30 MR. J, SMITH ON THE ORIGIN OF COLOUR 



Shadow is abstraction of some of the rays of hght in any 

 luminous medium. To reflect light on the "confines of 

 shadow " is not to abstract any rays, and consequently is 

 not to alter the nature of the light. To alter the nature 

 of light we must either add to or subtract from its inten- 

 sity, and, taking the incident light as the unit, colour is 

 produced by abstraction and the co-ordinate sensation of 

 no-light. I have no wish to object to those who pre- 

 fer to speak in the usual philosophical language about 

 waves and undulations ; only I think that when I speak 

 of alternate vibrations of light with shadow, such lan- 

 guage is intelligible to the common understanding, while 

 the other, or the language of waves, is not even clear to 

 the understanding of the philosopher. For instance : we 

 cannot refrain from speaking of degrees of cold, although 

 cold is, philosophically, the negation of heat; and, gene- 

 rally, I cannot think it unphilosophical to use as a 

 positive term the name of any feeling or sensation that is 

 cognisable by the senses as being distinct from another, 

 and to which every nation and , every language under hea- 

 ven has given a name. The words which express our 

 feelings or sensations are of themselves the most perfect 

 definitions which can be given of these feelings or sensa- 

 tions ; no explanation can add to the accuracy of the con- 

 ceptions suggested by the words which recall them. Such 

 language I call intelligible, if not axiomatic ; it commends 

 itself to every one= Philosophy does not change the sen- 

 sations — it explains them ; and it is of the sensations I 

 am now speaking. 



49. But, waiving the philosophy of the language, if it is 

 possible to take any colour and making it vibrate alter- 

 nately with darkness or shadow, without refraction or with- 

 out decomposition, convert it into some other colour, then 

 this would be proving not only that light and shadow, or 

 alternate sensations of light and uo-light, produce a change 



