PROFESSOR AT KONIGSBERG 91 



Newton, which had been perpetuated in the following centuries ; 

 and had since his visit to Vienna been in correspondence with 

 Brucke, who was much occupied with such investigations. 

 On December 22, 1851, Brucke writes to Helmholtz: 'As 

 you know, Goethe in his unfortunate theory of colours 

 explains all colours by the overlapping of light and dark, 

 basing his argument on the well-known fact that transparent 

 media in front of a dark ground may look violet-grey, blue- 

 grey, and blue, while in transmitted light they look brown, 

 yellow, or red. I have also noticed in my experiments on 

 chamaeleons, how often very distinct colours are produced in 

 this way in the animal kingdom, and have not found this 

 phenomenon explained by the undulatory theory, although 

 the explanation seems obvious enough. . . . Pray tell me if the 

 different colouration of the reflected and refracted rays has 

 been considered in optics/ 



Brucke had no idea that Helmholtz had already made funda- 

 mental discoveries in this direction, which were to astonish 

 physicists and physiologists alike in the dissertation he was 

 about to publish. His father, to whom Helmholtz made a 

 short communication of the contents of the paper, writes to 

 him enthusiastically on April 5 : ' Your letter of the 2ist gave 

 us as much pleasure as all its predecessors, and there was the 

 usual murmur of impatience till every one had read it. May 

 God fulfil you ever more and more as a prophet of truth 

 and fountain of wisdom, so that you may not have lived in 

 vain for eternal Humanity, but may ever continue one of its 

 corner-stones on earth ; then I shall find consolation for the 

 lack of results in my own life. God have your health in His 

 keeping, and grant you increasingly such a position in externals 

 that your intellectual life may find its full development. I am 

 most curious about the interesting work that you have chosen 

 for your thesis ; you will clash with Goethe there ! ' 



He is delighted when Helmholtz tells him that the coming 

 summer may bring great changes in his external position : 



'There are three physiological vacancies in prospect. So 

 there may be a regular migration, in which each must try 

 for the best new place. Not that there are many candidates 

 in the field, du Bois, Eduard Weber in Leipzig, and I being 

 almost the only ones.' 



