24 MR. J. SMITH ON THE ORIGIN OF COLOUR 



shifting of logical premises to meet an anomaly, not in 

 the nature of light but in the received theory. 



38. This experiment fortifies my argument very strongly^ 

 and I have less and less hesitation in saying, in opposi- 

 tion to the received theories, that shadow appears to be as 

 important a principle in any theory of colour as centri- 

 fugal force in the theory of gravitation, as important as 

 the term minus in the theory of numbers, as important as 

 the term silence in the theory of music. 



Colour of the Sky. 



39. It is necessary, however, to search for other natural 

 phenomena in order to verify this conclusion, and among 

 these none stand more prominently forward than the 

 colour of the atmosphere. The colour of the air and sky 

 is explained by every writer on optics, and the common 

 theory is universally admitted to be correct. But it is 

 easier to acquiesce in the fancy of the poet when he sings, 



' Tis distance lends enchantment to the view 

 And robes the mountain in its azure hue, 



than in the science of the philosopher. As Newtou^s 

 opinion is still the opinion of the present day, in place of 

 quoting Newton, I shall quote from Cos?nos the opinion of 

 Arago, to which Humboldt agrees. 



"We cannot explain the diffusion of atmospheric light 

 by the reflection of solar rays on the surface of separation 

 of the strata of different density, of which we suppose the 

 atmosphere to be composed. In fact, if we suppose the 

 sun to be situated in the horizon, the surfaces of separa- 

 tion in the direction of the zenith will be horizontal, and 

 consequently the reflections will also be horizontal, and we 

 shall not be able to see any light in the zenith. On the 

 supposition that such strata exist, no ray would reach us 

 by means of direct reflection. Repeated reflections would 



