ESSAY-REVIEWS 63 



this was given up and he returned to Cambridge. On the other 

 hand, peculiarly enough, Lord Moulton soon gave up mathe- 

 matics for the Bar. After a few scattered papers on various 

 subjects, Darwin seems at once to have started on the line of 

 research along which all of his later work was directed. His 

 earliest paper in this connection, " On the influence of geological 

 changes in the Earth's axis of rotation," attracted the attention 

 of Lord Kelvin (then Sir William Thomson) and was published 

 by the Royal Society. In this way started an association of 

 great value to Darwin in his subsequent life. This success was 

 commended by his father in the following terms : 



" My dear Old George, 



" I have been quite delighted with your letter and 

 read it all with eagerness. You were very good to write it. 

 All of us were delighted, for considering what a man Sir 

 William Thomson is, it is most grand that you should have 

 staggered him so quickly, and that he should speak of your 

 ' discovery, etc' . . . Hurrah for the bowels of the earth and 

 their viscosity, and for the moon and for the Heavenly bodies 

 and for my son George (F.R.S. very soon). . . ." 



Darwin was at this time thirty- two years old, and almost 

 all of his later work lay in the development of his ideas in 

 various directions. Prof. Brown remarks on the homogeneous 

 nature of all his work, the aim which he had in view having 

 been apparently to apply the tests of mathematics to theories 

 of cosmogony. If existing mathematical methods did not 

 suffice for his purpose he would proceed to develop new 

 ones, as in his valuable paper on "Ellipsoid Harmonic Analysis," 

 or failing this he would obtain arithmetical solutions by the 

 methods of quadratures. It was largely to this singleness 

 of aim that his success was due, for his health was always 

 indifferent and precluded long hours of work. The second 

 characteristic of Darwin's work mentioned by Prof. Brown is 

 that behind all of it was the severely practical view of testing 

 physical hypotheses and reducing his results to figures. He was 

 an applied mathematician in the truer and older sense of the 

 word. Of late years a newer school of applied mathematicians 

 has arisen which is chiefly concerned with discussions of the 

 special functions and equations which occur so frequently in 

 all branches of mathematical physics, and with the conditions 



