of the Solar Spectrum on the Daguerreotype Plate. 131 
I further satisfied myself, 3rdly, in the experiments alluded 
to, that the law of photographic action on a, bromuretted 
silver plate is in like manner identical in respect of intensity, 
with that exhibited on paper prepared with bromuret of silver 
in Mr. Talbot’s method; the action being carried down in 
both cases zo, and considerably beyond, the extreme red ray. 
But no appearance of protection from the action of dispersed 
light, which is so conspicuous on the paper, was observed on 
the silver plate. [This plate I did not mercurialize. ] 
I had intended to conclude this communication with some 
remarks in detail on Professor Draper’s “ Tithonic rays,” 
but having already extended it to I fear an inadmissible 
length, I must limit myself to throwing in a general caveat 
against the adoption of a new name (and that a most fanci- 
ful one) for an old idea. The notion of chemical rays as di- 
stinct from those both of light and heat, is so perfectly familiar 
to every photologist, as hardly to need insisting on. The 
extension of chemical action to every part of the spectrum, 
and considerably beyond the extreme red, is fully demon- 
strated in my first memoir on this subject; where also the 
independence of the rays in which that action resides, and the 
simply luminous and colouring ones, is clearly proved by de- 
cisive experiments on the absorption of coloured media, per- 
fectly analogous to those brought forward by Dr. Draper, and 
which I am somewhat surprised he has not noticed, as he has 
evidently read that memoir. 
Should Dr. Draper succeed in establishing those points of 
analogy between the photographic chemical rays and those of 
heat, viz. that they are capable of accumulating in er on bo- 
dies exposed to them, thence radiating away in the manner of 
obscure heat (after undergoing such a change as to be no 
longer capable of traversing colourless glass), but with this 
marked distinction from such heat, that they are not conducted 
in this their new state by metallic bodies, no one will hesitate 
to regard him as having attached a new idea to the old one of 
chemical rays, and as entitled to impose on them a name. 
But I hope I shall not be considered as undervaluing the 
really interesting experiments he has brought forward in 
support of these propositions, if I profess myself as yet uncon- 
vinced by them. My own impression is, that there are two 
distinct kinds of chemical action; exercised, if we choose so 
to consider the subject, by two distinct and independent classes 
of rays (not opposed, but different), the one class being those 
which have been hitherto commonly called chemical, but 
which, being in this view of the subject not a distinctive 
name, I shall for the present call them photographic rays ; 
K 2 
