Geoscience Reference
In-Depth Information
The geologist found himself in the plight of Lear when his bodyguard of one hundred
knights was cut down. “What need you five-and-twenty, ten or five?” demands the inexorable
physicist, as he remorselessly strikes slice after slice from his allowance of geological time.
(19)
Kelvin had given geology a letter of credit in the amount of 20 million years
but would extend no more. His friend, fellow Scot, and coauthor Peter Tait, who
might well have been nicknamed “Kelvin's Bulldog,” reduced the allowance still
further. In a lengthy 1869 review of the Kelvin-Huxley debate, Tait derided geo-
logy as little more than “beetle-hunting or crab-catching,” its practitioners incap-
able of appreciating mathematics. Tait proved himself an even stricter bookkeeper
than Kelvin, allowing geologists only “ten or fifteen millions of years . . . and with
better experimental data, this period may be still farther reduced.”
3
Physicists who could reject the findings of geology and reduce the age of the
Earth from 100 to 50 to 24 to 10 million years might just decide to keep on going.
Speaking for his beloved profession, Geikie cried
Enough!
“There must be some
flaw in the physical argument,” he wrote. “Some assumption has been made, or
some consideration has been left out of sight, which will eventually be seen to viti-
ate the conclusions.”
4
Twenty Million in My Mouth
A new challenge to Kelvin came from Geikie's colleague at the Geological Survey
of Scotland, James Croll (1821-1890). Having taught himself physics and chem-
istry, Croll took a job as the caretaker of a Glasgow museum in order to have ac-
cess to its topics. He must have read and understood them, for he began to corres-
pond with Kelvin about his (Croll's) idea that variations in the Earth's orbit might
have caused the ice ages. Croll turned out to be right: orbital variations were the
cause, though, understandably, he got the details wrong.
In an 1877 article, like Huxley, Croll pointed out that Kelvin's result depended
on unprovable assumptions: “The utmost that any physicist is warranted in affirm-
ing,” said Croll, “is simply that it is impossible for him to conceive of any other
source [of the Sun's energy]. His inability, however, to conceive of another source
cannot be accepted as a proof that there is no other source.”
5
Another criticism of Kelvin's approach came from close to home and in math-
ematical form. John Perry (1850-1920) had been Kelvin's student and his assistant
at the University of Glasgow. As would be required for anyone aspiring to assist
Kelvin, Perry was himself an excellent mathematician. Underlying all of Kelvin's
work was the first law of thermodynamics: energy is conserved. As England et al.
