On the Source of Power in the Voltaic Pile. 331 



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 tliey 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 ai'guments 

 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 laAv 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 maunei^, 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 

 Avith one another. At the conclusion of the paper, the author de- 

 scribes some remarkable alternations in the phenomena which occur, 

 when 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 



