24 THE RADIATIONS OF IGNITED BODIES. [MEMOIR I. 



stated that when a solid begins to shine it first emits 

 red and then white rays; in others it is asserted that a 

 mixture of blue and red light is th first that appears. 



I have succeeded in escaping or overcoming many of 

 the difficulties of this problem, and have arrived at 

 satisfactory solutions of the main points; and as the 

 experiments now to be described lead to some striking 

 and perhaps unexpected analogies between light and 

 heat, they commend themselves to our attention, as hav- 

 ing a bearing on the question of the identity of those 

 principles. It is known that heretofore I have been led 

 to believe in the existence of cardinal distinctions not 

 only between these, but also other imponderable agents, 

 and I may therefore state that when this investigation 

 was first undertaken it was in the expectation that it 

 would lead to results very different from those which 

 have actually arisen. 



The following are the points on which I propose to 

 treat : 



1. To determine the point of incandescence of plati- 

 num, and to prove that different bodies become incan- 

 descent at the same temperature. 



2. To determine the color of the rays emitted by self- 

 luminous bodies at different temperatures. This is done 

 by the only reliable method analysis by the prism. 



From these experiments it will appear that as the 

 temperature rises the light increases in refrangibility; 

 and making due allowance for the physiological imper- 

 fection of the eye, the true order of the colors is red, 

 orange, yellow, green, blue, indigo, violet. 



3. To determine the relation between the brilliancy 

 of the light emitted by a shining body and its tempera- 

 ture. 



Here we shall find that the intensity of the light in- 

 creases far more rapidly than the temperature. For 



