274 M. C Lea—Action of the less refrangible rays of Lrght 
the dark green admitted principally green and yellow, cutting 
off the orange and red. 
A spectroscopic analysis gave the following results: 
Extreme limit of wave-length at less refrangible end of the 
nn adh LURE pas Race eae Bae rad iy Spiers oar as eer en) A 638 
Pet Wate aetrani wre Olid 5 8 eo ee WRT 
Point of maximum illumination, ..-..-.....--22.-..-.-- A570 
The limits here given are extreme limits at which the absorp- 
tion spectrum ended, It was estimated that at least nineteen- 
twentieths of the illumination was pure yellow, with perhaps a 
very faint admixture of orange, and of the less refrangible 
green rays, bordering on the yellow (any close observation of 
the spectrum will show how little pure yellow light it contains). 
Result.—Silver iodide showed itself also more sensitive to 
variable. Feb. 4, 1875, with exposure to bright sunlight from 
12 M. to 3 P. M., distinct images were got by development on 
to an equal strength in one-third the time. 
I conclude, therefore, that silver iodide and bromide are both 
sensitive to yellow light, and the iodide more so than the 
bromide. 
GreEeN Rays. 
Much of the green glass found in commerce admits nearly 
the whole spectrum except the red rays. There exists, however, 
a very dark shade of green, which narrows the transmitted band 
very much. When two such pieces of dark green were super- 
posed, their absorption spectrum was as follows: 
Extreme limit toward red end, A601 
Extreme limit toward blue end, ___.-_..-.--.--- A 488 
three plates were superposed. This involved such a reduction 
of illumination that the sun could be viewed through the glass 
without inconvenience. This combination gave the following 
measurement : 
Extreme limit toward red end, . ws. AGSI 
Extreme limit toward blue end, ..-.. ----..---- 4497 
