30(> Intelligence and Miscellaneous Articles. 



properties ; they possess the characters of the fundamental sensa- 

 1 ions of Young. I am about to demonstrate that they are also the 

 only ones to which these qualities belong. 



It is by no means sufficient, as Helmholtz says*", that when mixed 

 in suitable proportions they produce the sensation of white f. 

 Stated in these terms the problem is. indeterminate ; but from their 

 definition itself two other properties are deduced which singularly 

 contract the limits between which the choice can be made. (1) When 

 mixed two by two, they produce all the intermediate colours (even 

 those which, like purple, do not exist in the spectrum) ; (2) they 

 fulfil this condition without at the same time producing the sensa- 

 tion of white — or, more exactly speaking, producing it less than 

 any other colours which could be chosen in their place. 



These two conditions are precisely the opposite of those fulfilled 

 by the complementary colours, which on being mixed two by two 

 do not give rise to any intermediate colour, and, when mixed in 

 suitable proportions, produce only the sensation of white. By 

 their properties these two sorts of colours reciprocally limit one 

 another ; hence it follows that the study of the distribution of the 

 complementary colours in a chromatic circle permits the determi- 

 nation of the points of that circle which correspond to the funda- 

 mental sensations. 



2. With the aid of rotating disks I have sought, for each colour, 

 its complementary ; the following table gives the result (the nota- 

 tion employed being that of M. Chevreul) : — 



Colours equidistant Complementary Ratio of the 



to the eye. colours. intervals J. 



Orange-red .... 5th green 1 fi -. 



Bed 4th green J D : L 



Orange Blue-green 6 : 1 



Orange-yellow . . 1st blue-green .... 6 : 1 



Yellow.* Blue 6 : 5 



Green-yellow . . 3rd violet-blue .... 6:9 



Green 4th violet 6 : 7 



Blue-green .... Orange 6 : 19 



Blue Yellow 6 : 12 



Yiolet-blue .... 4th yellow ...... 6 : 4 



Yiolet 3rd green-yellow. . 6:5 



Yiolet-red .... 2nd green 6 : 5 



3. At first sight great irregularity is evident in the distribution 



* Optique Physiologique, p. 384, § 20. 



t I do not say " white light," because lights of the same appearance 

 may not be identical from the physical point of view: there are white 

 lights of which the compositions differ, but the eye cannot distinguish 

 them one from another. 



X Between two consecutive colours of the first column of this table 

 there are in reality intercalated five colours, designated by the numbers 1 

 to o ; so that six equidistant colours correspond to each name. 



