282 



The instruments used in the experiments of this paper for detect- 

 ing and estimating electric currents of small intensity, were con- 

 structed on the principles of the multiplier of Schweigger, and the 

 galvanometer of Prof. Gumming ; the suspended needle being sur- 

 rounded, in the direction of its length, with several coils of silked 

 wire, and having its directive force counteracted by two other needles 

 exterior to the coils, being a modification of the method employed 

 for a similar purpose by M. Nobili. For determining weak electri- 

 cities of tension, Volta's condenser, connected with Bennet's elec- 

 trometer, was employed ; or with one consisting of a silk filament, 

 rendered conducting by charcoal dust. Much dependence was, how- 

 ever, never placed on these instruments, unless their indications were 

 otherwise confirmed. 



The author now proceeds to the experimental inquiries, which 

 form the chief object of the lecture, and to the general views of 

 electro-chemical agency to which they appear to lead. First, he con- 

 siders the electrical and chemical effects exhibited by combinations 

 of one metal and one fluid. 



The nature of these effects is best explained by an example. When 

 two pieces of polished copper, each connected with the extremity of 

 the wire of the multiplier, are plunged into a solution of an alkaline 

 hydro-sulphuret, if introduced at the same instant, there is no action; 

 but if in succession, there is a distinct or even a violent electrical 

 effect, and the piece of metal first introduced is negative with re- 

 spect to the other. This effect depends on the formation of a coat of 

 sulphuret of copper on the plate first introduced, which is negative with 

 respect to metallic copper. Hence the combination is, in strictness, 

 one of these elements, copper, sulphuret of copper, and the solution. 



In like manner, protoxide of copper is negative with respect both 

 to pure copper and to the sulphuret. Hence, wherever instead of 

 pure copper, tarnished (i. e. oxidated), copper is used in the foregoing 

 experiment, the effect will be precisely the reverse ; and by this many 

 curious anomalies, in this and similar experiments, are explained. 



This production of electrical currents by single metals and single 

 fluids occurs generally whenever new products adhering to the me- 

 tallic surfaces are produced ; and if the same products be applied 

 artificially, the effects are the same as if their adhesion had been 

 caused by the natural action of the fluid on the metal. The chemical 

 changes produced in the fluid by the ternary combinations thus 

 formed, are in all cases such as tend to restore the deranged equi- 

 librium, hydrogen passing to the negative side, and oxygen to the 

 positive, until the oxides are revived. 



We come next to consider the case of two imperfect and one per- 

 fect conductor, as two fluids and a metal, or charcoal. And here the 

 author takes occasion to combat an opinion advanced on high au- 

 thority * respecting the active development of electricity in the com- 

 binations of acids and alkalies, which he refers to the contact of mc- 



* That of M. Becquerel. 



