48 MR. J. SMITH ON THE ORIGIN OF COLOUR 



another part of the same letter he says : " These things 

 being so^ it can be no longer disputed whether there be 

 colours in the dark, nor whether they be qualities of the 

 objects we see; no, nor perhaps whether light be a body. 

 For since colours are the qualities of light, having its rays 

 for their entire and immediate subject, how can we think 

 those rays qualities also unless one quality may be the 

 subject of and sustain another ; which in effect is to call 

 it substance. We should not know bodies for substances 

 were it not for their sensible qualities ; and the principal 

 of those being now found due to something else, we have 

 as good reason to believe that to be a substance also. 



" Besides who ever thought any quality to be a hetero- 

 geneous aggregate, such as light is discovered to be. But 

 to determine more absolutely what light is, after what 

 manner refracted, and by what modes or actions it pro- 

 duces in our minds the phantasms of colours, is not so 

 easy. And I shall not mingle conjectures with certainties.^^ 



70. The experiments which I am about to describe appear 

 to me to establish a theory the very opposite of Newton's. 

 They prove that the sun's light consists of but one sort of 

 rays, and that there are no such rays as red- making, 

 green-making, or violet-making rays. 



71. But it may be said that the undulatory theory 

 of light is directly opposed to that of Newton. In point 

 of fact, however, there is little difference between the 

 corpuscular theory, as explained by Newton, and the 

 undulatory, except in the more rational supposition by 

 the advocates of the latter of an ambient ether to convey 

 the sensations of colour, just as the air conveys the sen- 

 sations of sound. For the undulatory theory adopts 

 Newton's view of the composition of light, or, what is 

 the same thing, supposes that there are waves of dif- 

 ferent lengths either inherent in the nature of light 

 itself or produced by the nature of the refracting 



