BARON VON HELMHOLTZ. 597 



good purpose that he was soon able to read easily the most abstruse 

 treatises on these subjects, and to write his famous essay, " Ueber die 

 Erhaltung der Kraft," in which the great doctrine of the conserva- 

 tion of energy was first forced upon the attention of physicists. 

 The seven papers which Helraholtz published before he left the army 

 had already (in 1848) given him a high reputation among physiolo- 

 gists, and after a year spent as teacher of anatomy at the Kunst- 

 akademie at Berlin, he was called to a Professorship of Physiology and 

 Pathological Anatomy at Konigsberg. During the six years which he 

 spent here Helmholtz published about twenty papers, mostly of great 

 importance, and of these almost all, except those on the velocity of 

 propagation of nerve excitation, and on the duration of induced elec- 

 tric currents, had to do with physical or with physiological optics. 



These twenty papers, however, do not represent the whole of the 

 work which Helmholtz did at Konigsberg beyond his professional 

 duties, for he must have written here the greater part of his " Hand- 

 buch der Physiologischen Optik," the first edition of which appeared 

 in 1856. It was by this time clear that Helmholtz had become one 

 of the first of living physicists. Almost every one of his publications, 

 whatever its title, showed his mastery in some branch of physics, and 

 made some contribution to the world's knowledge of the subject. 



From Konigsberg, Helmholtz went to Bonn, and thence, in 1858, to 

 Heidelberg, where he remained as Professor of Physiology until 1871. 

 While at Bonn and Heidelberg he published forty-three considerable 

 papers, besides his " Lehre von den Tonempfindungen," which ap- 

 peared in 1862, and which he says in his Preface is fruit of work 

 stretching over eight years,* though of the fourteen publications 

 which he wrote in the six years after he left Konigsberg at least 

 five have to do with matter foreign to acoustics and to tone-sensations. 

 One of - these was an epoch making paper in mathematical physics, in 

 which it was shown that vortex rings and vortex filaments in perfect 

 fluids under the action of conservative forces are indestructible, and 

 that such rings and filaments apparently attract or repel one another 

 according to the relative signs of their vorticities. 



One may get some conception of the catholicity of Helmholtz's tastes 

 and of the extent of his knowledge by reading a list of the subjects 

 of the papers which he wrote at Heidelberg on Physiology, Physical 

 and Physiological Optics, Physical and Physiological Acoustics, the 



* " Indem ich die Fruchte achtjahriger Arbeit der Oeffentliclikeit uber- 

 gebe," etc. 



