Artificial Colour-Uindncss to Successive Contrast. 205 



The other school, from which the theory of Young may be considered 

 to have developed, seems to have been founded by ScherfFer, who, in 

 1761, published a long series of experiments on contrast based on 

 Buffon's work, but criticising his conclusions. Scherffer's standpoint is 

 briefly expressed in the following passage : — 



" Perhaps the Creator has so constructed the entire organ of vision 

 that each kind of ray can only act upon such of the parts of which 

 the eye is composed as are particularly appropriated to it. But I pre- 

 suppose that the whole action of light consists in attraction and repul- 

 sion It may be that a continuous action of, for instance, 



red light, may so. change the order and arrangement of the parts of 

 the back of the eye , , . . that those rays may be no longer 

 strong enough to communicate to these parts the necessary vibratory 

 movement, until a little rest shall have restored them to their condi- 

 tion .... and during this time the other rays of different 

 kinds will not cease to act . . . ." 



He points out that if this explanation of "accidental colours" is 

 the true one, it must follow that the after-image of a coloured object 

 viewed upon a ground of the same colour must . be black, just as a 

 white spot upon a dark ground gives a black after-image upon white 

 paper.* 



Two of his experiments may be specially noted : — 

 In order to determine the complementaries of the primary colours 

 by experiment, he projected the solar spectrum on a white surface, and 

 observed the colours of the after-image produced by it.f He then 

 -compared these with the corresponding colours, as calculated by 

 Newton's method. He gives the following list of colours observed : — 



Eed Blue, verging on green. 



Orange Blue, almost indigo. 



Yellow A more violet-blue. 



Green Purple. 



Blue Eed. 



Indigo . Orange, but rather pale. 



Violet A very yellow green. 



He also made drawings of flowers, and painted them with colours 

 complementary to those they naturally possessed. These, when steadily 

 looked at in a bright light, gave after-images in their true colours. He 

 €ven went so far as to copy a picture, painting it with a green face 

 shaded with yellow, white hair and eyebrows, black eye-balls with 

 white pupils, and green lips, so that the accidental image of it had the 

 colours of the original. J 



* Compare this paper, Section II (2), p. 208. 

 t Compare this paper, Section II (1), p. 208. 

 X Compare this paper, Section III, p. 213. 



