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would be six millions of years. In other words, the time required for
this one subordinate member of one geological formation, would be half
the total time assigned by Thomson and Helmholz for the total possible
past duration of the present supply of solar heat

Those who fully consider and appreciate any one of these instances
will not be astonished to hear that Sir C. Lyell, after carefully going over
and summing up the various lines of evidence afforded by the 100,000
feet of stratified and fossiliferous formations adove the Cambrian, came to
the conclusion that two hundred millions of years was the probable, and
one hundred millions the minimum possible duration of the existing order
of things that would explain the facts. And all subsequent discoveries,
and the best geological opinions, go to confirm this estimate. Thus,
when Lyell made his estimate, the great Laurentian system of gneissic and


other rocks which underlie the Cambrian was scarcely known, or assumed
to be a primitive portion of the earth's crust of Plutonic origin. But it is
now clearly proved to be bedded, and therefore an aqueous deposit from
the denudation of older rocks, though the minor signs of stratification
have disappeared, owing to metamorphism under heat and pressure.
This at once adds 30,000 feet to the known thickness of deposited strata.
It is not positively known to have contained life, for with the doubtful
exception of the Eozoon Canadiense, the fossils, if any, have disappeared
during this process of metamorphism; but it contains indirect evidence
of life on the most extensive scale. Thus, great quantities of graphite or
plumbago are found in it, and as ordinary coal can be traced first into an-
thracite and then into graphite, the inference is strong that the Laurentian
graphite must, like coal, have originated from masses of vegetable matter.
It contains also great beds of limestone, similar to those which, in later
formations, are known to have originated from the remains of corals and
other hard parts of marine animals, which derived their skeletons from cal-
careous matter dissolved in sea-water. Large beds of iron ore are also
found, which, in later formations, owe their origin to the solution of perox-
ide of iron and its deoxidation by organic agency. There is thus, there-
fore, evidence of the existence of life on a vast scale in this lowest of all
formations, which of itself adds more than a fourth to the thickness of
the whole of the previously known deposited strata of the earth's crust,
and therefore to the time presumably required for their deposit.

And yet, as we have seen, mathematicians affirm with equal confidence
that Lyell's figures must be divided by at least ten, or probably by twenty,
to arrive at the ten millions of years which is their estimate of the time
for which the sun has given out its present life-sustaining amount of light
and heat, and this short period has to provide not only for geological time,
but for the far larger time during which the earth was passing through its
earlier stages, and condensing from a gaseous vapor.

It is evident that there must be some fundamental error on one side or
the other, which some day will be detected, for the laws of nature are uni-
form, and there cannot be one code for astronomers and another for geol-
ogists. I am inclined to think that the error will be found in some of
the assumptions of the physicists. The data of geology seem more certain
and more capable of verification by an appeal to facts. Thus, the rate at
which rocks waste away, and lakes silt up; the amount of solid matter
carried down by rivers, and the number of feet or inches per square mile
thus denuded in a given time, are all matters of approximate and tolerably
accurate observation and calculation. But of the nature and constitution
>f the sun we really know very little, and are only beginning to get some
glimpses of them during the past ten or twenty years by the aid of the
spectroscope. The sun, as we see it, is not fluid, for if it were its rota-
tion must make it protuberant at the equator, which it is not It is not
solid, for if it were its equatorial region could not rotate, as it does, more


rapidly than that nearer the pole. We know its apparent volume and its
mean density; but we do not know how this density is distributed. The
conditions of matter under such extreme temperature and pressure are
quite conjectural. For aught we know to the contrary, the sun may have
a nucleus much smaller and much heavier than we are in the habit of as-

Above all, what makes me distrust these mathematical calculations
respecting the sun's heat is, that they do not really solve the problem, but
only remove it one step further back. Heat, they say, can be nothing
but transformed mechanical power; but where does the mechanical power
come from ? From gravity. And where does the gravity come from ?
They cannot tell. It is the old Hindoo cosmogony over again. The
world rests on an elephant; the elephant on a tortoise. But what does
the tortoise rest on ?

We are accustomed to speak of gravity as the one well-known and es-
tablished fact of the universe. And so it is as regards the various motions
which result from it, and the fact of its being an atribute of all matter
from atoms to stars. But of its real essence and modus operandi we know
nothing: less even than in the case of some of the other forms of energy
into which it can be transformed. In the case of light, for instance, we
know that it is caused by waves or vibrations of an exceedingly elastic
and imponderable medium or ether diffused through space. We can
measure and count these vibrations, and know the velocity with which
the light-wave travels, and trace its effects from impact on the eye,
through the retina and optic nerve up to the cells of the brain.

But in the case of gravity we know none of these things, and cannot
even form a conception of how one mass of matter can act upon another,
without connection and apparently without requiring time for the trans-
mission of the impulse. Is it a pulling or a pushing force ? We do not
even know this, and are not one whit advanced beyond the saying of
Newton that he could not conceive how one body could act on another
without some physical connection between them.

It seems to me that Sir W. Thompson starts from the assumption that
gravity is the one fundamental form of energy from which all other forms,
such as light and heat, are derived by transformation. But what a mere
drop in the ocean is the energy of gravity compared with the atomic and
molecular energies, which now in a latent and now in an active form
build up the universe of matter? How incalculably small must the
gravity of the sun be, compared with the sum of the energies of the atoms
of which its mass is composed.

If it were permissible to hazard a conjecture where there is no proof,
it would be that gravity may turn out to be one, and that by no means
the most important, manifestation of the primitive fund of energy, which
underlies the atoms of which all matter is composed.

Various ingenious attempts have been made to explain the cause of


gravity, as that of strain or stress of some intervening medium, or space-
filling, incompressible fluid; or by Le Sage's theory of infinite impacts of
mltramundane corpuscles, partially screened in the direction in which
gravity acts by the bodies which attract one another. But Clark Maxwell
and other accomplished mathematicians have shown fatal objections to
all these theories, and Tait in his Properties of Matter sums up the latest re-
sults almost in the identical words used by Newton in his letter to Bentley
"In fact, the cause of gravitation remains undiscovered."

Again, who can tell what is the constitution of the infinite space
through which our solar system and the universe of visible stars are
travelling, with a velocity which has been estimated in some cases as high
as two hundred or even four hundred miles per second ?

These facts of the proper motions of the stars, and especially of what
are known as the " runaway stars," seem conclusive against the assump-
tion that gravity is the sole and primitive form of energy, from which all
other forms, such as heat and light, are derived by transformation.
These star-motions are apparently in straight lines, in a variety of direc-
tions, and the velocities are such that it is impossible to account for them
bj any conceivable action of the force of gravity. Professor Newcomb
has shown by mathematical calculation that the gravitation of the whole
aniverse, assuming it to contain 100,000,000 of stars, each on the average
five times larger than the sun, would require to be sixty-four times greater
than it really is, to have given one star (1830 Groombridge) the velocity of
200 miles per second which is actually possesses, or to be able to arrest
its flight through space. Of course this applies with greater force to a
star like Arcturus, moving with a velocity of 400 miles per second. The
amount of energy of a star like this, whose volume has been computed to
be eleven times greater than that of the sun, moving with a velocity of
400 miles per second, must be enormously greater than any energy
exerted by it in the form of gravitation, and if its motion were arrested,
the heat engendered must be in an even larger proportion, seeing that it
depends on the square of the velocity, than any heat which could be sup-
plied by its gradual contraction, on the theory applied by Thomson and
Helmholtz to solar heat.

After all, what do we really know of the contents of space except this,
that it contains a vast number of stars which are suns like ours, scattered
at enormous distances from one another, and also innumerable meteorites ?
And also this, that the phenomena of light and heat prove the existence
of waves of known dimensions vibrating with known velocities and trans-
mitted at a known rate ; which waves compel us to assume a medium
or ether with certain calculable qualities. But these qualities are so ex-
traordinary that it may almost be doubted whether such an ether has a
real material existence, and is anything more than a sort of mathemati-
cal entity. Its elasticity must be a million million times that 'of air,
which, as we know, is equal to a pressure of about 1 5 Ibs. to the square



inch ; the number of its oscillations must be at least 700,000,000,000,000
in one second of time; and it must be destitute of any perceptible
amount of the ordinary qualities of matter, for it exerts no gravitating or
retarding force, even on the attenuated matter of comets moving through
it with immense velocities.

Beyond this we can only conjecture that space may contain a number
of larger meteors or dark suns, rushing through it in all directions, and
possibly in the state of dissociated atoms the elements of substances such
as carbon and oxygen, which are locked up in the earth's crust through
the medium of life and vegetation, in vastly greater quantities than could
be afforded by any conceivable supply derived from the atmosphere. And
it may be conjectured also that variations of temperature may exist in
different regions of space, helping to account for the secular variations of
temperature at the earth's surface, such as are shown by the Glacial period
or periods.

Even if we confine ourselves to the sun itself, leaving these cosmic
speculations to be discussed in a subsequent chapter, we find the greatest
uncertainty prevailing as to the conditions under which it exerts and
generates heat Thus, Professor Young says, "The sun's mass, dimen-
sions, and motions are, as a whole, pretty well determined and understood;
but when we come to questions relating to its constitution, the cause and
nature of the appearances presented upon its surface, the periodicy of it
spots, its temperature, and the maintenance of its heat, the extent of its
atmosphere, and the nature of the corona, we find the most radical dif-
ferences of opinion. "

Take the case of the spots. These were originally attributed by
Herschell to cyclones in the sun's atmosphere, showing us glimpses, as
through a funnel, of a cool and dark solid body below; by others they have
been thought to be splashes caused by the downfall of large masses of
meteoric matter; by some to be volcanic eruptions throwing up vast scoriae;
and finally, as the most probable solution, to be great whirlwinds, or
cyclonic convection currents, by which the cooler gases of the sun's
atmosphere are sucked down and replaced by hotter gases from the
interior. But none of these theories give an explanation of the observed
fact that these sun-spots have a regular maximum and minimum period of
about eleven years. Nor do they give the slightest clue to the other re-
markable fact that the outburst of large sun-spots often produces an
apparently instantaneous effect on the earth's magnetism; causing electric
telegraphs to write with a tongue of fire, magnets to oscillate violently, the
Aurora Borealis to appear, and otherwise indicating what is known as a
magnetic storm.

It is pretty clearly established that the spots are colder than the sun's
general surface, but not sufficiently so as to affect its general temperature,
or the cause of the seasons upon the earth; but the far more inexplicable


effect upon terrestrial magnetism is attested by too many observations to
be at all doubtful.

This opens up a new and quite unexplained field of speculation as to
the sun's electric energy. The physicists, who treat the attractive form of
gravity as the sole cause of the sun's energy, and convert it all into heat,
take no account of the energy which manifests itself as a repulsive force,
and takes the form of electricity. And yet electricity is one of the trans-
formable manifestations of energy as much as heat or mechanical power,
and the phenomena or comets' tails are sufficient to show that, under cer-
tain conditions, the sun can exercise an enormous repulsive force. The
question also may be raised whether, after all, it is certain that heat is
radiated out in all directions, so that out of 1,000,000 units of the life-
giving energy of the sun, 999,999 are^absolutely wasted in space, and one
only is utilized. Electricity, so far as we know, cannot exist without two
opposite poles, implying reciprocal action. Do the sun-spots, which affect
the earth's magnetism, radiate out an equal amount of magnetic energy in
all directions into space ? If not, how can we be sure that heat, into and
out of which electricity and magnetism can be transformed, does so ?

As Professor Young observes, "perhaps we assume with a little too
much confidence that in free space radiation does take place equally in
all directions," and he asks " whether the constitution of things may not
be such that radiation and transfer of energy can take place only between
ponderable masses; and that too, without the expenditure of energy upon
the transmitting agent (if such exists) along the line of transmission, even
in transitu. If this were the case, then the sun would send out its energy
only to planets, meteors and sister-stars, wasting none in empty space; and
so its loss of heat would be enormously diminished, and the time-scale of
the planetary system would be correspondingly extended."

The same difficulty applies in the case of gravity. We only know it as
an attractive force reciprocally exerted between two bodies in the propor-
tion of their masses and inverse squares of distances. Is it radiated out
in all directions into empty space, where it meets with no reciprocally
attracting body ? This affects not only the permanent maintenance of
the supply of gravity, but goes even deeper to the fundamental axiom of
all modern conceptions, whether scientific or philosophical, of the uni-
verse, viz., the Conservation of Energy. You cannot make something
out of nothing; you cannot create energy or matter, but only transform
them. Good; but how about that which is one of the principal manifes-
tations of energy in the universe that of gravity ? You can catch limited
portions of it, transform them into mechanical power, and then backwards
and forwards as you like in heat, light, chemical action, electricity and
magnetism, neither losing nor gaining a particle of the original energy by
any of these transformations. A water-wheel may turn a dynamo, which
generates electricity that may be stored in accumulators, and turn a wheel
a hundred miles off; and, if you could eliminate waste and friction, the


second wheel would give out exactly what the weight of the falling water
put into the first one. But whence came the gravity which made the
waterfall and the wheel turn ? Was it itself a transformation of heat or
electricity.? If not, what was it, and how came it there? If Thomson
and Helmholtz assume an infinite fund of energy in the form of gravity to
account for heat, why shall they not as well assume an infinite fund of
heat to account for gravity ? And if heat is dissipated by use until it is
exhausted, or reduced to one stationary average of temperature, and worlds
and suns die, why should gravity be gifted with perpetual youth, and es-
cape the general law of birth, maturity and death ?

These are problems which the present cannot answer. Possibly the
future may, but in the meantime we shall do well to keep a firm footing
on solid earth, and rely on conclusions based on ascertained facts and un-
doubted deductions from them, rather than on abstract and doubtful theo-
ries, even if they are presented to us in the apparently accurate form of
mathematical calculation. Or, to bring this chapter to a practical result,
we shall be more likely to arrive at just views respecting the constitution
of the earth and its inhabitants by following Darwin and Lyell as our
guides, than by accepting astronomical theories which would so reduce
geological time as to negative the idea of uniformity of law and evolution,
and introduce once more the chaos of catastrophes and supernatural inter-


WHAT is the universe made of ? Such is the question which has
been asked in many ages and countries by earnest men looking
up at the starry vault of heaven, and down into the recesses of their own
minds. The latest reply of science is, that it is made of shooting stars.
The idea may seem paradoxical to those whose only knowledge of shoot-
ing stars is derived from an occasional glimpse on a clear night, when
they have seen something like a small rocket flash across the sky, appar-
ently close to the earth, out of darkness into darkness, reminding them
of some human life

"Qui file, qui file et disparait."

And yet it is now presented to us by eminent authorities, and supported
by a long array of serious scientific arguments.

What do we know as certain facts with regard to shooting stars ?

i. They are vastly more numerous than any one has an idea of who
has not watched them continuously for many nights. Astronomers who
have kept a record for many years assure us that the average number seen
by one observer at one place on a clear moonless night is fourteen per
hour, which is shown by calculation to be equivalent to twenty millions
daily for the whole earth. But the number of meteorites met with by the
earth can only be the minutest fraction of those circulating in space. The
orbits of those we see do not coincide with the ecliptic, but lie in planes
inclined to it at all sorts of angles, and apparently having no relation to
the plane in which the earth travels round the sun, or to the solar system.
The chances are almost infinite against our minute speck of a planet en-
countering any single meteor, or stream of meteors, thus traversing space
in all directions, and as we do encounter some seven thousand millions
of these small bodies in the course of each year, their total number must
be an almost infinite multiple of this large figure. Moreover, the sun,
with its attendant system, is rushing through space with a velocity of some
20 miles per second, and therefore carrying us into new regions of the
universe at the rate of some six hundred millions of miles per annum, and
yet meteorites are met with everywhere. Granting, therefore, that each
separate meteorite may be very small, not exceeding on the average a
fraction of an ounce in weight, and that even in meteor streams they may


be, as some astronomers have calculated, 200 miles apart, the aggregate
amount of this meteoric matter in space must be practically almost

2. They are not terrestrial phenomena moving in the lower atmosphere,
but celestial bodies moving in orbits and with velocities comparable to
those of planets and comets. Their velocities are seldom under ten miks
a second or over fifty, and average about thirty, the velocity of the earth
in its orbit round the sun being eighteen.

3. They are of various composition, comprising both a large majority
of smaller particles which are set on fire by the resistance of the earth's
atmosphere, and entirely burned up and resolved into vapor long before
they reach its surface ; and a few larger ones, known as meteors, which
are only partially fused or glazed by heat, and reach the earth in the form
of stony or metallic masses.

4. They are not uniformly distributed through space, but collect m
meteoric swarms or streams, two at least of which revolve round the sun
in closed rings which are intersected by the earth's orbit, causing the
magnificent displays of shooting stars which are seen in August and

5. They are connected with comets, it having been demonstrated by
Schiaparelli that the orbit of the comet of 1866 is identical with that of
the August swarm of meteors known as the Perseids, and connections
between comets and meteor streams have been found in at least three
other cases. The fact is generally believed that comets are nothing but a
condensation of meteorites rendered incandescent by the heat generated
by their mutual collision when brought into close proximity.

6. Their composition, as inferred from that of the larger meteors which
reach the earth, is identical or nearly so with that of matter brought up
from great depths by volcanic eruptions. In each case they consist of
two classes : one, composed mainly of native iron alloyed with nickel,
the other of stony matter consisting mainly of compounds of silicon and
magnesium. Most meteorites consist of compounds of the two classes,
in which the stony parts seem to have broken into fragments by violent
collision, and become embedded in iron which has been fused by heat
into a plastic or pasty condition.

At this point our positive knowledge of meteorites from direct observa-
tion ceases, and we have to be guided by the spectroscope in further re-
searches. This marvellous instrument enables us, by analyzing the light
transmitted to us by all luminous objects however composed and however
distant, to ascertain their composition as accurately as if portions of them
had been brought down to earth and could be analyzed in our labora-
tories. We can tell whether they are gaseous, liquid, or solid ; whether
they shine by intrinsic or reflected light ; and by comparing the lines in
their spectra with those of known terrestrial elements, whether they con-
tain those elements, or are made up of matter in a state unknown to u.


The first result of spectroscopic discoveries was to establish the fact that
the sun, stars, nebulae, comets, and meteorites, all show such an identity
in their spectra with some one or more of those terrestial elements, as to
leave no doubt that the composition of matter is uniform throughout the

Further experiments, of which Mr. Norman Lockyer's paper, read to
the Royal Society, affords the latest and most complete summary, carry
this knowledge farther. They show that spectra are not fixed and invaria-
ble, but change according to the conditions of heat, pressure and other-
wise, affecting the bodies from which the spectra are given out. Thus
the spectrum of a comet in perhelion, when its component parts are
crowded together and intensely heated by the sun, is very different from
that of the same comet when it is at a great distance from the sun, either
in advancing towards it or receding from it Thus the spectrum of the

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