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yet with the present obliquity of the axis, the sun must have been below
the horizon in those latitudes from November till March.

At present, as we go north from the equator towards the Arctic circle,
we find species changing to accommodate themselves to the change of
environment Palms are succeeded by oaks and beeches ; these again by
pines and birches, and these by dwarf willows and lichens, until all vege-
tation, except of the very humblest forms, dies out as we approach the
pole. But in the geological records of earlier periods no such changes
are discernible. The Miocene magnolia of Spitzbergen is not even a
greatly modified magnolia, but of the same species as the magnolia of the
present day. The Miocene cypress is the common cypress. If there
were no such science as astronomy, geology would point to the conclusion
that until after the Miocene period climate was uniform ; there were no
distinct zones or seasons, and therefore no obliquity of the earth's axis,
or at any rate nothing like the present amount. With these conditions
there would have been perpetual spring, and all we should require would
be a higher average temperature for the whole earth. But to this con-
clusion astronomy opposes an inflexible non possumus. If there is one
thing more certain than another, it is that mathematical calculations,
based on Newton's law of gravity, explain all the movements of the solar
system. They do so with a certainty that enables us to predict the places
of the earth, moon, and planets years before-hand, with absolute accuracy.
And if there is one thing more certain than another in these calculations,
it is that no permanent change is possible in the inclination of the earth's
axis. The earth now spins, in twenty-four hours, round an axis inclined
at an angle of 66 to the plane on which it revolves round the sun in a
year. It must always have so spun, for there is no cause known to science
by which, when this rotation was once established, the inclination of the
axis could have been permanently altered. The plane of the equator
shifts its position slowly on that of the ecliptic, owing to various minor
actions of the force of gravity, the principal one being the precession of
the equinoxes, due to the protuberant matter at the earth's equator ; and
thus in 22,000 years, it makes a complete circuit, returning to its original
position. But during this circuit, its inclination to the plane of the
ecliptic remains practically constant, and the effect on the seasons is un-
changed, except that they come at different positions of the earth in its



PROBLEMS OF THE FUTURE. 37

orbit round the sun, so that summer and winter alternately come when we
are farthest from the sun or nearest to it. At present we are nearer the
sun in winter than in summer, and the winter half of the year is shorter
than the summer half in the Northern hemisphere. In 11,000 years this
position will be reversed, and winter will be shorter than summer in the
Southern hemisphere ; but there is nothing in these slight changes to aifect
the general course of the seasons, and as we happen to be now nearer
the sun in winter, the effect of any slight change due to precession would
rather be to increase the difference between summer and winter heat in
high northern latitudes, and so aggravate the difficulty of reconciling the
conclusions of the two conflicting sciences. And yet there must be some
way of reconciling them. Truth cannot speak with two voices, and the
laws of nature cannot give contradictory results.

Let us consider first what the undoubted facts of geology require us to
assume. Two things firstly, that the general temperature of the earth
was higher in former times than now ; secondly, that it was more uniform.
As regards the first condition, astronomy interposes no obstacle but affords
no aid, and it must be admitted that we are still in the region of conject-
ure rather than of certainty. The first obvious guess is that the earth was
formerly hotter, and has been gradually cooling. But this guess is con-
tradicted by mathematical calculations as to the cooling of heated bodies,
which show that after the earth had cooled down to the point of forming
a solid crust, many miles in thickness, of non-conducting rock, internal
heat could have had little or no effect on surface temperature. This is
confirmed by what we know of the climates of areas where large reservoirs
of internal heat lie comparatively near the surface, as in Iceland and other
volcanic districts. In the celebrated Comstock lode the heat of the earth
increases so rapidly, that it becomes impossible to work the mines below
a very moderate depth. Yet in all these cases the temperature at the sur-
face remains the same as that of other regions on the same isotherm, and
is determined by the same circumstances of latitude, elevation, aerial and
ocean currents, and other known conditions. Nor if the internal tem-
perature of the earth was a factor in the problem, would it be easy to
account for our recovery from the cold of the Glacial period, in the face
of a continued and progressive diminution of the planet's heat

Another conjecture is that the sun may have given out more heat
formerly. This, however, is a mere guess, confirmed by no theory or ex-
perience. On the contrary, theory rather points to the paradoxical con-
clusion that, as the sun has cooled, it has got hotter; that is, that a volume
of gas, in cooling, develops rather more heat by contracting than it loses
by radiating. Moreover, as we have already seen, the difficulty is to
understand how even the present supply of solar heat can have been main-
tained long enough for the time requisite to account for the facts of
geology; and the improvement in climate since the Glacial period is as
inconsistent with solar as it is with terrestrial refrigeration.



38 BEACON LIGHTS OF SCIENCE.

The passage of the solar system through wanner and colder regions of
space is another explanation which has been invoked. But this though
by no means improbable is as yet a mere possibility, and based on noth-
ing approaching to actual knowledge.

Of existing known causes there is one which seems, as far as it goes, to
be a vera causa which might have given the earth's surface a warmer
temperature in early ages. Its reality may be proved by the very simple
experiment of sleeping on a cold night without a blanket. Evidently,
other circumstances being the same, such as the reading of the thermom-
eter and blood heat of the body, the question of blanket or no blanket
makes an immense difference in the resulting temperature. Why is this
the case ? Because the blanket keeps the heat in, or in other words
radiates it back to the body instead of letting it radiate out into space.
There are other things which do this even more effectually than a wollen
blanket, for they let the heat of the sun's rays in, and having let it in,
catch it as in a trap, and do not let it out again. Glass, for instance, in
a conservatory, is such a trap, and, as we all know, will keep the
temperature inside much warmer than it is outside, even without the aid
of artificial heat. Many other substances have the same property, and
among them two which are essential elements of the earth's atmosphere,
water in the form of vapor, and carbonic dioxide. Tyndall, in his Heat
considered as a Mode of Motion, has shown clearly what an immense part
these gases have in maintaining the temperature of the earth's surface.
If the cold is more intense, especially at night, on high mountains, it is
not because less heat is received from the sun's rays during the twenty-four
hours, but because half the atmosphere is left below, and so the heat-
retaining blanket is thin and threadbare. So in deserts where the air is dry
and there is little aqueous vapor, the heat by day may be excessive and
yet the cold by night well-nigh intolerable. "The removal," says
Tyndall, " for a single summer's night of the aqueous vapor which covers
England would be attended by the destruction of every plant which a
freezing temperature could kill." And such a removal on a winter's
night would send the thermometer down far below zero.

This property of retaining heat is not confined to water in the form of
vapor ; it is common to other gases, and often in a higher degree.
Among these is one which is always present in the atmosphere carbonic-
dioxide, a gas formed by the combination of two atoms of oxygen with
one of carbon.

The percentage of this gas in the air is very small, only a fraction of
one per cent. , and yet it constitutes the sole source of supply of the
carbon required, directly for vegetable, and indirectly for animal life.
At present the balance between the two sorts of life seems to be kept up,
as in an aquarium, by animals restoring to the air, in the form of car-
bonic-dioxide, the carbon which has been abstracted from it by plants.
But when we look at the enormous amount of carbon which has been



PROBLEMS OF THE FUTURE. 39

locked up in coal, limestone, and other carboniferous formations of the
arth's crust, it is evident that it must be vastly greater than could be de-
rived from such a small percentage of carbonic-dioxide as now exists in
the atmosphere. It has been estimated by experienced geologists as
many hundred times greater. Where all this carbon could have come
from is a question not yet solved. Some have thought that it may have
been supplied from the interior of the earth by volcanoes ; but although
it is certain that some volcanic vents do emit carbonic-dioxide, as in the
case of Lake Avernus, and the Grotto-del-cane, near Naples, the quantity
is small, and the better opinion seems to be that it is only given out when
iubterranean fires come in contact with limestone, or some other form
of previously deposited carbon. Did the carbon, then, come from the
air ? If so, there must have been more than one hundred times as much
carbonic-dioxide in it in early geological times as there is at present

This would go some way towards explaining the difficulty of the
higher temperature prevailing in past ages, for more carbonic-dioxide
would undoubtedly be equivalent to an additional blanket to protect the
earth from cold ; and the higher temperature thus caused would enable
the air to hold more aqueous vapor in solution, and thus increase the
thickness of the water-blanket

It is conceivable that under such conditions a warm and humid climate
may have prevailed over a great part of the earth's surface, though this
would hardly meet the difficulty of the uniform existence of such a climate
in latitudes where the supply of heat from the sun must have been so
very different in winter and summer. Nor would this difficulty be re-
moved even if we were to suppose that the earth's axis might have been
nearly vertical to the plane of the ecliptic. This might meet the difficulty
as to light and actinic rays, for there would be everywhere twelve hours
of day throughout the year ; but it would not meet the difficulty as to
temperature, for if the air-blanket was sufficient to retain heat enough in
the Arctic Circle to prevent frosts, from a sun which never rose much
above the horizon, it must have retained far too much heat for existing
life and vegetation in latitudes nearer to the equator.

There are, however, many grave objections to considering this to be the
sole or even the principal cause of the warmer climates of early ages. It
is by no means certain that either animal or vegetable life, in anything
like known forms, could exist in an atmosphere so surcharged with car-
bon. Nor is carbon all ; we must account also for oxygen. If the
whole of the carbon now fixed in the different strata of the earth's crust
was derived from carbonic-dioxide originally present in the atmosphere,
so also must have been the oxygen, which in various forms of oxides now
forms an even larger constituent of that crust. Oxygen is a very active
element, which, under moderate conditions of heat and moisture, com-
bines readily with iron, silicon, calcium, aluminium, and all the metallic
bases. Many hundred times more oxygen must have been withdrawn



4 o BEACON LIGHTS OF SCIENCE.

from the air than now exists in it to form the rocks which are the principal
part of the earth's crust. But an excess of oxygen is as fatal to life as an
excess of carbonic-dioxide. Terrestrial life, as known to us, depends on
a very delicate adjustment of the quantities of oxygen and nitrogen in the
air. A very little excess or deficit of either would destroy all air-breath-
ing animals. With too much oxygen we should be burnt up even more
rapidly than the drunkard is by too much alcohol ; with too little, the
fire of life would be choked by ashes and refuse. If there was formerly a
hundred, or even ten times more oxygen in the atmosphere than there is
now, there must have been a corresponding excess of nitrogen to neutra-
lize it, and if so, what has become of the nitrogen ? Nitrogen is an in-
ert element which enters sparingly into combinations, and does not, like
oxygen and carbon, get locked up in great masses of the earth's solid
crust. Once in the atmosphere it would seem that it must have remained
there ; and if so, as oxygen was withdrawn in continually increasing
quantities, how could the life-sustaining proportion of the two gases have
been maintained and continued down to the present day ?

It has been said that life may have been so differently organized in
past geological ages as to have existed under very different conditions,
and the mammoth is appealed to as an instance of an elephant modified
so as to resist Arctic cold, and the result of deep-sea dredgings shows that
molluscs, crustaceans, and other low forms of life may exist in ice-cold
water and without light But we can hardly suppose such profound
modifications of existing genera and species of highly-organized plants
and animals as would enable them to breathe air of a very different com-
position.

For we must remember that the evidence for an elevated and uniform
temperature is not confined to remote geological ages, but come down to
the close of the Tertiary period, when existing forms, both of animal and
vegetable life, were firmly established, and several species have survived
to the present day without perceptible change. Thus when the magnolia
was growing in Spitzbergen, the dryopithecus was living in Southern
France. Can it be supposed that this anthropoid ape breathed a different
air from his congeners, the chimpanzee and gorilla ; and yet if his lungs
required the same air, how could excess of carbonic-dioxide have sup-
plied the extra warm blanket to protect the Spitzbergen magnolia ?

A different configuration of sea and land is the explanation which
many geologists, following Lyell, have advanced for different con-
ditions of climate. And no doubt aerial and oceanic currents, such as
now cause the trade-winds and Gulf Stream, are responsible for great
variations of climate, while low lands in low, and high lands in high
latitudes must always have had a considerable influence in raising or de-
pressing temperature. But changes of this description can more readily
account for the cold of the Glacial, than for the heat of the Tertiary and
preceding periods. We have now got the trade-winds and the Gulf



PROBLEMS OF THE FUTURE. 41

Stream in the North Atlantic, and although the diversion of the latter
might bring the ice-cap back to London and New York, and make the
climate of Scandinavia and Scotland the same as that of Greenland and
Labrador, its presence takes us a very short way towards enabling mag-
nolias to flourish in Spitzbergen.

In like manner, even if Croll's theory were established, which it is far
from being, and the effect of the obliquity of the earth's axis combined
with precession, though imperceptible while the earth's orbit was nearly
circular, became great in the two hemispheres alternately, when the
orbit was approaching its maximum eccentricity, this would not explain
the high and uniform temperature of past geological ages. If this theory
were true, what we should look for would be two or three Glacial periods
in the course of each geological epoch; for the least time required for any
of the great geological formations must have been long enough to include
two or three secular variations of the earth's orbit, from minimum to
maximum eccentricity. And each of these Glacial periods must have in-
cluded several changes, alternating, at intervals of 11,000 years, between
severe cold and genial heat, owing to the effect of the precession of the
equinoxes combined with great eccentricity.

Instead of uniform warmth, there must have been more than 100
Glacial periods during the immense lapse of time between the dawn of
life in the Cambrian, and the last of such periods in the Quaternary. It
is a moot point with geologists whether traces of a single one of such
periods, prior to the last one, have been found. There are a few con-
glomerates which look very like consolidated boulder-clays, and every
now and then we hear of some formation, supposed to be glaciated, be-
ing found in the Permian and in other formations in India, South Africa,
and Australia; but there is no evidence hitherto which commands the
general assent of geologists, for a single Glacial period prior to the recent
one which closed the Tertiary period. And there is abundant evidence
that during many formations, such as the Carboniferous and Coal-
measures, which must have taken millions of years to accumulate, there
were no vicissitudes of climate such as must have inevitably occurred if
any astronomical cause, such as precession or eccentricity, had been suffi-
cient to bring about great vicissitudes of heat and cold. And what is
still more conclusive, the evolution of vegetable and animal life, as shown
by fossils, affords no trace of the repeated modifications which must have
taken place within the limits of the same geological formation, if there
had been such vicissitudes of heat and cold as the theory requires.

It remains to be considered whether any change in the direction of the
earth's axis may have been possible. Clearly no such change can have
taken place within the earth itself, for its shape is that of an oblate
spheroid, revolving round its present axis. Any displacement of the
poles must displace the present equator, and tend to establish a new one
on a different plane. But the equatorial diameter of the earth if a6 mils*



42 BEACON LIGHTS OF SCIENCE.

longer than the polar diameter, so that any displacement of the poUt
must have tended to displace this enormous mass of protuberant matter,
and send such portion of it as was fluid in a diluvian wave, miles in
height, towards the new position of equilibrium; while the solid portion
remained in a plane no longer coincident with that of the earth's rotation.
There is no trace of anything of the sort having ever occurred, and if the
axis has shifted, the whole earth has shifted with it, which is just what
astronomers declare to be impossible by any known laws.

But are the whole of the laws really known ? There is nothing more
difficult than to account for the varying inclinations of the axes of rota-
tion of the different bodies of the solar system. On the nebular hypo-
thesis, which traces the sun, planets, and satellites back to the conden-
sation of a revolving mass of nebulous matter, one might have expected
to find the planes of rotation and revolution of planets and satellites, not
only in the same general direction from west to east, but nearly coinci-
dent Jupiter, however, is the only one of the planets which fulfills this
condition. Its axis of rotation is inclined at an angle of 87, or very
nearly at right angles, to the plane of its revolution round the sun. But
there is no certain rule. That of Saturn, which comes next in order on
the outside of Jupiter, has an inclination of 64 while that of the next
planet on the inside, Mars, is 61 18'. The earth's axis is inclined at
66 33', while we find its satellite, the moon, rotating like Jupiter in a
plane inclined only i 30', and the axis of Venus, on the other hand, is
so oblique, that in its winter the Arctic Circle almost extends to the
equator.

The case of the moon is most difficult to understand, for on any
theory of its origin, whether as a condensed ring left behind as the neb-
ulous matter of the earth contracted, or whether it was ejected from the
earth in some eruption of its fiery stages, it might have been expected to
retain nearly the same rotatory motion as its parent orb. But if so,
clearly some unkown force must have intervened, either to make the
earth's axis more, or that of the moon less oblique, than they were orig-
inally. No such force is known, nor has any plausible guess been made
as to what might have occasioned it ; but the same observation applies
to many of the phenomena of the solar system. How has the supply of
solar heat been kept up for the time required by geology ? How does
the energy we call gravitation act across space from atom to atom, and
from star to star, and how is its supply maintained ? Why is the axis
of the earth inclined at an angle of 66 30' to the ecliptic, while that of
Jupiter is almost perpendicular to it, and that of Venus oblique to the
extent of nearly two-thirds of a right angle ?

These are all problems which depend on natural laws, and must lie
within the limits of human reason ; but they are pebbles which have not
f et been picked up on the shore of the ocean of truth. It may bring
home to us the force of Newton's saying that w are but as children pick-



PROBLEMS OF THE FUTURE,



43



ing up such pebbles when we see what a multitude of the deepest prob-
lems, as to the constitution of the earth and of the universe, are raised
by the simple fact that Captain Nares brought back a specimen of coral
from latitude 81 40' in Greenland, and that luxuriant forests, of a sub-
tropical or warm temperate vegetation, flourished in Spitzbergen as
lately as the period when an anthropoid ape of the stature of man was liv-
ing in the south of France, and when man himself or his savage progeni-
tors, were possibly or even probat/1/ already chipping flints into rude im-
plements.



CHAPTER !V.

THE GLACIAL PERIOD.

THE date and duration of the Glacial period present a problem which
is in many respects of the highest interest. It comes nearest to us
as inaugurating the recent period in which we live, and for which we have
historical data. It affords the best chance of obtaining an approximate
standard by which to measure geological time in years or centuries. And
it touches directly on the great question of the Origin of Man.

For man is like the mammoth and cave bear, an essential part of the
Quaternary fauna, and whatever doubts may be entertained as to his ex-
istence in Tertiary times, there can be none as to the fact that his remains
are found in great numbers, and widely scattered over the four quarters of
the globe, in conjunction with those of the mammoth and other
characteristic Quaternary mammals, in deposits which date, probably from
the earlier, and certainly from the intermediate and later stages of the
Glacial period. A short date, therefore, for that period shortens that for
which we have positive proof of the existence of man, and a very short
date reduces it to a length during which it is simply impossible that such
a state of things as is found existing in Egypt 7000 years ago could have
grown up by natural laws and evolution, and therefore brings us back to
the old theories of repeated and recent acts of supernatural interference,
which, since the works of Lyell and of Darwin, have been generally con-
sidered to be completely exploded.

The question, therefore, is one of the highest theological as well as
scientific importance, and as such it has too often been approached with
theological prepossessions. An extreme instance of this is afforded by
Sir J. Dawson, who in his work on Fossil Man assigns 7000 years as the
probable date for the first appearance of man upon earth, ignoring the
fact that at this date a dense and civilized population already existed in
Egypt, with a highly-developed language and system of writing and
religion; and that the types of the various races of mankind, such as the
Negro, the Copt, the Semitic, and the Arian, are as clearly distinguished
in the paintings in Egyptian tombs, 5000 years ago, as they are at the
present day.

Sir J. Dawson, however, though an excellent geologist as long as the
older formations are concerned, is so dominated by the desire to square



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