36 MR. J. SMITH ON THE ORIGIN OF COLOUR 



55. So far, then, as our inquiry has gone, we have 

 seen that in every case in which we have attempted to 

 account for one of the primary colours, namely blue, it 

 has resolved itself into light associated with shadow, from 

 which I conclude that light must produce its effects by 

 beats or pulsations on the eye, and that these beats or 

 pulsations must be at appreciable intervals] for if light 

 were an uninterrupted succession of waves at intervals as 

 small as commonly supposed, there would be no use for 

 shadow; shadow could not be seen. It would not pro- 

 duce a new sensation when refracted or reflected. 



But it will be asked, can the same principles of reasoning 

 be applied to any other colour? Let us see how they 

 apply to 



Green, 



56. It is not easy to devise experiments on green which 

 are as readily performed as those described above on blue. 

 The experiment with the red and black wafer is not only 

 a difficult one to make, but it is one which, even when 

 successful, is not satisfactory to many minds. 



57. There is another experiment of the same kind which, 

 although satisfactory to myself, has the same disadvantage 

 of being difficult to make, and it requires moreover strong 

 sunshine. I have observed, when waving a red silk hand- 

 kerchief in the air, in strong sunshine, that the edges 

 appeared of a dark green. Although I have made this expe- 

 riment in the presence of young people with good eyes, and 

 have at the same time told them what to observe, still I 

 cannot say that I have ever got any one who really saw what 

 I directed him to look at. But this experiment proves, 

 when it is successful, that green or change of colour is 

 produced by red light and no-light. Beyond the red, no 

 light is reflected to the eye, and the bright red alternating 

 with darkness produces the sensation of green. Acciden- 



