23 



ing the light. Hence also it appears, why glass ground 

 very elaborately with sand on a eopper-plate, makes the 

 sand together with what is worn off from the glass and 

 copper, become very black : likewise, why black < sub- 

 stances exposed to the sun, are hot sooner than any 

 other. This may partly proceed from the multitude of 

 refractions in a little room, partly from the easy commo- 

 tion of so small particles, arid from their imbibing his 

 rays. Hence also we learn, why blacks are usually in- 

 clined to a bluish colour. Black borders on indigo, and 

 therefore reflects indigo-rays, if any. 



To try if black bodies receive heat more than others, 

 Mr. Boyle whited one half of a tile, and blacked the 

 other, and then exposed it to the summer sun. While 

 the white part still remained cool, the black part was 

 grown very hot. For farther satisfaction he exposed to 

 the sun a tile, part of which was blacked, part white, 

 and part of its natural fed : and after a while found the 

 black part hot, the red warm, and the white cool. 



" I laid on the snow, (says Dr. Franklin,) little pieces of 

 broad cloath, of divers colours, black, deep blue, light 

 blue, green, purple, red, yellow, white, in a bright sun- 

 shiny morning. In a few hours the black (being warmed 

 most) was sunk lowest, the dark blue almost as low, the 

 light blue not quite so much, the other colours less as 

 they were lighter, and the white not at all. This was an 

 easy and certain way of shewing which was heated most." 



All the secondary colours of natural bodies proceed 

 from their reflecting two or more sorts of rays together, 

 and absorbing the rest. 



Glass, crystal, diamond, and other transparent bodies, 

 lose their transparency, and are white, when reduced to 

 powder: the change of texture causing them to reflect 

 the rays which before they transmit. 



White loaf-sugar, melted over the fire, without wa- 

 ter, iirst turns brown, afterwards black. And a single 

 gram of this tinges a quart of fair water with a beauti- 



