240 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



langen a memoir on fluorescence, in which he divides all flu- 

 orescent bodies into three classes, the first comprising those 

 substances upon which each homogeneous ray of light capa- 

 ble of producing fluorescence produces the whole fluores- 

 cent spectrum; the second including those bodies upon which 

 the same ray of light produces only those rays of the fluo- 

 rescent spectrum which are of a less refrangibility than the 

 ray itself; and the third embracing those substances whose 

 fluorescent spectrum consists of two parts, one of which cor- 

 responds to fluorescence of the first, and the other to fluores- 

 cence of the second order. He enumerates nine bodies be- 

 longing to the first class, twenty-five of class second, and 

 seven of class third. He has not been able to prove that 

 class three is a mixture of classes one and two. 



Von Bezold and Engelhardt have examined the retina of 

 the living animal, and conclude that it also fluoresces under 

 the influence of the same rays whicli Helmholtz has stated 

 exercise a fluorescent action upon the retina of the dead ani- 

 mal. 



Abney has described to the London Physical Society the 

 method he had adopted for photographing the least re- 

 frangible end of the spectrum. He had succeeded in ob- 

 taining a compound which is sensitive at the same time to 

 the red and blue rays, by weighting silver bromide with 

 resin, subsequently, however, causing the silver bromide 

 molecules to weight themselves. While an ordinary silver 

 bromide plate was of a ruddy tint, showing absorption of 

 the blue rays, a plate containing weighted bromide of silver 

 transmitted blue light and absorbed red. The latter plates 

 are sensitive to the red and ultra-red rays, and photographs 

 of the spectrum were exhibited extending from the line C to 

 a wave-length of 10,000, the ultra-red showing remarkable 

 groupings of lines. He explained the reversing action ob- 

 tained by Draper at the red end as an oxidizing action, and 

 found it to be accelerated in solutions of permanganate, hy- 

 droxyl, etc. 



Chastaing has published an extended memoir on the chem- 

 ical action of light. ' He concludes (1) that on inorganic 

 bodies the violet end of the spectrum as far as the green 

 exerts a reducing, the red end an oxidizing action, the lat- 

 ter being less marked : whence the total action of white 



