Page:Scientific Memoirs, Vol. 1 (1837).djvu/633

Rh current produced by its removal is directly as the diagonals of the wires; for the electromotive power remains the same, but the resistance it experiences in being conducted decreases inversely as the diagonals; consequently the electric currents, or the quotients of the electromotive powers by the diagonals, increase as the diagonals.

Nobili and Antinori have in their first paper on the electrical phænomena produced by the magnet (Poggendorff's Annalen, 1832, No. 3) already determined the order in which four different metals are adapted to produce the electric current. They arrange them in the following order,—copper, iron, antimony, and bismuth.

It is particularly striking that this order is the same as that which the above metals occupy also in reference to their capacity of conducting electricity; and the idea suddenly struck me whether the electromotive power of the spirals did not remain the same in all metals, and whether the stronger current in the one metal did not arise from its being a better conductor of electricity than the other. With this view, therefore, I examined four metals, namely, copper, iron, platina, and brass, and pursued the following course: In order to avoid entirely the influence of different conduction, I brought at the same time into the metallic conducting circle through which the electric current had to pass, two spirals, equal in all respects excepting that they were of different metals, binding the one end of the first with the one conducting wire, the one end of the second with the other conducting wire, and connected the two ends of the spirals which had remained free with a distinct copper connecting wire. I now brought first the one spiral upon the iron armature of the horseshoe magnet, and proceeded in the same way with it as in the former experiments, and then the other. In this manner the resistance which the electric current suffered in each process was naturally quite the same.—I must also remark that I carefully avoided all thermo-electric disturbing forces, as I surrounded the places of connection of the various wires with several layers of blotting-paper, and after having arranged the apparatus I always waited several hours in order to give the places of connection time to take the temperature of the room.

The experiments themselves are as follows: