HELMHOLTZ IN KONIGSBERG 



Newton laid the foundation of the theory of com 

 pound colours. He showed that two beams that differ 

 optically, that is as regards the periods and amplitudes 

 of their ether vibrations, may be alike chromatically, 

 that is to say, they may give rise to the same kind of 

 colour sensation. Thus, by mixing red and yellow, 

 an orange colour may be produced like that of the 

 spectrum, but differing from it in that the former may 

 still be analysed by a prism into red and yellow, whereas 

 the orange of the spectrum cannot be so resolved. 

 By his well-known diagram of colour, Newton also 

 showed that in any mixture of colours, the quantity 

 and quality of each being given, it was possible to 

 determine the colour of the compound. While the 

 result of mixture of colours in the production of 

 compounds can thus, by a geometrical method, be 

 represented with approximate correctness, their true 

 relations, as was shown by Clerk Maxwell, 1 can only 

 be determined by direct experiment. 



With his usual experimental dexterity and philoso- 

 phical acumen, Thomas Young was led to a great 

 generalisation on the subject of colours, in which it is 

 asserted that the three simple colour sensations are 

 red, green and violet, and while these cannot be 

 produced except by the impact of light of a certain 

 wave-length on the retina, and are therefore simple, 

 any other colour may be matched by a mixture of 



1 An interesting account of Clerk Maxwell's work on the subject is 

 given by Glazebrook in his Life of Max-well. London, 1896, p. 93. 



