528 PROF. JACOBI ON THE APPLICATION OF ELECTRO-MAGNETISM 
vanced 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 con- 
formable to the remark which M. Nobili has added to the end of his 
first memoir, upon the theory of the electro-dynamic induction. (Anto- 
logia di Firenze, 1832, No. 42.) The ends of the connecting wire sur- 
rounding 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. 
20. 
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 versdé: 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 ¢ 6 plunged into the little cups filled with mercury ce, b. 
They thus formed a single connecting wire, the other ends of whick 
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 orf. 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 vol- 
taic 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 6 and ed. The wire 
eb was withdrawn. I expected, on breaking the circuit, to find that the 
magneto-electric current excited in the helix ac would be conducted 
quite entire by the helix 6d, and vice versé; 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 op- 
posed with relation to the wires a6, ed, unite in traversing a connect- 
ing wire placed in contact with the pointse f. If the galvanic excita+ 
