1826.] Uoyal Society, 63 



of all his researches. The instruments used in the experiments 

 of the present paper for detecting and estimating electric cur- 

 rents of low intensity, were constructed on the principles of the 

 multiplier of Prof. Schweigger, and the galvanometer of Prof. 

 Gumming. For determining weak electricities of tension, 

 Volta's condenser, connected with Bennet's electrometer, or 

 with one consisting of a silk filament rendered conducting by- 

 charcoal dust, was employed. Much dependence was, however, 

 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 his lecture, and to the general 

 views of electrochemical agency to which they appear to lead. 

 And first, he considers the electrical and chemical effects exhi- 

 bited 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 connected with one extremity of the 

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

 hydrosulphuret, if introduced at the same instant, there is no 

 action ; but if in succession, a sensible interval being allowed to 

 elapse, there is a distinct or even a violent electrical effect, and 

 the piece of metal first introduced is negative with respect to 

 the other: this effect depends on the formation of a coat of 

 sulphuret of copper on the plate first introduced, while it is 

 negative with respect to metaUic copper. Hence the combina- 

 tion is in strictness one of three elements ; copper, sulphuret of 

 copper, and the solution. In Hke manner, protoxide of copper 

 is negative with respect to pure copper, and to the sulphuret. 



The production of electrical currents by single metals and 

 single fluids occurs generally whenever new products adhering 

 to the metallic surfaces are produced ; and if the same products 

 be apphed artificially, the effects are the same, as if the adhesion 

 had been caused by the natural action of the fluid on the metal. 

 The chemical changes produced in the fluid by the ternary com- 

 binations thus formed are, in all cases, such as tend to restore 

 the deranged equilibrium, hydrogen passing to the negative 

 side, and oxygen to the positive, until the oxides are revived. 



The case of two imperfect and one perfect conductor is next 

 considered, as two fluids and a metal or charcoal. Here the 

 author controverts an opinion advanced on high authority, 

 respecting the alleged development of electricity on the combi- 

 nation of acids and alkalies, which he refers to the contact of 

 metals with these agents, to change of temperature, evaporation, 

 &c. and never to the mere union of these bodies : several expe- 

 riments are adduced in support of this opinion. 



When platinum is brought into contact with an acid, the pole 

 touching the acid is negative, the opposite pole positive, and 



