331 
On the Source of Po*uoer in the Voltaic Pile, 
diately attended with the circulation of an electrical current far more 
powerful than the thermo-electric current above-mentioned. A great 
number of combinations of other metals were successively tried in 
various ways, and they uniformly gave the same results as that of 
iron and platina. Similar experiments were then made with various 
metallic compounds, and also with other chemical agents ; and in all 
cases the same general fact was observed ; namely, that when no 
chemical action took place, no electrical current was excited ; thus 
furnishing, in the opinion of the author, unanswerable arguments 
against the truth of the theory of contact. The only way in which 
it is possible to explain these phenomena on that theory, would be 
by assuming, that the same law of compensation as to electro-motive 
power is observed by the sulphuret of potassium, and the other fluids 
of corresponding properties, as obtains in the Case of the metals, al- 
though that law does not apply to the generality of chemical agents ; 
and in like manner, different assumptions must be made in order to 
suit the result in each particular combination, and this without any 
definite relation to the chemical character of the substances them- 
selves ; assumptions, which no ingenuity could ever render consistent 
with one another. At the conclusion of the paper, the author de- 
scribes some remarkable alternations in the phenomena which occur, 
w'hen pieces of copper and silver, or two pieces of copper, or two of 
silver, form a circle with the yellow sulphuretted solution ; and 
which lead to the same conclusion as the former experiments. If 
the metals be copper and silver, the copper is at first positive, and 
the silver remains untarnished ; in a short time the action ceases, 
and the silver becomes positive, at the same time combining with 
sulphur, and becoming coated with sulphuret of silver ; in the course 
of a few minutes, the copper again becomes positive ; and thus the 
action changes from one side to the other in succession, and is ac- 
companied by a corresponding alternation of the electric current. 
March 5. — The reading of a paper entitled, “On the Chemi- 
cal Action of the Rays of the Solar Spectrum on Preparations of 
Silver and other Substances, both metallic and non-metallic ; and 
on some Photographic Processes ; ” by Sir John F. W. Herschel, 
Bart., V.P.R.S., &c., was resumed and concluded. 
The object which the author has in view in this memoir is 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 his 
notice in the course of his photographic experiments, suggested by 
the announcement of M. Daguerre’s discovery. After recapitulating 
the heads of his paper on this subject, which was read to the Society 
on the 14th of March, 1839, he remarks, that one of the most im- 
portant branches of the inquiry, in point of practical utility, is into 
the best means of obtaining the exact reproduction of indefinitely 
multiplied facsimiles of an original photograph, by which alone the 
publication of originals may be accomplished ; and for which purpose 
the use of paper, or other similar materials, appears to be essentially 
requisite. In order to avoid circumlocution, the author employs the 
