146 Mayow 



colour is propagated. But on the other hand if the 

 rays of light are entirely absorbed, without resistance, 

 by the surface of the illuminated body, or if the solid 

 body is of such a kind as offers little resistance to 

 luminous motion, black colour or rather the absence 

 of all colour is the result. For example, if an eye 

 situated in darkness is turned towards an illuminated 

 mirror, but in such a position that the rays falling on 

 the mirror are not reflected to the eye, the mirror will 

 appear of a black colour, or rather it will scarcely be 

 seen at all. Nay, although the mirror be so placed 

 that the rays of light reflected from it fall upon the 

 eye of the beholder, the rays will indeed flash like 

 lightning upon the eye, but the glass itself will 

 scarcely be seen at ,all. No doubt the luminous 

 particles impinging on the mirror, throw the nitro- 

 aerial particles which the glass contains — and which 

 are kindred with themselves — into their own 

 luminous motion, for it has elsewhere been shown 

 that very solid bodies, such as glass and the like, 

 have nitro-aerial particles inserted in them. But 

 since the particles of the glass yield to the motion of 

 the luminous particles and in no way resist it, these 

 luminous particles will acquire none of that motion of 

 vibration by which colours and the images of things 

 are propagated ; hence it is that glass of that kind 

 has no colour at all. 



As to red and the other colours which differ from 

 the glittering white, they seem to be due to various 

 mixtures of the glittering white with darkness. 



From what has been said, we must seek for an 

 explanation why substances of a white colour can 

 scarcely be kindled by solar rays collected by a 

 burning-glass, while, on the other hand, such as are 

 black easily take fire. For when nitro-aerial and 



