
is very decidedly protected from change. Upon placing the 
_ glass in a solution of hyposulphite of soda, and allowing it to 
_ remain for some time, the variations of action are more ap- 
_ parent :—lIst, the very dark centre; 2nd, a band of much 
a ieee! ie 
















weaker action; 3rd, a far more energetic band surrounding 
the whole ; and 4th, a protected band extending from the lower 
point far below this as a protected circle, as indicated by the 
shading in the figure. 
(52) 18. Mepium yveELLow (6), fig. 21.—Chemical action 
_ commences above the yellow ray, upon the confines of, but 7 
the green, commencing *40 above lower red, the space oc- 
cupied by the green rays being impressed as a well-defined 
oval of the length of *25, then a neck of very much lower in- 
tensity of ‘20; a large and well-defined oval 90 in length, 
exhibiting the greatest degree of intensity in the middle space, 
shaded off to the edges. The length of impressed spectrum 
1:40, and from the zero a! to end of chemical action 1°85, or 
length of action beyond luminous spectrum at @°85. Here 
we have an extinction of the violet and indigo rays; and over 
the space occupied by the blue rays a comparatively weak 
action, this action being continued with very much energy 
over the space occupied by the dark rays. The indication of 
protected spaces around the spectrum is less evident than in 
many other examples. 
(53) 114. LicHT RED-BROowN (11), fig. 22—Action com- 
mencing at “75 and extending with tolerably uniform inten- 
sity to 1°60, and gradually shading off to 1°85. At the lower 
end the action descends slowly to ‘65. A brown line of 
_ shading appears around this spectrum, but this is probably due 
to dispersed light, since this shading is considerably increased 
when many clouds are floating about. 
Glasses (B.) Red Media. 

ON THE CHEMICAL ACTION OF THE SOLAR RADIATIONS. 269 
contrast with the little darkening from extraneous light beyond the luminous 
image. The space between a and the lower end of the impressed spectrum 
Fig. 21. 
a 
(54) 13. VioLer cLass (13), fig. 23.—Chemical action commences at *60 
above 0, and is then continued with tolerable uniformity to 1°35, a faint sha- 
ding being prolonged about 15 further, or 50 beyond the luminous spectrum. 
The long dark oval in the interior of the spectrum exhibits a more intense 
chemical action than the other portion; this darkened space appears to 
Fig. 24. 
belong mainly to the upper oval of the luminous Fig. 23. 
| spectrum and over the dark space beyond it. In 
| some other experiments, during a period when 
| thesky was covered with light white clouds, and 
consequently when the intensity of the sunshine 
was varying, the chemical limits were subject se 
to constant changes, commencing sometimes as 
| high as °70 and terminating at -30. 
|. (55) 104. Lizac exass (18), fig. 24.—Che- 
mical action commences at *75 and ceases en- 
| tirely at 1-25, forming thus one small patch of 
L changed silver, commencing near the line H, and 
“occupying but about one half-inch of space. 4 


