RADIATION. 49 



discovered and investigated Fluorescence; for the new 

 phenomena here described I have proposed the term 

 Caloreseence. He, by the interposition of a proper me- 

 dium, 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 refrangi- 

 bility of the ultra-red rays is so exalted as to render 

 them visible. Looking through a prism at the incan- 

 descent image of the carbon points, the light of the 

 image is decomposed, and a complete spectrum is ob- 

 tained. The invisible rays of the electric light, re- 

 moulded by the atoms of the platinum, shine thus visi- 

 bly 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.* 



* On investigating the caloreseence produced by rays trans- 

 mitted through glasses of various colours, it was found that in 

 the case of certain specimens of blue glass, the platinum foil 

 glowed with ft pink or purplish light. The effect was not sub- 

 jective, and considerations 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 dia- 

 thermic than the former. In fact., carbon when perfectly dis- 

 solved and incorporated with a good white glass, is highly trans- 

 parent to the calorific rays, and by employing it as an absorbent 

 the phenomena of 'caloreseence' may be obtained, though in a 

 less striking form than with the iodine. The black glass chosen 

 for thermometers, and intended to absorb completely the solar 

 heat, may entirely fail in this object, if the glass in which the 



