Chap. XXVI.] 



MIXTURE OF COLOURS. 



The mixture of colours can be shown by taking a 

 rotating disc and placing sectors of different colours 

 on it. On rotating the disc rapidly the eye cannot 

 distinguish each colour separately, but the different 

 impressions are blended, and an impression of a com- 

 pound colour produced. If sectors of all the seven 

 colours of the spectrum are placed on a disc in this 

 way, in a definite proportion, and the disc rapidly 

 rotated, the impression is of white light, or, rather, 

 grey, because colours cannot be got of such purity as 

 those of the spectrum. The colour top of Clerk- 

 Maxwell is an application of this method. 



Fundamental and complementary 

 colours. Reference to the table shows that red 

 mixed with greenish-blue produced white, that orange 

 and blue produced white, yellow and indigo also, and 

 greenish-yellow and violet. To put it in another way : 

 given red, all that is necessary to produce white is 

 greenish-blue; given violet, all that is necessary for 

 white is yellowish-green. These colours, then, are 



