PROFESSOR AT BONN 155 



Hence, while still immersed in the preparation of Physiological 

 Optics, Helmholtz was planning his great work on the Theory 

 of the Sensations of Tone, busying himself in the first place 

 with the physiological questions it involved, the interest of 

 which is increased ' by the antiquity they have attained, un- 

 solved ', and with their significance for music and phonetics. 



Before setting out on his summer journey, he was gratified 

 by a visit from Bonders, and then left for Schwalbach on 

 August 15, 'in order,' as he writes to his father, 'to meet 

 Prof. Thomson from Glasgow, whom I visited last year in 

 Kreuznach, and who has principally concerned himself with 

 the Theory of the Conservation of Energy in England. He 

 is certainly one of the first mathematical physicists of the day, 

 with powers of rapid invention such as I have seen in no 

 other man.' 



After spending a day there, and the next morning trying 

 some new experiments with the siren, which had occurred 

 to Thomson in the night, and which 'if they succeed must 

 yield the most striking results ', he joined his travelling com- 

 panion for Switzerland, Dr. Otto Weber, Privatdocent of 

 surgery in Bonn, 'a talented young man who had previously 

 done a good deal of work in geology,' in Frankfurt. From 

 Heidelberg, where he 'found Kirchhoff already gone, and 

 Bunsen packing', he went to Basle, whence he sent his wife 

 an enthusiastic description of the Holbein drawings : ' They are 

 marvellously finished ; it is rare to find such a combination of 

 force, character, and dramatic vigour, though there is little 

 grace,' 



From there he went to Chamounix, and made several long 

 excursions on the mountains and glaciers, the beauties and 

 dangers of which he describes to his wife in glowing colours. 

 Fatigue and longing for work, however, took the 'thirty-five 

 year old dotard' back to Bonn by September i. A few days 

 later he received specimen copies of the first edition of the 

 Handbook of Physiological Optics, in which he gathers the results 

 of years of work into a harmonious whole. 



Besides the papers on physiological optics which have already 

 been mentioned, and an admirable review of all previous work 

 comprised under this heading, the book contained a store 

 of new and most important results, which provided a firm 



