498 
NATURE 
[SEPTEMBER 21, 1899 
well-known argument from the observed rate o1 increase of 
temperature downwards from the surface of the land. He 
astonished geologists by announcing to them that some definite 
limits to the age of our planet might be ascertained, and by 
declaring his belief that this age must be more than 20 millions, 
but less than 400 millions, of years. 
Nearly four years later he emphasised his dissent from what 
he considered to be the current geological opinions of the day 
by repeating the same argument in a more pointedly antagonistic 
form in a paper of only a few sentences, entitled, ‘‘ The Doctrine 
of Uniformity in Geology briefly refuted ” (Proc. Roy. Soc. Edin., 
vol. v. p. 512, December 18, 1865). 
Again, after a further lapse of about two years, when, as 
President of the Geological Society of Glasgow, it became his 
duty to give an address, he returned to the same topic and 
arraigned more boldly and explicitly than ever the geology of 
the time. He then declared that ‘‘a great reform in geological 
speculation seems now to have become necessary,” and he 
went so far as to affirm that ‘‘it is quite certain that a great 
mistake has been made—that British popular geology at the 
present time is in direct opposition to the principles of natural 
philosophy” ( 7vavs. Geol. Soc. Glasgow, vol. iii., February 1868, 
pp- I, 16). In pressing once more the original argument de- 
rived from the downward increase of terrestrial temperature, he 
now reinforced it by two further arguments, the one based on the 
retardation of the earth’s angular velocity by tidal friction, the 
other on the limitation of the age of the sun. 
These three lines of attack remain still those along which the 
assault from physics is delivered against the strongholds of 
geology. Lord Kelvin has repeatedly returned to the charge 
since 1868, his latest contribution to the controversy having been 
pronounced two years ago.’ While his physical arguments re- 
main the same, the limits of time which he deduces from them 
have been successively diminished. The original maximum of 
400 millions of years has now been restricted by him to not much 
more than 20 millions, while Prof. Tait grudgingly allows 
something less than 10 millions (‘‘ Recent Advances in Physical 
Science,” p. 174). 
Soon after the appearance of Lord Kelvin’s indictment of 
modern geology in 1868, the defence of the science was taken up 
by Huxley, who happened at the time to be President of the 
Geological Society of London. In his own inimitably brilliant 
way, half seriously, half playfully, this doughty combatant, with 
evident relish, tossed the physical arguments to and fro in the 
eyes of his geological brethren, as a barrister may flourish his 
brief before a sympathetic jury. He was willing to admit that 
‘* the rapidity of rotation of the earth #ay be diminishing, that 
the sun may be waxing dim, or that the earth itself »zay be cool- 
ing.” But he went on to add his suspicion that ‘‘ most of us 
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” (Presidential Address, Quart. Journ. Geol. 
Soc., 1869). 
For the indifference which their advocate thus professed on 
their behalf most geologists believed that they had ample 
justification. The limits within which the physicist would cir- 
cumscribe the earth’s history were so vague, yet so vast, that 
whether the time allowed were 400 millions or 100 millions of 
years did not seem to them greatly to matter. After all, it was 
not the time that chiefly interested them, but the grand 
succession of events which the time had witnessed. That 
succession had been established on observations so abundant 
and so precise that it could withstand attack from any quarter, 
and it had taken as firm and lasting a place among the solid 
achievements of science as could be claimed for any physical 
speculations whatsoever. Whether the time required for the 
transaction of this marvellous earth-history was some millions of 
years more or some millions of years less did not seem to the 
geologists to be a question on which their science stood in 
antagonism with the principles of natural philosophy, but one 
which the natural philosophers might be left to settle at their 
own good pleasure. 
For myself, I may be permitted here to say that I have never 
shared this feeling of indifference and unconcern. As far back 
as the year 1868, only a month after Lord Kelvin's first pre- 
sentation of his threefold argument in favour of limiting the age 
of the earth, I gave in my adhesion to the propriety of restricting 
1“ The Age of the Earth,” being the Annual Address to the Victoria 
Institute, June 2, 1897. ‘PAZ. Mag., January 1899, p. 66. 
NO. 1560, VOL. 60] 
the geological demands for time. I then showed that even the 
phenomena of denudation, which, from the time of Hutton 
downwards, had been most constantly and confidently appealed 
to in support of the inconceivably vast antiquity of our globe, 
might be accounted for, at the present rate of action, within 
such a period as 100 millions of years.!- To my mind it has 
always seemed that whatever tends to give more precision to the 
chronology of the geologist, and helps him to a clearer con- 
ception of the antiquity with which he has to deal, ought to be 
welcomed by him as a valuable assistance in his inquiries. And 
I feel sure that this view of the matter has now become general 
among those engaged in geological research. Frank recog- 
nition is made of the influence which Lord Kelvin’s persistent 
attacks have had upon our science. Geologists have been led 
by his criticisms to revise their chronology. They gratefully 
acknowledge that to him they owe the introduction of important 
new lines of investigation, which link the solution of the 
problems of geology with those of physics. They realise how 
much he has done to dissipate the former vague conceptions as 
to the duration of geological history, and even when they em- 
phatically dissent from the greatly restricted bounds within 
which he would now limit that history, and when they declare 
their inability to perceive that any reform of their speculations 
in this subject is needful, or that their science has placed herself 
in opposition to the principles of physics, they none the less pay 
their sincere homage to one who has thrown over geology, as 
over so many other departments of natural knowledge, the clear 
light of a penetrating and original genius. 
When Lord Kelvin first developed his strictures on modern 
geology he expressed his opposition in the most uncompromising 
language. In the short paper to which reference has already 
been made he announced, without hesitation or palliation, that 
he ‘‘ briefly refuted’ the doctrine of Uniformitarianism which 
had been espoused and illustrated by Lyell and a long list of the 
ablest geologists of the day. The severity of his judgment of 
British geology was not more marked than was his unqualified 
reliance on his own methods and results. This confident assur- 
ance of a distinguished physicist, together with a formidable 
array of mathematical formule, produced its effect on some 
geologists and palzeontologists who were not Gallios. Thus, even 
after Huxley’s brilliant defence, Darwin could not conceal the 
deep impression which Lord Kelvin’s arguments had made on 
his mind. In one letter he wrote that the proposed limitation 
of geological time was one of his ‘‘sorest troubles.” In 
another, he pronounced the physicist himself to be ‘fan odious 
spectre”’ (Darwin’s ‘‘ Life and Letters,” vol. iii. pp. 115, 146). 
The same self-confidence of assertion on the part of some, at 
least, of the disputants on the physical side has continued all 
through the controversy. Yet when we examine the three great 
physical arguments in themselves, we find them to rest on 
assumptions which, though certified as ‘‘ probable” or ‘‘ very 
sure,” are nevertheless admittedly assumptions. The conclusions 
to which these assumptions lead must depend for their validity 
on the degree of approximation to the truth in the premisses 
which are postulated. 
Now it is interesting to observe that neither the assumptions 
nor the conclusions drawn from them have commanded universal 
assent even among physicists themselves. If they were as self- 
evident as they have been claimed to be, they should at least 
receive the loyal support of all those whose function it is to 
pursue and extend the applications of physics. It will be 
remembered, however, that thirteen years ago Prof. George 
Darwin, who has so often shown his inherited sympathy in 
geological investigation, devoted his presidential address before 
the Mathematical Section of this Association to a review of the 
three famous physical arguments respecting the age of the 
earth. Tle summed up his judgment of them in the following 
words: ‘‘ In considering these three arguments I have adduced 
some reasons against the validity of the first (tidal friction) ; and 
have endeavoured to show that there are elements of uncertainty 
surrounding the second (secular cooling of the earth) ; neverthe- 
less they undoubtedly constitute a contribution of the first 
importance to physical geology. Whilst, then, we may protest 
against the precision with which Prof. Tait seeks to deduce 
results from them, we are fully justified in following Sir William 
Thomson, who says that ‘* the existing state of things on the 
earth, life on the earth—all geological history showing con- 
1 Trans. Geol. Soc, Glasgow, vol. iii, (March 26, 1868), p. 189. Sir W. 
Thomson acknowledged my adhesion in his reply to Huxley's criticism. 
Op. cit. p. 221. 
