48 THE RADIATIONS OF IGNITED BODIES. [MEMOIR I. 



analysis. He states the results given in the foregoing 

 pages, and adds : " In other words, the spectrum of the 

 strip of platinum which corresponds to the red extremity 

 of the prismatic spectrum is at first very short, and con- 

 tains only the less refrangible colors ; but as the tempera- 

 ture rises, the spectrum of incandescence extends towards 

 the violet extremity, obtaining the more refrangible tints, 

 and at last acquiring all the colors and all the extent of 

 the solar spectrum, except the terminal rays at the two 

 extremities, which escape the observer evidently on ac- 

 count of their extreme feebleness. The same cause (in- 

 sensibility due to a want of luminous energy) makes the 

 first spectrum appear at the red end a little shorter than 

 the last, because the less refrangible rays of that color 

 are, as is well known, so feeble even in the solar spec- 

 trum that we are unable to perceive them, unless they 

 are isolated in a place that is totally dark. Much more, 

 therefore, ought they to remain invisible to the observer 

 when the spectrum arises from luminous agencies so little 

 energetic as are those of the first periods of incandescence. 



" To a perfectly sensitive eye the variations of length 

 would evidently have taken place in the direction of the 

 more refrangible rays only, and all the spectra would 

 have commenced at the extreme limit of the red rays. 



" It results from all these observations that when the 

 incandescence of a body becomes more and more vivid 

 and brilliant by the elevation of its temperature, there is 

 not only an augmentation in the intensity of the result- 

 ing light, but also in the variety of elementary colors 

 which compose it ; there is, too, an addition of rays so 

 much the more refrangible as the temperature of the in- 

 candescent body is higher. In this there is, therefore, 

 established an intimate analogy between the progressive 

 development of light and that of heat. Indeed,' 1 M. Mel- 

 loni adds, " as soon as I had convinced myself of the 



