Page:Lectures on Ten British Physicists of the Nineteenth Century.djvu/72

 ages, the age and temperature of the Earth are not geology, it is difficult to adduce anything which has a right to that title. Yet Huxley in the name of the geologists said that they were intellectual Gallios, caring for none of these things. It is certainly a very remarkable, fact that one who fought all his life against ecclesiastical Gallios as regards evolution should, in the matter of the application of physical science to a geological problem, borrow their precise attitude and maxims.

The controversy has gone on ever since, and has enlivened many a meeting of the British Association. The geologists say to Lord Kelvin "Look at our arguments." Lord Kelvin says to the geologists "Look at mine." The former call out "cosmogonist"; the latter replied "geological calculus." As a result of the controversy the uniformitarian doctrine has disappeared; but no agreement has been reached about the age of the Earth when it became an abode for life. Kelvin's reasoning can be attacked only by questioning the values which are assumed for the constants, or by denying the conditions which are assumed to be true in applying Fourier's problem to the case of the Earth. The former course was adopted a few years ago by Prof. Perry; by modifying the constant $$k$$ he increased the time about tenfold. It is the only course which presents any avenue of escape such as the geologists desire to see. Is the Earth a body which was once molten hot, and has been subsequently left to cool, without any further generation of heat in the interior by oxidation of its contents? If the geologists had more mathematical training, they might be able to make better use of their data. As it is their reasoning is too much of this character: the Mississippi now carries down so much mud in a year, how long will it take at this rate to reduce the whole valley to the level of the Gulf of Mexico? This is a specimen of "logical calculus." A very slight knowledge of mathematics suffices, however, to show that natural changes take place at a variable rate which depends at any time on the amount to be changed, and until one gets a clear idea of a logarithm and an exponential he will not be able