170 SirJ. F. W. Herschel on the Action of the Rays 
9, _ (ah+a, 8) ry | 
®oYq (a B+, By) %oYo 
AL — Hr +(@B+e Ay) XHt+Bh By x? eel (E-+B1) yi—B By (aa) vy wm B By 
Ly Y2 & &) Yo" + (a Bay By) &2 Y2+B By LeP—a a (8B46)) yo—B By (a+) toa a B Pl 
ee, (44, +1, 2%, —2%B,) (4 ¥, +6 L,—@, f) | 
(% Yat B, Ly —a By) (% Yo+P ty—a, B)’ 
therefore, finally, 
(4Y, +B 2,—2,B)x, _ (a ¥,+B,£,—a8,) x, 
(% YotBr.—e, B)y, (ay, +P, 2;—2B,) yo” 
But these are the values of sa and =e obtained above, 
I 
and therefore + Oe. eo 8 
which is the criterion of the origin H, and the points C and K 
being in the same straight line, therefore the points of inter- 
section G, H, K range in the same straight line. 
and since ; consequently we have 
XXVII. On the Action of the Rays of the Solar Spectrum on 
Vegetable Colours, and on some new Photographic Processes. 
By Sir Joun F. W. Herscuet, Bart., K.H., F.B.S. 
[Continued from p. 116.] 
202. I SHALL conclude this part of my subject by remarking 
on the great number and variety of substances which, 
now that attention is drawn to the subject, appear to be pho- 
tographically impressible. It is no longer an insulated and 
anomalous affection of certain salts of silver and gold, but one 
which doubtless, in a greater or less degree per vades all na- 
ture, and connects itself intimately with the mechanism by 
which chemical combination and decomposition is operated. 
The general instability of organic combinations might lead 
us to expect the occurrence of numerous and remarkable cases 
of this affection among bodies of that class, but among metal- 
lic and other elements inorganically arranged, instances enough 
have already appeared, and more are daily presenting them- 
selves, to justify its extension to all cases in which chemical 
elements may be supposed combined with a certain degree 
of laxity, and so to speak, in a state of tottering equilibrium. 
There can be no doubt that the process, in a great majority 
if not all the cases which have been noticed among inorganic 
substances, is a deoxidizing one, so far as the more refrangible 
rays are concerned. It is obviously so in the cases of gold 
and silver. In that of the bichromate of potash it is most pro- 
bable that an atom of oxygen is parted with, and so of many 
others. A beautiful example of such deoxidizing action on a 
