AND THE THEORY OF LIGHT. 35 



understood as intervals of sound and silence^ and they will 

 even throw light on the science of sound. 



White Light. 



54. I have all along, in compliance with the common, 

 as well as philosophical, language of the day, spoken of 

 white light as if white were the colour of light. But why 

 should light have any particular colour ? Is it because 

 white is the most brilliant colour, that we call light white ? 

 It is by attributing to light a colour that we are led into 

 inextricable difficulties. Light is ether in motion, and 

 is, we might almost say, no more white than black. 

 Every one who has tried to expeiiment with light has 

 found it an extremely difficult thing to obtain a white 

 ray. Newton says that the light of the sun is yellow, and 

 he had consequently to modify some of his explanations 

 in accordance with that supposition; and Arago, as men- 

 tioned above, has said the same of the light of the moon. 

 From the yelloAV light of the sun we can obtain red, orange, 

 and the other colours of the spectrum, for we see the effect 

 daily in the spectrum ; but how do we, on the supposition 

 that the prism analyses light, get the white which is 

 reflected from the silvered back of a mirror, or the daz- 

 zling white of snow ? • Of course I do not deny that white 

 light really exists, and that it is the brightest light we 

 know ; but I do not admit that light is white, or that 

 white light is a compound of various colours, and conse- 

 quently do not believe that refraction decomposes white 

 light. Every observation which I have made on the 

 nature of light leads me to the conclusion that it is a 

 homogeneous substance and, being a homogeneous sub- 

 stance, can have no colour but what it acquires from the 

 form or chemical character of the objects which reflect it, 

 and which introduce the negative element of which I am 

 speaking. But the discussion of this subject Avill be 

 resumed presently. 



