Either by bringing the two metals into contact, or by connecting them by means of a metallic conductor. But without subjecting a frog to any cruel experiments, I can easily make you sensible of this kind of electric action. Here is a piece of zinc, (one of the metals I mentioned in the list of elementary bodies)--put it _under_ your tongue, and this piece of silver _upon_ your tongue, and let both the metals project a little beyond the tip of the tongue--very well--now make the projecting parts of the metals touch each other, and you will instantly perceive a peculiar sensation. EMILY. Indeed I did, a singular taste, and I think a degree of heat: but I can hardly describe it. MRS. B. The action of these two pieces of metal on the tongue is, I believe, precisely similar to that made on the nerve of a frog. I shall not detain you by a detailed account of the theory by which Galvani attempted to account for this fact, as his explanation was soon overturned by subsequent experiments, which proved that _Galvanism_ (the name this new power had obtained) was nothing more than electricity. Galvani supposed that the virtue of this new agent resided in the nerves of the frog, but Volta, who prosecuted this subject with much greater success, shewed that the phenomena did not depend on the organs of the frog, but upon the electrical agency of the metals, which is excited by the moisture of the animal, the organs of the frog being only a delicate test of the presence of electric influence. CAROLINE. I suppose, then, the saliva of the mouth answers the same purpose as the moisture of the frog, in exciting the electricity of the pieces of silver and zinc with which Emily tried the experiment on her tongue. MRS. B. Precisely. It does not appear, however, necessary that the fluid used for this purpose should be of an animal nature. Water, and acids very much diluted by water, are found to be the most effectual in promoting the developement of electricity in metals; and, accordingly, the original apparatus which Volta first constructed for this purpose, consisted of a pile or succession of plates of zinc and copper, each pair of which was connected by pieces of cloth or paper impregnated with water; and this instrument, from its original inconvenient structure and limited strength, has gradually arrived at its present state of power and improvement, such as is exhibited in the Voltaic battery. In this apparatus, a specimen of which you see before you (PLATE VI. fig. 1.), the plates of zinc and copper are soldered together in pairs, each pair being placed at regular distances in wooden troughs and the interstices being filled with fluid. [Illustration: Plate VI. p. 151. Fig. 1. Voltaic Battery. Fig. 2. Fig. 4. Fig. 1. 2. & 4. Voltaic Batteries Fig. 3. Electrical Machine. A the Cylinder. B the Conductor. R the Rubber. C the Chain.] CAROLINE.