RADIATION. 49 



liscovered and investigated Fluorescence ; for the new 

 jhenomena here described I have proposed the term 

 Oalorescence. He, by the interposition of a proper 

 medium, so lowered the refrangibility of the ultra- 

 violet rays of the spectrum as to render them visible. 

 Here, by the interposition of the platinum foil, the 

 'refrangibility of the ultra-red rays is so exalted as to 

 'render them visible. Looking through a prism at the 

 [incandescent image of the carbon points, the light of 

 >bhe image is decomposed, and a complete spectrum is 

 bbtained. The invisible rays of the electric light, 

 [remoulded by the atoms of the platinum, shine thus 

 'visibly forth ; ultra-red rays being converted into red, 

 brange, yellow, green, blue, indigo, violet, and ultra- 

 violet ones. Could we, moreover, raise the original 

 source of rays to a sufficiently high temperature, we 

 might not only obtain from the dark rays of such a 

 source a single incandescent image, but from the dark 

 'rays of this image we might obtain a second one, from the 

 [dark rays of the second a third, and so on a series of 

 complete images and spectra being thus extracted from 

 the invisible emission of the primitive source. 1 



1 On investigating the calorescence produced by rays transmitted 

 through glasses of various colours, it was found that in the case of 

 certain specimens of blue glass, the platinum foil glowed with a 

 pink orpwrplish light. The effect was not subjective, and consider- 

 ations of obvious interest are suggested by it. Different kinds of 

 black glass differ notably as to their power of -transmitting radiant 

 heat. When thin, some descriptions tint the sun with a greenish 

 hue : others make it appear a glowing red without any trace of 

 green. The latter are far more diathermic than the former. In 

 fact, carbon when perfectly dissolved and incorporated with a good 

 white glass, is highly transparent to the calorific rays, and by em- 

 ploying it as an absorbent the phenomena of ' calorescence ' may be 

 obtained, though in a less striking form than with the iodine. The 

 black glass chosen for thermometers, and intended to absorb com- 

 pletely the solar heat, may entirely fail in this object, if the g 

 in which the carbon is incorporated be colourless. To render tU 



