for five or six years. It appears to most advantage, if 

 brought into a dark room, after being held in the sun. 



3. When the rays of light fall on opake bodies, they 

 are variously reflected to our eyes, according as the sur- 

 face of those bodies are variously disposed. And hence 

 arises our sensation of colours. These, as they exist in 

 the coloured bodies, are only the dispositions of their 

 surface, to reflect such particular sorls of rays. White 

 bodies reflect all rays every way, without any separation 

 of them. On the contrary black bodies imbibe all the 

 rays, and reflect none or very few, whereas Hue, yel- 

 low, and red bodies, reflect only one particular sort of 

 rays. The smallest sort of rays are supposed to be blue; 

 the next yellow, the largest red. 



To be a little more particular. There are eight true 

 primary colours, which are red, yellow, green, blue, 

 violet, purple, orange, and indigo. All the rest are com- 

 pounded of these, and are termed secondary colours. 

 But the more compound any colour, the less vivid it is. 

 And by too much composition they may be diluted and 

 weakened till they are destroyed. The most extraordi- 

 nary composition of all is that of whiteness. For to this 

 five at least of the primary colours are required, as also, 

 that they be mixed in a certain degree. And hence white 

 is the ordinary colour of light : light being an assemblage 

 of all colours. 



The transmutation of colours by mixing them toge- 

 ther, is not real, but merely apparent. Thus mix blue 

 and yellow powders, and they appear green. But view 

 them with a microscope, and the blue and yellow parti- 

 cles are seen as distinct from each other as before. 



To produce Hack, the particles must be less than 

 those which exhibit any other colour. Where they are 

 greater, there is too much light reflected to constitute 

 this colour. But if there be a little less than forms the 

 indigo, the body appears intensely black. 



And hence it appears, w hy fire and putrefaction turn 

 many substances black. Tney divide them into exceed- 

 ing small particles > which then absorb, instead of reflect- 



