of the prismatic Colours to heat and illuminate Objects. 267 



I. Badly illuminated, Very distinct. 

 V. There is hardly any illumination. 



Stb Experiment. The nail again, at 9 feet 6 inches from the 

 prism, by way of having the rays better separated. 



R. Badly illuminated. The bright points are very distinct. 



0. Much better illuminated. The bright points very distinct. 

 Y. Still better illuminated. All points extremely distinct. 



G. As well illuminated, and equally distinct. 

 B. Badly illuminated. The bright points are distinct ; but the 

 others are not so. 



1. Very badly illuminated. I do not see distinctly; but I 

 believe it to be for want of light. 



V. So badly illuminated that I cannot see the object ; or at 

 least but barely perceive that it exists. 



gth Experiment. Black paper, at 8 feet from the prism. 



R. The object is hardly visible. I can only see a few faint 

 points. 



0. I see several bright points, and many faint ones. 

 Y. Numberless bright and small faint points. 



Between yellow and green, is the maximum of illumination. 

 G. The same as the yellow. 



B. Very indifferently illuminated ; but not so bad as in the 

 red rays. 



1. I cannot see the object. 

 V. Totally invisible. 



From these observations, which agree uncommonly well, with 

 respect to the illuminating power assigned to each colour, we 

 may conclude, that the red-making rays are very far from hav- 

 ing it in any eminent degree. The orange possess more of it 

 than the red ; and the yellow rays illuminate objects still more 



