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The Marquis of Salisbury’s 1894 address to the British Association for the Advancement of Science sparked an important development in the debate on the age of the Earth. It led John Perry, a physicist, to produce the first mathematical rebuttal of Lord Kelvin’s calculations, which had since 1862 functioned as an argument against the theory of evolution by natural selection. Perry wished to affirm the independence of geology from physics, keeping each branch of science to its proper domain. With the support of his mathematical friends, Perry tried privately to induce Kelvin to modify his views. This effort failed, however, and the discussion became public in Nature. Perry supported his calculations with Heaviside’s new mathematical methods, and also with empirical data, though these were later undermined by Kelvin’s experiments. Perry was uncomfortable with his position as Kelvin’s critic, however, because he held his old teacher in great esteem. Although Kelvin never stopped believing that the Earth was too young for natural selection to have taken place, geologists and biologists responded very positively to Perry’s results, and no longer felt they had to justify their conclusions to physicists. The answer to ‘Had Lord Kelvin a right?’, ultimately depended on one’s scientific politics.

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