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A History of Science, Volume 3

by Henry Smith Williams

April, 1999  [Etext #1707]


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A History of Science, Volume 3, by Henry Smith Williams

Scanned by Charles Keller with OmniPage Professional OCR software





A
HISTORY OF SCIENCE
BY
HENRY SMITH WILLIAMS, M.D., LL.D.
ASSISTED BY
EDWARD H. WILLIAMS, M.D.

IN FIVE VOLUMES
VOLUME III.

MODERN DEVELOPMENT OF THE
PHYSICAL SCIENCES




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 Olbers1--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 be 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 g 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 be 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; be 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 1 degrees centigrade corresponds to the fall of an
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





End of Project Gutenberg Etext of A History of Science, V 3, by Williams