expounds a complete cosmogony, in the shape of a theory of the causes
which have led to the development of the universe from diffused atoms of
matter endowed with simple attractive and repulsive forces.
"Give me matter," says Kant, "and I will build the world;" and he
proceeds to deduce from the simple data from which he starts, a doctrine
in all essential respects similar to the well-known "Nebular Hypothesis"
of Laplace.[51] He accounts for the relation of the masses and the
densities of the planets to their distances from the sun, for the
eccentricities of their orbits, for their rotations, for their
satellites, for the general agreement in the direction of rotation among
the celestial bodies, for Saturn's ring, and for the zodiacal light. He
finds, in each system of worlds, indications that the attractive force
of the central mass will eventually destroy its organization, by
concentrating upon itself the matter of the whole system; but, as the
result of this concentration, he argues for the development of an amount
of heat which will dissipate the mass once more into a molecular chaos
such as that in which it began.
Kant pictures to himself the universe as once an infinite expansion of
formless and diffused matter. At one point of this he supposes a single
centre of attraction set up; and, by strict deductions from admitted
dynamical principles, shows how this must result in the development of a
prodigious central body, surrounded by systems of solar and planetary
worlds in all stages of development. In vivid language he depicts the
great world-mælstrom, widening the margins of its prodigious eddy in the
slow progress of millions of ages, gradually reclaiming more and more of
the molecular waste, and converting chaos into cosmos. But what is
gained at the margin is lost in the centre; the attractions of the
central systems bring their constituents together, which then, by the
heat evolved, are converted once more into molecular chaos. Thus the
worlds that are, lie between the ruins of the worlds that have been and
the chaotic materials of the worlds that shall be; and, in spite of all
waste and destruction, Cosmos is extending his borders at the expense of
Chaos.
Kant's further application of his views to the earth itself is to be
found in his "Treatise on Physical Geography"[52] (a term under which
the then unknown science of geology was included), a subject which he
had studied with very great care and on which he lectured for many
years. The fourth section of the first part of this Treatise is called
"History of the great Changes which the Earth has formerly undergone and
is still undergoing," and is, in fact, a brief and pregnant essay upon
the principles of geology. Kant gives an account first "of the gradual
changes which are now taking place" under the heads of such as are
caused by earthquakes, such as are brought about by rain and rivers,
such as are effected by the sea, such as are produced by winds and
frost; and, finally, such as result from the operations of man.
The second part is devoted to the "Memorials of the Changes which the
Earth has undergone in remote antiquity." These are enumerated as:--A.
Proofs that the sea formerly covered the whole earth. B. Proofs that the
sea has often been changed into dry land and then again into sea. C. A
discussion of the various-theories of the earth put forward by
Scheuchzer, Moro, Bonnet, Woodward, White, Leibnitz, Linnæus, and
Buffon.
The third part contains an "Attempt to give a sound explanation of the
ancient history of the earth."
I suppose that it would be very easy to pick holes in the details of
Kant's speculations, whether cosmological, or specially telluric, in
their application. But, for all that, he seems to me to have been the
first person to frame a complete system of geological speculation by
founding the doctrine of evolution.
With as much truth as Hutton, Kant could say, "I take things just as I
find them at present, and, from these, I reason with regard to that
which must have been." Like Hutton, he is never tired of pointing out
that "in Nature there is wisdom, system, and consistency." And, as in
these great principles, so in believing that the cosmos has a
reproductive operation "by which a ruined constitution may be repaired,"
he forestalls Hutton; while, on the other hand, Kant is true to science.
He knows no bounds to geological speculation but those of the intellect.
He reasons back to a beginning of the present state of things; he admits
the possibility of an end.
I have said that the three schools of geological speculation which I
have termed Catastrophism, Uniformitarianism, and Evolutionism are
commonly supposed to be antagonistic to one another; and I presume it
will have become obvious that, in my belief, the last is destined to
swallow up the other two. But it is proper to remark that each of the
latter has kept alive the tradition of precious truths.
CATASTROPHISM has insisted upon the existence of a practically
unlimited bank of force, on which the theorist might draw; and it has
cherished the idea of the development of the earth from a state in which
its form, and the forces which it exerted, were very different from
those we now know. That such difference of form and power once existed
is a necessary part of the doctrine of evolution.
UNIFORMITARIANISM, on the other hand, has with equal justice
insisted upon a practically unlimited bank of time, ready to discount
any quantity of hypothetical paper. It has kept before our eyes the
power of the infinitely little, time being granted, and has compelled us
to exhaust known causes, before flying to the unknown.
To my mind there appears to be no sort of necessary theoretical
antagonism between Catastrophism and Uniformitarianism. On the contrary,
it is very conceivable that catastrophes may be part and parcel of
uniformity. Let me illustrate my case by analogy. The working of a clock
is a model of uniform action; good time-keeping means uniformity of
action. But the striking of the clock is essentially a catastrophe; the
hammer might be made to blow up a barrel of gunpowder, or turn on a
deluge of water; and, by proper arrangement, the clock, instead of
marking the hours, might strike at all sorts of irregular periods, never
twice alike, in the intervals, force, or number of its blows.
Nevertheless, all these irregular, and apparently lawless, catastrophes
would be the result of an absolutely uniformitarian action; and we might
have two schools of clock-theorists, one studying the hammer and the
other the pendulum.
Still less is there any necessary antagonism between either of these
doctrines and that of Evolution, which embraces all that is sound in
both Catastrophism and Uniformitarianism, while it rejects the arbitrary
assumptions of the one and the, as arbitrary, limitations of the other.
Nor is the value of the doctrine of Evolution to the philosophic thinker
diminished by the fact that it applies the same method to the living and
the not-living world; and embraces, in one stupendous analogy, the
growth of a solar system from molecular chaos, the shaping of the earth
from the nebulous cubhood of its youth, through innumerable changes and
immeasurable ages, to its present form; and the development of a living
being from the shapeless mass of protoplasm we term a germ.
I do not know whether Evolutionism can claim that amount of currency
which would entitle it to be called British popular geology; but, more
or less vaguely, it is assuredly present in the minds of most
geologists.
Such being the three phases of geological speculation, we are now in a
position to inquire which of these it is that Sir William Thomson calls
upon us to reform in the passages which I have cited.
It is obviously Uniformitarianism which the distinguished physicist
takes to be the representative of geological speculation in general. And
thus a first issue is raised, inasmuch as many persons (and those not
the least thoughtful among the younger geologists) do not accept strict
Uniformitarianism as the final form of geological speculation. We should
say, if Hutton and Playfair declare the course of the world to have been
always the same, point out the fallacy by all means; but, in so doing,
do not imagine that you are proving modern geology to be in opposition
to natural philosophy. I do not suppose that, at the present day, any
geologist would be found to maintain absolute Uniformitarianism, to deny
that the rapidity of the rotation of the earth _may_ be diminishing,
that the sun _may_ be waxing dim, or that the earth itself _may_ be
cooling. Most of us, I suspect, are Gallios, "who care for none of these
things," being of opinion that, true or fictitious, they have made no
practical difference to the earth, during the period of which, a record
is preserved in stratified deposits.
The accusation that we have been running counter to the _principles_ of
natural philosophy, therefore, is devoid of foundation. The only
question which can arise is whether we have, or have not, been tacitly
making assumptions which are in opposition to certain conclusions which
may be drawn from those principles. And this question subdivides itself
into two:--the first, are we really contravening such conclusions? the
second, if we are, are those conclusions so firmly based that we may not
contravene them? I reply in the negative to both these questions, and I
will give you my reasons for so doing. Sir William Thomson believes that
he is able to prove, by physical reasonings, "that the existing state of
things on the earth, life on the earth--all geological history showing
continuity of life--must be limited within some such period of time as
one hundred million years" (loc. cit. p. 25).
The first inquiry which arises plainly is, has it ever been denied that
this period _may_ be enough for the purposes of geology?
The discussion of this question is greatly embarrassed by the vagueness
with which the assumed limit is, I will not say defined, but
indicated,--"some such period of past time as one hundred million
years." Now does this mean that it may have been two, or three, or four
hundred million years? Because this really makes all the difference.[53]
I presume that 100,000 feet may be taken as a full allowance for the
total thickness of stratified rocks containing traces of life; 100,000
divided by 100,000,000 = 0.001. Consequently, the deposit of 100,000
feet of stratified rock in 100,000,000 years means that the deposit has
taken place at the rate of 1/1000 of a foot, or, say, 1/83 of an inch,
per annum.
Well, I do not know that any one is prepared to maintain that, even
making all needful allowances, the stratified rocks may not have been
formed, on the average, at the rate of 1/83 of an inch per annum. I
suppose that if such could be shown to be the limit of world-growth, we
could put up with the allowance without feeling that our speculations
had undergone any revolution. And perhaps, after all, the qualifying
phrase "some such period" may not necessitate the assumption of more
than 1/166, or 1/249, or 1/332 of an inch of deposit per year, which, of
course, would give us still more ease and comfort.
But, it may be said, that it is biology, and not geology, which asks for
so much time--that the succession of life demands vast intervals; but
this appears to me to be reasoning in a circle. Biology takes her time
from geology. The only reason we have for believing in the slow rate of
the change in living forms is the fact that they persist through a
series of deposits which, geology informs us, have taken a long while to
make. If the geological clock is wrong, all the naturalist will have to
do is to modify his notions of the rapidity of change accordingly. And I
venture to point out that, when we are told that the limitation of the
period during which living beings have inhabited this planet to one,
two, or three hundred million years requires a complete revolution in
geological speculation, the _onus probandi_ rests on the maker of the
assertion, who brings forward not a shadow of evidence in its support.
Thus, if we accept the limitation of time placed before us by Sir W.
Thomson, it is not obvious, on the face of the matter, that we shall
have to alter, or reform, our ways in any appreciable degree; and we may
therefore proceed with much calmness, and indeed much indifference, as
to the result, to inquire whether that limitation is justified by the
arguments employed in its support.
These arguments are three in number:--
I. The first is based upon the undoubted fact that the tides tend to
retard the rate of the earth's rotation upon its axis. That this must be
so is obvious, if one considers, roughly, that the tides result from the
pull which the sun and the moon exert upon the sea, causing it to act as
a sort of break upon the rotating solid earth.
Kant, who was by no means a mere "abstract philosopher," but a good
mathematician and well versed in the physical science of his time, not
only proved this in an essay of exquisite clearness and intelligibility,
now more than a century old,[54] but deduced from it some of its more
important consequences, such as the constant turning of one face of the
moon towards the earth.
But there is a long step from the demonstration of a tendency to the
estimation of the practical value of that tendency, which is all with
which we are at present concerned. The facts bearing on this point
appear to stand as follow:--
It is a matter of observation that the moon's mean motion is (and has
for the last 3,000 years been) undergoing an acceleration, relatively to
the rotation of the earth. Of course this may result from one of two
causes: the moon may really have been moving more swiftly in its orbit;
or the earth may have been rotating more slowly on its axis.
Laplace believed he had accounted for this phænomenon by the fact that
the eccentricity of the earth's orbit has been diminishing throughout
these 3,000 years. This would produce a diminution of the mean
attraction of the sun on the moon; or, in other words, an increase in
the attraction of the earth on the moon: and, consequently, an increase
in the rapidity of the orbital motion of the latter body. Laplace,
therefore, laid the responsibility of the acceleration upon the moon;
and if his views were correct, the tidal retardation must either be
insignificant in amount, or be counteracted by some other agency.
Our great astronomer, Adams, however, appears to have found a flaw in
Laplace's calculation, and to have shown that only half the observed
retardation could be accounted for in the way he had suggested. There
remains, therefore, the other half to be accounted for; and here, in the
absence of all positive knowledge, three sets of hypotheses have been
suggested.
(a) M. Delaunay suggests that the earth is at fault, in consequence
of the tidal retardation. Messrs. Adams, Thomson, and Tait work out this
suggestion, and, "on a certain assumption as to the proportion of
retardations due to the sun and the moon," find the earth may lose
twenty-two seconds of time in a century from this cause.[55]
(b) But M. Dufour suggests that the retardation of the earth (which
is hypothetically assumed to exist) may be due in part, or wholly, to
the increase of the moment of inertia of the earth by meteors falling
upon its surface. This suggestion also meets with the entire approval of
Sir W. Thomson, who shows that meteor-dust, accumulating at the rate of
one foot in 4,000 years, would account for the remainder of
retardation.[56]
(c) Thirdly, Sir W. Thomson brings forward an hypothesis of his own
with respect to the cause of the hypothetical retardation of the earth's
rotation:--
"Let us suppose ice to melt from the polar regions (20° round each pole,
we may say) to the extent of something more than a foot thick, enough to
give 1.1 foot of water over those areas, or 0.006 of a foot of water if
spread over the whole globe, which would, in reality, raise the
sea-level by only some such undiscoverable difference as three-fourths
of an inch or an inch. This, or the reverse, which we believe might
happen any year, and could certainly not be detected without far more
accurate observations and calculations for the mean sea-level than any
hitherto made, would slacken or quicken the earth's rate as a timekeeper
by one-tenth of a second per year."[57]
I do not presume to throw the slightest doubt upon the accuracy of any
of the calculations made by such distinguished mathematicians as those
who have made the suggestions I have cited. On the contrary, it is
necessary to my argument to assume that they are all correct. But I
desire to point out that this seems to be one of the many cases in which
the admitted accuracy of mathematical processes is allowed to throw a
wholly inadmissible appearance of authority over the results obtained by
them. Mathematics may be compared to a mill of exquisite workmanship,
which grinds you stuff of any degree of fineness; but, nevertheless,
what you get out depends on what you put in; and as the grandest mill in
the world will not extract wheat-flour from peascods, so pages of
formulæ will not get a definite result out of loose data.
In the present instance it appears to be admitted:--
1. That it is not absolutely certain, after all, whether the moon's mean
motion is undergoing acceleration, or the earth's rotation
retardation.[58] And yet this is the key of the whole position.
2. If the rapidity of the earth's rotation is diminishing, it is not
certain how much of that retardation is due to tidal friction,--how much
to meteors,--how much to possible excess of melting over accumulation of
polar ice, during the period covered by observation, which amounts, at
the outside, to not more than 2,600 years.
3. The effect of a different distribution of land and water in modifying
the retardation caused by tidal friction, and of reducing it, under some
circumstances, to a minimum, does not appear to be taken into account.
4. During the Miocene epoch the polar ice was certainly many feet
thinner than it has been during, or since, the Glacial epoch. Sir W.
Thomson tells us that the accumulation of something more than a foot of
ice around the poles (which implies the withdrawal of, say, an inch of
water from the general surface of the sea) will cause the earth to
rotate quicker by one-tenth of a second per annum. It would appear,
therefore, that the earth may have been rotating, throughout the whole
period which has elapsed from the commencement of the Glacial epoch down
to the present time, one, or more, seconds per annum quicker than it
rotated during the Miocene epoch.
But, according to Sir W. Thomson's calculation, tidal retardation will
only account for a retardation of 22" in a century, or 22/100 (say 1/5)
of a second per annum.
Thus, assuming that the accumulation of polar ice since the Miocene
epoch has only been sufficient to produce ten times the effect of a coat
of ice one foot thick, we shall have an accelerating cause which covers
all the loss from tidal action, and leaves a balance of 4/5 a second per
annum in the way of acceleration.
If tidal retardation can be thus checked and overthrown by other
temporary conditions, what becomes of the confident assertion, based
upon the assumed uniformity of tidal retardation, that ten thousand
million years ago the earth must have been rotating more than twice as
fast as at present, and, therefore, that we geologists are "in direct
opposition to the principles of Natural Philosophy" if we spread
geological history over that time?
II. The second argument is thus stated by Sir W. Thomson:--"An article,
by myself, published in 'Macmillan's Magazine' for March 1862, on the
age of the sun's heat, explains results of investigation into various
questions as to possibilities regarding the amount of heat that the sun
could have, dealing with it as you would with a stone, or a piece of
matter, only taking into account the sun's dimensions, which showed it
to be possible that the sun may have already illuminated the earth for
as many as one hundred million years, but at the same time rendered it
almost certain that he had not illuminated the earth for five hundred
millions of years. The estimates here are necessarily very vague; but
yet, vague as they are, I do not know that it is possible, upon any
reasonable estimate founded on known properties of matter, to say that
we can believe the sun has really illuminated the earth for five hundred
million years."[59]
I do not wish to "Hansardize" Sir William Thomson by laying much stress
on the fact that, only fifteen years ago, he entertained a totally
different view of the origin of the sun's heat, and believed that the
energy radiated from year to year was supplied from year to year--a
doctrine which would have suited Hutton perfectly. But the fact that so
eminent a physical philosopher has, thus recently, held views opposite
to those which he now entertains, and that he confesses his own
estimates to be "very vague," justly entitles us to disregard those
estimates, if any distinct facts on our side go against them. However, I
am not aware that such facts exist. As I have already said, for anything
I know, one, two, or three hundred millions of years may serve the needs
of geologists perfectly well.
III. The third line of argument is based upon the temperature of the
interior of the earth. Sir W. Thomson refers to certain investigations
which prove that the present thermal condition of the interior of the
earth implies either a heating of the earth within the last 20,000 years
of as much as 100° F., or a greater heating all over the surface at some
time further back than 20,000 years, and then proceeds thus:--
"Now, are geologists prepared to admit that, at some time within the
last 20,000 years, there has been all over the earth so high a
temperature as that? I presume not; no geologist--no _modern_
geologist--would for a moment admit the hypothesis that the present
state of underground heat is due to a heating of the surface at so late
a period as 20,000 years ago. If that is not admitted, we are driven to
a greater heat at some time more than 20,000 years ago. A greater
heating all over the surface than 100° Fahrenheit would kill nearly all
existing plants and animals, I may safely say. Are modern geologists
prepared to say that all life was killed off the earth 50,000, 100,000,
or 200,000 years ago? For the uniformity theory, the further back the
time of high surface-temperature is put the better; but the further back
the time of heating, the hotter it must have been. The best for those
who draw most largely on time is that which puts it furthest back; and
that is the theory that the heating was enough to melt the whole. But
even if it was enough to melt the whole, we must still admit some limit,
such as fifty million years, one hundred million years, or two or three
hundred million years ago. Beyond that we cannot go."[60]
It will be observed that the "limit" is once again of the vaguest,
ranging from 50,000,000 years to 300,000,000. And the reply is, once
more, that, for anything that can be proved to the contrary, one or two
hundred million years might serve the purpose, even of a thorough-going
Huttonian uniformitarian, very well.
But if, on the other hand, the 100,000,000 or 200,000,000 years appear
to be insufficient for geological purposes, we must closely criticise
the method by which the limit is reached. The argument is simple enough.
_Assuming_ the earth to be nothing but a cooling mass, the quantity of
heat lost per year, _supposing_ the rate of cooling to have been
uniform, multiplied by any given number of years, will be given the
minimum temperature that number of years ago.
But is the earth nothing but a cooling mass, "like a hot-water jar such
as is used in carriages," or "a globe of sandstone?" and has its cooling
been uniform? An affirmative answer to both these questions seems to be
necessary to the validity of the calculations on which Sir W. Thomson
lays so much stress.