198 FLUORESCENCE. SECT. XXII. 



Professor Draper, of New York, proved that the result is the 

 same whether the incident light be polarized or not, and that 

 the dispersed or degraded light is never polarized, but that it 

 emanates in all directions, as if the substance were self-luminous ; 

 he made experiments with light from all parts of the solar 

 spectrum, and with various substances, and always found that 

 the refrangibility of the incident ray was diminished by internal 

 dispersion, and that the colour was changed to suit the new re- 

 frangibility. Professor Draper has also shown that the law of 

 action and reaction prevails in all the phenomena of the sunbeam, 

 as in every other department of nature ; so that a beam cannot 

 be reflected, refracted, much less absorbed, without producing 

 some change upon the recipient medium ; and Mr. Power proved 

 analytically that the solar rays can exercise no action upon any 

 medium through which they are transmitted, without being 

 accompanied 'by a diminution of refraction. He says, "The 

 new light emanating from the fluorescent media is just like any 

 other light of the same prismatic composition. In its physical 

 properties it retains no trace of its parentage ; it is of terrestrial 

 origin, and its colour depends simply on its new refrangibility, 

 having nothing to do with that of the producing rays, nor to the 

 circumstance of their belonging to the visible or invisible part 

 of the spectrum.'* These phenomena can only be explained by 

 the undulatory theory of light. 



