762 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1908. 



•various terms of the Fourier series. Wave problems always had a 

 fascination for him, and the work of the mathematicians Poisson and 

 Cauchy on the propagation of wave motion were familiar studies. 

 In his lectures he used to say, " The great struggle of 1815 " — and 

 then paused, while his students, thinking of Waterloo, began to 

 applaud — " was not that fought out on the plains of Belgium, but 

 who was to rule the waves, Cauch}^ or Poisson." In 1871 Helmholtz 

 went with Sir William Thomson on the yacht Lalla Rookh to the 

 races at Inverary, and on some longer excursions to the Hebrides. 

 Together they studied the theory of waves, " which he loved," says 

 Helmholtz, " to treat as a race between us." Returning, they visited 

 many friends. " It was all very friendly," wrote Helmholtz, " and 

 unconstrained. Thomson presumed so much on his intimacy with 

 them that he always carried his mathematical notebook about with 

 him, and would begin to calculate in the midst of the company if 

 anything occurred to him, which was treated with a certain awe by 

 the party." He possessed, indeed, the faculty of detachment, and 

 would settle quietly down with his green book, almost unconscious of 

 things going on around him. On calm days he and Helmholtz ex- 

 perimented on the rate at which the smallest ripples on the surface of 

 the water were propagated. Almost the last publications of Lord 

 Kelvin were a series of papers on " Deep-Sea Ship Waves," com- 

 municated between 1904 and 1907 to the Eoyal Society of Edinburgh. 



In 1874, on June 17, Sir William Thomson married Miss Frances 

 Anna Blandy, of Madeira, whom he had met on cable-laying expedi- 

 tions. Lady Kelvin, who survives him, became the center of his 

 home in Glasgow and the inseparable companion of all his later trav- 

 els. He built at Netherhall, near Largs, a beautiful mansion in the 

 Scottish baronial style ; and though he latterly had a London house 

 in Eaton Place, Netherhall was the home to which he retired when 

 he withdrew from active w^ork in the University of Glasgow. 



Throughout the seventies and eighties Sir William Thomson's 

 scientific activities were continued wdth untiring zeal. In 1874 he 

 was elected president of the Society of Telegraph Engineers, of 

 which, in 1871, he had been a foundation member and vice-president. 

 In 1876 he visited America, bringing back with him a pair of Graham 

 Bell's earliest experimental telephones. He was president of the 

 Mathematical and Physical Section of the British Association of that 

 year at Glasgow\ 



Among the matters that can not be omitted in any notice of his life 

 was Lord Kelvin's controversy with the geologists. He had from 

 three independent lines of argument inferred that the age of the 

 earth could not be infinite, and that the time demanded by the geolo- 

 gists and biologists for the development of life must be finite. He 



