334? 'Royal Society : — Sir John Herschel on the Chemical 
lity is next investigated ; and the author inquires more particularly 
into the elfects of the combined action of a red ray ’with any other 
single ray in the spectrum ; whether any, and w'hat differences exist 
between the joint, and the successive action of rays of any two dif- 
ferent and definite refrangibilities ; and whether this action be ca- 
pable, or not, of producing effects, which neither of them, acting alone, 
would be competent to produce. The result was that, although the 
previous action of the less refrangible rays does not appear to mo- 
dify the subsequent effects produced by the more refrangible ; yet 
the converse of this proposition does not obtain, and the simultaneous 
action of both produces photographic effects very different from those 
which either of them, acting separately, are capable of producing, 
8. In the next section, the chemical action of the solar spectrum 
is traced much beyond the extreme red rays, and the red rays them- 
selves are shown to exercise, under certain circumstances, a black- 
ening or deoxidating power. 
9 . The author then enters into a speculation suggested by some in- 
dications which seem to have been afforded of an absorptive action 
in the sun’s atmosphere ; of a difference in the chemical agencies 
of those rays which issue from the central parts of his disc, and those 
which, emanating from its borders, have undergone the absorptive 
action of a much greater depth of his atmosphere ; and consequently 
of the existence of an absorptive solar atmosphere extending beyond 
the luminous one. 
10. An account is next given of the effect of the spectrum uncer- 
tain vegetable colours, as determined by a series of experiments, 
which the author has commenced, but in which the unfavourable 
state of the weather has, as yet, prevented him from making much 
progress. 
1 1 . The w^hitening power of the several rays of the spectrum under 
the influence of hydriodic salts, on paper variously prepared and 
previously darkened by the action of solar light. The singular pro- 
perty belonging to the hydriodate of potash of rendering darkened 
photographic paper susceptible of being whitened by further expo- 
sure to light is here analysed, and shown to afford a series of new 
relations among the different parts of the spectrum, with respect to 
their chemical actions. 
12. The Analysis of the Chemical Rays of the Spectrum by ab- 
sorbent media, which forms the subject of the next section, opens a 
singularly wide field of inquiry ; and the author describes a variety 
of remarkable phenomena which have presented themselves in the 
course of his experiments on this subject. They prove that the pho- 
tographic properties of coloured media do not conform to their colo- 
rific character ; the laws of their absorptive action as exerted on the 
chemical, being different and independent of those on the luminous 
rays : instances are given of the absence of any darkening effect in 
green and other rays of the more refrangible kind, which yet produce 
considerable illumination on the paper that receives them. 
13. The exalting and depressing power exercised by certain media, 
under peculiar circumstances of solar light, on the intensity of its che- 
