38 MR. J. SMITH ON THE ORIGIN OF COLOUR 



produced. Even in this experiment, then, one of the 

 most accurate experiments on record, we see that the 

 colour green is associated with shadow, and is caused by 

 intervals of red and darkness, a conclusion which may be 

 arrived at by other experiments without subjecting the 

 light to refraction, as it is in this instance. 



59. There is another observation strongly corroborative 

 of this conclusion ; but since the effect, just as in the pre- 

 ceding instance, might be supposed to be due to refrac- 

 tion, I have great reluctance in bringing it forward at this 

 stage of the investigation, but I found it of great assist- 

 ance in my inquiries into the cause of colour. Often on a 

 frosty night I have remarked on shop windows the light 

 within surrounded with a halo, similar to that which is 

 frequently seen around the moon, and of a similar colour. 

 Between the image of the light and the halo there was a 

 dark ring, which was in many cases quite black, but in 

 others a very distinct green of various hues. The question 

 arises, What is the cause of this green colour ? Consider- 

 able difficulties attended the explanation of the phenome- 

 non. For a long time I could discover no explanation, 

 and to resort to hypothesis was contrary to the rule which 

 I had laid down for myself. I resolved to wait patiently, 

 and observe as carefully as possible, until nature told her 

 own tale. On riding rapidly along, these appearances 

 struck me more frequently. On such occasions I con- 

 stantly observed either the green or the black ring. After 

 continued observation I became convinced that the green 

 was only perceived when another light than that causing 

 the halo was reflected from the window. This I saw was 

 constantly the case when there was a light opposite the 

 one creating the halo. Now this fact led to the same 

 inference as that to which I was conducted by my other 

 observations, viz., that light proceeds by pulsations, and 

 that colour is connected with darkness or shadow, with 



