766 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1908. 



This use of models has become characteristic of the tone and temper 

 of British physicists. Where Poisson or Laplace saw a mathematical 

 formula, Kelvin, with true physical imagination, discerned a reality 

 which could be roughly simulated in the concrete. And throughout 

 all his mathematics his grip of the physical reality never left him. 

 According to the standard that Kelvin set before him, it is not suffi- 

 cient to apply pure analysis to obtain a solution that can be com- 

 puted. Every equation, " every line of the mathematical process 

 must have a physical meaning, every step in the process must be asso- 

 ciated with some intuition ; the w^hole argument must be capable of 

 being conducted in concrete physical terms." ° In other words, Lord 

 Kelvin, being a highly accomplished mathematician, used his mathe- 

 matical equipment with supreme ability as a tool; he remained its 

 master and did not become its slave. 



Once Lord Kelvin astonished the audience at the Roj'al Institu- 

 tion by a discourse on " Isoperimetrical problems," endeavoring to 

 give a popular account of the mathematical process of determining 

 a maximum or minimum, which he illustrated by Dido's task of 

 cutting an oxhide into strips so as to inclose the largest piece of 

 ground ; by Horatius Cocles's prize of the largest plot that a team 

 of oxen could plow in a day; and by the problem of running the 

 shortest railway line between two given points over an uneven coun- 

 try. On another occasion he entertained the Royal Society with a 

 discourse on the " Homogeneous partitioning of space," in which the 

 fundamental packing of atoms was geometrically treated, affording 

 incidentally the theory of the designing of wall-paper patterns. 



To the last Lord Kelvin took an intense interest in the most re- 

 cent discoveries. Electrons — or " electrions," as he called them — 

 were continually under discussion. He prided himself that he had 

 read Rutherford's book on Radio-activity again and again. He ob- 

 jected, however, in toto to the notion that the atom was capable of 

 division and disintegration. In 1903, in a paper called "Aepinus 

 atomized," he reconsidered the views of Aepinus and Father Bosco- 

 vich from the newest standpoint, modifying Aepinus's theory to 

 suit the notion of electrons. 



After taking part in the British Association meeting of 1907 at 

 Leicester, where he entered with surprising activity into the dis- 

 cussions of radio-activity and kindred questions, he went to Aix les 

 Bains for change. He had barely reached home at Largs in Sep- 

 tember when Lady Kelvin was struck down with a paralytic seizure. 

 Lord Kelvin's misery at her hopeless condition was intense. He had 

 himself suffered for fifteen years from recurrent attacks of facial 

 neuralgia, and in 1906 underwent a severe operation. Under these 



«Prof. A. E. II. Love. 



