RADIATION. 49 



discovered and investigated Fluorescence ; for the new 

 phenomena here described I have proposed the term 

 Calorescence. 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 

 the image is decomposed, and a complete spectrum is 

 obtained. 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, 

 orange, 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 oipivrplish 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 glass 

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



