Annual Report of the Council. 231 



succession the chair of Physiology at Heidelberg (1859 — 

 1871) and Physics at Berlin (1871 — 1888). The last years 

 of his life were spent in organising the work of the 

 Physikalisch-technische Reichsanstalt at Charlottenburg. 

 It is impossible to give within the space of a short obituary 

 notice an adequate idea of the work accomplished by one 

 who must for ever be recognised as one of the foremost 

 thinkers of the century, and I can only briefly indicate the 

 most important of his contributions to science. 



Helmholtz is one of the founders of the modern theory 

 of the " Conservation of Energy." The first treatment of 

 the subject is contained in a pamphlet, "Ueber die Erhaltung 

 der Kraft" (1852). Maxwell {Nature, Vol. XV.) thus refers 

 to this paper : — 



" To appreciate the full scientific value of Helmholtz's 

 little essay on this subject, we should have to ask those to 

 whom we owe the greatest discoveries in thermodynamics 

 and other branches of modern physics how many times 

 they have read it over, and how often during their researches, 

 they felt the weighty statements of Helmholtz acting on 

 their minds like an irresistible driving-power." 



Helmholtz's physiological work includes the invention of 

 the ophthalmoscope, the measurement of the rate of 

 propagation of sensational impulse along the nerves, and 

 those researches on the sense of hearing which are contained 

 in the celebrated volume on the " Ton-Empfindungen." 



His mathematical powers are shown in a series of 

 researches on hydrodynamics, the best known of which is 

 the one on vortex motion, " in which," to quote Maxwell 

 once more, " he establishes principles in pure hydrodynamics 

 which had escaped the penetrative power of all the mathe- 

 maticians who preceded him, including Lagrange himself." 

 The results of the paper are perhaps best known by the 

 application and further developments they have received at 

 the hands of Lord Kelvin, who founded on them his cele- 



