PHILOSOPHICAL TRANSACTIONS. 
I. On the Chemical Action of the Rays of the Solar Spectrum on Preparations of 
Silver and other Substances, both metallic and non-metallic, and on some Photo- 
graphic Processes. By Sir John F. W. Herschel, Bart. K.H. V.P.R.S. tyc. 
Received and Read February 20, 1840. 
i. Lest the title of this communication should induce an expectation of its con- 
taining any regular and systematic series of researches developing definite laws, or 
pointing to any distinct theory of photographic action, it may be as well to commence 
it by stating its pretensions to be of a much lower kind, its object being simply to 
place on record a number of insulated facts and observations respecting the relations 
both of white light and of the differently refrangible rays to various chemical agents, 
which have offered themselves to my notice in the course of photographic experi- 
ments originating in the announcement of M. Daguerre’s discovery. The facts 
themselves, in the present state of our knowledge, will, I believe, be found by no 
means devoid of interest, and may lead, in the hands of others more favourably situ- 
ated for such researches, and, I may add, in a better climate than ours, to inquiries 
of the utmost interest. 
2. In a communication to this Society, which was read on the 14th of March, 1839, 
and of which an abstract will be found in the notices of its proceedings for that sit- 
ting, I have stated the circumstances which first directed my attention to this subject, 
and the progress I had then made, both in the scientific part of the inquiry and in 
its application to the photographic art. As that paper was (at my own request) with- 
drawn from the further immediate notice of the Society, and as the abstract alluded 
to may not fall into the hands of those who may read the present communication, a 
brief recapitulation of its contents will be necessary to preserve the connexion by 
which my inquiries have been linked together. 
3. The principal points of that communication are as follows. 1st. The use of the 
liquid hyposulphites for fixing the photographic impression, in virtue of the property 
which they possess (and which was, I believe, first pointed out in my paper on those 
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