chemical action alone ; contrasting them with the numerous cases given in the previous series, where contact without chemical action, whether it be the contact of metal with metal, or with chemically inactive electrolytes, can produce no voltaic current.
The author then considers the sufficiency of chemical action to account for all the phenomena of the pile. He shows that che- mical action does actually evolve electricity ; that according as chemical action diminishes or ceases, so the electrical current di- minishes or ceases also ; that where the chemical action changes from side to side, the direction of the current likewise changes with it ; that where no chemical action occurs, no current is produced, but that a current occurs the moment chemical action com- mences ; and that when the chemical action which has, or could have produced a current, is, as it were, reversed or undone, the cur- rent is reversed or undone likewise ; that is, it occurs in the oppo- site direction, in exact correspondence with the direction taken by the transferred anions and cathions. The accordance of the che- mical theory of excitation with these phenomena is considered by the author as of the strictest kind.
The phenomena of thermo-electricity are considered by some philosophers as affording proofs of the efficacy of mere metallic contact in exciting an electric current. The author proceeds, there- fore, to examine these phenomena in relation to such an action, and arrives at the conclusion, that they, in fact, disprove the existence of such a power. In thermo-electricity, the metals have an order which is so different from that belonging to them in any electrolyte, that it appears impossible to consider their succession, in any case, as due to any mutual effect of the metals on each other, common to both modes of excitation. Thus, in the thermo-circuit, the electric cur- rent is, at the hot place, from silver to antimony, and from bismuth to silver ; but in a voltaic series, including dilute sulphuric or nitric acids, or strong nitric acid, or solution of potash, the electric current is from silver to both antimony and bismuth ; whilst if the yellow sulphuret of potash be used, it is from both antimony and bismuth to silver ; or if the hydro-sulphuret of potash be used, it is from bismuth to silver, and from silver to antimony ; and, finally, if strong muriatic acid be used, it is precisely the reverse, that is, from antimony to silver, and from silver to bismuth. The inconsistency of these results with the contact theory is then insisted on and farther developed.
The last section of this series is on the improbability of there ex- isting any such force as the assumed contact force. The author contends that it is against all natural analogy and probability that two particles which, being placed in contact, have by their mutual action acquired opposite electrical states, should be able to discharge these states one to the other, and yet remain in the same state they were in at the first, that is, entirely unchanged in every point by what has previously taken place ; or, that the force which has enabled two particles by their mutual action to attain a certain state, should not be sufficient to make them keep that state. To admit such ef-
