I02 GREAT MEN OF SCIENCE 



spectrum; thus purple, for example, is a mixture of red and 

 violet . He also gives a rule , the colour circle , by means of which 

 the results of such mixtures may be predicted approximately. 

 It is noteworthy that he already recognises how imperfect 

 the eye is (without the assistance of a prism) in judging mix- 

 tures of colours; for example, the eye perceives as 'white' 

 mixtures in which by no means all colours are present, as 

 they are in ordinary white light; fewer colours are sufficient 

 when mixed in suitable proportion, to produce the sen- 

 sation of white in a way indistinguishable from the ordinary 

 sensation. 



These results of Newton's, stated so clearly with so much 

 detail, and with admirable caution, long suffered a pecuUar 

 fate: they met with very sharp opposition. Best known from 

 later years is perhaps Goethe's appearance on the field with 

 his colour theory; but even immediately after the appearance 

 of Newton's publication many objections were made. As 

 is often the case in the history of science, when fundamental 

 work, which brings something quite new, appears, simple 

 misunderstanding is responsible. Such misunderstanding 

 frequently depends upon loose terms, which everyone 

 imagines to understand when they are used, but nevertheless 

 does not understand. A bad term of this description is 

 the word colour; it has at least three different meanings; 'red' 

 for example may mean: (i) red light, that is the ray of light 

 which when falling on the eye produces the sensation of red; 

 (2) red may meaA this sensation itself, the sensation of colour 

 in the observer; (3) red may also mean a red colouring matter, 

 that is a substance which reflects or transmits red light better 

 than other kinds of light, and hence makes red light out of 

 white light. It is obvious that the scientist who wishes to 

 explain the nature of light, will, like Newton, mean the first, 

 which by the way, Newton himself states with complete 

 clarity.^ It is equally true that the artist like Goethe, who in 



^ Opticks, book 1, part 2, prop. 2, definition. 



