256 On the Application of Magnetism 



per-plate, I found, that, on diminishing the distance, the de- 

 viation of the needle placed under their connecting wire con- 

 tinued to increase, until they were in actual contact. The law 

 of that increase, ascertamed by the method I have just men- 

 tioned, was such, that the tangent of deviation varied inversely 

 as the square root of the distances of the plates. In the con- 

 struction of a Voltaic series composed of many plates, the 

 advantages to be obtained by placing them very near each 

 other, would be counterbalanced, by the risk of their intensity 

 becomuig sufficient to penetrate through a small distance ; but 

 in using large plates, with electricity of low intensity, it is ob- 

 vious, that provided they are not in actual contact, they can- 

 not be placed too near each other. By availing myself of this 

 observation, I have been enabled to repeat, with a single pair 

 of plates, the experiments of Ampere and Arago, which were 

 originally performed with a battery of twelve paii's. — Of these, 

 one of the most singular is that by which a spiral connecting 

 wire is made to communicate permanent magnetism to a steel 

 wire placed within in*. — This experiment I find may be 

 varied, by using a straight connecting wire, and twisting round 

 it a small steel bar ; the zmc and copper ends of the bar re- 

 ceiving the northern or southern magnetism respectively, ac- 

 cording as its spiral is from right to left, or the contrary. The 

 repetition of this experiment led me to discover the cause of 

 a singular effect, which I had the honour of exhibiting to this 

 Society. The magnet, which was deprived of its attractive 

 power when its north pole was connected with the zinc wire 

 of a pair of galvanic plates, had been placed in tlie circuit, by 

 twisting the wire romid its poles from left to right: on making 

 this spiral from right to left I reversed the effect ; and when 

 the spirals round its two poles were in opposite directions, the 

 weights suspended from them were oppositely affected at the 

 same time, the attractive power of one pole being increased 

 when that of the other was destroyed. 



The singular effects produced by using a large conducting 

 wire, I have me.itioned in my former paper on this subject, 

 and the analogy it forms between the galvanic and the com- 

 mon form of magnetism. — In the further examination of this 

 diffusion of the magnetic influence, I have found it to be far 

 more extensive than I had at first imagined. — On making the 

 connexion between a pair of plates containing about \\ foot of 

 surface, through a copper globe of more than a foot diameter, 

 and therefore containing full four square feet of surface, every 

 part of it exhibited magnetic effects, either upon a horizontal 



* In these, as in the previous experiments, I find that if the spiral be 

 made of large wii-c it is rouch more efficacious than if of small. 



