Intelligence and Miscellaneous Articles. 



539 



"When the colours have not the same complementary, the graphic 

 construction is indispensable for the determination of the intensity. 



From the point O, I draw three lines OA=OB=OC, the length 

 of which is proportional to the intensity of the colours A, B, C, 

 which I regard as primary sensations, and which, for that reason, 

 are placed at an angular distance of 120° from one another. The 

 places of the colours resulting from the mixture, in twos, of the 

 three primary sensations are necessarily upon the sides of the 

 triangle ABC. Their distances from the vertices are in the 

 inverse ratio of the coloured sectors necessary to produce them; 

 and their distances from the point O represent their coloration- 

 intensities. In this conception the point O is not regarded as the 

 centre of gravity of the triangle ; it represents not the place of the 

 white, but the absolute black. 



The intensity of the binary colours being given by the con- 

 struction, it is easy, with the aid of rotating disks, to compare 

 with it the coloured surfaces the intensity of which we wish to 

 know. 



Let there be required to find the intensity of coloration of a red 

 surface S. I mix C and B so as to obtain red, which I reproduce, 

 in another part, with a sector S, of which the angle a is given by 

 experiment. Let B (in the figure) be the point occupied by the 

 red : we have 



OB 

 OB 



360' 



from which we get for the intensity of coloration I of the surface S 

 OE x 360 



1 a x OB' 



This method is susceptible of verification. 



Knowing the in- 



