Page:Scientific Memoirs, Vol. 1 (1837).djvu/540

528 in proportion as the needle of the former receded. This might have been expected, provided the counter-current in the secondary branch has the same direction as the voltaic current: it is quite conformable to the remark which M. Nobili has added to the end of his first memoir, upon the theory of the electro-dynamic induction. (Antologia di Firenze, 1832, No. 42.) The ends of the connecting wire surrounding the bars must be considered as the poles of an electro-motive apparatus: moreover the magnetizing power of this counter-current has been proved by making it pass through a helix bent round a bar of soft iron.

In short all tended to prove that the greatest part of the counter-current might be rendered available by employing two apparatus of the same kind, the connecting wires of which, wound spirally round bars of each system, should terminate at the same pile. The counter-current produced by the movement of one apparatus would serve to strengthen the magnetism of the other, and vice versâ: the counter-currents would counterbalance each other to destroy their effects. The experiment could be made on a small scale with the bar above described, the branches of which were encircled with separate helices. Fig. 4. shows the form of the experiment. The two helices were connected by the dotted wire $$c\, b$$ plunged into the little cups filled with mercury $$c,\, b$$. They thus formed a single connecting wire, the other ends of which $$a,\, d$$ were united with a pile $$C\, Z$$. With my hands dipped in acidulated water I took hold of the connecting wire at the place $$e,\,f$$, and I broke the circuit at the place $$g$$ or $$h$$. I felt a violent shock. In other respects the experiment was the same as the beautiful one of Mr. Jenkins related by Mr. Faraday. By interposing the multiplying wire of a galvanometer $$m$$ in the circuit, the needle deviated to 48° by the voltaic current. Then applying the armature, it receded from 48° to 40°. The deviation on removing the armature was unobservable, the latter being too firmly attached. Now the helices were connected with the pile in two branches separated by means of the wires $$a\, b$$ and $$c\, d$$. The wire $$c\, b$$ was withdrawn. I expected, on breaking the circuit, to find that the magneto-electric current excited in the helix $$a\, c$$ would be conducted quite entire by the helix $$b\, d$$, and vice versâ; but I was mistaken: the shock was not much less: the needle nevertheless receded. I was struck by this experiment, but after all I believe I may regard this magneto-electric arrangement as an unclosed voltaic pile, consisting of two elements united in such a manner as to form only a single pair of plates, as is represented in fig. 5. The currents whose direction is opposed with relation to the wires $$a\, b$$, $$c\, d$$, unite in traversing a connecting wire placed in contact with the points $$e\, f$$. If the galvanic