528 PROF. JACOBI ON THE APPLICATION OF ELECTRO-MAGNETISM 



vancecl 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.) Tlie 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 s]nraUy 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 versa : 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 

 «, 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 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 firndy attached. Now the helices were connected with the pile 

 in two branches separated by means of the wires a b and c d. Tlie wire 

 cb was withdrawn.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 versa ; 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 ab, cd, unite in traversing a connect^ 

 ing wire placed in contact with the points ef. If the galvanic excita? 



