[ '3' ] 



we may obferve, that the moft intenfe and vivid, natural red bo- 

 dies do, in fad, refled a very great proportion of blue rays, be- 

 caufe they appear of a ftrong blue colour when placed in the 

 blue part of the fpedrum ; and therefore they refled juft as many 

 when the dired, white folar light falls on them, in which all that 

 blue is involved ; though by the predominance of the red rays, 

 they appear of that colour, without any vifible tindure of 

 blue. 



In order to determine whether the purple appearance of the red 

 extremity of the fpedrum, when viewed through a blue glafs, 

 was caufed by'any of the white folar light, which might perhaps 

 be refleded from the air, or furroundlng objeds to the fpedrum, 

 and thus throw on that part fuch a quantity of blue as might 

 produce a fenfible effed ; I caufed the middle and moft intenfe 

 part of the red to pafs through a hole in a blackened paper, and 

 then fall on an optical fcreen ; by which I was fure that I had as 

 pure and uncompounded a red as could be defired ; which alfo un- 

 derwent the ufual teft of purity by fubfequent refradion, without 

 any change in the form of the fpedrum ; I then looked at the 

 body which was illuminated with this red, through the fame blue 

 glafs, and the efFed was the fame as before. 



To try this dodrine of three parent colours flill farther, I con- 

 fidcrcd, that if the orange were really compounded of the red and 

 yellow rays, then by looking at the orange through a red glafs, 

 © R 2 the 



