PROFESSOR AT BONN 149 



which shows up the intention of its author in no amiable light 



I was told that people said I brought a good deal of physiology 

 and chemistry into my anatomy, which restricted the amount 

 of anatomy proper, and they made jokes* at the introduction 

 of a cosine in physiological optics. But I received many 

 indications of interest and appreciation of my lectures from 

 the older students, and from my colleagues also/ At the close 

 of this letter Helmholtz sends heartiest congratulations 'to 

 the young sucking-philosopher, who has taken up his abode 

 with you, and is doubtless already occupied with such difficult 

 questions as the formation of concepts of time and space of 

 which he knows more now than all the learned physiologists 

 in the world'. 



Nor was it as a teacher alone that Helmholtz had found 

 a congenial sphere of activity. He sought to acquaint the medical 

 world of Bonn, who were somewhat remote from his stand- 

 point, with his nerve-work, by reading a paper on the ' Con- 

 traction Curves of the Muscles of the Frog ' recorded with the 

 myograph, to the Nieder-Rheinische Gesellschaft on May 14. 

 He also endeavoured, while preparing his Physiological Optics, 

 to interest his scientific colleagues in these new and difficult 

 investigations. 



On March 6 he made a short, but important and interesting 

 communication to the same Society ' On the Explanation of 



Lustre'. Helmholtz started from the fact that in looking at 

 dull surfaces, they appear equally illuminated, and equally 

 coloured, to both eyes, while for shining surfaces the contrary 

 is the case, since one eye may be affected by the more or 

 less regularly reflected light from the smooth surface, and 

 the other not. The surfaces then appear brighter to the one 

 eye, and if the reflected light differs in colour from that of 

 the surfaces, of a different colour also, although these differ- 

 ences of colour as presented in daily experience to both eyes 

 by shining surfaces are usually insignificant. Now if the 

 observer looks with the stereoscope at any surface that appears 

 brighter or somewhat differently coloured to one eye than 

 to the other, he will conclude from the analogy of everyday 

 experience that this surface is lustrous, a phenomenon that 

 had long been known, but had found no adequate explanation. 

 With greater differences of colour, empirical analogy is totally 



