236 Professor Joseph Larmor [May 1, 



of the study of scientific history is thus to trace the beginnings of 

 creative ideas, to see how shght sometimes was the obstacle that 

 delayed the discovery of a new field of knowledge ; though here the 

 temptation to read back our own refined knowledge into the past lays 

 many snares. In no part of science is this interest greater than in 

 the doctrine of Available Energy ; the generality of outlook, leading 

 to recasting of the fundamental ideas regarding physical force and 

 power, which was secured by Thomson away back in the fifties, is on 

 the least favourable view a matter for wonder. 



In the years following, the powers of Helmholtz were concentrated 

 largely on his great task of the exploration of the physical foundations 

 of the activity of the senses, a subject of fundamental importance 

 because they supply our only outlook into the external world ; while 

 Thomson's efforts were employed in the problem, then urgent and 

 preparatory to Maxwell, of the dynamical interpretation of the ideas 

 of Faraday, and in the creation of the fundamental science above 

 referred to which constitutes Thermodynamics in its widest sense, the 

 all-pervading doctrine of Available Physical Energy to which it seems 

 appropriate that Rankine's name Energetics should belong. In later 

 days of close friendship their fields of activity had much in common, 

 Helmholtz apparently often brooding over, and developing into fuller 

 and more varied aspects, fertile points of view, such as the influence of 

 wind and surface-tension on waves, and the generalisation of dynamics 

 by the inclusion of latent cyclic motions, that had been already thrown 

 off in more summary fashion by his colleague. On the institution of 

 the Helmholtz memorial medal, the first award Wcus to Lord Kelvin. 



In a letter to Tait in 1876,* who was preparing a biographical 

 notice for ' Nature,' Helmholtz had given an estimate of the work 

 of his friend at that period. " His peculiar merit, according to my 

 own opinion, consists in his method of treating problems of mathe- 

 matical physics. He has striven with great consistency to purify the 

 mathematical theory from hypothetical assumptions that were not 

 a pure expression of the facts. In this way he has done very much 

 to destroy the old unnatural separation between experimental and 

 mathematical physics, and to reduce the latter to a precise and pure 

 expression of the laws of phenomena. He is an eminent mathe- 

 matician, but the gift to translate real facts into mathematical 

 equations, and vice versa, is by far more rare than that to find the 

 solution of a given mathematical problem, and in this direction 

 Sir William Thomson is most eminent and original. His electrical 

 instruments and methods of observation, by which he has rendered, 

 amongst other things, electrostatical phenomena as precisely measur- 

 able as magnetic or galvanic forces, give the most striking illustration 

 how much can be gained for practical purposes by a clear insight into 

 theoretical questions ; and the series of his papers on thermodynamics 



* Nature, xiv. 18T6, p. 388. 



