PROFESSOR AT KONIGSBERG 93 



unaffected popular style. You make the conclusions of 

 science comprehensible even to the laity, showing where the 

 details are leading to, and what is the way and aim. It 

 almost seems to me that this mathematical-empirical method ' 

 of investigation, when once it develops into a definite art, and 

 no longer depends upon individual genius, may inaugurate 

 a new, perhaps slow, but certain way to philosophy, which 

 will at any rate define exactly the objective substratum of all 

 knowledge, rendering its nature indubitably clear, and thus 

 establishing the ego-doctrine of Fichte as the only possible 

 mode of philosophical thought.' 



In a letter written in September, to announce the birth of 

 his son Richard, Helrnholtz gratified his father by admitting 

 that it had (as the latter surmised) been his intention in the 

 lecture to give an empirical statement of Fichte's fundamental 

 views of sense-perception, and expresses pleasure that his 

 father is content with the form of the dissertation, and approves 

 of his philosophical opinions. 



His general philosophical and epistemological views were, 

 however, quite unlike Fichte's, since they were based upon 

 exact investigations, the results of which he set forth in the 

 inaugural thesis ' On the Theory of Compound Colours ', and 

 in the paper published in Poggendorjfs Annalen, 'On Sir 

 David Brewster's New Analysis of Solar Light/ which laid 

 the foundation of the whole of the modern theory of colour. 

 After Newton's discovery of the composition of white light, 

 he assumed the existence of seven principal colours in the 

 spectrum, apparently taking this number from the analogy 

 which he sought to establish between these colours and the 

 intervals of the musical scale. But while two tones of different 

 vibration-frequency and musical pitch produce sensations of 

 harmony or dissonance when struck together, but can still 

 be distinguished separately by the ear, luminous rays of 

 different wave-length and colour give rise to impressions 

 which fuse into a single new colour-sensation. This combina- 

 tion is due to a purely physiological phenomenon involved 

 in the specific mode of reaction of the optic nerve. Before 

 the discovery that white light is due to a mixture of coloured 

 lights, the mixture of pigments had led to the theory of 

 the three elementary colours, red, yellow, blue, from which 



