agassiz published a paper in which the results of his Alpine
studies were elaborated.

"Let us consider," he says, "those more considerable changes to which
glaciers are subject, or rather, the immense extent which they had in
the prehistoric period. This former immense extension, greater than any
that tradition has preserved, is proved, in the case of nearly every
valley in the Alps, by facts which are both many and well established.
The study of these facts is even easy if the student is looking out for
them, and if he will seize the least indication of their presence; and,
if it were a long time before they were observed and connected with
glacial action, it is because the evidences are often isolated and occur
at places more or less removed from the glacier which originated them.
If it be true that it is the prerogative of the scientific observer to
group in the field of his mental vision those facts which appear to be
without connection to the vulgar herd, it is, above all, in such a case
as this that he is called upon to do so. I have often compared these
feeble effects, produced by the glacial action of former ages, with the
appearance of the markings upon a lithographic stone, prepared for the
purpose of preservation, and upon which one cannot see the lines of the
draughtsman's work unless it is known beforehand where and how to search
for them.

"The fact of the former existence of glaciers which have now disappeared
is proved by the survival of the various phenomena which always
accompany them, and which continue to exist even after the ice has
melted. These phenomena are as follows:

"1. Moraines.--The disposition and composition of moraines enable them
to be always recognized, even when they are no longer adjacent to a
glacier nor immediately surround its lower extremities. I may remark
that lateral and terminal moraines alone enable us to recognize with
certainty the limits of glacial extension, because they can be easily
distinguished from the dikes and irregularly distributed stones carried
down by the Alpine torrents, The lateral moraines deposited upon the
sides of valleys are rarely affected by the larger torrents, but they
are, however, often cut by the small streams which fall down the side of
a mountain, and which, by interfering with their continuity, make them
so much more difficult to recognize.

"2. The Perched Bowlders.--It often happens that glaciers encounter
projecting points of rock, the sides of which become rounded, and around
which funnel-like cavities are formed with more or less profundity. When
glaciers diminish and retire, the blocks which have fallen into these
funnels often remain perched upon the top of the projecting rocky point
within it, in such a state of equilibrium that any idea of a current of
water as the cause of their transportation is completely inadmissible
on account of their position. When such points of rock project above
the surface of the glacier or appear as a more considerable islet in
the midst of its mass (such as is the case in the Jardin of the Mer de
Glace, above Montavert), such projections become surrounded on all
sides by stones which ultimately form a sort of crown around the summit
whenever the glaciers decrease or retire completely. Water currents
never produce anything like this; but, on the contrary, whenever a
stream breaks itself against a projecting rock, the stones which it
carries down are turned aside and form a more or less regular trail.
Never, under such circumstances, can the stones remain either at the
top or at the sides of the rock, for, if such a thing were possible,
the rapidity of the current would be accelerated by the increased
resistance, and the moving bowlders would be carried beyond the
obstruction before they were finally deposited.

"3. The polished and striated rocks, such as have been described in
Chapter XIV., afford yet further evidence of the presence of a glacier;
for, as has been said already, neither a current nor the action of waves
upon an extensive beach produces such effects. The general direction of
the channels and furrows indicates the direction of the general movement
of the glacier, and the streaks which vary more or less from this
direction are produced by the local effects of oscillation and retreat,
as we shall presently see.

"4. The Lapiaz, or Lapiz, which the inhabitants of German Switzerland
call Karrenfelder, cannot always be distinguished from erosions,
because, both produced as they are by water, they do not differ in their
exterior characteristics, but only in their positions. Erosions due to
torrents are always found in places more or less depressed, and never
occur upon large inclined surfaces. The Lapiaz, on the contrary, are
frequently found upon the projecting parts of the sides of valleys in
places where it is not possible to suppose that water has ever formed
a current. Some geologists, in their embarrassment to explain these
phenomena, have supposed that they were due to the infiltration of
acidulated water, but this hypothesis is purely gratuitous.

"We will now describe the remains of these various phenomena as they are
found in the Alps outside the actual glacial limits, in order to prove
that at a certain epoch glaciers were much larger than they are to-day.

"The ancient moraines, situated as they are at a great distance from
those of the present day, are nowhere so distinct or so frequent as
in Valais, where MM. Venetz and J. de Charpentier noticed them for the
first time; but as their observations are as yet unpublished, and they
themselves gave me the information, it would be an appropriation of
their discovery if I were to describe them here in detail. I will limit
myself to say that there can be found traces, more or less distinct, of
ancient terminal moraines in the form of vaulted dikes at the foot of
every glacier, at a distance of a few minutes' walk, a quarter of an
hour, a half-hour, an hour, and even of several leagues from their
present extremities. These traces become less distinct in proportion
to their distance from the glacier, and, since they are also often
traversed by torrents, they are not as continuous as the moraines which
are nearer to the glaciers. The farther these ancient moraines are
removed from the termination of a glacier, the higher up they reach upon
the sides of the valley, which proves to us that the thickness of the
glacier must have been greater when its size was larger. At the same
time, their number indicates so many stopping-places in the retreat of
the glacier, or so many extreme limits of its extension--limits which
were never reached again after it had retired. I insist upon this point,
because if it is true that all these moraines demonstrate a larger
extent of the glacier, they also prove that their retreat into their
present boundaries, far from having been catastrophic, was marked on the
contrary by periods of repose more or less frequent, which caused the
formation of a series of concentric moraines which even now indicate
their retrogression.

"The remains of longitudinal moraines are less frequent, less distinct,
and more difficult to investigate, because, indicating as they do the
levels to which the edges of the glacier reached at different epochs,
it is generally necessary to look for them above the line of the
paths along the escarpments of the valleys, and hence it is not always
possible to follow them along a valley. Often, also, the sides of a
valley which enclosed a glacier are so steep that it is only here and
there that the stones have remained in place. They are, nevertheless,
very distinct in the lower part of the valley of the Rhone, between
Martigny and the Lake of Geneva, where several parallel ridges can be
observed, one above the other, at a height of one thousand, one thousand
two hundred, and even one thousand five hundred feet above the Rhone.
It is between St. Maurice and the cascade of Pissevache, close to the
hamlet of Chaux-Fleurie, that they are most accessible, for at this
place the sides of the valley at different levels ascend in little
terraces, upon which the moraines have been preserved. They are also
very distinct above the Bains de Lavey, and above the village of Monthey
at the entrance of the Val d'Illiers, where the sides of the valley are
less inclined than in many other places.

"The perched bowlders which are found in the Alpine valleys, at
considerable distances from the glaciers, occupy at times positions so
extraordinary that they excite in a high degree the curiosity of those
who see them. For instance, when one sees an angular stone perched upon
the top of an isolated pyramid, or resting in some way in a very steep
locality, the first inquiry of the mind is, When and how have these
stones been placed in such positions, where the least shock would seem
to turn them over? But this phenomenon is not in the least astonishing
when it is seen to occur also within the limits of actual glaciers, and
it is recalled by what circumstances it is occasioned.

"The most curious examples of perched stones which can be cited are
those which command the northern part of the cascade of Pissevache,
close to Chaux-Fleurie, and those above the Bains de Lavey, close to the
village of Morcles; and those, even more curious, which I have seen in
the valley of St. Nicolas and Oberhasli. At Kirchet, near Meiringen, can
be seen some very remarkable crowns of bowlders around several domes
of rock which appear to have been projected above the surface of the
glacier which surrounded them. Something very similar can be seen around
the top of the rock of St. Triphon.

"The extraordinary phenomenon of perched stones could not escape the
observing eye of De Saussure, who noticed several at Saleve, of which
he described the positions in the following manner: 'One sees,' said he,
'upon the slope of an inclined meadow, two of these great bowlders of
granite, elevated one upon the other, above the grass at a height of two
or three feet, upon a base of limestone rock on which both rest. This
base is a continuation of the horizontal strata of the mountain, and is
even united with it visibly on its lower face, being cut perpendicularly
upon the other sides, and is not larger than the stone which it
supports.' But seeing that the entire mountain is composed of the same
limestone, De Saussure naturally concluded that it would be absurd to
think that it was elevated precisely and only beneath the blocks of
granite. But, on the other hand, since he did not know the manner in
which these perched stones are deposited in our days by glacial action,
he had recourse to another explanation: He supposes that the rock was
worn away around its base by the continual erosion of water and air,
while the portion of the rock which served as the base for the granite
had been protected by it. This explanation, although very ingenious,
could no longer be admitted after the researches of M. Elie de Beaumont
had proved that the action of atmospheric agencies was not by a good
deal so destructive as was theretofore supposed. De Saussure speaks
also of a detached bowlder, situated upon the opposite side of the
Tete-Noire, 'which is,' he says, 'of so great a size that one is tempted
to believe that it was formed in the place it occupies; and it is called
Barme russe, because it is worn away beneath in the form of a cave which
can afford accommodation for more than thirty persons at a time."(4)

But the implications of the theory of glaciers extend, so Agassiz has
come to believe, far beyond the Alps. If the Alps had been covered with
an ice sheet, so had many other regions of the northern hemisphere.
Casting abroad for evidences of glacial action, Agassiz found them
everywhere in the form of transported erratics, scratched and polished
outcropping rocks, and moraine-like deposits. Finally, he became
convinced that the ice sheet that covered the Alps had spread over the
whole of the higher latitudes of the northern hemisphere, forming an
ice cap over the globe. Thus the common-sense induction of the
chamois-hunter blossomed in the mind of Agassiz into the conception of a
universal ice age.

In 1837 Agassiz had introduced his theory to the world, in a paper read
at Neuchatel, and three years later he published his famous Etudes sur
les Glaciers, from which we have just quoted. Never did idea make a more
profound disturbance in the scientific world. Von Buch treated it
with alternate ridicule, contempt, and rage; Murchison opposed it with
customary vigor; even Lyell, whose most remarkable mental endowment was
an unfailing receptiveness to new truths, could not at once discard
his iceberg theory in favor of the new claimant. Dr. Buckland, however,
after Agassiz had shown him evidence of former glacial action in his own
Scotland, became a convert--the more readily, perhaps, as it seemed to
him to oppose the uniformitarian idea. Gradually others fell in line,
and after the usual imbittered controversy and the inevitable full
generation of probation, the idea of an ice age took its place among
the accepted tenets of geology. All manner of moot points still demanded
attention--the cause of the ice age, the exact extent of the ice sheet,
the precise manner in which it produced its effects, and the exact
nature of these effects; and not all of these have even yet been
determined. But, details aside, the ice age now has full recognition
from geologists as an historical period. There may have been many ice
ages, as Dr. Croll contends; there was surely one; and the conception
of such a period is one of the very few ideas of our century that no
previous century had even so much as faintly adumbrated.


THE GEOLOGICAL AGES

But, for that matter, the entire subject of historical geology is
one that had but the barest beginning before our century. Until the
paleontologist found out the key to the earth's chronology, no one--not
even Hutton--could have any definite idea as to the true story of the
earth's past. The only conspicuous attempt to classify the strata was
that made by Werner, who divided the rocks into three systems, based on
their supposed order of deposition, and called primary, transition, and
secondary.

Though Werner's observations were confined to the small province of
Saxony, he did not hesitate to affirm that all over the world the
succession of strata would be found the same as there, the concentric
layers, according to this conception, being arranged about the earth
with the regularity of layers on an onion. But in this Werner was
as mistaken as in his theoretical explanation of the origin of the
"primary" rocks. It required but little observation to show that the
exact succession of strata is never precisely the same in any widely
separated regions. Nevertheless, there was a germ of truth in Werner's
system. It contained the idea, however faultily interpreted, of a
chronological succession of strata; and it furnished a working outline
for the observers who were to make out the true story of geological
development. But the correct interpretation of the observed facts could
only be made after the Huttonian view as to the origin of strata had
gained complete acceptance.

When William Smith, having found the true key to this story, attempted
to apply it, the territory with which he had to deal chanced to be one
where the surface rocks are of that later series which Werner termed
secondary. He made numerous subdivisions within this system, based
mainly on the fossils. Meantime it was found that, judged by the
fossils, the strata that Brongniart and Cuvier studied near Paris were
of a still more recent period (presumed at first to be due to the latest
deluge), which came to be spoken of as tertiary. It was in these beds,
some of which seemed to have been formed in fresh-water lakes, that many
of the strange mammals which Cuvier first described were found.

But the "transition" rocks, underlying the "secondary" system that Smith
studied, were still practically unexplored when, along in the thirties,
they were taken in hand by Roderick Impey Murchison, the reformed
fox-hunter and ex-captain, who had turned geologist to such notable
advantage, and Adam Sedgwick, the brilliant Woodwardian professor at
Cambridge.

Working together, these two friends classified the

transition rocks into chronological groups, since familiar to every one
in the larger outlines as the Silurian system (age of invertebrates) and
the Devonian system (age of fishes)--names derived respectively from the
country of the ancient Silures, in Wales and Devonshire, England. It
was subsequently discovered that these systems of strata, which crop out
from beneath newer rocks in restricted areas in Britain, are spread out
into broad, undisturbed sheets over thousands of miles in continental
Europe and in America. Later on Murchison studied them in Russia,
and described them, conjointly with Verneuil and Von Kerserling, in
a ponderous and classical work. In America they were studied by Hall,
Newberry, Whitney, Dana, Whitfield, and other pioneer geologists, who
all but anticipated their English contemporaries.

The rocks that are of still older formation than those studied by
Murchison and Sedgwick (corresponding in location to the "primary" rocks
of Werner's conception) are the surface feature of vast areas in Canada,
and were first prominently studied there by William I. Logan, of the
Canadian Government Survey, as early as 1846, and later on by Sir
William Dawson. These rocks--comprising the Laurentian system--were
formerly supposed to represent parts of the original crust of the earth,
formed on first cooling from a molten state; but they are now more
generally regarded as once-stratified deposits metamorphosed by the
action of heat.

Whether "primitive" or metamorphic, however, these Canadian rocks, and
analogous ones beneath the fossiliferous strata of other countries,
are the oldest portions of the earth's crust of which geology has any
present knowledge. Mountains of this formation, as the Adirondacks and
the Storm King range, overlooking the Hudson near West Point, are the
patriarchs of their kind, beside which Alleghanies and Sierra Nevadas
are recent upstarts, and Rockies, Alps, and Andes are mere parvenus of
yesterday.

The Laurentian rocks were at first spoken of as representing "Azoic"
time; but in 1846 Dawson found a formation deep in their midst which was
believed to b e the fossil relic of a very low form of life, and after
that it became customary to speak of the system as "Eozoic." Still more
recently the title of Dawson's supposed fossil to rank as such has been
questioned, and Dana's suggestion that the early rocks be termed merely
Archman has met with general favor. Murchison and Sedgwick's Silurian,
Devonian, and Carboniferous groups (the ages of invertebrates, of
fishes, and of coal plants, respectively) are together spoken of as
representing Paleozoic time. William Smith's system of strata, next
above these, once called "secondary," represents Mesozoic time, or
the age of reptiles. Still higher, or more recent, are Cuvier and
Brongniart's tertiary rocks, representing the age of mammals. Lastly,
the most recent formations, dating back, however, to a period far enough
from recent in any but a geological sense, are classed as quaternary,
representing the age of man.

It must not be supposed, however, that the successive "ages" of the
geologist are shut off from one another in any such arbitrary way as
this verbal classification might seem to suggest. In point of fact,
these "ages" have no better warrant for existence than have the
"centuries" and the "weeks" of every-day computation. They are
convenient, and they may even stand for local divisions in the strata,
but they are bounded by no actual gaps in the sweep of terrestrial
events.

Moreover, it must be understood that the "ages" of different continents,
though described under the same name, are not necessarily of exact
contemporaneity. There is no sure test available by which it could be
shown that the Devonian age, for instance, as outlined in the strata of
Europe, did not begin millions of years earlier or later than the period
whose records are said to represent the Devonian age in America. In
attempting to decide such details as this, mineralogical data fail us
utterly. Even in rocks of adjoining regions identity of structure is no
proof of contemporaneous origin; for the veritable substance of the
rock of one age is ground up to build the rocks of subsequent ages.
Furthermore, in seas where conditions change but little the same form
of rock may be made age after age. It is believed that chalk-beds still
forming in some of our present seas may form one continuous mass dating
back to earliest geologic ages. On the other hand, rocks different in
character maybe formed at the same time in regions not far apart--say
a sandstone along shore, a coral limestone farther seaward, and a
chalk-bed beyond. This continuous stratum, broken in the process of
upheaval, might seem the record of three different epochs.

Paleontology, of course, supplies far better chronological tests, but
even these have their limitations. There has been no time since rocks
now in existence were formed, if ever, when the earth had a uniform
climate and a single undiversified fauna over its entire land surface,
as the early paleontologists supposed. Speaking broadly, the same
general stages have attended the evolution of organic forms everywhere,
but there is nothing to show that equal periods of time witnessed
corresponding changes in diverse regions, but quite the contrary.
To cite but a single illustration, the marsupial order, which is the
dominant mammalian type of the living fauna of Australia to-day,
existed in Europe and died out there in the tertiary age. Hence a future
geologist might think the Australia of to-day contemporaneous with a
period in Europe which in reality antedated it by perhaps millions of
years.

All these puzzling features unite to render the subject of historical
geology anything but the simple matter the fathers of the science
esteemed it. No one would now attempt to trace the exact sequence of
formation of all the mountains of the globe, as Elie de Beaumont did
a half-century ago. Even within the limits of a single continent, the
geologist must proceed with much caution in attempting to chronicle the
order in which its various parts rose from the matrix of the sea. The
key to this story is found in the identification of the strata that
are the surface feature in each territory. If Devonian rocks are at
the surface in any given region, for example, it would appear that this
region became a land surface in the Devonian age, or just afterwards.
But a moment's consideration shows that there is an element of
uncertainty about this, due to the steady denudation that all land
surfaces undergo. The Devonian rocks may lie at the surface simply
because the thousands of feet of carboniferous strata that once lay
above them have been worn away. All that the cautious geologist dare
assert, therefore, is that the region in question did not become
permanent land surface earlier than the Devonian age.

But to know even this is much--sufficient, indeed, to establish the
chronological order of elevation, if not its exact period, for all parts
of any continent that have been geologically explored--understanding
always that there must be no scrupling about a latitude of a few
millions or perhaps tens of millions of years here and there.

Regarding our own continent, for example, we learn through the
researches of a multitude of workers that in the early day it was a mere
archipelago. Its chief island--the backbone of the future continent--was
a great V-shaped area surrounding what is now Hudson Bay, an area built
tip, perhaps, through denudation of a yet more ancient polar continent,
whose existence is only conjectured. To the southeast an island that
is now the Adirondack Mountains, and another that is now the Jersey
Highlands rose above the waste of waters, and far to the south stretched
probably a line of islands now represented by the Blue Ridge Mountains.
Far off to the westward another line of islands foreshadowed our present
Pacific border. A few minor islands in the interior completed the
archipelago.

From this bare skeleton the continent grew, partly by the deposit of
sediment from the denudation of the original islands (which once towered
miles, perhaps, where now they rise thousands of feet), but largely also
by the deposit of organic remains, especially in the interior sea, which
teemed with life. In the Silurian ages, invertebrates--brachiopods and
crinoids and cephalopods--were the dominant types. But very early--no
one knows just when--there came fishes of many strange forms, some of
the early ones enclosed in turtle-like shells. Later yet, large spaces
within the interior sea having risen to the surface, great marshes or
forests of strange types of vegetation grew and deposited their remains
to form coal-beds. Many times over such forests were formed, only to be
destroyed by the oscillations of the land surface. All told, the strata
of this Paleozoic period aggregate several miles in thickness, and the
time consumed in their formation stands to all later time up to the
present, according to Professor Dana's estimate, as three to one.

Towards the close of this Paleozoic era the Appalachian Mountains
were slowly upheaved in great convoluted folds, some of them probably
reaching three or four miles above the sea-level, though the tooth
of time has since gnawed them down to comparatively puny limits. The
continental areas thus enlarged were peopled during the ensuing Mesozoic
time with multitudes of strange reptiles, many of them gigantic in size.
The waters, too, still teeming with invertebrates and fishes, had their
quota of reptilian monsters; and in the air were flying reptiles, some
of which measured twenty-five feet from tip to tip of their batlike
wings. During this era the Sierra Nevada Mountains rose. Near the
eastern border of the forming continent the strata were perhaps now too
thick and stiff to bend into mountain folds, for they were rent into
great fissures, letting out floods of molten lava, remnants of which are
still in evidence after ages of denudation, as the Palisades along the
Hudson, and such elevations as Mount Holyoke in western Massachusetts.

Still there remained a vast interior sea, which later on, in the
tertiary age, was to be divided by the slow uprising of the land, which
only yesterday--that is to say, a million, or three or five or ten
million, years ago--became the Rocky Mountains. High and erect these
young mountains stand to this day, their sharp angles and rocky contours
vouching for their youth, in strange contrast with the shrunken forms
of the old Adirondacks, Green Mountains, and Appalachians, whose lowered
heads and rounded shoulders attest the weight of ages. In the vast lakes
which still remained on either side of the Rocky range, tertiary
strata were slowly formed to the ultimate depth of two or three miles,
enclosing here and there those vertebrate remains which were to be
exposed again to view by denudation when the land rose still higher,
and then, in our own time, to tell so wonderful a story to the
paleontologist.

Finally, the interior seas were filled, and the shore lines of the
continent assumed nearly their present outline.

Then came the long winter of the glacial epoch--perhaps of a succession
of glacial epochs. The ice sheet extended southward to about the
fortieth parallel, driving some animals before it, and destroying those
that were unable to migrate. At its fulness, the great ice mass lay
almost a mile in depth over New England, as attested by the scratched
and polished rock surfaces and deposited erratics in the White
Mountains. Such a mass presses down with a weight of about one hundred
and twenty-five tons to the square foot, according to Dr. Croll's
estimate. It crushed and ground everything beneath it more or less, and
in some regions planed off hilly surfaces into prairies. Creeping slowly
forward, it carried all manner of debris with it. When it melted away
its terminal moraine built up the nucleus of the land masses now known
as Long Island and Staten Island; other of its deposits formed the
"drumlins" about Boston famous as Bunker and Breed's hills; and it left
a long, irregular line of ridges of "till" or bowlder clay and scattered
erratics clear across the country at about the latitude of New York
city.

As the ice sheet slowly receded it left minor moraines all along its
course. Sometimes its deposits dammed up river courses or inequalities
in the surface, to form the lakes which everywhere abound over Northern
territories. Some glacialists even hold the view first suggested by
Ramsey, of the British Geological Survey, that the great glacial sheets
scooped out the basins of many lakes, including the system that feeds
the St. Lawrence. At all events, it left traces of its presence all
along the line of its retreat, and its remnants exist to this day as
mountain glaciers and the polar ice cap. Indeed, we live on the border
of the last glacial epoch, for with the closing of this period the long
geologic past merges into the present.


PAST, PRESENT, AND FUTURE

And the present, no less than the past, is a time of change. This is the
thought which James Hutton conceived more than a century ago, but which
his contemporaries and successors were so very slow to appreciate. Now,
however, it has become axiomatic--one can hardly realize that it was
ever doubted. Every new scientific truth, says Agassiz, must pass
through three stages--first, men say it is not true; then they declare
it hostile to religion; finally, they assert that every one has known
it always. Hutton's truth that natural law is changeless and eternal
has reached this final stage. Nowhere now could you find a scientist
who would dispute the truth of that text which Lyell, quoting from
Playfair's Illustrations of the Huttonian Theory, printed on the
title-page of his Principles: "Amid all the revolutions of the globe
the economy of Nature has been uniform, and her laws are the only things
that have resisted the general movement. The rivers and the rocks, the
seas and the continents, have been changed in all their parts; but
the laws which direct those changes, and the rules to which they are
subject, have remained invariably the same."

But, on the other hand, Hutton and Playfair, and in particular Lyell,
drew inferences from this principle which the modern physicist can by no
means admit. To them it implied that the changes on the surface of the
earth have always been the same in degree as well as in kind, and must
so continue while present forces hold their sway. In other words, they
thought of the world as a great perpetual-motion machine. But the
modern physicist, given truer mechanical insight by the doctrines of the
conservation and the dissipation of energy, will have none of that. Lord
Kelvin, in particular, has urged that in the periods of our earth's in
fancy and adolescence its developmental changes must have been, like
those of any other infant organism, vastly more rapid and pronounced
than those of a later day; and to every clear thinker this truth also
must now seem axiomatic.

Whoever thinks of the earth as a cooling globe can hardly doubt that its
crust, when thinner, may have heaved under strain of the moon's tidal
pull--whether or not that body was nearer--into great billows, daily
rising and falling, like waves of the present seas vastly magnified.

Under stress of that same lateral pressure from contraction which now
produces the slow depression of the Jersey coast, the slow rise of
Sweden, the occasional belching of an insignificant volcano, the jetting
of a geyser, or the trembling of an earthquake, once large areas were
rent in twain, and vast floods of lava flowed over thousands of square
miles of the earth's surface, perhaps, at a single jet; and, for aught
we know to the contrary, gigantic mountains may have heaped up their
contorted heads in cataclysms as spasmodic as even the most ardent
catastrophist of the elder day of geology could have imagined.

The atmosphere of that early day, filled with vast volumes of carbon,
oxygen, and other chemicals that have since been stored in beds of coal,
limestone, and granites, may have worn down the rocks on the one hand
and built up organic forms on the other, with a rapidity that would now
seem hardly conceivable.

And yet while all these anomalous things went on, the same laws held
sway that now are operative; and a true doctrine of uniformitarianism
would make no unwonted concession in conceding them all--though most of
the imbittered geological controversies of the middle of the nineteenth
century were due to the failure of both parties to realize that simple
fact.

And as of the past and present, so of the future. The same forces will
continue to operate; and under operation of these unchanging forces each
day will differ from every one that has preceded it. If it be true,
as every physicist believes, that the earth is a cooling globe, then,
whatever its present stage of refrigeration, the time must come when its
surface contour will assume a rigidity of level not yet attained. Then,
just as surely, the slow action of the elements will continue to wear
away the land surfaces, particle by particle, and transport them to the
ocean, as it does to-day, until, compensation no longer being afforded
by the upheaval of the continents, the last foot of dry land will sink
for the last time beneath the water, the last mountain-peak melting
away, and our globe, lapsing like any other organism into its second
childhood, will be on the surface--as presumably it was before the first
continent rose--one vast "waste of waters." As puny man conceives time
and things, an awful cycle will have lapsed; in the sweep of the cosmic
life, a pulse-beat will have throbbed.



V. THE NEW SCIENCE OF METEOROLOGY


METEORITES

"An astonishing miracle has just occurred in our district," wrote M.
Marais, a worthy if undistinguished citizen of France, from his home at
L'Aigle, under date of "the 13th Floreal, year 11"--a date which outside
of France would be interpreted as meaning May 3, 1803. This "miracle"
was the appearance of a "fireball" in broad daylight--"perhaps it was
wildfire," says the naive chronicle--which "hung over the meadow," being
seen by many people, and then exploded with a loud sound, scattering
thousands of stony fragments over the surface of a territory some miles
in extent.

Such a "miracle" could not have been announced at a more opportune time.
For some years the scientific world had been agog over the question
whether such a form of lightning as that reported--appearing in a clear
sky, and hurling literal thunderbolts--had real existence. Such
cases had been reported often enough, it is true. The "thunderbolts"
themselves were exhibited as sacred relics before many an altar, and
those who doubted their authenticity had been chided as having "an
evil heart of unbelief." But scientific scepticism had questioned the
evidence, and late in the eighteenth century a consensus of opinion
in the French Academy had declined to admit that such stones had been
"conveyed to the earth by lightning," let alone any more miraculous
agency.

In 1802, however, Edward Howard had read a paper before the Royal
Society in which, after reviewing the evidence recently put forward,
he had reached the conclusion that the fall of stones from the sky,
sometimes or always accompanied by lightning, must be admitted as
an actual phenomenon, however inexplicable. So now, when the great
stone-fall at L'Aigle was announced, the French Academy made haste to
send the brilliant young physicist Jean Baptiste Biot to investigate
it, that the matter might, if possible, be set finally at rest.
The investigation was in all respects successful, and Biot's report
transferred the stony or metallic lightning-bolt--the aerolite or
meteorite--from the realm of tradition and conjecture to that of
accepted science.

But how explain this strange phenomenon? At once speculation was rife.
One theory contended that the stony masses had not actually fallen, but
had been formed from the earth by the action of the lightning; but this
contention was early abandoned. The chemists were disposed to believe
that the aerolites had been formed by the combination of elements
floating in the upper atmosphere. Geologists, on the other hand, thought
them of terrestrial origin, urging that they might have been thrown up
by volcanoes. The astronomers, as represented by Olbers and Laplace,
modified this theory by suggesting that the stones might, indeed, have
been cast out by volcanoes, but by volcanoes situated not on the earth,
but on the moon.

And one speculator of the time took a step even more daring, urging that
the aerolites were neither of telluric nor selenitic origin, nor yet
children of the sun, as the old Greeks had, many of them, contended,
but that they are visitants from the depths of cosmic space. This bold
speculator was the distinguished German physicist Ernst F. F. Chladni,
a man of no small repute in his day. As early as 1794 he urged his
cosmical theory of meteorites, when the very existence of meteorites was
denied by most scientists. And he did more: he declared his belief
that these falling stones were really one in origin and kind with those
flashing meteors of the upper atmosphere which are familiar everywhere
as "shooting-stars."

Each of these coruscating meteors, he affirmed, must tell of the
ignition of a bit of cosmic matter entering the earth's atmosphere. Such
wandering bits of matter might be the fragments of shattered worlds, or,
as Chladni thought more probable, merely aggregations of "world stuff"
never hitherto connected with any large planetary mass.

Naturally enough, so unique a view met with very scant favor.
Astronomers at that time saw little to justify it; and the
non-scientific world rejected it with fervor as being "atheistic and
heretical," because its acceptance would seem to imply that the universe
is not a perfect mechanism.

Some light was thrown on the moot point presently by the observations of
Brandes and Benzenberg, which tended to show that falling-stars travel
at an actual speed of from fifteen to ninety miles a second. This
observation tended to discredit the selenitic theory, since an object,
in order to acquire such speed in falling merely from the moon, must
have been projected with an initial velocity not conceivably to be given
by any lunar volcanic impulse. Moreover, there was a growing conviction
that there are no active volcanoes on the moon, and other considerations
of the same tenor led to the complete abandonment of the selenitic
theory.

But the theory of telluric origin of aerolites was by no means so easily
disposed of. This was an epoch when electrical phenomena were exciting
unbounded and universal interest, and there was a not unnatural tendency
to appeal to electricity in explanation of every obscure phenomenon; and
in this case the seeming similarity between a lightning flash and the
flash of an aerolite lent color to the explanation. So we find Thomas
Forster, a meteorologist of repute, still adhering to the atmospheric
theory of formation of aerolites in his book published in 1823; and,
indeed, the prevailing opinion of the time seemed divided between
various telluric theories, to the neglect of any cosmical theory
whatever.

But in 1833 occurred a phenomenon which set the matter finally at
rest. A great meteoric shower occurred in November of that year, and
in observing it Professor Denison Olmstead, of Yale, noted that all
the stars of the shower appeared to come from a single centre or
vanishing-point in the heavens, and that this centre shifted its
position with the stars, and hence was not telluric. The full
significance of this observation was at once recognized by astronomers;
it demonstrated beyond all cavil the cosmical origin of the
shooting-stars. Some conservative meteorologists kept up the argument
for the telluric origin for some decades to come, as a matter of
course--such a band trails always in the rear of progress. But even
these doubters were silenced when the great shower of shooting-stars
appeared again in 1866, as predicted by Olbers and Newton, radiating
from the same point of the heavens as before.

Since then the spectroscope has added its confirmatory evidence as to
the identity of meteorite and shooting-star, and, moreover, has linked
these atmospheric meteors with such distant cosmic residents as comets
and nebulae. Thus it appears that Chladni's daring hypothesis of
1794 has been more than verified, and that the fragments of matter
dissociated from planetary connection--which be postulated and was
declared atheistic for postulating--have been shown to be billions
of times more numerous than any larger cosmic bodies of which we have
cognizance--so widely does the existing universe differ from man's
preconceived notions as to what it should be.

Thus also the "miracle" of the falling stone, against which the
scientific scepticism of yesterday presented "an evil heart of
unbelief," turns out to be the most natural phenomena, inasmuch as it is
repeated in our atmosphere some millions of times each day.


THE AURORA BOREALIS

If fire-balls were thought miraculous and portentous in days of yore,
what interpretation must needs have been put upon that vastly more
picturesque phenomenon, the aurora? "Through all the city," says the
Book of Maccabees, "for the space of almost forty days, there were seen
horsemen running in the air, in cloth of gold, armed with lances, like
a band of soldiers: and troops of horsemen in array encountering and
running one against another, with shaking of shields and multitude of
pikes, and drawing of swords, and casting of darts, and glittering of
golden ornaments and harness." Dire omens these; and hardly less ominous
the aurora seemed to all succeeding generations that observed it down
well into the eighteenth century--as witness the popular excitement in
England in 1716 over the brilliant aurora of that year, which became
famous through Halley's description.

But after 1752, when Franklin dethroned the lightning, all spectacular
meteors came to be regarded as natural phenomena, the aurora among the
rest. Franklin explained the aurora--which was seen commonly enough in
the eighteenth century, though only recorded once in the seventeenth--as
due to the accumulation of electricity on the surface of polar snows,
and its discharge to the equator through the upper atmosphere. Erasmus
Darwin suggested that the luminosity might be due to the ignition of
hydrogen, which was supposed by many philosophers to form the upper
atmosphere. Dalton, who first measured the height of the aurora,
estimating it at about one hundred miles, thought the phenomenon due
to magnetism acting on ferruginous particles in the air, and his
explanation was perhaps the most popular one at the beginning of the
last century.

Since then a multitude of observers have studied the aurora, but the
scientific grasp has found it as elusive in fact as it seems to casual
observation, and its exact nature is as undetermined to-day as it was a
hundred years ago. There has been no dearth of theories concerning it,
however. Blot, who studied it in the Shetland Islands in 1817, thought
it due to electrified ferruginous dust, the origin of which he ascribed
to Icelandic volcanoes. Much more recently the idea of ferruginous
particles has been revived, their presence being ascribed not to
volcanoes, but to the meteorites constantly being dissipated in the
upper atmosphere. Ferruginous dust, presumably of such origin, has been
found on the polar snows, as well as on the snows of mountain-tops, but
whether it could produce the phenomena of auroras is at least an open
question.

Other theorists have explained the aurora as due to the accumulation of
electricity on clouds or on spicules of ice in the upper air. Yet others
think it due merely to the passage of electricity through rarefied air
itself. Humboldt considered the matter settled in yet another way when
Faraday showed, in 1831, that magnetism may produce luminous effects.
But perhaps the prevailing theory of to-day assumes that the aurora is
due to a current of electricity generated at the equator and passing
through upper regions of space, to enter the earth at the magnetic
poles--simply reversing the course which Franklin assumed.

The similarity of the auroral light to that generated in a vacuum
bulb by the passage of electricity lends support to the long-standing
supposition that the aurora is of electrical origin, but the subject
still awaits complete elucidation. For once even that mystery-solver the
spectroscope has been baffled, for the line it sifts from the aurora is
not matched by that of any recognized substance. A like line is found
in the zodiacal light, it is true, but this is of little aid, for the
zodiacal light, though thought by some astronomers to be due to meteor
swarms about the sun, is held to be, on the whole, as mysterious as the
aurora itself.

Whatever the exact nature of the aurora, it has long been known to
be intimately associated with the phenomena of terrestrial magnetism.
Whenever a brilliant aurora is visible, the world is sure to be visited
with what Humboldt called a magnetic storm--a "storm" which manifests
itself to human senses in no way whatsoever except by deflecting the
magnetic needle and conjuring with the electric wire. Such magnetic
storms are curiously associated also with spots on the sun--just how no
one has explained, though the fact itself is unquestioned. Sun-spots,
too, seem directly linked with auroras, each of these phenomena passing
through periods of greatest and least frequency in corresponding cycles
of about eleven years' duration.

It was suspected a full century ago by Herschel that the variations in
the number of sun-spots had a direct effect upon terrestrial weather,
and he attempted to demonstrate it by using the price of wheat as a
criterion of climatic conditions, meantime making careful observation
of the sun-spots. Nothing very definite came of his efforts in this
direction, the subject being far too complex to be determined without
long periods of observation. Latterly, however, meteorologists,
particularly in the tropics, are disposed to think they find evidence
of some such connection between sun-spots and the weather as Herschel
suspected. Indeed, Mr. Meldrum declares that there is a positive
coincidence between periods of numerous sun-spots and seasons of
excessive rain in India.

That some such connection does exist seems intrinsically probable. But
the modern meteorologist, learning wisdom of the past, is extremely
cautious about ascribing casual effects to astronomical phenomena.
He finds it hard to forget that until recently all manner of climatic
conditions were associated with phases of the moon; that not so very
long ago showers of falling-stars were considered "prognostic" of
certain kinds of weather; and that the "equinoctial storm" had
been accepted as a verity by every one, until the unfeeling hand of
statistics banished it from the earth.

Yet, on the other hand, it is easily within the possibilities that the
science of the future may reveal associations between the weather and
sun-spots, auroras, and terrestrial magnetism that as yet are hardly
dreamed of. Until such time, however, these phenomena must feel
themselves very grudgingly admitted to the inner circle of meteorology.
More and more this science concerns itself, in our age of concentration
and specialization, with weather and climate. Its votaries no
longer concern themselves with stars or planets or comets or
shooting-stars--once thought the very essence of guides to weather
wisdom; and they are even looking askance at the moon, and asking her
to show cause why she also should not be excluded from their domain.
Equally little do they care for the interior of the earth, since they
have learned that the central emanations of heat which Mairan imagined
as a main source of aerial warmth can claim no such distinction. Even
such problems as why the magnetic pole does not coincide with the
geographical, and why the force of terrestrial magnetism decreases from
the magnetic poles to the magnetic equator, as Humboldt first discovered
that it does, excite them only to lukewarm interest; for magnetism,
they say, is not known to have any connection whatever with climate or
weather.


EVAPORATION, CLOUD FORMATION, AND DEW

There is at least one form of meteor, however, of those that interested
our forebears whose meteorological importance they did not overestimate.
This is the vapor of water. How great was the interest in this familiar
meteor at the beginning of the century is attested by the number of
theories then extant regarding it; and these conflicting theories bear
witness also to the difficulty with which the familiar phenomenon of the
evaporation of water was explained.

Franklin had suggested that air dissolves water much as water dissolves
salt, and this theory was still popular, though Deluc had disproved it
by showing that water evaporates even more rapidly in a vacuum than
in air. Deluc's own theory, borrowed from earlier chemists, was that
evaporation is the chemical union of particles of water with particles
of the supposititious element heat. Erasmus Darwin combined the two
theories, suggesting that the air might hold a variable quantity of
vapor in mere solution, and in addition a permanent moiety in chemical
combination with caloric.

Undisturbed by these conflicting views, that strangely original
genius, John Dalton, afterwards to be known as perhaps the greatest
of theoretical chemists, took the question in hand, and solved it by
showing that water exists in the air as an utterly independent gas. He
reached a partial insight into the matter in 1793, when his first volume
of meteorological essays was published; but the full elucidation of
the problem came to him in 1801. The merit of his studies was at once
recognized, but the tenability of his hypothesis was long and ardently
disputed.

While the nature of evaporation was in dispute, as a matter of course
the question of precipitation must be equally undetermined. The most
famous theory of the period was that formulated by Dr. Hutton in a paper
read before the Royal Society of Edinburgh, and published in the volume
of transactions which contained also the same author's epoch-making
paper on geology. This "theory of rain" explained precipitation as due
to the cooling of a current of saturated air by contact with a colder
current, the assumption being that the surplusage of moisture was
precipitated in a chemical sense, just as the excess of salt dissolved
in hot water is precipitated when the water cools. The idea that the
cooling of the saturated air causes the precipitation of its moisture
is the germ of truth that renders this paper of Hutton's important. All
correct later theories build on this foundation.

"Let us suppose the surface of this earth wholly covered with water,"
said Hutton, "and that the sun were stationary, being always vertical in
one place; then, from the laws of heat and rarefaction, there would be
formed a circulation in the atmosphere, flowing from the dark and cold
hemisphere to the heated and illuminated place, in all directions,
towards the place of the greatest cold.

"As there is for the atmosphere of this earth a constant cooling cause,
this fluid body could only arrive at a certain degree of heat; and this
would be regularly decreasing from the centre of illumination to the
opposite point of the globe, most distant from the light and heat.
Between these two regions of extreme heat and cold there would, in every
place, be found two streams of air following in opposite directions. If
those streams of air, therefore, shall be supposed as both sufficiently
saturated with humidity, then, as they are of different temperatures,
there would be formed a continual condensation of aqueous vapor, in some
middle region of the atmosphere, by the commixtion of part of those two
opposite streams.

"Hence there is reason to believe that in this supposed case there would
be formed upon the surface of the globe three different regions--the
torrid region, the temperate, and the frigid. These three regions would
continue stationary; and the operations of each would be continual. In
the torrid region, nothing but evaporation and heat would take place;
no cloud could be formed, because in changing the transparency of the
atmosphere to opacity it would be heated immediately by the operation of
light, and thus the condensed water would be again evaporated. But this
power of the sun would have a termination; and it is these that would
begin the region of temperate heat and of continual rain. It is not
probable that the region of temperance would reach far beyond the region
of light; and in the hemisphere of darkness there would be found a
region of extreme cold and perfect dryness.

"Let us now suppose the earth as turning on its axis in the equinoctial
situation. The torrid region would thus be changed into a zone, in
which there would be night and day; consequently, here would be much
temperance, compared with the torrid region now considered; and here
perhaps there would be formed periodical condensation and evaporation of
humidity, corresponding to the seasons of night and day. As temperance
would thus be introduced into the region of torrid extremity, so would
the effect of this change be felt over all the globe, every part of
which would now be illuminated, consequently heated in some degree. Thus
we would have a line of great heat and evaporation, graduating each way
into a point of great cold and congelation. Between these two extremes
of heat and cold there would be found in each hemisphere a region
of much temperance, in relation to heat, but of much humidity in the
atmosphere, perhaps of continual rain and condensation.

"The supposition now formed must appear extremely unfit for making this
globe a habitable world in every part; but having thus seen the effect
of night and day in temperating the effects of heat and cold in every
place, we are now prepared to contemplate the effects of supposing this
globe to revolve around the sun with a certain inclination of its axis.
By this beautiful contrivance, that comparatively uninhabited globe is
now divided into two hemispheres, each of which is thus provided with
a summer and a winter season. But our present view is limited to the
evaporation and condensation of humidity; and, in this contrivance of
the seasons, there must appear an ample provision for those alternate
operations in every part; for as the place of the vertical sun is moved
alternately from one tropic to the other, heat and cold, the original
causes of evaporation and condensation, must be carried over all the
globe, producing either annual seasons of rain or diurnal seasons of
condensation and evaporation, or both these seasons, more or less--that
is, in some degree.

"The original cause of motion in the atmosphere is the influence of the
sun heating the surface of the earth exposed to that luminary. We have
not supposed that surface to have been of one uniform shape and similar
substance; from whence it has followed that the annual propers of
the sun, perhaps also the diurnal propers, would produce a regular
condensation of rain in certain regions, and the evaporation of humidity
in others; and this would have a regular progress in certain determined
seasons, and would not vary. But nothing can be more distant from this
supposition, that is the natural constitution of the earth; for the
globe is composed of sea and land, in no regular shape or mixture, while
the surface of the land is also irregular with respect to its elevations
and depressions, and various with regard to the humidity and dryness of
that part which is exposed to heat as the cause of evaporation. Hence a
source of the most valuable motions in the fluid atmosphere with aqueous
vapor, more or less, so far as other natural operations will admit; and
hence a source of the most irregular commixture of the several parts of
this elastic fluid, whether saturated or not with aqueous vapor.

"According to the theory, nothing is required for the production of rain
besides the mixture of portions of the atmosphere with humidity, and of
mixing the parts that are in different degrees of heat. But we have seen
the causes of saturating every portion of the atmosphere with humidity
and of mixing the parts which are in different degrees of heat.
Consequently, over all the surface of the globe there should happen
occasionally rain and evaporation, more or less; and also, in every
place, those vicissitudes should be observed to take place with some
tendency to regularity, which, however, may be so disturbed as to be
hardly distinguishable upon many occasions. Variable winds and variable
rains should be found in proportion as each place is situated in an
irregular mixture of land and water; whereas regular winds should be
found in proportion to the uniformity of the surface; and regular rains
in proportion to the regular changes of those winds by which the mixture
of the atmosphere necessary to the rain may be produced. But as it will
be acknowledged that this is the case in almost all this earth where
rain appears according to the conditions here specified, the theory is
found to be thus in conformity with nature, and natural appearances are
thus explained by the theory."(1)


The next ambitious attempt to explain the phenomena of aqueous meteors
was made by Luke Howard, in his remarkable paper on clouds, published in
the Philosophical Magazine in 1803--the paper in which the names cirrus,
cumulus, stratus, etc., afterwards so universally adopted, were first
proposed. In this paper Howard acknowledges his indebtedness to Dalton
for the theory of evaporation; yet he still clings to the idea that
the vapor, though independent of the air, is combined with particles of
caloric. He holds that clouds are composed of vapor that has previously
risen from the earth, combating the opinions of those who believe
that they are formed by the union of hydrogen and oxygen existing
independently in the air; though he agrees with these theorists that
electricity has entered largely into the modus operandi of cloud
formation. He opposes the opinion of Deluc and De Saussure that clouds
are composed of particles of water in the form of hollow vesicles
(miniature balloons, in short, perhaps filled with hydrogen), which
untenable opinion was a revival of the theory as to the formation of all
vapor which Dr. Halley had advocated early in the eighteenth century.

Of particular interest are Howard's views as to the formation of dew,
which he explains as caused by the particles of caloric forsaking the
vapor to enter the cool body, leaving the water on the surface. This
comes as near the truth, perhaps, as could be expected while the old
idea as to the materiality of heat held sway. Howard believed, however,
that dew is usually formed in the air at some height, and that it
settles to the surface, opposing the opinion, which had gained vogue
in France and in America (where Noah Webster prominently advocated it),
that dew ascends from the earth.

The complete solution of the problem of dew formation--which really
involved also the entire question of precipitation of watery vapor in
any form--was made by Dr. W. C. Wells, a man of American birth, whose
life, however, after boyhood, was spent in Scotland (where as a young
man he enjoyed the friendship of David Hume) and in London. Inspired,
no doubt, by the researches of Mack, Hutton, and their confreres of
that Edinburgh school, Wells made observations on evaporation and
precipitation as early as 1784, but other things claimed his attention;
and though he asserts that the subject was often in his mind, he did not
take it up again in earnest until about 1812.

Meantime the observations on heat of Rumford and Davy and Leslie had
cleared the way for a proper interpretation of the facts--about the
facts themselves there had long been practical unanimity of opinion. Dr.
Black, with his latent-heat observations, had really given the clew to
all subsequent discussions of the subject of precipitation of vapor;
and from this time on it had been known that heat is taken up when water
evaporates, and given out again when it condenses. Dr. Darwin had shown
in 1788, in a paper before the Royal Society, that air gives off heat
on contracting and takes it up on expanding; and Dalton, in his essay
of 1793, had explained this phenomenon as due to the condensation and
vaporization of the water contained in the air.

But some curious and puzzling observations which Professor Patrick
Wilson, professor of astronomy in the University of Glasgow, had
communicated to the Royal Society of Edinburgh in 1784, and some similar
ones made by Mr. Six, of Canterbury, a few years later, had remained
unexplained. Both these gentlemen observed that the air is cooler where
dew is forming than the air a few feet higher, and they inferred
that the dew in forming had taken up heat, in apparent violation of
established physical principles.

It remained for Wells, in his memorable paper of 1816, to show that
these observers had simply placed the cart before the horse. He made it
clear that the air is not cooler because the dew is formed, but that
the dew is formed because the air is cooler--having become so through
radiation of heat from the solids on which the dew forms. The dew
itself, in forming, gives out its latent heat, and so tends to equalize
the temperature.

Wells's paper is so admirable an illustration of the lucid presentation
of clearly conceived experiments and logical conclusions that we should
do it injustice not to present it entire. The author's mention of
the observations of Six and Wilson gives added value to his own
presentation.


Dr. Wells's Essay on Dew

"I was led in the autumn of 1784, by the event of a rude experiment,
to think it probable that the formation of dew is attended with the
production of cold. In 1788, a paper on hoar-frost, by Mr. Patrick
Wilson, of Glasgow, was published in the first volume of the
Transactions of the Royal Society of Edinburgh, by which it appeared
that this opinion bad been entertained by that gentleman before it
had occurred to myself. In the course of the same year, Mr. Six, of
Canterbury, mentioned in a paper communicated to the Royal Society
that on clear and dewy nights he always found the mercury lower in a
thermometer laid upon the ground in a meadow in his neighborhood than
it was in a similar thermometer suspended in the air six feet above the
former; and that upon one night the difference amounted to five degrees
of Fahrenheit's scale. Mr. Six, however, did not suppose, agreeably to
the opinion of Mr. Wilson and myself, that the cold was occasioned by
the formation of dew, but imagined that it proceeded partly from the
low temperature of the air, through which the dew, already formed in the
atmosphere, had descended, and partly from the evaporation of moisture
from the ground, on which his thermometer had been placed. The
conjecture of Mr. Wilson and the observations of Mr. Six, together
with many facts which I afterwards learned in the course of reading,
strengthened my opinion; but I made no attempt, before the autumn of
1811, to ascertain by experiment if it were just, though it had in
the mean time almost daily occurred to my thoughts. Happening, in
that season, to be in that country in a clear and calm night, I laid a
thermometer upon grass wet with dew, and suspended a second in the air,
two feet above the other. An hour afterwards the thermometer on the
grass was found to be eight degrees lower, by Fahrenheit's division,
than the one in the air. Similar results having been obtained from
several similar experiments, made during the same autumn, I determined
in the next spring to prosecute the subject with some degree of
steadiness, and with that view went frequently to the house of one of my
friends who lives in Surrey.

"At the end of two months I fancied that I had collected information
worthy of being published; but, fortunately, while preparing an account
of it I met by accident with a small posthumous work by Mr. Six, printed
at Canterbury in 1794, in which are related differences observed on dewy
nights between thermometers placed upon grass and others in the air that
are much greater than those mentioned in the paper presented by him to
the Royal Society in 1788. In this work, too, the cold of the grass is
attributed, in agreement with the opinion of Mr. Wilson, altogether to
the dew deposited upon it. The value of my own observations appearing to
me now much diminished, though they embraced many points left untouched
by Mr. Six, I gave up my intentions of making them known. Shortly after,
however, upon considering the subject more closely, I began to suspect
that Mr. Wilson, Mr. Six, and myself had all committed an error
regarding the cold which accompanies dew as an effect of the formation
of that fluid. I therefore resumed my experiments, and having by means
of them, I think, not only established the justness of my suspicions,
but ascertained the real cause both of dew and of several other natural
appearances which have hitherto received no sufficient explanation, I
venture now to submit to the consideration of the learned an account
of some of my labors, without regard to the order of time in which they
were performed, and of various conclusions which may be drawn from them,
mixed with facts and opinions already published by others:

"There are various occurrences in nature which seem to me strictly
allied to dew, though their relation to it be not always at first sight
perceivable. The statement and explanation of several of these will form
the concluding part of the present essay.

"1. I observed one morning, in winter, that the insides of the panes of
glass in the windows of my bedchamber were all of them moist, but that
those which had been covered by an inside shutter during the night were
much more so than the others which had been uncovered. Supposing that
this diversity of appearance depended upon a difference of temperature,
I applied the naked bulbs of two delicate thermometers to a covered
and uncovered pane; on which I found that the former was three degrees
colder than the latter. The air of the chamber, though no fire was kept
in it, was at this time eleven and one-half degrees warmer than that
without. Similar experiments were made on many other mornings, the
results of which were that the warmth of the internal air exceeded that
of the external from eight to eighteen degrees, the temperature of the
covered panes would be from one to five degrees less than the uncovered;
that the covered were sometimes dewed, while the uncovered were dry;
that at other times both were free from moisture; that the outsides of
the covered and uncovered panes had similar differences with respect to
heat, though not so great as those of the inner surfaces; and that no
variation in the quantity of these differences was occasioned by the
weather's being cloudy or fair, provided the heat of the internal air
exceeded that of the external equally in both of those states of the
atmosphere.

"The remote reason of these differences did not immediately present
itself. I soon, however, saw that the closed shutter shielded the glass
which it covered from the heat that was radiated to the windows by
the walls and furniture of the room, and thus kept it nearer to the
temperature of the external air than those parts could be which, from
being uncovered, received the heat emitted to them by the bodies just
mentioned.

"In making these experiments, I seldom observed the inside of any pane
to be more than a little damped, though it might be from eight to twelve
degrees colder than the general mass of the air in the room; while, in
the open air, I had often found a great dew to form on substances
only three or four degrees colder than the atmosphere. This at first
surprised me; but the cause now seems plain. The air of the chamber had
once been a portion of the external atmosphere, and had afterwards
been heated, when it could receive little accessories to its original
moisture. It constantly required being cooled considerably before it
was even brought back to its former nearness to repletion with water;
whereas the whole external air is commonly, at night, nearly replete
with moisture, and therefore readily precipitates dew on bodies only a
little colder than itself.

"When the air of a room is warmer than the external atmosphere, the
effect of an outside shutter on the temperature of the glass of the
window will be directly opposite to what has just been stated; since
it must prevent the radiation, into the atmosphere, of the heat of the
chamber transmitted through the glass.

"2. Count Rumford appears to have rightly conjectured that the
inhabitants of certain hot countries, who sleep at nights on the tops of
their houses, are cooled during this exposure by the radiation of their
heat to the sky; or, according to his manner of expression, by receiving
frigorific rays from the heavens. Another fact of this kind seems to be
the greater chill which we often experience upon passing at night from
the cover of a house into the air than might have been expected from the
cold of the external atmosphere. The cause, indeed, is said to be the
quickness of transition from one situation to another. But if this were
the whole reason, an equal chill would be felt in the day, when the
difference, in point of heat, between the internal and external air was
the same as at night, which is not the case. Besides, if I can trust my
own observation, the feeling of cold from this cause is more remarkable
in a clear than in a cloudy night, and in the country than in towns. The
following appears to be the manner in which these things are chiefly to
be explained:

"During the day our bodies while in the open air, although not
immediately exposed to the sun's rays, are yet constantly deriving
heat from them by means of the reflection of the atmosphere. This heat,
though it produces little change on the temperature of the air which it
traverses, affords us some compensation for the heat which we radiate to
the heavens. At night, also, if the sky be overcast, some compensation
will be made to us, both in the town and in the country, though in a
less degree than during the day, as the clouds will remit towards the
earth no inconsiderable quantity of heat. But on a clear night, in an
open part of the country, nothing almost can be returned to us from
above in place of the heat which we radiate upward. In towns, however,
some compensation will be afforded even on the clearest nights for the
heat which we lose in the open air by that which is radiated to us from
the sun round buildings.

"To our loss of heat by radiation at times that we derive little
compensation from the radiation of other bodies is probably to be
attributed a great part of the hurtful effects of the night air.
Descartes says that these are not owing to dew, as was the common
opinion of his contemporaries, but to the descent of certain noxious
vapors which have been exhaled from the earth during the heat of the
day, and are afterwards condensed by the cold of a serene night. The
effects in question certainly cannot be occasioned by dew, since that
fluid does not form upon a healthy human body in temperate climates; but
they may, notwithstanding, arise from the same cause that produces dew
on those substances which do not, like the human body, possess the power
of generating heat for the supply of what they lose by radiation or any
other means."(2)


This explanation made it plain why dew forms on a clear night, when
there are no clouds to reflect the radiant heat. Combined with Dalton's
theory that vapor is an independent gas, limited in quantity in any
given space by the temperature of that space, it solved the problem of
the formation of clouds, rain, snow, and hoar-frost. Thus this paper
of Wells's closed the epoch of speculation regarding this field of
meteorology, as Hutton's paper of 1784 had opened it. The fact that the
volume containing Hutton's paper contained also his epoch-making paper
on geology finds curiously a duplication in the fact that Wells's volume
contained also his essay on Albinism, in which the doctrine of natural
selection was for the first time formulated, as Charles Darwin freely
admitted after his own efforts had made the doctrine famous.


ISOTHERMS AND OCEAN CURRENTS

The very next year after Dr. Wells's paper was published there appeared
in France the third volume of the Memoires de Physique et de Chimie de
la Societe d'Arcueil, and a new epoch in meteorology was inaugurated.
The society in question was numerically an inconsequential band, listing
only a dozen members; but every name was a famous one: Arago, Berard,
Berthollet, Biot, Chaptal, De Candolle, Dulong, Gay-Lussac, Humboldt,
Laplace, Poisson, and Thenard--rare spirits every one. Little danger
that the memoirs of such a band would be relegated to the dusty shelves
where most proceedings of societies belong--no milk-for-babes fare would
be served to such a company.

The particular paper which here interests us closes this third and
last volume of memoirs. It is entitled "Des Lignes Isothermes et de
la Distribution de la Chaleursurle Globe." The author is Alexander
Humboldt. Needless to say, the topic is handled in a masterly
manner. The distribution of heat on the surface of the globe, on the
mountain-sides, in the interior of the earth; the causes that regulate
such distribution; the climatic results--these are the topics discussed.
But what gives epochal character to the paper is the introduction of
those isothermal lines circling the earth in irregular course, joining
together places having the same mean annual temperature, and thus laying
the foundation for a science of comparative climatology.

It is true the attempt to study climates comparatively was not new.
Mairan had attempted it in those papers in which he developed his
bizarre ideas as to central emanations of heat. Euler had brought
his profound mathematical genius to bear on the topic, evolving the
"extraordinary conclusion that under the equator at midnight the
cold ought to be more rigorous than at the poles in winter." And
in particular Richard Kirwan, the English chemist, had combined the
mathematical and the empirical methods and calculated temperatures for
all latitudes. But Humboldt differs from all these predecessors in that
he grasps the idea that the basis of all such computations should be
not theory, but fact. He drew his isothermal lines not where some occult
calculation would locate them on an ideal globe, but where practical
tests with the thermometer locate them on our globe as it is. London,
for example, lies in the same latitude as the southern extremity of
Hudson Bay; but the isotherm of London, as Humboldt outlines it, passes
through Cincinnati.

Of course such deviations of climatic conditions between places in the
same latitude had long been known. As Humboldt himself observes,
the earliest settlers of America were astonished to find themselves
subjected to rigors of climate for which their European experience had
not at all prepared them. Moreover, sagacious travellers, in particular
Cook's companion on his second voyage, young George Forster, had
noted as a general principle that the western borders of continents
in temperate regions are always warmer than corresponding latitudes of
their eastern borders; and of course the general truth of temperatures
being milder in the vicinity of the sea than in the interior of
continents had long been familiar. But Humboldt's isothermal lines for
the first time gave tangibility to these ideas, and made practicable a
truly scientific study of comparative climatology.

In studying these lines, particularly as elaborated by further
observations, it became clear that they are by no means haphazard in
arrangement, but are dependent upon geographical conditions which in
most cases are not difficult to determine. Humboldt himself pointed out
very clearly the main causes that tend to produce deviations from the
average--or, as Dove later on called it, the normal--temperature of any
given latitude. For example, the mean annual temperature of a region
(referring mainly to the northern hemisphere) is raised by the proximity
of a western coast; by a divided configuration of the continent into
peninsulas; by the existence of open seas to the north or of radiating
continental surfaces to the south; by mountain ranges to shield from
cold winds; by the infrequency of swamps to become congealed; by the
absence of woods in a dry, sandy soil; and by the serenity of sky in the
summer months and the vicinity of an ocean current bringing water which
is of a higher temperature than that of the surrounding sea.

Conditions opposite to these tend, of course, correspondingly to lower
the temperature. In a word, Humboldt says the climatic distribution of
heat depends on the relative distribution of land and sea, and on the
"hypsometrical configuration of the continents"; and he urges that
"great meteorological phenomena cannot be comprehended when considered
independently of geognostic relations"--a truth which, like most other
general principles, seems simple enough once it is pointed out.

With that broad sweep of imagination which characterized him, Humboldt
speaks of the atmosphere as the "aerial ocean, in the lower strata
and on the shoals of which we live," and he studies the atmospheric
phenomena always in relation to those of that other ocean of water. In
each of these oceans there are vast permanent currents, flowing
always in determinate directions, which enormously modify the climatic
conditions of every zone. The ocean of air is a vast maelstrom, boiling
up always under the influence of the sun's heat at the equator, and
flowing as an upper current towards either pole, while an undercurrent
from the poles, which becomes the trade-winds, flows towards the equator
to supply its place.

But the superheated equatorial air, becoming chilled, descends to the
surface in temperate latitudes, and continues its poleward journey as
the anti-trade-winds. The trade-winds are deflected towards the west,
because in approaching the equator they constantly pass over surfaces of
the earth having a greater and greater velocity of rotation, and so, as
it were, tend to lag behind--an explanation which Hadley pointed out in
1735, but which was not accepted until Dalton independently worked it
out and promulgated it in 1793. For the opposite reason, the anti-trades
are deflected towards the east; hence it is that the western, borders
of continents in temperate zones are bathed in moist sea-breezes, while
their eastern borders lack this cold-dispelling influence.

In the ocean of water the main currents run as more sharply
circumscribed streams--veritable rivers in the sea. Of these the best
known and most sharply circumscribed is the familiar Gulf Stream,
which has its origin in an equatorial current, impelled westward by
trade-winds, which is deflected northward in the main at Cape St. Roque,
entering the Caribbean Sea and Gulf of Mexico, to emerge finally through
the Strait of Florida, and journey off across the Atlantic to warm the
shores of Europe.

Such, at least, is the Gulf Stream as Humboldt understood it. Since his
time, however, ocean currents in general, and this one in particular,
have been the subject of no end of controversy, it being hotly disputed
whether either causes or effects of the Gulf Stream are just what
Humboldt, in common with others of his time, conceived them to be. About
the middle of the century Lieutenant M. F. Maury, the distinguished
American hydrographer and meteorologist, advocated a theory of
gravitation as the chief cause of the currents, claiming that difference
in density, due to difference in temperature and saltness, would
sufficiently account for the oceanic circulation. This theory gained
great popularity through the wide circulation of Maury's Physical
Geography of the Sea, which is said to have passed through more editions
than any other scientific book of the period; but it was ably and
vigorously combated by Dr. James Croll, the Scottish geologist, in his
Climate and Time, and latterly the old theory that ocean currents are
due to the trade-winds has again come into favor. Indeed, very recently
a model has been constructed, with the aid of which it is said to have
been demonstrated that prevailing winds in the direction of the actual
trade-winds would produce such a current as the Gulf Stream.

Meantime, however, it is by no means sure that gravitation does not
enter into the case to the extent of producing an insensible general
oceanic circulation, independent of the Gulf Stream and similar marked
currents, and similar in its larger outlines to the polar-equatorial
circulation of the air. The idea of such oceanic circulation was first
suggested in detail by Professor Lenz, of St. Petersburg, in 1845, but
it was not generally recognized until Dr. Carpenter independently hit
upon the idea more than twenty years later. The plausibility of the
conception is obvious; yet the alleged fact of such circulation has been
hotly disputed, and the question is still sub judice.

But whether or not such general circulation of ocean water takes place,
it is beyond dispute that the recognized currents carry an enormous
quantity of heat from the tropics towards the poles. Dr. Croll, who has
perhaps given more attention to the physics of the subject than almost
any other person, computes that the Gulf Stream conveys to the North
Atlantic one-fourth as much heat as that body receives directly from the
sun, and he argues that were it not for the transportation of heat by
this and similar Pacific currents, only a narrow tropical region of the
globe would be warm enough for habitation by the existing faunas. Dr.
Croll argues that a slight change in the relative values of northern
and southern trade-winds (such as he believes has taken place at various
periods in the past) would suffice to so alter the equatorial current
which now feeds the Gulf Stream that its main bulk would be deflected
southward instead of northward, by the angle of Cape St. Roque. Thus the
Gulf Stream would be nipped in the bud, and, according to Dr. Croll's
estimates, the results would be disastrous for the northern hemisphere.
The anti-trades, which now are warmed by the Gulf Stream, would then
blow as cold winds across the shores of western Europe, and in all
probability a glacial epoch would supervene throughout the northern
hemisphere.

The same consequences, so far as Europe is concerned at least, would
apparently ensue were the Isthmus of Panama to settle into the sea,
allowing the Caribbean current to pass into the Pacific. But the
geologist tells us that this isthmus rose at a comparatively recent
geological period, though it is hinted that there had been some time
previously a temporary land connection between the two continents. Are
we to infer, then, that the two Americas in their unions and disunions
have juggled with the climate of the other hemisphere? Apparently so, if
the estimates made of the influence of the Gulf Stream be tenable. It is
a far cry from Panama to Russia. Yet it seems within the possibilities
that the meteorologist may learn from the geologist of Central America
something that will enable him to explain to the paleontologist of
Europe how it chanced that at one time the mammoth and rhinoceros roamed
across northern Siberia, while at another time the reindeer and musk-ox
browsed along the shores of the Mediterranean.

Possibilities, I said, not probabilities. Yet even the faint glimmer of
so alluring a possibility brings home to one with vividness the truth
of Humboldt's perspicuous observation that meteorology can be properly
comprehended only when studied in connection with the companion
sciences. There are no isolated phenomena in nature.


CYCLONES AND ANTI-CYCLONES

Yet, after all, it is not to be denied that the chief concern of the
meteorologist must be with that other medium, the "ocean of air, on
the shoals of which we live." For whatever may be accomplished by water
currents in the way of conveying heat, it is the wind currents that
effect the final distribution of that heat. As Dr. Croll has urged, the
waters of the Gulf Stream do not warm the shores of Europe by direct
contact, but by warming the anti-trade-winds, which subsequently blow
across the continent. And everywhere the heat accumulated by water
becomes effectual in modifying climate, not so much by direct radiation
as by diffusion through the medium of the air.

This very obvious importance of aerial currents led to their practical
study long before meteorology had any title to the rank of science, and
Dalton's explanation of the trade-winds had laid the foundation for a
science of wind dynamics before the beginning of the nineteenth century.
But no substantial further advance in this direction was effected until
about 1827, when Heinrich W. Dove, of Konigsberg, afterwards to be known
as perhaps the foremost meteorologist of his generation, included
the winds among the subjects of his elaborate statistical studies in
climatology.

Dove classified the winds as permanent, periodical, and variable. His
great discovery was that all winds, of whatever character, and not
merely the permanent winds, come under the influence of the earth's
rotation in such a way as to be deflected from their course, and hence
to take on a gyratory motion--that, in short, all local winds are minor
eddies in the great polar-equatorial whirl, and tend to reproduce in
miniature the character of that vast maelstrom. For the first time,
then, temporary or variable winds were seen to lie within the province
of law.

A generation later, Professor William Ferrel, the American
meteorologist, who had been led to take up the subject by a perusal of
Maury's discourse on ocean winds, formulated a general mathematical law,
to the effect that any body moving in a right line along the surface of
the earth in any direction tends to have its course deflected, owing to
the earth's rotation, to the right hand in the northern and to the left
hand in the southern hemisphere. This law had indeed been stated as
early as 1835 by the French physicist Poisson, but no one then thought
of it as other than a mathematical curiosity; its true significance was
only understood after Professor Ferrel had independently rediscovered it
(just as Dalton rediscovered Hadley's forgotten law of the trade-winds)
and applied it to the motion of wind currents.

Then it became clear that here is a key to the phenomena of atmospheric
circulation, from the great polar-equatorial maelstrom which manifests
itself in the trade-winds to the most circumscribed riffle which is
announced as a local storm. And the more the phenomena were studied,
the more striking seemed the parallel between the greater maelstrom
and these lesser eddies. Just as the entire atmospheric mass of each
hemisphere is seen, when viewed as a whole, to be carried in a great
whirl about the pole of that hemisphere, so the local disturbances
within this great tide are found always to take the form of whirls about
a local storm-centre--which storm-centre, meantime, is carried along
in the major current, as one often sees a little whirlpool in the water
swept along with the main current of the stream. Sometimes, indeed, the
local eddy, caught as it were in an ancillary current of the great
polar stream, is deflected from its normal course and may seem to travel
against the stream; but such deviations are departures from the rule. In
the great majority of cases, for example, in the north temperate zone, a
storm-centre (with its attendant local whirl) travels to the northeast,
along the main current of the anti-trade-wind, of which it is a part;
and though exceptionally its course may be to the southeast instead, it
almost never departs so widely from the main channel as to progress to
the westward. Thus it is that storms sweeping over the United States can
be announced, as a rule, at the seaboard in advance of their coming by
telegraphic communication from the interior, while similar storms
come to Europe off the ocean unannounced. Hence the more practical
availability of the forecasts of weather bureaus in the former country.

But these local whirls, it must be understood, are local only in a very
general sense of the word, inasmuch as a single one may be more than
a thousand miles in diameter, and a small one is two or three hundred
miles across. But quite without regard to the size of the whirl, the air
composing it conducts itself always in one of two ways. It never whirls
in concentric circles; it always either rushes in towards the centre in
a descending spiral, in which case it is called a cyclone, or it spreads
out from the centre in a widening spiral, in which case it is called an
anti-cyclone. The word cyclone is associated in popular phraseology with
a terrific storm, but it has no such restriction in technical usage. A
gentle zephyr flowing towards a "storm-centre" is just as much a
cyclone to the meteorologist as is the whirl constituting a West-Indian
hurricane. Indeed, it is not properly the wind itself that is called the
cyclone in either case, but the entire system of whirls--including the
storm-centre itself, where there may be no wind at all.

What, then, is this storm-centre? Merely an area of low barometric
pressure--an area where the air has become lighter than the air of
surrounding regions. Under influence of gravitation the air seeks its
level just as water does; so the heavy air comes flowing in from
all sides towards the low-pressure area, which thus becomes a
"storm-centre." But the inrushing currents never come straight to their
mark. In accordance with Ferrel's law, they are deflected to the right,
and the result, as will readily be seen, must be a vortex current, which
whirls always in one direction--namely, from left to right, or in the
direction opposite to that of the hands of a watch held with its face
upward. The velocity of the cyclonic currents will depend largely upon
the difference in barometric pressure between the storm-centre and the
confines of the cyclone system. And the velocity of the currents will
determine to some extent the degree of deflection, and hence the exact
path of the descending spiral in which the wind approaches the centre.
But in every case and in every part of the cyclone system it is true, as
Buys Ballot's famous rule first pointed out, that a person standing with
his back to the wind has the storm-centre at his left.

The primary cause of the low barometric pressure which marks the
storm-centre and establishes the cyclone is expansion of the air through
excess of temperature. The heated air, rising into cold upper regions,
has a portion of its vapor condensed into clouds, and now a new dynamic
factor is added, for each particle of vapor, in condensing, gives up its
modicum of latent heat. Each pound of vapor thus liberates, according
to Professor Tyndall's estimate, enough heat to melt five pounds of cast
iron; so the amount given out where large masses of cloud are forming
must enormously add to the convection currents of the air, and hence to
the storm-developing power of the forming cyclone. Indeed, one school
of meteorologists, of whom Professor Espy was the leader, has held that,
without such added increment of energy constantly augmenting the dynamic
effects, no storm could long continue in violent action. And it is
doubted whether any storm could ever attain, much less continue, the
terrific force of that most dreaded of winds of temperate zones, the
tornado--a storm which obeys all the laws of cyclones, but differs from
ordinary cyclones in having a vortex core only a few feet or yards in
diameter--without the aid of those great masses of condensing vapor
which always accompany it in the form of storm-clouds.

The anti-cyclone simply reverses the conditions of the cyclone. Its
centre is an area of high pressure, and the air rushes out from it in
all directions towards surrounding regions of low pressure. As before,
all parts of the current will be deflected towards the right, and
the result, clearly, is a whirl opposite in direction to that of the
cyclone. But here there is a tendency to dissipation rather than to
concentration of energy, hence, considered as a storm-generator, the
anti-cyclone is of relative insignificance.

In particular the professional meteorologist who conducts a "weather
bureau"--as, for example, the chief of the United States signal-service
station in New York--is so preoccupied with the observation of this
phenomenon that cyclone-hunting might be said to be his chief pursuit.
It is for this purpose, in the main, that government weather bureaus
or signal-service departments have been established all over the world.
Their chief work is to follow up cyclones, with the aid of telegraphic
reports, mapping their course and recording the attendant meteorological
conditions. Their so-called predictions or forecasts are essentially
predications, gaining locally the effect of predictions because the
telegraph outstrips the wind.

At only one place on the globe has it been possible as yet for the
meteorologist to make long-time forecasts meriting the title of
predictions. This is in the middle Ganges Valley of northern India.
In this country the climatic conditions are largely dependent upon the
periodical winds called monsoons, which blow steadily landward from
April to October, and seaward from October to April. The summer monsoons
bring the all-essential rains; if they are delayed or restricted
in extent, there will be drought and consequent famine. And such
restriction of the monsoon is likely to result when there has been an
unusually deep or very late snowfall on the Himalayas, because of the
lowering of spring temperature by the melting snow. Thus here it is
possible, by observing the snowfall in the mountains, to predict with
some measure of success the average rainfall of the following summer.
The drought of 1896, with the consequent famine and plague that
devastated India the following winter, was thus predicted some months in
advance.

This is the greatest present triumph of practical meteorology. Nothing
like it is yet possible anywhere in temperate zones. But no one can
say what may not be possible in times to come, when the data now being
gathered all over the world shall at last be co-ordinated, classified,
and made the basis of broad inductions. Meteorology is pre-eminently a
science of the future.



VI. MODERN THEORIES OF HEAT AND LIGHT

THE eighteenth-century philosopher made great strides in his studies
of the physical properties of matter and the application of these
properties in mechanics, as the steam-engine, the balloon, the optic
telegraph, the spinning-jenny, the cotton-gin, the chronometer, the
perfected compass, the Leyden jar, the lightning-rod, and a host of
minor inventions testify. In a speculative way he had thought out more
or less tenable conceptions as to the ultimate nature of matter, as
witness the theories of Leibnitz and Boscovich and Davy, to which we
may recur. But he had not as yet conceived the notion of a distinction
between matter and energy, which is so fundamental to the physics of a
later epoch. He did not speak of heat, light, electricity, as forms
of energy or "force"; he conceived them as subtile forms of matter--as
highly attenuated yet tangible fluids, subject to gravitation and
chemical attraction; though he had learned to measure none of them but
heat with accuracy, and this one he could test only within narrow limits
until late in the century, when Josiah Wedgwood, the famous potter,
taught him to gauge the highest temperatures with the clay pyrometer.

He spoke of the matter of heat as being the most universally distributed
fluid in nature; as entering in some degree into the composition of
nearly all other substances; as being sometimes liquid, sometimes
condensed or solid, and as having weight that could be detected with
the balance. Following Newton, he spoke of light as a "corpuscular
emanation" or fluid, composed of shining particles which possibly are
transmutable into particles of heat, and which enter into chemical
combination with the particles of other forms of matter. Electricity
he considered a still more subtile kind of matter-perhaps an attenuated
form of light. Magnetism, "vital fluid," and by some even a "gravic
fluid," and a fluid of sound were placed in the same scale; and, taken
together, all these supposed subtile forms of matter were classed as
"imponderables."

This view of the nature of the "imponderables" was in some measure a
retrogression, for many seventeenth-century philosophers, notably
Hooke and Huygens and Boyle, had held more correct views; but the
materialistic conception accorded so well with the eighteenth-century
tendencies of thought that only here and there a philosopher like Euler
called it in question, until well on towards the close of the century.
Current speech referred to the materiality of the "imponderables"
unquestioningly. Students of meteorology--a science that was just
dawning--explained atmospheric phenomena on the supposition that heat,
the heaviest imponderable, predominated in the lower atmosphere, and
that light, electricity, and magnetism prevailed in successively higher
strata. And Lavoisier, the most philosophical chemist of the century,
retained heat and light on a par with oxygen, hydrogen, iron, and the
rest, in his list of elementary substances.


COUNT RUMFORD AND THE VIBRATORY THEORY OF HEAT

But just at the close of the century the confidence in the status of
the imponderables was rudely shaken in the minds of philosophers by the
revival of the old idea of Fra Paolo and Bacon and Boyle, that heat,
at any rate, is not a material fluid, but merely a mode of motion or
vibration among the particles of "ponderable" matter. The new champion
of the old doctrine as to the nature of heat was a very distinguished
philosopher and diplomatist of the time, who, it may be worth recalling,
was an American. He was a sadly expatriated American, it is true, as his
name, given all the official appendages, will amply testify; but he had
been born and reared in a Massachusetts village none the less, and
he seems always to have retained a kindly interest in the land of his
nativity, even though he lived abroad in the service of other powers
during all the later years of his life, and was knighted by England,
ennobled by Bavaria, and honored by the most distinguished scientific
bodies of Europe. The American, then, who championed the vibratory
theory of heat, in opposition to all current opinion, in this closing
era of the eighteenth century, was Lieutenant-General Sir Benjamin
Thompson, Count Rumford, F.R.S.

Rumford showed that heat may be produced in indefinite quantities by
friction of bodies that do not themselves lose any appreciable matter
in the process, and claimed that this proves the immateriality of heat.
Later on he added force to the argument by proving, in refutation of the
experiments of Bowditch, that no body either gains or loses weight in
virtue of being heated or cooled. He thought he had proved that heat is
only a form of motion.

His experiment for producing indefinite quantities of heat by friction
is recorded by him in his paper entitled, "Inquiry Concerning the Source
of Heat Excited by Friction."

"Being engaged, lately, in superintending the boring of cannon in the
workshops of the military arsenal at Munich," he says, "I was struck
with the very considerable degree of heat which a brass gun acquires in
a short time in being bored; and with the still more intense heat (much
greater than that of boiling water, as I found by experiment) of the
metallic chips separated from it by the borer.

"Taking a cannon (a brass six-pounder), cast solid, and rough, as it
came from the foundry, and fixing it horizontally in a machine used
for boring, and at the same time finishing the outside of the cannon by
turning, I caused its extremity to be cut off; and by turning down
the metal in that part, a solid cylinder was formed, 7 3/4 inches in
diameter and 9 8/10 inches long; which, when finished, remained joined
to the rest of the metal (that which, properly speaking, constituted the
cannon) by a small cylindrical neck, only 2 1/5 inches in diameter and 3
8/10 inches long.

"This short cylinder, which was supported in its horizontal position,
and turned round its axis by means of the neck by which it remained
united to the cannon, was now bored with the horizontal borer used in
boring cannon.

"This cylinder being designed for the express purpose of generating heat
by friction, by having a blunt borer forced against its solid bottom at
the same time that it should be turned round its axis by the force of
horses, in order that the heat accumulated in the cylinder might from
time to time be measured, a small, round hole 0.37 of an inch only in
diameter and 4.2 inches in depth, for the purpose of introducing a small
cylindrical mercurial thermometer, was made in it, on one side, in a
direction perpendicular to the axis of the cylinder, and ending in the
middle of the solid part of the metal which formed the bottom of the
bore.

"At the beginning of the experiment, the temperature of the air in the
shade, as also in the cylinder, was just sixty degrees Fahrenheit. At
the end of thirty minutes, when the cylinder had made 960 revolutions
about its axis, the horses being stopped, a cylindrical mercury
thermometer, whose bulb was 32/100 of an inch in diameter and 3 1/4
inches in length, was introduced into the hole made to receive it in
the side of the cylinder, when the mercury rose almost instantly to one
hundred and thirty degrees.

"In order, by one decisive experiment, to determine whether the air
of the atmosphere had any part or not in the generation of the heat, I
contrived to repeat the experiment under circumstances in which it was
evidently impossible for it to produce any effect whatever. By means
of a piston exactly fitted to the mouth of the bore of the cylinder,
through the middle of which piston the square iron bar, to the end of
which the blunt steel borer was fixed, passed in a square hole made
perfectly air-tight, the excess of the external air, to the inside of
the bore of the cylinder, was effectually prevented. I did not find,
however, by this experiment that the exclusion of the air diminished in
the smallest degree the quantity of heat excited by the friction.

"There still remained one doubt, which, though it appeared to me to be
so slight as hardly to deserve any attention, I was, however, desirous
to remove. The piston which choked the mouth of the bore of the
cylinder, in order that it might be air-tight, was fitted into it with
so much nicety, by means of its collars of leather, and pressed against
it with so much force, that, notwithstanding its being oiled, it
occasioned a considerable degree of friction when the hollow cylinder
was turned round its axis. Was not the heat produced, or at least some
part of it, occasioned by this friction of the piston? and, as the
external air had free access to the extremity of the bore, where it came
into contact with the piston, is it not possible that this air may have
had some share in the generation of the heat produced?

"A quadrangular oblong deal box, water-tight, being provided with
holes or slits in the middle of each of its ends, just large enough to
receive, the one the square iron rod to the end of which the blunt steel
borer was fastened, the other the small cylindrical neck which joined
the hollow cylinder to the cannon; when this box (which was occasionally
closed above by a wooden cover or lid moving on hinges) was put into
its place--that is to say, when, by means of the two vertical opening
or slits in its two ends, the box was fixed to the machinery in such
a manner that its bottom being in the plane of the horizon, its axis
coincided with the axis of the hollow metallic cylinder, it is evident,
from the description, that the hollow, metallic cylinder would occupy
the middle of the box, without touching it on either side; and that,
on pouring water into the box and filling it to the brim, the cylinder
would be completely covered and surrounded on every side by that fluid.
And, further, as the box was held fast by the strong, square iron rod
which passed in a square hole in the centre of one of its ends, while
the round or cylindrical neck which joined the hollow cylinder to the
end of the cannon could turn round freely on its axis in the round hole
in the centre of the other end of it, it is evident that the machinery
could be put in motion without the least danger of forcing the box out
of its place, throwing the water out of it, or deranging any part of the
apparatus."

Everything being thus ready, the box was filled with cold water, having
been made water-tight by means of leather collars, and the machinery put
in motion. "The result of this beautiful experiment," says Rumford, "was
very striking, and the pleasure it afforded me amply repaid me for
all the trouble I had had in contriving and arranging the complicated
machinery used in making it. The cylinder, revolving at the rate of
thirty-two times in a minute, had been in motion but a short time when I
perceived, by putting my hand into the water and touching the outside
of the cylinder, that heat was generated, and it was not long before the
water which surrounded the cylinder began to be sensibly warm.

"At the end of one hour I found, by plunging a thermometer into the
box,... that its temperature had been raised no less than forty-seven
degrees Fahrenheit, being now one hundred and seven degrees Fahrenheit.
... One hour and thirty minutes after the machinery had been put in
motion the heat of the water in the box was one hundred and forty-two
degrees. At the end of two hours... it was raised to one hundred and
seventy-eight degrees; and at two hours and thirty minutes it ACTUALLY
BOILED!

"It would be difficult to describe the surprise and astonishment
expressed in the countenances of the bystanders on seeing so large a
quantity of cold water heated, and actually made to boil, without any
fire. Though there was, in fact, nothing that could justly be considered
as a surprise in this event, yet I acknowledge fairly that it afforded
me a degree of childish pleasure which, were I ambitious of the
reputation of a GRAVE PHILOSOPHER, I ought most certainly rather to hide
than to discover...."

Having thus dwelt in detail on these experiments, Rumford comes now to
the all-important discussion as to the significance of them--the
subject that had been the source of so much speculation among the
philosophers--the question as to what heat really is, and if there
really is any such thing (as many believed) as an igneous fluid, or a
something called caloric.

"From whence came this heat which was continually given off in this
manner, in the foregoing experiments?" asks Rumford. "Was it furnished
by the small particles of metal detached from the larger solid masses
on their being rubbed together? This, as we have already seen, could not
possibly have been the case.

"Was it furnished by the air? This could not have been the case; for,
in three of the experiments, the machinery being kept immersed in water,
the access of the air of the atmosphere was completely prevented.

"Was it furnished by the water which surrounded the machinery? That this
could not have been the case is evident: first, because this water was
continually RECEIVING heat from the machinery, and could not, at the
same time, be GIVING TO and RECEIVING HEAT FROM the same body; and,
secondly, because there was no chemical decomposition of any part of
this water. Had any such decomposition taken place (which, indeed, could
not reasonably have been expected), one of its component elastic fluids
(most probably hydrogen) must, at the same time, have been set at
liberty, and, in making its escape into the atmosphere, would have been
detected; but, though I frequently examined the water to see if any
air-bubbles rose up through it, and had even made preparations for
catching them if they should appear, I could perceive none; nor was
there any sign of decomposition of any kind whatever, or other chemical
process, going on in the water.

"Is it possible that the heat could have been supplied by means of the
iron bar to the end of which the blunt steel borer was fixed? Or by the
small neck of gun-metal by which the hollow cylinder was united to the
cannon? These suppositions seem more improbable even than either of
the before-mentioned; for heat was continually going off, or OUT OF THE
MACHINERY, by both these passages during the whole time the experiment
lasted.

"And in reasoning on this subject we must not forget to consider that
most remarkable circumstance, that the source of the heat generated by
friction in these experiments appeared evidently to be INEXHAUSTIBLE.

"It is hardly necessary to add that anything which any INSULATED body,
or system of bodies, can continue to furnish WITHOUT LIMITATION cannot
possibly be a MATERIAL substance; and it appears to me to be extremely
difficult, if not quite impossible, to form any distinct idea of
anything capable of being excited and communicated, in the manner
the heat was excited and communicated in these experiments, except in
MOTION."(1)


THOMAS YOUNG AND THE WAVE THEORY OF LIGHT

But contemporary judgment, while it listened respectfully to Rumford,
was little minded to accept his verdict. The cherished beliefs of a
generation are not to be put down with a single blow. Where many minds
have a similar drift, however, the first blow may precipitate a
general conflict; and so it was here. Young Humphry Davy had duplicated
Rumford's experiments, and reached similar conclusions; and soon others
fell into line. Then, in 1800, Dr. Thomas Young--"Phenomenon Young" they
called him at Cambridge, because he was reputed to know everything--took
up the cudgels for the vibratory theory of light, and it began to be
clear that the two "imponderables," heat and light, must stand or
fall together; but no one as yet made a claim against the fluidity of
electricity.

Before we take up the details of the assault made by Young upon the
old doctrine of the materiality of light, we must pause to consider the
personality of Young himself. For it chanced that this Quaker physician
was one of those prodigies who come but few times in a century, and
the full list of whom in the records of history could be told on one's
thumbs and fingers. His biographers tell us things about him that read
like the most patent fairy-tales. As a mere infant in arms he had been
able to read fluently. Before his fourth birthday came he had read the
Bible twice through, as well as Watts's Hymns--poor child!--and when
seven or eight he had shown a propensity to absorb languages much as
other children absorb nursery tattle and Mother Goose rhymes. When
he was fourteen, a young lady visiting the household of his tutor
patronized the pretty boy by asking to see a specimen of his penmanship.
The pretty boy complied readily enough, and mildly rebuked his
interrogator by rapidly writing some sentences for her in fourteen
languages, including such as, Arabian, Persian, and Ethiopic.

Meantime languages had been but an incident in the education of the lad.
He seems to have entered every available field of thought--mathematics,
physics, botany, literature, music, painting, languages, philosophy,
archaeology, and so on to tiresome lengths--and once he had entered any
field he seldom turned aside until he had reached the confines of the
subject as then known and added something new from the recesses of his
own genius. He was as versatile as Priestley, as profound as Newton
himself. He had the range of a mere dilettante, but everywhere the full
grasp of the master. He took early for his motto the saying that what
one man has done, another man may do. Granting that the other man has
the brain of a Thomas Young, it is a true motto.

Such, then, was the young Quaker who came to London to follow out
the humdrum life of a practitioner of medicine in the year 1801. But
incidentally the young physician was prevailed upon to occupy the
interims of early practice by fulfilling the duties of the chair of
Natural Philosophy at the Royal Institution, which Count Rumford
had founded, and of which Davy was then Professor of Chemistry--the
institution whose glories have been perpetuated by such names as Faraday
and Tyndall, and which the Briton of to-day speaks of as the "Pantheon
of Science." Here it was that Thomas Young made those studies which have
insured him a niche in the temple of fame not far removed from that of
Isaac Newton.

As early as 1793, when he was only twenty, Young had begun to
Communicate papers to the Royal Society of London, which were adjudged
worthy to be printed in full in the Philosophical Transactions; so it
is not strange that he should have been asked to deliver the Bakerian
lecture before that learned body the very first year after he came to
London. The lecture was delivered November 12, 1801. Its subject was
"The Theory of Light and Colors," and its reading marks an epoch in
physical science; for here was brought forward for the first time
convincing proof of that undulatory theory of light with which every
student of modern physics is familiar--the theory which holds that light
is not a corporeal entity, but a mere pulsation in the substance of
an all-pervading ether, just as sound is a pulsation in the air, or in
liquids or solids.

Young had, indeed, advocated this theory at an earlier date, but it was
not until 1801 that he hit upon the idea which enabled him to bring it
to anything approaching a demonstration. It was while pondering over the
familiar but puzzling phenomena of colored rings into which white
light is broken when reflected from thin films--Newton's rings, so
called--that an explanation occurred to him which at once put the entire
undulatory theory on a new footing. With that sagacity of insight which
we call genius, he saw of a sudden that the phenomena could be explained
by supposing that when rays of light fall on a thin glass, part of the
rays being reflected from the upper surface, other rays, reflected from
the lower surface, might be so retarded in their course through the
glass that the two sets would interfere with one another, the forward
pulsation of one ray corresponding to the backward pulsation of another,
thus quite neutralizing the effect. Some of the component pulsations of
the light being thus effaced by mutual interference, the remaining
rays would no longer give the optical effect of white light; hence the
puzzling colors.

Here is Young's exposition of the subject:

Of the Colors of Thin Plates

"When a beam of light falls upon two refracting surfaces, the partial
reflections coincide perfectly in direction; and in this case the
interval of retardation taken between the surfaces is to their radius as
twice the cosine of the angle of refraction to the radius.

"Let the medium between the surfaces be rarer than the surrounding
mediums; then the impulse reflected at the second surface, meeting a
subsequent undulation at the first, will render the particles of the
rarer medium capable of wholly stopping the motion of the denser and
destroying the reflection, while they themselves will be more strongly
propelled than if they had been at rest, and the transmitted light will
be increased. So that the colors by reflection will be destroyed, and
those by transmission rendered more vivid, when the double thickness or
intervals of retardation are any multiples of the whole breadth of
the undulations; and at intermediate thicknesses the effects will be
reversed according to the Newtonian observation.

"If the same proportions be found to hold good with respect to thin
plates of a denser medium, which is, indeed, not improbable, it will be
necessary to adopt the connected demonstrations of Prop. IV., but, at
any rate, if a thin plate be interposed between a rarer and a denser
medium, the colors by reflection and transmission may be expected to
change places."


OF THE COLORS OF THICK PLATES

"When a beam of light passes through a refracting surface, especially
if imperfectly polished, a portion of it is irregularly scattered, and
makes the surface visible in all directions, but most conspicuously
in directions not far distant from that of the light itself; and if a
reflecting surface be placed parallel to the refracting surface, this
scattered light, as well as the principal beam, will be reflected, and
there will be also a new dissipation of light, at the return of the beam
through the refracting surface. These two portions of scattered light
will coincide in direction; and if the surfaces be of such a form as to
collect the similar effects, will exhibit rings of colors. The interval
of retardation is here the difference between the paths of the principal
beam and of the scattered light between the two surfaces; of course,
wherever the inclination of the scattered light is equal to that of the
beam, although in different planes, the interval will vanish and all the
undulations will conspire. At other inclinations, the interval will be
the difference of the secants from the secant of the inclination, or
angle of refraction of the principal beam. From these causes, all the
colors of concave mirrors observed by Newton and others are necessary
consequences; and it appears that their production, though somewhat
similar, is by no means as Newton imagined, identical with the
production of thin plates."(2)


By following up this clew with mathematical precision, measuring the
exact thickness of the plate and the space between the different rings
of color, Young was able to show mathematically what must be the length
of pulsation for each of the different colors of the spectrum. He
estimated that the undulations of red light, at the extreme lower end
of the visible spectrum, must number about thirty-seven thousand six
hundred and forty to the inch, and pass any given spot at a rate of four
hundred and sixty-three millions of millions of undulations in a second,
while the extreme violet numbers fifty-nine thousand seven hundred and
fifty undulations to the inch, or seven hundred and thirty-five millions
of millions to the second.


The Colors of Striated Surfaces

Young similarly examined the colors that are produced by scratches on
a smooth surface, in particular testing the light from "Mr. Coventry's
exquisite micrometers," which consist of lines scratched on glass at
measured intervals. These microscopic tests brought the same results as
the other experiments. The colors were produced at certain definite
and measurable angles, and the theory of interference of undulations
explained them perfectly, while, as Young affirmed with confidence, no
other hypothesis hitherto advanced would explain them at all. Here are
his words:

"Let there be in a given plane two reflecting points very near each
other, and let the plane be so situated that the reflected image of a
luminous object seen in it may appear to coincide with the points; then
it is obvious that the length of the incident and reflected ray, taken
together, is equal with respect to both points, considering them as
capable of reflecting in all directions. Let one of the points be
now depressed below the given plane; then the whole path of the
light reflected from it will be lengthened by a line which is to the
depression of the point as twice the cosine of incidence to the radius.

"If, therefore, equal undulations of given dimensions be reflected
from two points, situated near enough to appear to the eye but as one,
whenever this line is equal to half the breadth of a whole undulation
the reflection from the depressed point will so interfere with the
reflection from the fixed point that the progressive motion of the one
will coincide with the retrograde motion of the other, and they will
both be destroyed; but when this line is equal to the whole breadth of
an undulation, the effect will be doubled, and when to a breadth and
a half, again destroyed; and thus for a considerable number of
alternations, and if the reflected undulations be of a different kind,
they will be variously affected, according to their proportions to the
various length of the line which is the difference between the lengths
of their two paths, and which may be denominated the interval of a
retardation.

"In order that the effect may be the more perceptible, a number of pairs
of points must be united into two parallel lines; and if several such
pairs of lines be placed near each other, they will facilitate the
observation. If one of the lines be made to revolve round the other as
an axis, the depression below the given plane will be as the sine of the
inclination; and while the eye and the luminous object remain fixed the
difference of the length of the paths will vary as this sine.

"The best subjects for the experiment are Mr. Coventry's exquisite
micrometers; such of them as consist of parallel lines drawn on glass,
at a distance of one-five-hundredth of an inch, are the most convenient.
Each of these lines appears under a microscope to consist of two or more
finer lines, exactly parallel, and at a distance of somewhat more than
a twentieth more than the adjacent lines. I placed one of these so as to
reflect the sun's light at an angle of forty-five degrees, and fixed
it in such a manner that while it revolved round one of the lines as an
axis, I could measure its angular motion; I found that the longest red
color occurred at the inclination 10 1/4 degrees, 20 3/4 degrees, 32
degrees, and 45 degrees; of which the sines are as the numbers 1, 2, 3,
and 4. At all other angles also, when the sun's light was reflected from
the surface, the color vanished with the inclination, and was equal at
equal inclinations on either side.

This experiment affords a very strong confirmation of the theory. It is
impossible to deduce any explanation of it from any hypothesis hitherto
advanced; and I believe it would be difficult to invent any other
that would account for it. There is a striking analogy between this
separation of colors and the production of a musical note by successive
echoes from equidistant iron palisades, which I have found to correspond
pretty accurately with the known velocity of sound and the distances of
the surfaces.

"It is not improbable that the colors of the integuments of some
insects, and of some other natural bodies, exhibiting in different
lights the most beautiful versatility, may be found to be of this
description, and not to be derived from thin plates. In some cases a
single scratch or furrow may produce similar effects, by the reflection
of its opposite edges."(3)


This doctrine of interference of undulations was the absolutely novel
part of Young's theory. The all-compassing genius of Robert Hooke had,
indeed, very nearly apprehended it more than a century before, as Young
himself points out, but no one else bad so much as vaguely conceived
it; and even with the sagacious Hooke it was only a happy guess, never
distinctly outlined in his own mind, and utterly ignored by all
others. Young did not know of Hooke's guess until he himself had fully
formulated the theory, but he hastened then to give his predecessor
all the credit that could possibly be adjudged his due by the most
disinterested observer. To Hooke's contemporary, Huygens, who was the
originator of the general doctrine of undulation as the explanation of
light, Young renders full justice also. For himself he claims only the
merit of having demonstrated the theory which these and a few others of
his predecessors had advocated without full proof.

The following year Dr. Young detailed before the Royal Society
other experiments, which threw additional light on the doctrine of
interference; and in 1803 he cited still others, which, he affirmed,
brought the doctrine to complete demonstration. In applying this
demonstration to the general theory of light, he made the striking
suggestion that "the luminiferous ether pervades the substance of all
material bodies with little or no resistance, as freely, perhaps, as the
wind passes through a grove of trees." He asserted his belief also that
the chemical rays which Ritter had discovered beyond the violet end of
the visible spectrum are but still more rapid undulations of the same
character as those which produce light. In his earlier lecture he had
affirmed a like affinity between the light rays and the rays of
radiant heat which Herschel detected below the red end of the spectrum,
suggesting that "light differs from heat only in the frequency of its
undulations or vibrations--those undulations which are within certain
limits with respect to frequency affecting the optic nerve and
constituting light, and those which are slower and probably stronger
constituting heat only." From the very outset he had recognized the
affinity between sound and light; indeed, it had been this affinity that
led him on to an appreciation of the undulatory theory of light.

But while all these affinities seemed so clear to the great
co-ordinating brain of Young, they made no such impression on the minds
of his contemporaries. The immateriality of light had been substantially
demonstrated, but practically no one save its author accepted the
demonstration. Newton's doctrine of the emission of corpuscles was too
firmly rooted to be readily dislodged, and Dr. Young had too many other
interests to continue the assault unceasingly. He occasionally wrote
something touching on his theory, mostly papers contributed to
the Quarterly Review and similar periodicals, anonymously or
under pseudonym, for he had conceived the notion that too great
conspicuousness in fields outside of medicine would injure his practice
as a physician. His views regarding light (including the original papers
from the Philosophical Transactions of the Royal Society) were again
given publicity in full in his celebrated volume on natural philosophy,
consisting in part of his lectures before the Royal Institution,
published in 1807; but even then they failed to bring conviction to
the philosophic world. Indeed, they did not even arouse a controversial
spirit, as his first papers had done.


ARAGO AND FRESNEL CHAMPION THE WAVE THEORY

So it chanced that when, in 1815, a young French military engineer,
named Augustin Jean Fresnel, returning from the Napoleonic wars,
became interested in the phenomena of light, and made some experiments
concerning diffraction which seemed to him to controvert the accepted
notions of the materiality of light, he was quite unaware that his
experiments had been anticipated by a philosopher across the Channel.
He communicated his experiments and results to the French Institute,
supposing them to be absolutely novel. That body referred them to a
committee, of which, as good fortune would have it, the dominating
member was Dominique Francois Arago, a man as versatile as Young
himself, and hardly less profound, if perhaps not quite so original.
Arago at once recognized the merit of Fresnel's work, and soon became a
convert to the theory. He told Fresnel that Young had anticipated him
as regards the general theory, but that much remained to be done, and
he offered to associate himself with Fresnel in prosecuting the
investigation. Fresnel was not a little dashed to learn that his
original ideas had been worked out by another while he was a lad, but he
bowed gracefully to the situation and went ahead with unabated zeal.

The championship of Arago insured the undulatory theory a hearing
before the French Institute, but by no means sufficed to bring about
its general acceptance. On the contrary, a bitter feud ensued, in which
Arago was opposed by the "Jupiter Olympus of the Academy," Laplace, by
the only less famous Poisson, and by the younger but hardly less able
Biot. So bitterly raged the feud that a life-long friendship between
Arago and Biot was ruptured forever. The opposition managed to delay the
publication of Fresnel's papers, but Arago continued to fight with his
customary enthusiasm and pertinacity, and at last, in 1823, the Academy
yielded, and voted Fresnel into its ranks, thus implicitly admitting the
value of his work.

It is a humiliating thought that such controversies as this must mar
the progress of scientific truth; but fortunately the story of the
introduction of the undulatory theory has a more pleasant side. Three
men, great both in character and in intellect, were concerned in
pressing its claims--Young, Fresnel, and Arago--and the relations of
these men form a picture unmarred by any of those petty jealousies that
so often dim the lustre of great names. Fresnel freely acknowledged
Young's priority so soon as his attention was called to it; and Young
applauded the work of the Frenchman, and aided with his counsel in the
application of the undulatory theory to the problems of polarization of
light, which still demanded explanation, and which Fresnel's fertility
of experimental resource and profundity of mathematical insight sufficed
in the end to conquer.

After Fresnel's admission to the Institute in 1823 the opposition
weakened, and gradually the philosophers came to realize the merits of
a theory which Young had vainly called to their attention a full
quarter-century before. Now, thanks largely to Arago, both Young and
Fresnel received their full meed of appreciation. Fresnel was given the
Rumford medal of the Royal Society of England in 1825, and chosen one of
the foreign members of the society two years later, while Young in turn
was elected one of the eight foreign members of the French Academy. As
a fitting culmination of the chapter of felicities between the three
friends, it fell to the lot of Young, as Foreign Secretary of the
Royal Society, to notify Fresnel of the honors shown him by England's
representative body of scientists; while Arago, as Perpetual Secretary
of the French Institute, conveyed to Young in the same year the
notification that he had been similarly honored by the savants of
France.

A few months later Fresnel was dead, and Young survived him only two
years. Both died prematurely, but their great work was done, and
the world will remember always and link together these two names in
connection with a theory which in its implications and importance ranks
little below the theory of universal gravitation.



VII. THE MODERN DEVELOPMENT OF ELECTRICITY AND MAGNETISM

GALVANI AND VOLTA

The full importance of Young's studies of light might perhaps have
gained earlier recognition had it not chanced that, at the time when
they were made, the attention of the philosophic world was turned with
the fixity and fascination of a hypnotic stare upon another field, which
for a time brooked no rival. How could the old, familiar phenomenon,
light, interest any one when the new agent, galvanism, was in view? As
well ask one to fix attention on a star while a meteorite blazes across
the sky.

Galvanism was so called precisely as the Roentgen ray was christened at
a later day--as a safe means of begging the question as to the nature of
the phenomena involved. The initial fact in galvanism was the discovery
of Luigi Galvani (1737-1798), a physician of Bologna, in 1791, that
by bringing metals in contact with the nerves of a frog's leg violent
muscular contractions are produced. As this simple little experiment led
eventually to the discovery of galvanic electricity and the invention
of the galvanic battery, it may be regarded as the beginning of modern
electricity.

The story is told that Galvani was led to his discovery while preparing
frogs' legs to make a broth for his invalid wife. As the story runs, he
had removed the skins from several frogs' legs, when, happening to touch
the exposed muscles with a scalpel which had lain in close proximity to
an electrical machine, violent muscular action was produced. Impressed
with this phenomenon, he began a series of experiments which finally
resulted in his great discovery. But be this story authentic or not, it
is certain that Galvani experimented for several years upon frogs' legs
suspended upon wires and hooks, until he finally constructed his arc
of two different metals, which, when arranged so that one was placed
in contact with a nerve and the other with a muscle, produced violent
contractions.

These two pieces of metal form the basic principle of the modern
galvanic battery, and led directly to Alessandro Volta's invention
of his "voltaic pile," the immediate ancestor of the modern galvanic
battery. Volta's experiments were carried on at the same time as those
of Galvani, and his invention of his pile followed close upon Galvani's
discovery of the new form of electricity. From these facts the new form
of electricity was sometimes called "galvanic" and sometimes "voltaic"
electricity, but in recent years the term "galvanism" and "galvanic
current" have almost entirely supplanted the use of the term voltaic.

It was Volta who made the report of Galvani's wonderful discovery to
the Royal Society of London, read on January 31, 1793. In this letter he
describes Galvani's experiments in detail and refers to them in glowing
terms of praise. He calls it one of the "most beautiful and important
discoveries," and regarded it as the germ or foundation upon which other
discoveries were to be made. The prediction proved entirely correct,
Volta himself being the chief discoverer.

Working along lines suggested by Galvani's discovery, Volta constructed
an apparatus made up of a number of disks of two different kinds of
metal, such as tin and silver, arranged alternately, a piece of some
moist, porous substance, like paper or felt, being interposed between
each pair of disks. With this "pile," as it was called, electricity
was generated, and by linking together several such piles an electric
battery could be formed.

This invention took the world by storm. Nothing like the enthusiasm it
created in the philosophic world had been known since the invention
of the Leyden jar, more than half a century before. Within a few weeks
after Volta's announcement, batteries made according to his plan were
being experimented with in every important laboratory in Europe.

As the century closed, half the philosophic world was speculating as to
whether "galvanic influence" were a new imponderable, or only a form of
electricity; and the other half was eagerly seeking to discover what new
marvels the battery might reveal. The least imaginative man could see
that here was an invention that would be epoch-making, but the most
visionary dreamer could not even vaguely adumbrate the real measure of
its importance.

It was evident at once that almost any form of galvanic battery,
despite imperfections, was a more satisfactory instrument for generating
electricity than the frictional machine hitherto in use, the advantage
lying in the fact that the current from the galvanic battery could
be controlled practically at will, and that the apparatus itself
was inexpensive and required comparatively little attention. These
advantages were soon made apparent by the practical application of the
electric current in several fields.

It will be recalled that despite the energetic endeavors of such
philosophers as Watson, Franklin, Galvani, and many others, the field
of practical application of electricity was very limited at the close of
the eighteenth century. The lightning-rod had come into general use, to
be sure, and its value as an invention can hardly be overestimated. But
while it was the result of extensive electrical discoveries, and is
a most practical instrument, it can hardly be called one that puts
electricity to practical use, but simply acts as a means of warding
off the evil effects of a natural manifestation of electricity. The
invention, however, had all the effects of a mechanism which turned
electricity to practical account. But with the advent of the new kind of
electricity the age of practical application began.


DAVY AND ELECTRIC LIGHT

Volta's announcement of his pile was scarcely two months old when two
Englishmen, Messrs. Nicholson and Carlisle, made the discovery that
the current from the galvanic battery had a decided effect upon certain
chemicals, among other things decomposing water into its elements,
hydrogen and oxygen. On May 7, 1800, these investigators arranged the
ends of two brass wires connected with the poles of a voltaic pile,
composed of alternate silver and zinc plates, so that the current coming
from the pile was discharged through a small quantity of "New River
water." "A fine stream of minute bubbles immediately began to flow from
the point of the lower wire in the tube which communicated with the
silver," wrote Nicholson, "and the opposite point of the upper wire
became tarnished, first deep orange and then black...." The product of
gas during two hours and a half was two-thirtieths of a cubic inch.
"It was then mixed with an equal quantity of common air," continues
Nicholson, "and exploded by the application of a lighted waxen thread."

This demonstration was the beginning of the very important science of
electro-chemistry.

The importance of this discovery was at once recognized by Sir Humphry
Davy, who began experimenting immediately in this new field. He
constructed a series of batteries in various combinations, with which
he attacked the "fixed alkalies," the composition of which was then
unknown. Very shortly he was able to decompose potash into bright
metallic globules, resembling quicksilver. This new substance he named
"potassium." Then in rapid succession the elementary substances sodium,
calcium, strontium, and magnesium were isolated.

It was soon discovered, also, that the new electricity, like the old,
possessed heating power under certain conditions, even to the fusing of
pieces of wire. This observation was probably first made by Frommsdorff,
but it was elaborated by Davy, who constructed a battery of two thousand
cells with which he produced a bright light from points of carbon--the
prototype of the modern arc lamp. He made this demonstration before the
members of the Royal Institution in 1810. But the practical utility of
such a light for illuminating purposes was still a thing of the future.
The expense of constructing and maintaining such an elaborate battery,
and the rapid internal destruction of its plates, together with the
constant polarization, rendered its use in practical illumination out of
the question. It was not until another method of generating electricity
was discovered that Davy's demonstration could be turned to practical
account.

In Davy's own account of his experiment he says:

"When pieces of charcoal about an inch long and one-sixth of an inch in
diameter were brought near each other (within the thirtieth or fortieth
of an inch), a bright spark was produced, and more than half the volume
of the charcoal became ignited to whiteness; and, by withdrawing the
points from each other, a constant discharge took place through the
heated air, in a space equal to at least four inches, producing a most
brilliant ascending arch of light, broad and conical in form in the
middle. When any substance was introduced into this arch, it instantly
became ignited; platina melted as readily in it as wax in a common
candle; quartz, the sapphire, magnesia, lime, all entered into fusion;
fragments of diamond and points of charcoal and plumbago seemed to
evaporate in it, even when the connection was made in the receiver of an
air-pump; but there was no evidence of their having previously undergone
fusion. When the communication between the points positively and
negatively electrified was made in the air rarefied in the receiver of
the air-pump, the distance at which the discharge took place increased
as the exhaustion was made; and when the atmosphere in the vessel
supported only one-fourth of an inch of mercury in the barometrical
gauge, the sparks passed through a space of nearly half an inch; and, by
withdrawing the points from each other, the discharge was made through
six or seven inches, producing a most brilliant coruscation of purple
light; the charcoal became intensely ignited, and some platina wire
attached to it fused with brilliant scintillations and fell in large
globules upon the plate of the pump. All the phenomena of
chemical decomposition were produced with intense rapidity by this
combination."(1)

But this experiment demonstrated another thing besides the possibility
of producing electric light and chemical decomposition, this being the
heating power capable of being produced by the electric current. Thus
Davy's experiment of fusing substances laid the foundation of the modern
electric furnaces, which are of paramount importance in several great
commercial industries.

While some of the results obtained with Davy's batteries were
practically as satisfactory as could be obtained with modern cell
batteries, the batteries themselves were anything but satisfactory. They
were expensive, required constant care and attention, and, what was more
important from an experimental standpoint at least, were not constant in
their action except for a very limited period of time, the current soon
"running down." Numerous experimenters, therefore, set about devising a
satisfactory battery, and when, in 1836, John Frederick Daniell produced
the cell that bears his name, his invention was epoch-making in the
history of electrical progress. The Royal Society considered it of
sufficient importance to bestow the Copley medal upon the inventor,
whose device is the direct parent of all modern galvanic cells. From the
time of the advent of the Daniell cell experiments in electricity were
rendered comparatively easy. In the mean while, however, another great
discovery was made.


ELECTRICITY AND MAGNETISM

For many years there had been a growing suspicion, amounting in
many instances to belief in the close relationship existing between
electricity and magnetism. Before the winter of 1815, however, it was
a belief that was surmised but not demonstrated. But in that year it
occurred to Jean Christian Oersted, of Denmark, to pass a current of
electricity through a wire held parallel with, but not quite touching, a
suspended magnetic needle. The needle was instantly deflected and swung
out of its position.

"The first experiments in connection with the subject which I am
undertaking to explain," wrote Oersted, "were made during the course
of lectures which I held last winter on electricity and magnetism. From
those experiments it appeared that the magnetic needle could be moved
from its position by means of a galvanic battery--one with a closed
galvanic circuit. Since, however, those experiments were made with an
apparatus of small power, I undertook to repeat and increase them with a
large galvanic battery.

"Let us suppose that the two opposite ends of the galvanic apparatus are
joined by a metal wire. This I shall always call the conductor for
the sake of brevity. Place a rectilinear piece of this conductor in
a horizontal position over an ordinary magnetic needle so that it is
parallel to it. The magnetic needle will be set in motion and will
deviate towards the west under that part of the conductor which comes
from the negative pole of the galvanic battery. If the wire is not more
than four-fifths of an inch distant from the middle of this needle, this
deviation will be about forty-five degrees. At a greater distance
the angle of deviation becomes less. Moreover, the deviation varies
according to the strength of the battery. The conductor can be moved
towards the east or west, so long as it remains parallel to the needle,
without producing any other result than to make the deviation smaller.

"The conductor can consist of several combined wires or metal coils. The
nature of the metal does not alter the result except, perhaps, to make
it greater or less. We have used wires of platinum, gold, silver, brass,
and iron, and coils of lead, tin, and quicksilver with the same result.
If the conductor is interrupted by water, all effect is not cut off,
unless the stretch of water is several inches long.

"The conductor works on the magnetic needle through glass, metals, wood,
water, and resin, through clay vessels and through stone, for when we
placed a glass plate, a metal plate, or a board between the conductor
and the needle the effect was not cut off; even the three together
seemed hardly to weaken the effect, and the same was the case with an
earthen vessel, even when it was full of water. Our experiments also
demonstrated that the said effects were not altered when we used a
magnetic needle which was in a brass case full of water.

"When the conductor is placed in a horizontal plane under the magnetic
needle all the effects we have described take place in precisely the
same way, but in the opposite direction to what took place when the
conductor was in a horizontal plane above the needle.

"If the conductor is moved in a horizontal plane so that it gradually
makes ever-increasing angles with the magnetic meridian, the deviation
of the magnetic needle from the magnetic meridian is increased when the
wire is turned towards the place of the needle; it decreases, on the
other hand, when it is turned away from that place.

"A needle of brass which is hung in the same way as the magnetic needle
is not set in motion by the influence of the conductor. A needle of
glass or rubber likewise remains static under similar experiments. Hence
the electrical conductor affects only the magnetic parts of a substance.
That the electrical current is not confined to the conducting wire,
but is comparatively widely diffused in the surrounding space, is
sufficiently demonstrated from the foregoing observations."(2)


The effect of Oersted's demonstration is almost incomprehensible. By it
was shown the close relationship between magnetism and electricity. It
showed the way to the establishment of the science of electrodynamics;
although it was by the French savant Andre Marie Ampere (1775-1836) that
the science was actually created, and this within the space of one week
after hearing of Oersted's experiment in deflecting the needle. Ampere
first received the news of Oersted's experiment on September 11, 1820,
and on the 18th of the same month he announced to the Academy the
fundamental principles of the science of electro-dynamics--seven days of
rapid progress perhaps unequalled in the history of science.

Ampere's distinguished countryman, Arago, a few months later, gave
the finishing touches to Oersted's and Ampere's discoveries, by
demonstrating conclusively that electricity not only influenced a
magnet, but actually produced magnetism under proper circumstances--a
complemental fact most essential in practical mechanics.

Some four years after Arago's discovery, Sturgeon made the first
"electro-magnet" by winding a soft iron core with wire through which
a current of electricity was passed. This study of electro-magnets was
taken up by Professor Joseph Henry, of Albany, New York, who succeeded
in making magnets of enormous lifting power by winding the iron core
with several coils of wire. One of these magnets, excited by a single
galvanic cell of less than half a square foot of surface, and containing
only half a pint of dilute acids, sustained a weight of six hundred and
fifty pounds.

Thus by Oersted's great discovery of the intimate relationship of
magnetism and electricity, with further elaborations and discoveries by
Ampere, Volta, and Henry, and with the invention of Daniell's cell, the
way was laid for putting electricity to practical use. Soon followed the
invention and perfection of the electro-magnetic telegraph and a host of
other but little less important devices.


FARADAY AND ELECTRO-MAGNETIC INDUCTION

With these great discoveries and inventions at hand, electricity became
no longer a toy or a "plaything for philosophers," but of enormous
and growing importance commercially. Still, electricity generated
by chemical action, even in a very perfect cell, was both feeble and
expensive, and, withal, only applicable in a comparatively limited
field. Another important scientific discovery was necessary before such
things as electric traction and electric lighting on a large scale were
to become possible; but that discovery was soon made by Sir Michael
Faraday.

Faraday, the son of a blacksmith and a bookbinder by trade, had
interested Sir Humphry Davy by his admirable notes on four of Davy's
lectures, which he had been able to attend. Although advised by the
great scientist to "stick to his bookbinding" rather than enter the
field of science, Faraday became, at twenty-two years of age, Davy's
assistant in the Royal Institution. There, for several years, he devoted
all his spare hours to scientific investigations and experiments,
perfecting himself in scientific technique.

A few years later he became interested, like all the scientists of
the time, in Arago's experiment of rotating a copper disk underneath a
suspended compass-needle. When this disk was rotated rapidly, the
needle was deflected, or even rotated about its axis, in a manner quite
inexplicable. Faraday at once conceived the idea that the cause of this
rotation was due to electricity, induced in the revolving disk--not only
conceived it, but put his belief in writing. For several years, however,
he was unable to demonstrate the truth of his assumption, although he
made repeated experiments to prove it. But in 1831 he began a series
of experiments that established forever the fact of electro-magnetic
induction.

In his famous paper, read before the Royal Society in 1831, Faraday
describes the method by which he first demonstrated electro-magnetic
induction, and then explained the phenomenon of Arago's revolving disk.

"About twenty-six feet of copper wire, one-twentieth of an inch in
diameter, were wound round a cylinder of wood as a helix," he said,
"the different spires of which were prevented from touching by a thin
interposed twine. This helix was covered with calico, and then a
second wire applied in the same manner. In this way twelve helices were
"superposed, each containing an average length of wire of twenty-seven
feet, and all in the same direction. The first, third, fifth, seventh,
ninth, and eleventh of these helices were connected at their extremities
end to end so as to form one helix; the others were connected in a
similar manner; and thus two principal helices were produced, closely
interposed, having the same direction, not touching anywhere, and each
containing one hundred and fifty-five feet in length of wire.

One of these helices was connected with a galvanometer, the other with
a voltaic battery of ten pairs of plates four inches square, with double
coppers and well charged; yet not the slightest sensible deflection of
the galvanometer needle could be observed.

"A similar compound helix, consisting of six lengths of copper and six
of soft iron wire, was constructed. The resulting iron helix contained
two hundred and eight feet; but whether the current from the trough was
passed through the copper or the iron helix, no effect upon the other
could be perceived at the galvanometer.

"In these and many similar experiments no difference in action of any
kind appeared between iron and other metals.

"Two hundred and three feet of copper wire in one length were passed
round a large block of wood; other two hundred and three feet of similar
wire were interposed as a spiral between the turns of the first, and
metallic contact everywhere prevented by twine. One of these helices was
connected with a galvanometer and the other with a battery of a hundred
pairs of plates four inches square, with double coppers and well
charged. When the contact was made, there was a sudden and very slight
effect at the galvanometer, and there was also a similar slight effect
when the contact with the battery was broken. But whilst the voltaic
current was continuing to pass through the one helix, no galvanometrical
appearances of any effect like induction upon the other helix could be
perceived, although the active power of the battery was proved to be
great by its heating the whole of its own helix, and by the brilliancy
of the discharge when made through charcoal.

"Repetition of the experiments with a battery of one hundred and twenty
pairs of plates produced no other effects; but it was ascertained, both
at this and at the former time, that the slight deflection of the needle
occurring at the moment of completing the connection was always in one
direction, and that the equally slight deflection produced when the
contact was broken was in the other direction; and, also, that these
effects occurred when the first helices were used.

"The results which I had by this time obtained with magnets led me
to believe that the battery current through one wire did, in reality,
induce a similar current through the other wire, but that it continued
for an instant only, and partook more of the nature of the electrical
wave passed through from the shock of a common Leyden jar than of that
from a voltaic battery, and, therefore, might magnetize a steel needle
although it scarcely affected the galvanometer.

"This expectation was confirmed; for on substituting a small hollow
helix, formed round a glass tube, for the galvanometer, introducing
a steel needle, making contact as before between the battery and the
inducing wire, and then removing the needle before the battery contact
was broken, it was found magnetized.

"When the battery contact was first made, then an unmagnetized needle
introduced, and lastly the battery contact broken, the needle was found
magnetized to an equal degree apparently with the first; but the poles
were of the contrary kinds."(3)

To Faraday these experiments explained the phenomenon of Arago's
rotating disk, the disk inducing the current from the magnet, and, in
reacting, deflecting the needle. To prove this, he constructed a disk
that revolved between the poles of an electro-magnet, connecting the
axis and the edge of the disk with a galvanometer. "... A disk of
copper, twelve inches in diameter, fixed upon a brass axis," he says,
"was mounted in frames so as to be revolved either vertically or
horizontally, its edge being at the same time introduced more or less
between the magnetic poles. The edge of the plate was well amalgamated
for the purpose of obtaining good but movable contact; a part round the
axis was also prepared in a similar manner.

"Conductors or collectors of copper and lead were constructed so as to
come in contact with the edge of the copper disk, or with other forms
of plates hereafter to be described. These conductors we're about four
inches long, one-third of an inch wide, and one-fifth of an inch thick;
one end of each was slightly grooved, to allow of more exact adaptation
to the somewhat convex edge of the plates, and then amalgamated. Copper
wires, one-sixteenth of an inch in thickness, attached in the ordinary
manner by convolutions to the other ends of these conductors, passed
away to the galvanometer.

"All these arrangements being made, the copper disk was adjusted, the
small magnetic poles being about one-half an inch apart, and the edge
of the plate inserted about half their width between them. One of the
galvanometer wires was passed twice or thrice loosely round the brass
axis of the plate, and the other attached to a conductor, which itself
was retained by the hand in contact with the amalgamated edge of the
disk at the part immediately between the magnetic poles. Under these
circumstances all was quiescent, and the galvanometer exhibited no
effect. But the instant the plate moved the galvanometer was influenced,
and by revolving the plate quickly the needle could be deflected ninety
degrees or more."(4)


This rotating disk was really a dynamo electric machine in miniature,
the first ever constructed, but whose direct descendants are the
ordinary dynamos. Modern dynamos range in power from little machines
operating machinery requiring only fractions of a horsepower to great
dynamos operating street-car lines and lighting cities; but all
are built on the same principle as Faraday's rotating disk. By this
discovery the use of electricity as a practical and economical motive
power became possible.


STORAGE BATTERIES

When the discoveries of Faraday of electro-magnetic induction had made
possible the means of easily generating electricity, the next natural
step was to find a means of storing it or accumulating it. This,
however, proved no easy matter, and as yet a practical storage or
secondary battery that is neither too cumbersome, too fragile, nor too
weak in its action has not been invented. If a satisfactory storage
battery could be made, it is obvious that its revolutionary effects
could scarcely be overestimated. In the single field of aeronautics, it
would probably solve the question of aerial navigation. Little wonder,
then, that inventors have sought so eagerly for the invention of
satisfactory storage batteries. As early as 1803 Ritter had attempted to
make such a secondary battery. In 1843 Grove also attempted it. But it
was not until 1859, when Gaston Planche produced his invention, that
anything like a reasonably satisfactory storage battery was made.
Planche discovered that sheets of lead immersed in dilute sulphuric acid
were very satisfactory for the production of polarization effects. He
constructed a battery of sheets of lead immersed in sulphuric acid, and,
after charging these for several hours from the cells of an ordinary
Bunsen battery, was able to get currents of great strength and
considerable duration. This battery, however, from its construction of
lead, was necessarily heavy and cumbersome. Faure improved it somewhat
by coating the lead plates with red-lead, thus increasing the capacity
of the cell. Faure's invention gave a fresh impetus to inventors, and
shortly after the market was filled with storage batteries of various
kinds, most of them modifications of Planche's or Faure's. The ardor
of enthusiastic inventors soon flagged, however, for all these storage
batteries proved of little practical account in the end, as compared
with other known methods of generating power.

Three methods of generating electricity are in general use: static or
frictional electricity is generated by "plate" or "static" machines;
galvanic, generated by batteries based on Volta's discovery; and
induced, or faradic, generated either by chemical or mechanical action.
There is still another kind, thermo-electricity, that may be generated
in a most simple manner. In 1821 Seebecle, of Berlin, discovered that
when a circuit was formed of two wires of different metals, if there
be a difference in temperature at the juncture of these two metals
an electrical current will be established. In this way heat may
be transmitted directly into the energy of the current without the
interposition of the steam-engine. Batteries constructed in this way
are of low resistance, however, although by arranging several of them
in "series," currents of considerable strength can be generated. As yet,
however, they are of little practical importance.

About the middle of the century Clerk-Maxwell advanced the idea that
light waves were really electro-magnetic waves. If this were true and
light proved to be simply one form of electrical energy, then the same
would be true of radiant heat. Maxwell advanced this theory, but failed
to substantiate it by experimental confirmation. But Dr. Heinrich
Hertz, a few years later, by a series of experiments, demonstrated the
correctness of Maxwell's surmises. What are now called "Hertzian waves"
are waves apparently identical with light waves, but of much lower
pitch or period. In his experiments Hertz showed that, under proper
conditions, electric sparks between polished balls were attended by
ether waves of the same nature as those of light, but of a pitch of
several millions of vibrations per second. These waves could be dealt
with as if they were light waves--reflected, refracted, and polarized.
These are the waves that are utilized in wireless telegraphy.


ROENTGEN RAYS, OR X-RAYS

In December of 1895 word came out of Germany of a scientific discovery
that startled the world. It came first as a rumor, little credited; then
as a pronounced report; at last as a demonstration. It told of a new
manifestation of energy, in virtue of which the interior of opaque
objects is made visible to human eyes. One had only to look into a tube
containing a screen of a certain composition, and directed towards
a peculiar electrical apparatus, to acquire clairvoyant vision more
wonderful than the discredited second-sight of the medium. Coins within
a purse, nails driven into wood, spectacles within a leather case,
became clearly visible when subjected to the influence of this magic
tube; and when a human hand was held before the tube, its bones stood
revealed in weird simplicity, as if the living, palpitating flesh about
them were but the shadowy substance of a ghost.

Not only could the human eye see these astounding revelations, but the
impartial evidence of inanimate chemicals could be brought forward to
prove that the mind harbored no illusion. The photographic film recorded
the things that the eye might see, and ghostly pictures galore soon gave
a quietus to the doubts of the most sceptical. Within a month of the
announcement of Professor Roentgen's experiments comment upon the
"X-ray" and the "new photography" had become a part of the current
gossip of all Christendom.

It is hardly necessary to say that such a revolutionary thing as the
discovery of a process whereby opaque objects became transparent, or
translucent, was not achieved at a single bound with no intermediate
discoveries. In 1859 the German physicist Julius Plucker (1801-1868)
noticed that when there was an electrical discharge through an exhausted
tube at a low pressure, on the surrounding walls of the tube near the
negative pole, or cathode, appeared a greenish phosphorescence. This
discovery was soon being investigated by a number of other scientists,
among others Hittorf, Goldstein, and Professor (now Sir William)
Crookes. The explanations given of this phenomenon by Professor Crookes
concern us here more particularly, inasmuch as his views did not
accord exactly with those held by the other two scientists, and as his
researches were more directly concerned in the discovery of the
Roentgen rays. He held that the heat and phosphorescence produced in a
low-pressure tube were caused by streams of particles, projected from
the cathode with great velocity, striking the sides of the glass tube.
The composition of the glass seemed to enter into this phosphorescence
also, for while lead glass produced blue phosphorescence, soda glass
produced a yellowish green. The composition of the glass seemed to
be changed by a long-continued pelting of these particles, the
phosphorescence after a time losing its initial brilliancy, caused by
the glass becoming "tired," as Professor Crookes said. Thus when some
opaque substance, such as iron, is placed between the cathode and the
sides of the glass tube so that it casts a shadow in a certain spot
on the glass for some little time, it is found on removing the opaque
substance or changing its position that the area of glass at first
covered by the shadow now responded to the rays in a different manner
from the surrounding glass.

The peculiar ray's, now known as the cathode rays, not only cast a
shadow, but are deflected by a magnet, so that the position of the
phosphorescence on the sides of the tube may be altered by the proximity
of a powerful magnet. From this it would seem that the rays are composed
of particles charged with negative electricity, and Professor J. J.
Thomson has modified the experiment of Perrin to show that negative
electricity is actually associated with the rays. There is reason for
believing, therefore, that the cathode rays are rapidly moving charges
of negative electricity. It is possible, also, to determine the velocity
at which these particles are moving by measuring the deflection produced
by the magnetic field.

From the fact that opaque substances cast a shadow in these rays it was
thought at first that all solids were absolutely opaque to them. Hertz,
however, discovered that a small amount of phosphorescence occurred on
the glass even when such opaque substances as gold-leaf or aluminium
foil were interposed between the cathode and the sides of the tube.
Shortly afterwards Lenard discovered that the cathode rays can be made
to pass from the inside of a discharge tube to the outside air. For
convenience these rays outside the tube have since been known as "Lenard
rays."

In the closing days of December, 1895, Professor Wilhelm Konrad
Roentgen, of Wurzburg, announced that he had made the discovery of the
remarkable effect arising from the cathode rays to which reference
was made above. He found that if a plate covered with a phosphorescent
substance is placed near a discharge tube exhausted so highly that the
cathode rays produced a green phosphorescence, this plate is made to
glow in a peculiar manner. The rays producing this glow were not the
cathode rays, although apparently arising from them, and are what have
since been called the Roentgen rays, or X-rays.

Roentgen found that a shadow is thrown upon the screen by substances
held between it and the exhausted tube, the character of the shadow
depending upon the density of the substance. Thus metals are almost
completely opaque to the rays; such substances as bone much less so, and
ordinary flesh hardly so at all. If a coin were held in the hand that
had been interposed between the tube and the screen the picture formed
showed the coin as a black shadow; and the bones of the hand, while
casting a distinct shadow, showed distinctly lighter; while the soft
tissues produced scarcely any shadow at all. The value of such a
discovery was obvious from the first; and was still further enhanced by
the discovery made shortly that, photographic plates are affected by the
rays, thus making it possible to make permanent photographic records of
pictures through what we know as opaque substances.

What adds materially to the practical value of Roentgen's discovery is
the fact that the apparatus for producing the X-rays is now so simple
and relatively inexpensive that it is within the reach even of amateur
scientists. It consists essentially of an induction coil attached either
to cells or a street-current plug for generating the electricity, a
focus tube, and a phosphorescence screen. These focus tubes are made in
various shapes, but perhaps the most popular are in the form of a glass
globe, not unlike an ordinary small-sized water-bottle, this tube being
closed and exhausted, and having the two poles (anode and cathode)
sealed into the glass walls, but protruding at either end for attachment
to the conducting wires from the induction coil. This tube may be
mounted on a stand at a height convenient for manipulation.
The phosphorescence screen is usually a plate covered with some
platino-cyanide and mounted in the end of a box of convenient size, the
opposite end of which is so shaped that it fits the contour of the face,
shutting out the light and allowing the eyes of the observer to focalize
on the screen at the end. For making observations the operator has
simply to turn on the current of electricity and apply the screen to
his eyes, pointing it towards the glowing tube, when the shadow of any
substance interposed between the tube and the screen will appear upon
the phosphorescence plate.

The wonderful shadow pictures produced on the phosphorescence screen,
or the photographic plate, would seem to come from some peculiar form
of light, but the exact nature of these rays is still an open question.
Whether the Roentgen rays are really a form of light--that is, a form
of "electro-magnetic disturbance propagated through ether," is not fully
determined. Numerous experiments have been undertaken to determine this,
but as yet no proof has been found that the rays are a form of light,
although there appears to be nothing in their properties inconsistent
with their being so. For the moment most investigators are content to
admit that the term X-ray virtually begs the question as to the intimate
nature of the form of energy involved.



VIII. THE CONSERVATION OF ENERGY


As we have seen, it was in 1831 that Faraday opened up the field of
magneto-electricity. Reversing the experiments of his predecessors, who
had found that electric currents may generate magnetism, he showed that
magnets have power under certain circumstances to generate electricity;
he proved, indeed, the interconvertibility of electricity and magnetism.
Then he showed that all bodies are more or less subject to the influence
of magnetism, and that even light may be affected by magnetism as to its
phenomena of polarization. He satisfied himself completely of the
true identity of all the various forms of electricity, and of the
convertibility of electricity and chemical action. Thus he linked
together light, chemical affinity, magnetism, and electricity. And,
moreover, he knew full well that no one of these can be produced in
indefinite supply from another. "Nowhere," he says, "is there a pure
creation or production of power without a corresponding exhaustion of
something to supply it."

When Faraday wrote those words in 1840 he was treading on the very heels
of a greater generalization than any which he actually formulated; nay,
he had it fairly within his reach. He saw a great truth without fully
realizing its import; it was left for others, approaching the same truth
along another path, to point out its full significance.

The great generalization which Faraday so narrowly missed is the truth
which since then has become familiar as the doctrine of the conservation
of energy--the law that in transforming energy from one condition to
another we can never secure more than an equivalent quantity; that, in
short, "to create or annihilate energy is as impossible as to create or
annihilate matter; and that all the phenomena of the material universe
consist in transformations of energy alone." Some philosophers think
this the greatest generalization ever conceived by the mind of man. Be
that as it may, it is surely one of the great intellectual landmarks
of the nineteenth century. It stands apart, so stupendous and so
far-reaching in its implications that the generation which first saw the
law developed could little appreciate it; only now, through the vista of
half a century, do we begin to see it in its true proportions.

A vast generalization such as this is never a mushroom growth, nor does
it usually spring full grown from the mind of any single man. Always a
number of minds are very near a truth before any one mind fully grasps
it. Pre-eminently true is this of the doctrine of the conservation of
energy. Not Faraday alone, but half a dozen different men had an inkling
of it before it gained full expression; indeed, every man who advocated
the undulatory theory of light and heat was verging towards the goal.
The doctrine of Young and Fresnel was as a highway leading surely on
to the wide plain of conservation. The phenomena of electro-magnetism
furnished another such highway. But there was yet another road which led
just as surely and even more readily to the same goal. This was the road
furnished by the phenomena of heat, and the men who travelled it were
destined to outstrip their fellow-workers; though, as we have seen,
wayfarers on other roads were within hailing distance when the leaders
passed the mark.

In order to do even approximate justice to the men who entered into
the great achievement, we must recall that just at the close of the
eighteenth century Count Rumford and Humphry Davy independently showed
that labor may be transformed into heat; and correctly interpreted this
fact as meaning the transformation of molar into molecular motion. We
can hardly doubt that each of these men of genius realized--vaguely, at
any rate--that there must be a close correspondence between the amount
of the molar and the molecular motions; hence that each of them was in
sight of the law of the mechanical equivalent of heat. But neither of
them quite grasped or explicitly stated what each must vaguely have
seen; and for just a quarter of a century no one else even came abreast
their line of thought, let alone passing it.

But then, in 1824, a French philosopher, Sadi Carnot, caught step with
the great Englishmen, and took a long leap ahead by explicitly stating
his belief that a definite quantity of work could be transformed into
a definite quantity of heat, no more, no less. Carnot did not, indeed,
reach the clear view of his predecessors as to the nature of heat, for
he still thought it a form of "imponderable" fluid; but he reasoned none
the less clearly as to its mutual convertibility with mechanical work.
But important as his conclusions seem now that we look back upon
them with clearer vision, they made no impression whatever upon his
contemporaries. Carnot's work in this line was an isolated phenomenon
of historical interest, but it did not enter into the scheme of the
completed narrative in any such way as did the work of Rumford and Davy.

The man who really took up the broken thread where Rumford and Davy had
dropped it, and wove it into a completed texture, came upon the scene
in 1840. His home was in Manchester, England; his occupation that of
a manufacturer. He was a friend and pupil of the great Dr. Dalton.
His name was James Prescott Joule. When posterity has done its final
juggling with the names of the nineteenth century, it is not unlikely
that the name of this Manchester philosopher will be a household word,
like the names of Aristotle, Copernicus, and Newton.

For Joule's work it was, done in the fifth decade of the century, which
demonstrated beyond all cavil that there is a precise and absolute
equivalence between mechanical work and heat; that whatever the form of
manifestation of molar motion, it can generate a definite and measurable
amount of heat, and no more. Joule found, for example, that at the
sea-level in Manchester a pound weight falling through seven hundred and
seventy-two feet could generate enough heat to raise the temperature
of a pound of water one degree Fahrenheit. There was nothing haphazard,
nothing accidental, about this; it bore the stamp of unalterable law.
And Joule himself saw, what others in time were made to see, that this
truth is merely a particular case within a more general law. If
heat cannot be in any sense created, but only made manifest as a
transformation of another kind of motion, then must not the same
thing be true of all those other forms of "force"--light, electricity,
magnetism--which had been shown to be so closely associated, so mutually
convertible, with heat? All analogy seemed to urge the truth of
this inference; all experiment tended to confirm it. The law of the
mechanical equivalent of heat then became the main corner-stone of the
greater law of the conservation of energy.

But while this citation is fresh in mind, we must turn our attention
with all haste to a country across the Channel--to Denmark, in
short--and learn that even as Joule experimented with the transformation
of heat, a philosopher of Copenhagen, Colding by name, had hit upon the
same idea, and carried it far towards a demonstration. And then, without
pausing, we must shift yet again, this time to Germany, and consider the
work of three other men, who independently were on the track of the same
truth, and two of whom, it must be admitted, reached it earlier than
either Joule or Colding, if neither brought it to quite so clear a
demonstration. The names of these three Germans are Mohr, Mayer,
and Helmholtz. Their share in establishing the great doctrine of
conservation must now claim our attention.

As to Karl Friedrich Mohr, it may be said that his statement of the
doctrine preceded that of any of his fellows, yet that otherwise it was
perhaps least important. In 1837 this thoughtful German had grasped
the main truth, and given it expression in an article published in the
Zeitschrift fur Physik, etc. But the article attracted no attention
whatever, even from Mohr's own countrymen. Still, Mohr's title to
rank as one who independently conceived the great truth, and perhaps
conceived it before any other man in the world saw it as clearly, even
though he did not demonstrate its validity, is not to be disputed.

It was just five years later, in 1842, that Dr. Julius Robert Mayer,
practising physician in the little German town of Heilbronn, published a
paper in Liebig's Annalen on "The Forces of Inorganic Nature," in which
not merely the mechanical theory of heat, but the entire doctrine of
the conservation of energy, is explicitly if briefly stated. Two years
earlier Dr. Mayer, while surgeon to a Dutch India vessel cruising in the
tropics, had observed that the venous blood of a patient seemed redder
than venous blood usually is observed to be in temperate climates. He
pondered over this seemingly insignificant fact, and at last reached
the conclusion that the cause must be the lesser amount of oxidation
required to keep up the body temperature in the tropics. Led by this
reflection to consider the body as a machine dependent on outside forces
for its capacity to act, he passed on into a novel realm of thought,
which brought him at last to independent discovery of the mechanical
theory of heat, and to the first full and comprehensive appreciation
of the great law of conservation. Blood-letting, the modern physician
holds, was a practice of very doubtful benefit, as a rule, to the
subject; but once, at least, it led to marvellous results. No straw is
go small that it may not point the receptive mind of genius to new and
wonderful truths.


MAYER'S PAPER OF 1842

The paper in which Mayer first gave expression to his revolutionary
ideas bore the title of "The Forces of Inorganic Nature," and was
published in 1842. It is one of the gems of scientific literature, and
fortunately it is not too long to be quoted in its entirety. Seldom if
ever was a great revolutionary doctrine expounded in briefer compass:

"What are we to understand by 'forces'? and how are different forces
related to each other? The term force conveys for the most part the idea
of something unknown, unsearchable, and hypothetical; while the term
matter, on the other hand, implies the possession, by the object in
question, of such definite properties as weight and extension. An
attempt, therefore, to render the idea of force equally exact with that
of matter is one which should be welcomed by all those who desire to
have their views of nature clear and unencumbered by hypothesis.

"Forces are causes; and accordingly we may make full application in
relation to them of the principle causa aequat effectum. If the cause
c has the effect e, then c = e; if, in its turn, e is the cause of a
second effect of f, we have e = f, and so on: c = e = f... = c. In a
series of causes and effects, a term or a part of a term can never, as
is apparent from the nature of an equation, become equal to nothing.
This first property of all causes we call their indestructibility.

"If the given cause c has produced an effect e equal to itself, it has
in that very act ceased to be--c has become e. If, after the production
of e, c still remained in the whole or in part, there must be still
further effects corresponding to this remaining cause: the total effect
of c would thus be > e, which would be contrary to the supposition c =
e. Accordingly, since c becomes e, and e becomes f, etc., we must regard
these various magnitudes as different forms under which one and the same
object makes its appearance. This capability of assuming various forms
is the second essential property of all causes. Taking both properties
together, we may say, causes an INDESTRUCTIBLE quantitatively, and
quantitatively CONVERTIBLE objects.

"There occur in nature two causes which apparently never pass one into
the other," said Mayer. "The first class consists of such causes as
possess the properties of weight and impenetrability. These are kinds of
matter. The other class is composed of causes which are wanting in the
properties just mentioned--namely, forces, called also imponderables,
from the negative property that has been indicated. Forces are therefore
INDESTRUCTIBLE, CONVERTIBLE, IMPONDERABLE OBJECTS.

"As an example of causes and effects, take matter: explosive gas, H + O,
and water, HO, are related to each other as cause and effect; therefore
H + O = HO. But if H + O becomes HO, heat, cal., makes its appearance
as well as water; this heat must likewise have a cause, x, and we have
therefore H + O + X = HO + cal. It might be asked, however, whether H
+ O is really = HO, and x = cal., and not perhaps H + O = cal., and x =
HO, whence the above equation could equally be deduced; and so in many
other cases. The phlogistic chemists recognized the equation between
cal. and x, or phlogiston as they called it, and in so doing made a
great step in advance; but they involved themselves again in a system of
mistakes by putting x in place of O. In this way they obtained H = HO +
x.

"Chemistry teaches us that matter, as a cause, has matter for its
effect; but we may say with equal justification that to force as a cause
corresponds force as effect. Since c = e, and e = c, it is natural to
call one term of an equation a force, and the other an effect of force,
or phenomenon, and to attach different notions to the expression force
and phenomenon. In brief, then, if the cause is matter, the effect is
matter; if the cause is a force, the effect is also a force.

"The cause that brings about the raising of a weight is a force. The
effect of the raised weight is, therefore, also a force; or, expressed
in a more general form, SEPARATION IN SPACE OF PONDERABLE OBJECTS IS
A FORCE; and since this force causes the fall of bodies, we call it
FALLING FORCE. Falling force and fall, or, still more generally,
falling force and motion, are forces related to each other as cause and
effect--forces convertible into each other--two different forms of one
and the same object. For example, a weight resting on the ground is not
a force: it is neither the cause of motion nor of the lifting of another
weight. It becomes so, however, in proportion as it is raised above the
ground. The cause--that is, the distance between a weight and the earth,
and the effect, or the quantity of motion produced, bear to each other,
as shown by mechanics, a constant relation.

"Gravity being regarded as the cause of the falling of bodies, a
gravitating force is spoken of; and thus the ideas of PROPERTY and
of FORCE are confounded with each other. Precisely that which is
the essential attribute of every force--that is, the UNION of
indestructibility with convertibility--is wanting in every property:
between a property and a force, between gravity and motion, it is
therefore impossible to establish the equation required for a rightly
conceived causal relation. If gravity be called a force, a cause
is supposed which produces effects without itself diminishing, and
incorrect conceptions of the causal connections of things are thereby
fostered. In order that a body may fall, it is just as necessary that it
be lifted up as that it should be heavy or possess gravity. The fall of
bodies, therefore, ought not to be ascribed to their gravity alone. The
problem of mechanics is to develop the equations which subsist between
falling force and motion, motion and falling force, and between
different motions. Here is a case in point: The magnitude of the falling
force v is directly proportional (the earth's radius being assumed--oo)
to the magnitude of the mass m, and the height d, to which it is
raised--that is, v = md. If the height d = l, to which the mass m is
raised, is transformed into the final velocity c = l of this mass, we
have also v = mc; but from the known relations existing between d and c,
it results that, for other values of d or of c, the measure of the
force v is mc squared; accordingly v = md = mcsquared. The law of the
conservation of vis viva is thus found to be based on the general law of
the indestructibility of causes.

"In many cases we see motion cease without having caused another motion
or the lifting of a weight. But a force once in existence cannot be
annihilated--it can only change its form. And the question therefore
arises, what other forms is force, which we have become acquainted with
as falling force and motion, capable of assuming? Experience alone
can lead us to a conclusion on this point. That we may experiment to
advantage, we must select implements which, besides causing a real
cessation of motion, are as little as possible altered by the objects
to be examined. For example, if we rub together two metal plates, we see
motion disappear, and heat, on the other hand, make its appearance, and
there remains to be determined only whether MOTION is the cause of heat.
In order to reach a decision on this point, we must discuss the question
whether, in the numberless cases in which the expenditure of motion is
accompanied by the appearance of heat, the motion has not some other
effect than the production of heat, and the heat some other cause than
the motion.

"A serious attempt to ascertain the effects of ceasing motion has never
been made. Without wishing to exclude a priori the hypothesis which
it may be possible to establish, therefore, we observe only that, as a
rule, this effect cannot be supposed to be an alteration in the state of
aggregation of the moved (that is, rubbing, etc.) bodies. If we assume
that a certain quantity of motion v is expended in the conversion of a
rubbing substance m into n, we must then have m + v - n, and n = m + v;
and when n is reconverted into m, v must appear again in some form or
other.

"By the friction of two metallic plates continued for a very long time,
we can gradually cause the cessation of an immense quantity of movement;
but would it ever occur to us to look for even the smallest trace of the
force which has disappeared in the metallic dust that we could collect,
and to try to regain it thence? We repeat, the motion cannot have been
annihilated; and contrary, or positive and negative, motions cannot be
regarded as = o any more than contrary motions can come out of nothing,
or a weight can raise itself.

"Without the recognition of a causal relation between motion and heat,
it is just as difficult to explain the production of heat as it is
to give any account of the motion that disappears. The heat cannot be
derived from the diminution of the volume of the rubbing substances.
It is well known that two pieces of ice may be melted by rubbing them
together in vacuo; but let any one try to convert ice into water by
pressure, however enormous. The author has found that water undergoes
a rise of temperature when shaken violently. The water so heated (from
twelve to thirteen degrees centigrade) has a greater bulk after being
shaken than it had before. Whence now comes this quantity of heat, which
by repeated shaking may be called into existence in the same apparatus
as often as we please? The vibratory hypothesis of heat is an approach
towards the doctrine of heat being the effect of motion, but it does not
favor the admission of this causal relation in its full generality. It
rather lays the chief stress on restless oscillations.

"If it be considered as now established that in many cases no other
effect of motion can be traced except heat, and that no other cause
than motion can be found for the heat that is produced, we prefer the
assumption that heat proceeds from motion to the assumption of a cause
without effect and of an effect without a cause. Just as the chemist,
instead of allowing oxygen and hydrogen to disappear without further
investigation, and water to be produced in some inexplicable manner,
establishes a connection between oxygen and hydrogen on the one hand,
and water on the other.

"We may conceive the natural connection existing between falling force,
motion, and heat as follows: We know that heat makes its appearance
when the separate particles of a body approach nearer to each other;
condensation produces heat. And what applies to the smallest particles
of matter, and the smallest intervals between them, must also apply to
large masses and to measurable distances. The falling of a weight is a
diminution of the bulk of the earth, and must therefore without doubt be
related to the quantity of heat thereby developed; this quantity of heat
must be proportional to the greatness of the weight and its distance
from the ground. From this point of view we are easily led to the
equations between falling force, motion, and heat that have already been
discussed.

"But just as little as the connection between falling force and motion
authorizes the conclusion that the essence of falling force is motion,
can such a conclusion be adopted in the case of heat. We are, on the
contrary, rather inclined to infer that, before it can become heat,
motion must cease to exist as motion, whether simple, or vibratory, as
in the case of light and radiant heat, etc.

"If falling force and motion are equivalent to heat, heat must also
naturally be equivalent to motion and falling force. Just as heat
appears as an EFFECT of the diminution of bulk and of the cessation
of motion, so also does heat disappear as a CAUSE when its effects are
produced in the shape of motion, expansion, or raising of weight.

"In water-mills the continual diminution in bulk which the earth
undergoes, owing to the fall of the water, gives rise to motion, which
afterwards disappears again, calling forth unceasingly a great quantity
of heat; and, inversely, the steam-engine serves to decompose heat again
into motion or the raising of weights. A locomotive with its train may
be compared to a distilling apparatus; the heat applied under the boiler
passes off as motion, and this is deposited again as heat at the axles
of the wheels."

Mayer then closes his paper with the following deduction: "The solution
of the equations subsisting between falling force and motion requires
that the space fallen through in a given time--e. g., the first
second--should be experimentally determined. In like manner, the
solution of the equations subsisting between falling force and motion on
the one hand and heat on the other requires an answer to the question,
How great is the quantity of heat which corresponds to a given quantity
of motion or falling force? For instance, we must ascertain how high a
given weight requires to be raised above the ground in order that its
falling force maybe equivalent to the raising of the temperature of
an equal weight of water from 0 degrees to 1 degrees centigrade. The
attempt to show that such an equation is the expression of a physical
truth may be regarded as the substance of the foregoing remarks.

"By applying the principles that have been set forth to the relations
subsisting between the temperature and the volume of gases, we find
that the sinking of a mercury column by which a gas is compressed is
equivalent to the quantity of heat set free by the compression; and
hence it follows, the ratio between the capacity for heat of air under
constant pressure and its capacity under constant volume being taken as
= 1.421, that the warming of a given weight of water from 0 degrees to
 equal weight from the height of about three hundred and sixty-five
metres. If we compare with this result the working of our best
steam-engines, we see how small a part only of the heat applied under
the boiler is really transformed into motion or the raising of weights;
and this may serve as justification for the attempts at the profitable
production of motion by some other method than the expenditure of the
chemical difference between carbon and oxygen--more particularly by
the transformation into motion of electricity obtained by chemical
means."(1)


MAYER AND HELMHOLTZ

Here, then, was this obscure German physician, leading the humdrum life
of a village practitioner, yet seeing such visions as no human being in
the world had ever seen before.

The great principle he had discovered became the dominating thought of
his life, and filled all his leisure hours. He applied it far and wide,
amid all the phenomena of the inorganic and organic worlds. It taught
him that both vegetables and animals are machines, bound by the same
laws that hold sway over inorganic matter, transforming energy, but
creating nothing. Then his mind reached out into space and met a
universe made up of questions. Each star that blinked down at him as he
rode in answer to a night-call seemed an interrogation-point asking,
How do I exist? Why have I not long since burned out if your theory
of conservation be true? No one had hitherto even tried to answer that
question; few had so much as realized that it demanded an answer. But
the Heilbronn physician understood the question and found an answer.
His meteoric hypothesis, published in 1848, gave for the first time a
tenable explanation of the persistent light and heat of our sun and the
myriad other suns--an explanation to which we shall recur in another
connection.

All this time our isolated philosopher, his brain aflame with the glow
of creative thought, was quite unaware that any one else in the world
was working along the same lines. And the outside world was equally
heedless of the work of the Heilbronn physician. There was no friend to
inspire enthusiasm and give courage, no kindred spirit to react on this
masterful but lonely mind. And this is the more remarkable because there
are few other cases where a master-originator in science has come upon
the scene except as the pupil or friend of some other master-originator.
Of the men we have noticed in the present connection, Young was the
friend and confrere of Davy; Davy, the protege of Rumford; Faraday, the
pupil of Davy; Fresnel, the co-worker with Arago; Colding, the confrere
of Oersted; Joule, the pupil of Dalton. But Mayer is an isolated
phenomenon--one of the lone mountain-peak intellects of the century.
That estimate may be exaggerated which has called him the Galileo of the
nineteenth century, but surely no lukewarm praise can do him justice.

Yet for a long time his work attracted no attention whatever. In 1847,
when another German physician, Hermann von Helmholtz, one of the most
massive and towering intellects of any age, had been independently
led to comprehension of the doctrine of the conservation of energy
and published his treatise on the subject, he had hardly heard of his
countryman Mayer. When he did hear of him, however, he hastened to
renounce all claim to the doctrine of conservation, though the world at
large gives him credit of independent even though subsequent discovery.


JOULE'S PAPER OF 1843

Meantime, in England, Joule was going on from one experimental
demonstration to another, oblivious of his German competitors and almost
as little noticed by his own countrymen. He read his first paper before
the chemical section of the British Association for the Advancement of
Science in 1843, and no one heeded it in the least. It is well worth our
while, however, to consider it at length. It bears the title, "On the
Calorific Effects of Magneto-Electricity, and the Mechanical Value
of Heat." The full text, as published in the Report of the British
Association, is as follows:

"Although it has been long known that fine platinum wire can be ignited
by magneto-electricity, it still remained a matter of doubt whether heat
was evolved by the COILS in which the magneto-electricity was generated;
and it seemed indeed not unreasonable to suppose that COLD was produced
there in order to make up for the heat evolved by the other part of
the circuit. The author therefore has endeavored to clear up this
uncertainty by experiment. His apparatus consisted of a small compound
electro-magnet, immersed in water, revolving between the poles of a
powerful stationary magnet. The magneto-electricity developed in the
coils of the revolving electro-magnet was measured by an accurate
galvanometer; and the temperature of the water was taken before and
after each experiment by a very delicate thermometer. The influence of
the temperature of the surrounding atmospheric air was guarded against
by covering the revolving tube with flannel, etc., and by the adoption
of a system of interpolation. By an extensive series of experiments with
the above apparatus the author succeeded in proving that heat is evolved
by the coils of the magneto-electrical machine, as well as by any other
part of the circuit, in proportion to the resistance to conduction
of the wire and the square of the current; the magneto having, under
comparable circumstances, the same calorific power as the voltaic
electricity.

"Professor Jacobi, of St. Petersburg, bad shown that the motion of an
electro-magnetic machine generates magneto-electricity in opposition
to the voltaic current of the battery. The author had observed the same
phenomenon on arranging his apparatus as an electro-magnetic machine;
but had found that no additional heat was evolved on account of the
conflict of forces in the coil of the electro-magnet, and that the heat
evolved by the coil remained, as before, proportional to the square of
the current. Again, by turning the machine contrary to the direction of
the attractive forces, so as to increase the intensity of the voltaic
current by the assistance of the magneto-electricity, he found that the
evolution of heat was still proportional to the square of the current.
The author discovered, therefore, that the heat evolved by the voltaic
current is invariably proportional to the square of the current, however
the intensity of the current may be varied by magnetic induction. But
Dr. Faraday has shown that the chemical effects of the current
are simply as its quantity. Therefore he concluded that in the
electro-magnetic engine a part of the heat due to the chemical actions
of the battery is lost by the circuit, and converted into mechanical
power; and that when the electro-magnetic engine is turned CONTRARY to
the direction of the attractive forces, a greater quantity of heat is
evolved by the circuit than is due to the chemical reactions of the
battery, the over-plus quantity being produced by the conversion of the
mechanical force exerted in turning the machine. By a dynamometrical
apparatus attached to his machine, the author has ascertained that,
in all the above cases, a quantity of heat, capable of increasing the
temperature of a pound of water by one degree of Fahrenheit's scale, is
equal to the mechanical force capable of raising a weight of about eight
hundred and thirty pounds to the height of one foot."(2)


JOULE OR MAYER?

Two years later Joule wished to read another paper, but the chairman
hinted that time was limited, and asked him to confine himself to
a brief verbal synopsis of the results of his experiments. Had the
chairman but known it, he was curtailing a paper vastly more important
than all the other papers of the meeting put together. However, the
synopsis was given, and one man was there to hear it who had the genius
to appreciate its importance. This was William Thomson, the present
Lord Kelvin, now known to all the world as among the greatest of natural
philosophers, but then only a novitiate in science. He came to
Joule's aid, started rolling the ball of controversy, and subsequently
associated himself with the Manchester experimenter in pursuing his
investigations.

But meantime the acknowledged leaders of British science viewed the
new doctrine askance. Faraday, Brewster, Herschel--those were the great
names in physics at that day, and no one of them could quite accept
the new views regarding energy. For several years no older physicist,
speaking with recognized authority, came forward in support of the
doctrine of conservation. This culminating thought of the first half
of the nineteenth century came silently into the world, unheralded and
unopposed. The fifth decade of the century had seen it elaborated and
substantially demonstrated in at least three different countries, yet
even the leaders of thought did not so much as know of its existence.
In 1853 Whewell, the historian of the inductive sciences, published a
second edition of his history, and, as Huxley has pointed out, he did
not so much as refer to the revolutionizing thought which even then was
a full decade old.

By this time, however, the battle was brewing. The rising generation
saw the importance of a law which their elders could not appreciate, and
soon it was noised abroad that there were more than one claimant to the
honor of discovery. Chiefly through the efforts of Professor Tyndall,
the work of Mayer became known to the British public, and a most
regrettable controversy ensued between the partisans of Mayer and those
of Joule--a bitter controversy, in which Davy's contention that science
knows no country was not always regarded, and which left its scars upon
the hearts and minds of the great men whose personal interests were
involved.

And so to this day the question who is the chief discoverer of the law
of the conservation of energy is not susceptible of a categorical answer
that would satisfy all philosophers. It is generally held that the first
choice lies between Joule and Mayer. Professor Tyndall has expressed the
belief that in future each of these men will be equally remembered in
connection with this work. But history gives us no warrant for such a
hope. Posterity in the long run demands always that its heroes shall
stand alone. Who remembers now that Robert Hooke contested with Newton
the discovery of the doctrine of universal gravitation? The judgment of
posterity is unjust, but it is inexorable. And so we can little doubt
that a century from now one name will be mentioned as that of the
originator of the great doctrine of the conservation of energy. The man
whose name is thus remembered will perhaps be spoken of as the Galileo,
the Newton, of the nineteenth century; but whether the name thus
dignified by the final verdict of history will be that of Colding, Mohr,
Mayer, Helmholtz, or Joule, is not as, yet decided.


LORD KELVIN AND THE DISSIPATION OF ENERGY

The gradual permeation of the field by the great doctrine of
conservation simply repeated the history of the introduction of every
novel and revolutionary thought. Necessarily the elder generation, to
whom all forms of energy were imponderable fluids, must pass away before
the new conception could claim the field. Even the word energy, though
Young had introduced it in 1807, did not come into general use till some
time after the middle of the century. To the generality of philosophers
(the word physicist was even less in favor at this time) the various
forms of energy were still subtile fluids, and never was idea
relinquished with greater unwillingness than this. The experiments of
Young and Fresnel had convinced a large number of philosophers that
light is a vibration and not a substance; but so great an authority as
Biot clung to the old emission idea to the end of his life, in 1862, and
held a following.

Meantime, however, the company of brilliant young men who had just
served their apprenticeship when the doctrine of conservation came upon
the scene had grown into authoritative positions, and were battling
actively for the new ideas. Confirmatory evidence that energy is a
molecular motion and not an "imponderable" form of matter accumulated
day by day. The experiments of two Frenchmen, Hippolyte L. Fizeau and
Leon Foucault, served finally to convince the last lingering sceptics
that light is an undulation; and by implication brought heat into the
same category, since James David Forbes, the Scotch physicist, had shown
in 1837 that radiant heat conforms to the same laws of polarization
and double refraction that govern light. But, for that matter, the
experiments that had established the mechanical equivalent of
heat hardly left room for doubt as to the immateriality of this
"imponderable." Doubters had indeed, expressed scepticism as to
the validity of Joule's experiments, but the further researches,
experimental and mathematical, of such workers as Thomson (Lord Kelvin),
Rankine, and Tyndall in Great Britain, of Helmholtz and Clausius in
Germany, and of Regnault in France, dealing with various manifestations
of heat, placed the evidence beyond the reach of criticism.

Out of these studies, just at the middle of the century, to which
the experiments of Mayer and Joule had led, grew the new science
of thermo-dynamics. Out of them also grew in the mind of one of the
investigators a new generalization, only second in importance to the
doctrine of conservation itself. Professor William Thomson (Lord Kelvin)
in his studies in thermodynamics was early impressed with the fact that
whereas all the molar motion developed through labor or gravity could
be converted into heat, the process is not fully reversible. Heat can,
indeed, be converted into molar motion or work, but in the process a
certain amount of the heat is radiated into space and lost. The same
thing happens whenever any other form of energy is converted into molar
motion. Indeed, every transmutation of energy, of whatever character,
seems complicated by a tendency to develop heat, part of which is
lost. This observation led Professor Thomson to his doctrine of the
dissipation of energy, which he formulated before the Royal Society of
Edinburgh in 1852, and published also in the Philosophical Magazine the
same year, the title borne being, "On a Universal Tendency in Nature to
the Dissipation of Mechanical Energy."

From the principle here expressed Professor Thomson drew the startling
conclusion that, "since any restoration of this mechanical energy
without more than an equivalent dissipation is impossible," the
universe, as known to us, must be in the condition of a machine
gradually running down; and in particular that the world we live on has
been within a finite time unfit for human habitation, and must again
become so within a finite future. This thought seems such a commonplace
to-day that it is difficult to realize how startling it appeared half a
century ago. A generation trained, as ours has been, in the doctrines
of the conservation and dissipation of energy as the very alphabet
of physical science can but ill appreciate the mental attitude of a
generation which for the most part had not even thought it problematical
whether the sun could continue to give out heat and light forever. But
those advance thinkers who had grasped the import of the doctrine of
conservation could at once appreciate the force of Thomson's doctrine
of dissipation, and realize the complementary character of the two
conceptions.

Here and there a thinker like Rankine did, indeed, attempt to fancy
conditions under which the energy lost through dissipation might be
restored to availability, but no such effort has met with success, and
in time Professor Thomson's generalization and his conclusions as to the
consequences of the law involved came to be universally accepted.

The introduction of the new views regarding the nature of energy
followed, as I have said, the course of every other growth of new ideas.
Young and imaginative men could accept the new point of view; older
philosophers, their minds channelled by preconceptions, could not get
into the new groove. So strikingly true is this in the particular case
now before us that it is worth while to note the ages at the time of the
revolutionary experiments of the men whose work has been mentioned as
entering into the scheme of evolution of the idea that energy is merely
a manifestation of matter in motion. Such a list will tell the story
better than a volume of commentary.

Observe, then, that Davy made his epochal experiment of melting ice by
friction when he was a youth of twenty. Young was no older when he
made his first communication to the Royal Society, and was in his
twenty-seventh year when he first actively espoused the undulatory
theory. Fresnel was twenty-six when he made his first important
discoveries in the same field; and Arago, who at once became his
champion, was then but two years his senior, though for a decade he had
been so famous that one involuntarily thinks of him as belonging to an
elder generation.

Forbes was under thirty when he discovered the polarization of heat,
which pointed the way to Mohr, then thirty-one, to the mechanical
equivalent. Joule was twenty-two in 1840, when his great work was
begun; and Mayer, whose discoveries date from the same year, was then
twenty-six, which was also the age of Helmholtz when he published his
independent discovery of the same law. William Thomson was a youth just
past his majority when he came to the aid of Joule before the British
Society, and but seven years older when he formulated his own doctrine
of the dissipation of energy. And Clausius and Rankine, who are usually
mentioned with Thomson as the great developers of thermo-dynamics, were
both far advanced with their novel studies before they were thirty.
With such a list in mind, we may well agree with the father of inductive
science that "the man who is young in years may be old in hours."

Yet we must not forget that the shield has a reverse side. For was not
the greatest of observing astronomers, Herschel, past thirty-five before
he ever saw a telescope, and past fifty before he discovered the heat
rays of the spectrum? And had not Faraday reached middle life before he
turned his attention especially to electricity? Clearly, then, to make
this phrase complete, Bacon should have added that "the man who is
old in years may be young in imagination." Here, however, even more
appropriate than in the other case--more's the pity--would have been the
application of his qualifying clause: "but that happeneth rarely."


THE FINAL UNIFICATION

There are only a few great generalizations as yet thought out in any
single field of science. Naturally, then, after a great generalization
has found definitive expression, there is a period of lull before
another forward move. In the case of the doctrines of energy, the
lull has lasted half a century. Throughout this period, it is true, a
multitude of workers have been delving in the field, and to the casual
observer it might seem as if their activity had been boundless, while
the practical applications of their ideas--as exemplified, for example,
in the telephone, phonograph, electric light, and so on--have been
little less than revolutionary. Yet the most competent of living
authorities, Lord Kelvin, could assert in 1895 that in fifty years he
had learned nothing new regarding the nature of energy.

This, however, must not be interpreted as meaning that the world has
stood still during these two generations. It means rather that the rank
and file have been moving forward along the road the leaders had
already travelled. Only a few men in the world had the range of thought
regarding the new doctrine of energy that Lord Kelvin had at the middle
of the century. The few leaders then saw clearly enough that if one
form of energy is in reality merely an undulation or vibration among the
particles of "ponderable" matter or of ether, all other manifestations
of energy must be of the same nature. But the rank and file were not
even within sight of this truth for a long time after they had partly
grasped the meaning of the doctrine of conservation. When, late in
the fifties, that marvellous young Scotchman, James Clerk-Maxwell,
formulating in other words an idea of Faraday's, expressed his belief
that electricity and magnetism are but manifestations of various
conditions of stress and motion in the ethereal medium (electricity a
displacement of strain, magnetism a whirl in the ether), the idea met
with no immediate popularity. And even less cordial was the reception
given the same thinker's theory, put forward in 1863, that the ethereal
undulations producing the phenomenon we call light differ in no respect
except in their wave-length from the pulsations of electro-magnetism.

At about the same time Helmholtz formulated a somewhat similar
electro-magnetic theory of light; but even the weight of this combined
authority could not give the doctrine vogue until very recently, when
the experiments of Heinrich Hertz, the pupil of Helmholtz, have shown
that a condition of electrical strain may be developed into a wave
system by recurrent interruptions of the electric state in the
generator, and that such waves travel through the ether with the
rapidity of light. Since then the electro-magnetic theory of light has
been enthusiastically referred to as the greatest generalization of
the century; but the sober thinker must see that it is really only
what Hertz himself called it--one pier beneath the great arch of
conservation. It is an interesting detail of the architecture, but the
part cannot equal the size of the whole.

More than that, this particular pier is as yet by no means a very firm
one. It has, indeed, been demonstrated that waves of electro-magnetism
pass through space with the speed of light, but as yet no one has
developed electric waves even remotely approximating the shortness of
the visual rays. The most that can positively be asserted, therefore,
is that all the known forms of radiant energy-heat, light,
electro-magnetism--travel through space at the same rate of speed, and
consist of traverse vibrations--"lateral quivers," as Fresnel said of
light--known to differ in length, and not positively known to differ
otherwise. It has, indeed, been suggested that the newest form of
radiant energy, the famous X-ray of Professor Roentgen's discovery, is
a longitudinal vibration, but this is a mere surmise. Be that as it
may, there is no one now to question that all forms of radiant energy,
whatever their exact affinities, consist essentially of undulatory
motions of one uniform medium.

A full century of experiment, calculation, and controversy has thus
sufficed to correlate the "imponderable fluids" of our forebears, and
reduce them all to manifestations of motion among particles of matter.
At first glimpse that seems an enormous change of view. And yet, when
closely considered, that change in thought is not so radical as the
change in phrase might seem to imply. For the nineteenth-century
physicist, in displacing the "imponderable fluids" of many kinds--one
each for light, heat, electricity, magnetism--has been obliged to
substitute for them one all-pervading fluid, whose various quivers,
waves, ripples, whirls or strains produce the manifestations which in
popular parlance are termed forms of force. This all-pervading fluid the
physicist terms the ether, and he thinks of it as having no weight. In
effect, then, the physicist has dispossessed the many imponderables in
favor of a single imponderable--though the word imponderable has been
banished from his vocabulary. In this view the ether--which, considered
as a recognized scientific verity, is essentially a nineteenth-century
discovery--is about the most interesting thing in the universe.
Something more as to its properties, real or assumed, we shall have
occasion to examine as we turn to the obverse side of physics, which
demands our attention in the next chapter.



IX. THE ETHER AND PONDERABLE MATTER


"Whatever difficulties we may have in forming a consistent idea of the
constitution of the ether, there can be no doubt that the interplanetary
and interstellar spaces are not empty, but are occupied by a material
substance or body which is certainly the largest and probably the most
uniform body of which we have any knowledge."

Such was the verdict pronounced some thirty years ago by James
Clerk-Maxwell, one of the very greatest of nineteenth-century
physicists, regarding the existence of an all-pervading plenum in the
universe, in which every particle of tangible matter is immersed.
And this verdict may be said to express the attitude of the entire
philosophical world of our day. Without exception, the authoritative
physicists of our time accept this plenum as a verity, and reason about
it with something of the same confidence they manifest in speaking of
"ponderable" matter or of, energy. It is true there are those among them
who are disposed to deny that this all-pervading plenum merits the name
of matter. But that it is a something, and a vastly important something
at that, all are agreed. Without it, they allege, we should know nothing
of light, of radiant heat, of electricity or magnetism; without it there
would probably be no such thing as gravitation; nay, they even hint that
without this strange something, ether, there would be no such thing as
matter in the universe. If these contentions of the modern physicist are
justified, then this intangible ether is incomparably the most important
as well as the "largest and most uniform substance or body" in the
universe. Its discovery may well be looked upon as one of the most
important feats of the nineteenth century.

For a discovery of that century it surely is, in the sense that all
the known evidences of its existence were gathered in that epoch.
True dreamers of all ages have, for metaphysical reasons, imagined the
existence of intangible fluids in space--they had, indeed, peopled
space several times over with different kinds of ethers, as Maxwell
remarks--but such vague dreamings no more constituted the discovery of
the modern ether than the dream of some pre-Columbian visionary that
land might lie beyond the unknown waters constituted the discovery
of America. In justice it must be admitted that Huyghens, the
seventeenth-century originator of the undulatory theory of light, caught
a glimpse of the true ether; but his contemporaries and some eight
generations of his successors were utterly deaf to his claims; so
he bears practically the same relation to the nineteenth-century
discoverers of ether that the Norseman bears to Columbus.

The true Columbus of the ether was Thomas Young. His discovery was
consummated in the early days of the nineteenth century, when he brought
forward the first, conclusive proofs of the undulatory theory of light.
To say that light consists of undulations is to postulate something that
undulates; and this something could not be air, for air exists only in
infinitesimal quantity, if at all, in the interstellar spaces, through
which light freely penetrates. But if not air, what then? Why, clearly,
something more intangible than air; something supersensible, evading all
direct efforts to detect it, yet existing everywhere in seemingly
vacant space, and also interpenetrating the substance of all transparent
liquids and solids, if not, indeed, of all tangible substances. This
intangible something Young rechristened the Luminiferous Ether.

In the early days of his discovery Young thought of the undulations
which produce light and radiant heat as being longitudinal--a forward
and backward pulsation, corresponding to the pulsations of sound--and as
such pulsations can be transmitted by a fluid medium with the properties
of ordinary fluids, he was justified in thinking of the ether as being
like a fluid in its properties, except for its extreme intangibility.
But about 1818 the experiments of Fresnel and Arago with polarization
of light made it seem very doubtful whether the theory of longitudinal
vibrations is sufficient, and it was suggested by Young, and
independently conceived and demonstrated by Fresnel, that the
luminiferous undulations are not longitudinal, but transverse; and all
the more recent experiments have tended to confirm this view. But it
happens that ordinary fluids--gases and liquids--cannot transmit lateral
vibrations; only rigid bodies are capable of such a vibration. So
it became necessary to assume that the luminiferous ether is a body
possessing elastic rigidity--a familiar property of tangible solids, but
one quite unknown among fluids.

The idea of transverse vibrations carried with it another puzzle. Why
does not the ether, when set aquiver with the vibration which gives us
the sensation we call light, have produced in its substance subordinate
quivers, setting out at right angles from the path of the original
quiver? Such perpendicular vibrations seem not to exist, else we might
see around a corner; how explain their absence? The physicist could
think of but one way: they must assume that the ether is incompressible.
It must fill all space--at any rate, all space with which human
knowledge deals--perfectly full.

These properties of the ether, incompressibility and elastic rigidity,
are quite conceivable by themselves; but difficulties of thought appear
when we reflect upon another quality which the ether clearly
must possess--namely, frictionlessness. By hypothesis this rigid,
incompressible body pervades all space, imbedding every particle of
tangible matter; yet it seems not to retard the movements of this matter
in the slightest degree. This is undoubtedly the most difficult to
comprehend of the alleged properties of the ether. The physicist
explains it as due to the perfect elasticity of the ether, in virtue
of which it closes in behind a moving particle with a push exactly
counterbalancing the stress required to penetrate it in front.

To a person unaccustomed to think of seemingly solid matter as really
composed of particles relatively wide apart, it is hard to understand
the claim that ether penetrates the substance of solids--of glass,
for example--and, to use Young's expression, which we have previously
quoted, moves among them as freely as the wind moves through a grove
of trees. This thought, however, presents few difficulties to the mind
accustomed to philosophical speculation. But the question early arose
in the mind of Fresnel whether the ether is not considerably affected by
contact with the particles of solids. Some of his experiments led him to
believe that a portion of the ether which penetrates among the molecules
of tangible matter is held captive, so to speak, and made to move along
with these particles. He spoke of such portions of the ether as "bound"
ether, in contradistinction to the great mass of "free" ether. Half a
century after Fresnel's death, when the ether hypothesis had become
an accepted tenet of science, experiments were undertaken by Fizeau
in France, and by Clerk-Maxwell in England, to ascertain whether any
portion of ether is really thus bound to particles of matter; but the
results of the experiments were negative, and the question is still
undetermined.

While the undulatory theory of light was still fighting its way, another
kind of evidence favoring the existence of an ether was put forward by
Michael Faraday, who, in the course of his experiments in electrical and
magnetic induction, was led more and more to perceive definite lines or
channels of force in the medium subject to electro-magnetic influence.
Faraday's mind, like that of Newton and many other philosophers,
rejected the idea of action at a distance, and he felt convinced that
the phenomena of magnetism and of electric induction told strongly for
the existence of an invisible plenum everywhere in space, which might
very probably be the same plenum that carries the undulations of light
and radiant heat.

Then, about the middle of the century, came that final revolution of
thought regarding the nature of energy which we have already outlined in
the preceding chapter, and with that the case for ether was considered
to be fully established. The idea that energy is merely a "mode
of motion" (to adopt Tyndall's familiar phrase), combined with the
universal rejection of the notion of action at a distance, made the
acceptance of a plenum throughout space a necessity of thought--so, at
any rate, it has seemed to most physicists of recent decades. The proof
that all known forms of radiant energy move through space at the same
rate of speed is regarded as practically a demonstration that but one
plenum--one ether--is concerned in their transmission. It has, indeed,
been tentatively suggested, by Professor J. Oliver Lodge, that there may
be two ethers, representing the two opposite kinds of electricity, but
even the author of this hypothesis would hardly claim for it a high
degree of probability.

The most recent speculations regarding the properties of the ether have
departed but little from the early ideas of Young and Fresnel. It is
assumed on all sides that the ether is a continuous, incompressible
body, possessing rigidity and elasticity. Lord Kelvin has even
calculated the probable density of this ether, and its coefficient of
rigidity. As might be supposed, it is all but infinitely tenuous as
compared with any tangible solid, and its rigidity is but infinitesimal
as compared with that of steel. In a word, it combines properties of
tangible matter in a way not known in any tangible substance. Therefore
we cannot possibly conceive its true condition correctly. The nearest
approximation, according to Lord Kelvin, is furnished by a mould of
transparent jelly. It is a crude, inaccurate analogy, of course, the
density and resistance of jelly in particular being utterly different
from those of the ether; but the quivers that run through the jelly when
it is shaken, and the elastic tension under which it is placed when its
mass is twisted about, furnish some analogy to the quivers and strains
in the ether, which are held to constitute radiant energy, magnetism,
and electricity.

The great physicists of the day being at one regarding the existence of
this all-pervading ether, it would be a manifest presumption for any one
standing without the pale to challenge so firmly rooted a belief. And,
indeed, in any event, there seems little ground on which to base such
a challenge. Yet it may not be altogether amiss to reflect that the
physicist of to-day is no more certain of his ether than was his
predecessor of the eighteenth century of the existence of certain
alleged substances which he called phlogiston, caloric, corpuscles of
light, and magnetic and electric fluids. It would be but the repetition
of history should it chance that before the close of another century the
ether should have taken its place along with these discarded creations
of the scientific imagination of earlier generations. The philosopher of
to-day feels very sure that an ether exists; but when he says there is
"no doubt" of its existence he speaks incautiously, and steps beyond the
bounds of demonstration. He does not KNOW that action cannot take place
at a distance; he does not KNOW that empty space itself may not perform
the functions which he ascribes to his space-filling ether.

Meantime, however, the ether, be it substance or be it only dream-stuff,
is serving an admirable purpose in furnishing a fulcrum for modern
physics. Not alone to the student of energy has it proved invaluable,
but to the student of matter itself as well. Out of its hypothetical
mistiness has been reared the most tenable theory of the constitution of
ponderable matter which has yet been suggested--or, at any rate, the
one that will stand as the definitive nineteenth-century guess at
this "riddle of the ages." I mean, of course, the vortex theory of
atoms--that profound and fascinating doctrine which suggests that
matter, in all its multiform phases, is neither more nor less than ether
in motion.

The author of this wonderful conception is Lord Kelvin. The idea was
born in his mind of a happy union of mathematical calculations with
concrete experiments. The mathematical calculations were largely the
work of Hermann von Helmholtz, who, about the year 1858, had undertaken
to solve some unique problems in vortex motions. Helmholtz found that
a vortex whirl, once established in a frictionless medium, must go on,
theoretically, unchanged forever. In a limited medium such a whirl may
be V-shaped, with its ends at the surface of the medium. We may imitate
such a vortex by drawing the bowl of a spoon quickly through a cup
of water. But in a limitless medium the vortex whirl must always be
a closed ring, which may take the simple form of a hoop or circle, or
which may be indefinitely contorted, looped, or, so to speak, knotted.
Whether simple or contorted, this endless chain of whirling matter (the
particles revolving about the axis of the loop as the particles of a
string revolve when the string is rolled between the fingers) must, in
a frictionless medium, retain its form and whirl on with undiminished
speed forever.

While these theoretical calculations of Helmholtz were fresh in his
mind, Lord Kelvin (then Sir William Thomson) was shown by Professor
P. G. Tait, of Edinburgh, an apparatus constructed for the purpose
of creating vortex rings in air. The apparatus, which any one may
duplicate, consisted simply of a box with a hole bored in one side, and
a piece of canvas stretched across the opposite side in lieu of boards.
Fumes of chloride of ammonia are generated within the box, merely to
render the air visible. By tapping with the band on the canvas side
of the box, vortex rings of the clouded air are driven out, precisely
similar in appearance to those smoke-rings which some expert
tobacco-smokers can produce by tapping on their cheeks, or to those
larger ones which we sometimes see blown out from the funnel of a
locomotive.

The advantage of Professor Tait's apparatus is its manageableness and
the certainty with which the desired result can be produced. Before Lord
Kelvin's interested observation it threw out rings of various sizes,
which moved straight across the room at varying rates of speed,
according to the initial impulse, and which behaved very strangely when
coming in contact with one another. If, for example, a rapidly moving
ring overtook another moving in the same path, the one in advance seemed
to pause, and to spread out its periphery like an elastic band, while
the pursuer seemed to contract, till it actually slid through the
orifice of the other, after which each ring resumed its original size,
and continued its course as if nothing had happened. When, on the other
hand, two rings moving in slightly different directions came near each
other, they seemed to have an attraction for each other; yet if they
impinged, they bounded away, quivering like elastic solids. If an effort
were made to grasp or to cut one of these rings, the subtle thing shrank
from the contact, and slipped away as if it were alive.

And all the while the body which thus conducted itself consisted simply
of a whirl in the air, made visible, but not otherwise influenced, by
smoky fumes. Presently the friction of the surrounding air wore the
ring away, and it faded into the general atmosphere--often, however, not
until it had persisted for many seconds, and passed clear across a large
room. Clearly, if there were no friction, the ring's inertia must make
it a permanent structure. Only the frictionless medium was lacking to
fulfil all the conditions of Helmholtz's indestructible vortices. And
at once Lord Kelvin bethought him of the frictionless medium which
physicists had now begun to accept--the all-pervading ether. What
if vortex rings were started in this ether, must they not have the
properties which the vortex rings in air had exhibited--inertia,
attraction, elasticity? And are not these the properties of ordinary
tangible matter? Is it not probable, then, that what we call matter
consists merely of aggregations of infinitesimal vortex rings in the
ether?

Thus the vortex theory of atoms took form in Lord Kelvin's mind, and its
expression gave the world what many philosophers of our time regard as
the most plausible conception of the constitution of matter hitherto
formulated. It is only a theory, to be sure; its author would be the
last person to claim finality for it. "It is only a dream," Lord Kelvin
said to me, in referring to it not long ago. But it has a basis in
mathematical calculation and in analogical experiment such as no other
theory of matter can lay claim to, and it has a unifying or monistic
tendency that makes it, for the philosophical mind, little less than
fascinating. True or false, it is the definitive theory of matter of the
twentieth century.

Quite aside from the question of the exact constitution of the ultimate
particles of matter, questions as to the distribution of such particles,
their mutual relations, properties, and actions, came in for a full
share of attention during the nineteenth century, though the foundations
for the modern speculations were furnished in a previous epoch. The most
popular eighteenth-century speculation as to the ultimate constitution
of matter was that of the learned Italian priest, Roger Joseph
Boscovich, published in 1758, in his Theoria Philosophiae Naturalis.
"In this theory," according to an early commentator, "the whole mass of
which the bodies of the universe are composed is supposed to consist
of an exceedingly great yet finite number of simple, indivisible,
inextended atoms. These atoms are endued by the Creator with REPULSIVE
and ATTRACTIVE forces, which vary according to the distance. At very
small distances the particles of matter repel each other; and this
repulsive force increases beyond all limits as the distances are
diminished, and will consequently forever prevent actual contact. When
the particles of matter are removed to sensible distances, the repulsive
is exchanged for an attractive force, which decreases in inverse ratio
with the squares of the distances, and extends beyond the spheres of the
most remote comets."

This conception of the atom as a mere centre of force was hardly such
as could satisfy any mind other than the metaphysical. No one made a
conspicuous attempt to improve upon the idea, however, till just at the
close of the century, when Humphry Davy was led, in the course of
his studies of heat, to speculate as to the changes that occur in the
intimate substance of matter under altered conditions of temperature.
Davy, as we have seen, regarded heat as a manifestation of motion among
the particles of matter. As all bodies with which we come in contact
have some temperature, Davy inferred that the intimate particles of
every substance must be perpetually in a state of vibration. Such
vibrations, he believed, produced the "repulsive force" which (in common
with Boscovich) he admitted as holding the particles of matter at a
distance from one another. To heat a substance means merely to increase
the rate of vibration of its particles; thus also, plainly, increasing
the repulsive forces and expanding the bulk of the mass as a whole. If
the degree of heat applied be sufficient, the repulsive force may become
strong enough quite to overcome the attractive force, and the particles
will separate and tend to fly away from one another, the solid then
becoming a gas.

Not much attention was paid to these very suggestive ideas of Davy,
because they were founded on the idea that heat is merely a motion,
which the scientific world then repudiated; but half a century later,
when the new theories of energy had made their way, there came a revival
of practically the same ideas of the particles of matter (molecules they
were now called) which Davy had advocated. Then it was that Clausius in
Germany and Clerk-Maxwell in England took up the investigation of
what came to be known as the kinetic theory of gases--the now familiar
conception that all the phenomena of gases are due to the helter-skelter
flight of the showers of widely separated molecules of which they are
composed. The specific idea that the pressure or "spring" of gases is
due to such molecular impacts was due to Daniel Bournelli, who advanced
it early in the eighteenth century. The idea, then little noticed, had
been revived about a century later by William Herapath, and again with
some success by J. J. Waterston, of Bombay, about 1846; but it gained
no distinct footing until taken in hand by Clausius in 1857 and by
Clerk-Maxwell in 1859.

The considerations that led Clerk-Maxwell to take up the computations
may be stated in his own words, as formulated in a paper "On the Motions
and Collisions of Perfectly Elastic Spheres."

"So many of the properties of matter, especially when in the gaseous
form," he says, "can be deduced from the hypothesis that their minute
parts are in rapid motion, the velocity increasing with the temperature,
that the precise nature of this motion becomes a subject of rational
curiosity. Daniel Bournelli, Herapath, Joule, Kronig, Clausius, etc.,
have shown that the relations between pressure, temperature, and density
in a perfect gas can be explained by supposing the particles to move
with uniform velocities in straight lines, striking against the sides of
the containing vessel and thus producing pressure. It is not necessary
to suppose each particle to travel to any great distance in the same
straight line; for the effect in producing pressure will be the same
if the particles strike against each other; so that the straight line
described may be very short. M. Clausius has determined the mean length
of path in terms of the average of the particles, and the distance
between the centres of two particles when the collision takes place. We
have at present no means of ascertaining either of these distances;
but certain phenomena, such as the internal friction of gases, the
conduction of heat through a gas, and the diffusion of one gas through
another, seem to indicate the possibility of determining accurately the
mean length of path which a particle describes between two successive
collisions. In order to lay the foundation of such investigations on
strict mechanical principles, I shall demonstrate the laws of motion
of an indefinite number of small, hard, and perfectly elastic spheres
acting on one another only during impact. If the properties of such a
system of bodies are found to correspond to those of gases, an important
physical analogy will be established, which may lead to more accurate
knowledge of the properties of matter. If experiments on gases are
inconsistent with the hypothesis of these propositions, then our theory,
though consistent with itself, is proved to be incapable of explaining
the phenomena of gases. In either case it is necessary to follow out
these consequences of the hypothesis.

"Instead of saying that the particles are hard, spherical, and elastic,
we may, if we please, say the particles are centres of force, of which
the action is insensible except at a certain very small distance, when
it suddenly appears as a repulsive force of very great intensity. It is
evident that either assumption will lead to the same results. For the
sake of avoiding the repetition of a long phrase about these repulsive
bodies, I shall proceed upon the assumption of perfectly elastic
spherical bodies. If we suppose those aggregate molecules which move
together to have a bounding surface which is not spherical, then the
rotatory motion of the system will close up a certain proportion of the
whole vis viva, as has been shown by Clausius, and in this way we may
account for the value of the specific heat being greater than on the
more simple hypothesis."(1)


The elaborate investigations of Clerk-Maxwell served not merely to
substantiate the doctrine, but threw a flood of light upon the entire
subject of molecular dynamics. Soon the physicists came to feel as
certain of the existence of these showers of flying molecules making up
a gas as if they could actually see and watch their individual actions.
Through study of the viscosity of gases--that is to say, of the degree
of frictional opposition they show to an object moving through them
or to another current of gas--an idea was gained, with the aid of
mathematics, of the rate of speed at which the particles of the gas are
moving, and the number of collisions which each particle must experience
in a given time, and of the length of the average free path traversed
by the molecule between collisions, These measurements were confirmed
by study of the rate of diffusion at which different gases mix together,
and also by the rate of diffusion of heat through a gas, both these
phenomena being chiefly due to the helter-skelter flight of the
molecules.

It is sufficiently astonishing to be told that such measurements as
these have been made at all, but the astonishment grows when one hears
the results. It appears from Clerk-Maxwell's calculations that the mean
free path, or distance traversed by the molecules between collisions in
ordinary air, is about one-half-millionth of an inch; while the speed of
the molecules is such that each one experiences about eight billions
of collisions per second! It would be hard, perhaps, to cite an
illustration showing the refinements of modern physics better than
this; unless, indeed, one other result that followed directly from these
calculations be considered such--the feat, namely, of measuring the size
of the molecules themselves. Clausius was the first to point out how
this might be done from a knowledge of the length of free path; and the
calculations were made by Loschmidt in Germany and by Lord Kelvin in
England, independently.

The work is purely mathematical, of course, but the results are regarded
as unassailable; indeed, Lord Kelvin speaks of them as being absolutely
demonstrative within certain limits of accuracy. This does not mean,
however, that they show the exact dimensions of the molecule; it means
an estimate of the limits of size within which the actual size of the
molecule may lie. These limits, Lord Kelvin estimates, are about
the one-ten-millionth of a centimetre for the maximum, and the
one-one-hundred-millionth of a centimetre for the minimum. Such figures
convey no particular meaning to our blunt senses, but Lord Kelvin has
given a tangible illustration that aids the imagination to at least a
vague comprehension of the unthinkable smallness of the molecule. He
estimates that if a ball, say of water or glass, about "as large as
a football, were to be magnified up to the size of the earth, each
constituent molecule being magnified in the same proportion, the
magnified structure would be more coarse-grained than a heap of shot,
but probably less coarse-grained than a heap of footballs."

Several other methods have been employed to estimate the size of
molecules. One of these is based upon the phenomena of contact
electricity; another upon the wave-theory of light; and another upon
capillary attraction, as shown in the tense film of a soap-bubble! No
one of these methods gives results more definite than that due to the
kinetic theory of gases, just outlined; but the important thing is that
the results obtained by these different methods (all of them due to Lord
Kelvin) agree with one another in fixing the dimensions of the molecule
at somewhere about the limits already mentioned. We may feel very sure
indeed, therefore, that the molecules of matter are not the unextended,
formless points which Boscovich and his followers of the eighteenth
century thought them. But all this, it must be borne in mind, refers
to the molecule, not to the ultimate particle of matter, about which we
shall have more to say in another connection. Curiously enough, we shall
find that the latest theories as to the final term of the series are
not so very far afield from the dreamings of the eighteenth-century
philosophers; the electron of J. J. Thompson shows many points of
resemblance to the formless centre of Boscovich.

Whatever the exact form of the molecule, its outline is subject to
incessant variation; for nothing in molecular science is regarded as
more firmly established than that the molecule, under all ordinary
circumstances, is in a state of intense but variable vibration. The
entire energy of a molecule of gas, for example, is not measured by its
momentum, but by this plus its energy of vibration and rotation, due
to the collisions already referred to. Clausius has even estimated
the relative importance of these two quantities, showing that the
translational motion of a molecule of gas accounts for only three-fifths
of its kinetic energy. The total energy of the molecule (which we call
"heat") includes also another factor--namely, potential energy, or
energy of position, due to the work that has been done on expanding,
in overcoming external pressure, and internal attraction between the
molecules themselves. This potential energy (which will be recovered
when the gas contracts) is the "latent heat" of Black, which so long
puzzled the philosophers. It is latent in the same sense that the energy
of a ball thrown into the air is latent at the moment when the ball
poises at its greatest height before beginning to fall.

It thus appears that a variety of motions, real and potential, enter
into the production of the condition we term heat. It is, however,
chiefly the translational motion which is measurable as temperature;
and this, too, which most obviously determines the physical state of the
substance that the molecules collectively compose--whether, that is to
say, it shall appear to our blunt perceptions as a gas, a liquid, or a
solid. In the gaseous state, as we have seen, the translational motion
of the molecules is relatively enormous, the molecules being widely
separated. It does not follow, as we formerly supposed, that this
is evidence of a repulsive power acting between the molecules. The
physicists of to-day, headed by Lord Kelvin, decline to recognize any
such power. They hold that the molecules of a gas fly in straight lines
by virtue of their inertia, quite independently of one another, except
at times of collision, from which they rebound by virtue of their
elasticity; or on an approach to collision, in which latter case, coming
within the range of mutual attraction, two molecules may circle about
each other, as a comet circles about the sun, then rush apart again, as
the comet rushes from the sun.

It is obvious that the length of the mean free path of the molecules
of a gas may be increased indefinitely by decreasing the number of the
molecules themselves in a circumscribed space. It has been shown by
Professors Tait and Dewar that a vacuum may be produced artificially of
such a degree of rarefaction that the mean free path of the remaining
molecules is measurable in inches. The calculation is based on
experiments made with the radiometer of Professor Crookes, an instrument
which in itself is held to demonstrate the truth of the kinetic theory
of gases. Such an attenuated gas as this is considered by Professor
Crookes as constituting a fourth state of matter, which he terms
ultra-gaseous.

If, on the other hand, a gas is subjected to pressure, its molecules are
crowded closer together, and the length of their mean free path is thus
lessened. Ultimately, the pressure being sufficient, the molecules are
practically in continuous contact. Meantime the enormously increased
number of collisions has set the molecules more and more actively
vibrating, and the temperature of the gas has increased, as, indeed,
necessarily results in accordance with the law of the conservation
of energy. No amount of pressure, therefore, can suffice by itself to
reduce the gas to a liquid state. It is believed that even at the centre
of the sun, where the pressure is almost inconceivably great, all matter
is to be regarded as really gaseous, though the molecules must be so
packed together that the consistency is probably more like that of a
solid.

If, however, coincidently with the application of pressure, opportunity
be given for the excess of heat to be dissipated to a colder surrounding
medium, the molecules, giving off their excess of energy, become
relatively quiescent, and at a certain stage the gas becomes a liquid.
The exact point at which this transformation occurs, however, differs
enormously for different substances. In the case of water, for
example, it is a temperature more than four hundred degrees above zero,
centigrade; while for atmospheric air it is one hundred and ninety-four
degrees centigrade below zero, or more than a hundred and fifty degrees
below the point at which mercury freezes.

Be it high or low, the temperature above which any substance is always
a gas, regardless of pressure, is called the critical temperature, or
absolute boiling-point, of that substance. It does not follow, however,
that below this point the substance is necessarily a liquid. This is a
matter that will be determined by external conditions of pressure. Even
far below the critical temperature the molecules have an enormous degree
of activity, and tend to fly asunder, maintaining what appears to be
a gaseous, but what technically is called a vaporous, condition--the
distinction being that pressure alone suffices to reduce the vapor to
the liquid state. Thus water may change from the gaseous to the liquid
state at four hundred degrees above zero, but under conditions of
ordinary atmospheric pressure it does not do so until the temperature
is lowered three hundred degrees further. Below four hundred degrees,
however, it is technically a vapor, not a gas; but the sole difference,
it will be understood, is in the degree of molecular activity.

It thus appeared that the prevalence of water in a vaporous and liquid
rather than in a "permanently" gaseous condition here on the globe is a
mere incident of telluric evolution. Equally incidental is the fact that
the air we breathe is "permanently" gaseous and not liquid or solid,
as it might be were the earth's surface temperature to be lowered to a
degree which, in the larger view, may be regarded as trifling. Between
the atmospheric temperature in tropical and in arctic regions there is
often a variation of more than one hundred degrees; were the temperature
reduced another hundred, the point would be reached at which oxygen
gas becomes a vapor, and under increased pressure would be a liquid.
Thirty-seven degrees more would bring us to the critical temperature of
nitrogen.

Nor is this a mere theoretical assumption; it is a determination of
experimental science, quite independent of theory. The physicist in the
laboratory has produced artificial conditions of temperature enabling
him to change the state of the most persistent gases. Some fifty years
since, when the kinetic theory was in its infancy, Faraday liquefied
carbonic-acid gas, among others, and the experiments thus inaugurated
have been extended by numerous more recent investigators, notably
by Cailletet in Switzerland, by Pictet in France, and by Dr. Thomas.
Andrews and Professor James Dewar in England. In the course of these
experiments not only has air been liquefied, but hydrogen also, the most
subtle of gases; and it has been made more and more apparent that gas
and liquid are, as Andrews long ago asserted, "only distant stages of
a long series of continuous physical changes." Of course, if the
temperature be lowered still further, the liquid becomes a solid; and
this change also has been effected in the case of some of the most
"permanent" gases, including air.

The degree of cold--that is, of absence of heat--thus produced is
enormous, relatively to anything of which we have experience in nature
here at the earth now, yet the molecules of solidified air, for
example, are not absolutely quiescent. In other words, they still have
a temperature, though so very low. But it is clearly conceivable that
a stage might be reached at which the molecules became absolutely
quiescent, as regards either translational or vibratory motion. Such a
heatless condition has been approached, but as yet not quite
attained, in laboratory experiments. It is called the absolute zero
of temperature, and is estimated to be equivalent to two hundred and
seventy-three degrees Centigrade below the freezing-point of water, or
ordinary zero.

A temperature (or absence of temperature) closely approximating this
is believed to obtain in the ethereal ocean of interplanetary and
interstellar space, which transmits, but is thought not to absorb,
radiant energy. We here on the earth's surface are protected from
exposure to this cold, which would deprive every organic thing of life
almost instantaneously, solely by the thin blanket of atmosphere with
which the globe is coated. It would seem as if this atmosphere,
exposed to such a temperature at its surface, must there be incessantly
liquefied, and thus fall back like rain to be dissolved into gas again
while it still is many miles above the earth's surface. This may be the
reason why its scurrying molecules have not long ago wandered off into
space and left the world without protection.

But whether or not such liquefaction of the air now occurs in our outer
atmosphere, there can be no question as to what must occur in its entire
depth were we permanently shut off from the heating influence of the
sun, as the astronomers threaten that we may be in a future age.
Each molecule, not alone of the atmosphere, but of the entire earth's
substance, is kept aquiver by the energy which it receives, or has
received, directly or indirectly, from the sun. Left to itself, each
molecule would wear out its energy and fritter it off into the
space about it, ultimately running completely down, as surely as any
human-made machine whose power is not from time to time restored. If,
then, it shall come to pass in some future age that the sun's rays
fail us, the temperature of the globe must gradually sink towards the
absolute zero. That is to say, the molecules of gas which now fly about
at such inconceivable speed must drop helpless to the earth; liquids
must in turn become solids; and solids themselves, their molecular
quivers utterly stilled, may perhaps take on properties the nature of
which we cannot surmise.

Yet even then, according to the current hypothesis, the heatless
molecule will still be a thing instinct with life. Its vortex whirl will
still go on, uninfluenced by the dying-out of those subordinate quivers
that produced the transitory effect which we call temperature. For those
transitory thrills, though determining the physical state of matter as
measured by our crude organs of sense, were no more than non-essential
incidents; but the vortex whirl is the essence of matter itself. Some
estimates as to the exact character of this intramolecular motion,
together with recent theories as to the actual structure of the
molecule, will claim our attention in a later volume. We shall also
have occasion in another connection to make fuller inquiry as to the
phenomena of low temperature.



APPENDIX

  REFERENCE-LIST

  CHAPTER I

  THE SUCCESSORS OF NEWTON IN ASTRONOMY (1) (p. 10). An Account of Several
  Extraordinary Meteors or Lights in the Sky, by Dr. Edmund Halley. Phil.
  Trans. of Royal Society of London, vol. XXIX, pp. 159-162. Read before
  the Royal Society in the autumn of 1714. (2) (p. 13). Phil. Trans. of
  Royal Society of London for 1748, vol. XLV., pp. 8, 9. From A Letter to
  the Right Honorable George, Earl of Macclesfield, concerning an Apparent
  Motion observed in some of the Fixed Stars, by James Bradley, D.D.,
  Astronomer Royal and F.R.S.

  CHAPTER II

  THE PROGRESS OF MODERN ASTRONOMY

  (1) (p. 25). William Herschel, Phil. Trans. for 1783, vol. LXXIII. (2)
  (p. 30). Kant's Cosmogony, ed. and trans. by W. Hartie, D.D., Glasgow,
  900, pp. 74-81. (3) (p. 39). Exposition du systeme du monde (included in
  oeuvres Completes), by M. le Marquis de Laplace, vol. VI., p. 498. (4)
  (p. 48). From The Scientific Papers of J. Clerk-Maxwell, edited by W.
  D. Nevin, M.A. (2 vols.), vol. I., pp. 372-374. This is a reprint of
  Clerk-Maxwell's prize paper of 1859.

  CHAPTER III

  THE NEW SCIENCE OF PALEONTOLOGY

  (1) (p. 81). Baron de Cuvier, Theory of the Earth, New York, 1818, p.
  98. (2) (p. 88). Charles Lyell, Principles of Geology (4 vols.),
  London, 1834. (p. 92). Ibid., vol. III., pp. 596-598. (4) (p. 100). Hugh
  Falconer, in Paleontological Memoirs, vol. II., p. 596. (5) (p. 101).
  Ibid., p. 598. (6) (p. 102). Ibid., p. 599. (7) (p. 111). Fossil Horses
  in America (reprinted from American Naturalist, vol. VIII., May, 1874),
  by O. C. Marsh, pp. 288, 289.

  CHAPTER IV

  THE ORIGIN AND DEVELOPMENT OF MODERN GEOLOGY

  (1) (p. 123). James Hutton, from Transactions of the Royal Society of
  Edinburgh, 1788, vol. I., p. 214. A paper on the "Theory of the Earth,"
  read before the Society in 1781. (2) (p. 128). Ibid., p. 216. (3)
  (p. 139). Consideration on Volcanoes, by G. Poulett Scrope, Esq., pp.
  228-234. (4) (p. 153). L. Agassiz, Etudes sur les glaciers, Neufchatel,
  1840, p. 240.

  CHAPTER V

  THE NEW SCIENCE OF METEOROLOGY

  (1) (p. 182). Theory of Rain, by James Hutton, in Transactions of the
  Royal Society of Edinburgh, 1788, vol. 1, pp. 53-56. (2) (p. 191). Essay
  on Dew, by W. C. Wells, M.D., F.R.S., London, 1818, pp. 124 f.

  CHAPTER VI

  MODERN THEORIES OF HEAT AND LIGHT

  (1) (p. 215). Essays Political, Economical, and Philosophical, by
  Benjamin Thompson, Count of Rumford (2 vols.), Vol. II., pp. 470-493,
  London; T. Cadell, Jr., and W. Davies, 1797. (2) (p. 220). Thomas Young,
  Phil. Trans., 1802, p. 35. (3) (p. 223). Ibid., p. 36.

  CHAPTER VII

  THE MODERN DEVELOPMENT OF ELECTRICITY AND MAGNETISM

  (1) (p. 235). Davy's paper before Royal Institution, 1810. (2) (p. 238).
  Hans Christian Oersted, Experiments with the Effects of the Electric
  Current on the Magnetic Needle, 1815. (3) (p. 243). On the Induction
  of Electric Currents, by Michael Faraday, F.R.S., Phil. Trans. of Royal
  Society of London for 1832, pp. 126-128. (4) (p. 245). Explication of
  Arago's Magnetic Phenomena, by Michael Faraday, F.R.S., Phil. Trans.
  Royal Society of London for 1832, pp. 146-149.

  CHAPTER VIII

  THE CONSERVATION OF ENERGY

  (1) (p. 267). The Forces of Inorganic Nature, a paper by Dr. Julius
  Robert Mayer, Liebig's Annalen, 1842. (2) (p. 272). On the Calorific
  Effects of Magneto-Electricity and the Mechanical Value of Heat, by J.
  P. Joule, in Report of the British Association for the Advancement of
  Science, vol. XII., p. 33.

  CHAPTER IX

  THE ETHER AND PONDERABLE MATTER

  (1) (p. 297). James Clerk-Maxwell, Philosophical Magazine for January
  and July, 1860.

END OF VOL. III





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