O. N. Rood on action of Electric Light on Iodized Plates. 209 
Among the Geisler tubes belonging to the college I found one 
in which bulbs of uranium glass were alternated with small 
tubes of plain colorless glass. When the room was darkened, 
and the electric discharge passed through it, owing to their fluo- 
rescence the s shone very brightly, invisible or faintly visi- 
ble light being converted into bright green light. On taking a 
photograph of the tube, it was quite surprising to see how blank 
were the spaces on the plate, where the images of the green 
bulbs had fallen; after an exposure of four minutes only one of 
the bulbs could be faintly traced, though other portions of the 
bright sky fell directly through it on the lens of the camera, 
the entire aperture of the lens (a ‘portrait combination” of 
six inches focal length) was used, and the exposure lasted one 
minute. An examination of the negative plate showed that the 
thin walls of the uranium bulbs had merely diminished to some 
extent the chemical power of the rays passing through them. 
The same experiment with a plate of uranium glass two-tenths 
of an inch in thickness gave a result like in kind only differin 
in degree: the chemical intensity of the light being iminishet 
about one-half. This shows, in accordance with theory, that 1t 
1s mainly the dispersed light which has lost its chemical power, 
and that through a plate of even this thickness many chemi 
Tays still penetrate. ppt 
_A photograph of another Geisler tube, in which the interior 
discharge tube was surrounded by a solution of sulphate of qui- 
line, was also taken: this liquid by its fluorescent property di- 
Minished, of course, the intensity of chemical action of the 
electric light, but by no means to the same extent as the ura- 
lum glass. 
Feb. 3d, 1864, 
