518 
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 
TI feel sure that this view of the matter has 
now become general among those engaged 
in geological research. Frank recognition 
is made of the influence which Lord Kel- 
vin’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 realize how much he has 
done to dissipate the former vague con- 
ceptions as to the duration of geological 
history, and even when they emphatically 
dissent from the greatly restricted bounds 
within which he would now limit that 
history, and when they declare their in- 
ability to perceive that any reform of their 
speculations in this subject is needful, or 
that their science has placed herself in op- 
position 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 an- 
nounced, 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 se- 
verity of his judgment of British geology 
was not more marked than was his un- 
qualified reliance on his own methods and 
results. This confident assurance of a dis- 
SCIENCE. 
[N.S. Vou. X. No. 250. 
tinguished physicist, together with a for- 
midable array of mathematical formule, 
produced its effect on some geologists and 
paleontologists who were not Gallios. Thus, 
even after Huxley’s brilliant defense, Dar- 
win 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 an- 
other, he pronounced the physicist himself 
to be ‘an odious spectre.”* 
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 argu- 
ments 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 de- 
pend for their validity on the degree of ap- 
proximation to the truth in the premises 
which are postulated. 
Now it is interesting to observe that 
neither the assumptions nor the conclusions 
drawn from them have commanded uni- 
versal assent even among physicists them- 
selves. 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 re- 
membered, however, that thirteen years ago 
Professor George Darwin, who has so often 
shown his inherited sympathy in geological 
investigation, devoted his presidential ad- 
dress before the Mathematical Section of 
this Association to a review of the three 
famous physical arguments respecting the 
age of the earth. He summed up his judg- 
ment of them in the following words: ‘In 
considering these three arguments I have 
adduced some reasons against the validity 
* Darwin’s Life and Letters, Vol. III., pp. 115, 146. 
