^{page 207 note *} The fluid for marking the degrees of action may consist of rectified spirit one part, distilled water three parts, coloured with tincture of cochineal; to which may be added as much sulphuric acid as will render the whole pleasantly sour. Mercury also, when the tube is fine, may be used with advantage.

^{page 208 note *} This experiment was likewise contemplated by my friend Mr Watkins, the curator of the apparatus, in the London University. In the course of a few trials with the instrument which I had the pleasure of making with him at his house, we succeeded in rendering sensible, the action of a small plate of zinc and copper, of only ¼th of an inch square, when placed in an extremely diluted acid, at upwards of 4 inches apart; the wire in the electrometer was in this instance extremely fine.

^{page 211 note *} Phil. Trans. for the year 1821, p. 435.

^{page 212 note *} Memoirs of Plymouth Institution, p. 68. and 84.

^{page 213 note *} Phil. Transactions for 1821, p. 438.

^{page 213 note †} This experiment with the electrometer had been previously tried by Mr Jonathan Hearder, of this place, to whose friendly assistance I have been occasionally much indebted, in the progress of these inquiries.

^{page 214 note *} This can be readily managed by one particular arrangement of the connecting wires, which admits of the two batteries operating separately.

^{page 218 note *} Transactions of the Royal Society of London, for the year 1821, p. 438.

^{page 220 note *} The conducting powers of antimony and bismuth have been determined subsequently to the period at which this paper was read. These metals were cast into bars, and compared with zinc, tin, and lead, treated in a similar way,—a process suggested to me by Mr Forbes, who was so good as to honour me with a communication on this subject. Mercury, in its fluid state, was examined in a somewhat similar way, by causing it to form a fluid bar of like dimensions to the preceding, by means of a groove cut in a support of dry mahogany. The bars were each six inches long, and about the one-eighth of an inch square. They were held securely between stout forcep-wires, having compressing screws, as in mn, Fig. 3, so as to insure a good contact, the surfaces being clean and fair. The conducting powers were ascertained according to the method described in section 12, exp. f. In this case, the battery was provided with two additional contact cups; with these the forcep-wires above mentioned, were made to connect at pleasure by the intervention of cups containing mercury in which they were secured, and sustained on pillars of glass, as in m n, Fig. 3.