ELECTRO-MAGNETISM. 



123 



with helical currents, thus affording a further corroboration of his theory of 

 magnetic action. 



Immediately after the publication of these experiments of Faraday, Davy 

 thought that the effect of the magnet on the current might be obtained in a 

 more simple state by transmitting the current through a fluid conductor, and 

 exposing the conductor to the action of a strong magnet. With this view, two 

 copper wires, about a sixth of an inch in diameter, coated with sealing-wax, 

 and flattened and polished at the ends, were cemented into two holes three 

 inches apart in the bottom of a glass dish, so that the direction of the wires 

 was perpendicular to the dish. The coating of sealing-wax rendered the wires 

 non-conductors, except at their flattened and polished ends, which were not 

 coated. Mercury was poured into the dish so as to cover the ends of the wires 

 to the depth of the tenth or twelfth of an inch. The parts of the wires pro- 

 ceeding from the bottom of the dish were now put in connexion with a power- 

 ful Voltaic battery, the positive current flowing into the mercury at one wire, 

 and passing from it at tue other. The moment the current commenced, the 

 mercury over each wire was thrown into a state of violent agitation. Its sur- 

 face was raised into the form of two small cones, one over each wire ; waves 

 flowed off in all direction from these cones. On holding the pole of a power- 

 ful bar magnet some indies above one of the cones, its vertex was lowered ; 

 and according as the magnet descended toward the mercury the subsidence of 

 the cone continued, and the propagation of waves around it ceased, until at 

 length the surface of the mercury became perfectly level, and a slow revolving 

 motion of the mercury round the pole of the magnet began to be manifested. 

 As the magnet was brought still closer to the mercury, this gyration of the 

 fluid became more rapid, nnd the centre round which the gyration took place 

 (which was directly over the end of the wire) became depressed. The rapid- 

 ity of the rotation of the mercury, and the depression of the centre of the vor- 

 tex, continued to increase ns the magnet was brought nearer to the mercury, 

 until no more mercury remained over the end of the wire than was barely suf- 

 ficient to cover it. This rotation took place with either pole of the magnet, 

 and over either wire, changing its direction when either the pole of the mag- 

 net or the direction of th*» current was changed. It is evident that these phe- 

 nomena are in accordance with, and referable to, the same general law as those 

 previously discovered by Faraday. The same effects were observed when 

 fused tin was substituted for mercury, and when steel wires were used to con- 

 duct the current. The current was also conducted to the dish by tubes filled 

 with mercury, with like results.* 



In order to determine whether the matter forming the conductor along which 

 the electric current passed had any influence on the electro-magnetic phenom- 

 ena which at this time engaged the attention of philosophers, Davy placed 

 two pieces of charcoal in connexion with the wires of a powerful Voltaic bat- 

 tery, and, by presenting their points toward each other, at a distance vary- 

 ing from one to four inches, according to the density of the air in which the 

 experiment was made, he obtained a column of electric fluid formed by the 

 current passing through the space between the charcoal points. This current 

 was not transmitted, as usual, along any conductor, but merely passed through 

 the air between the points ; and its presence was rendered manifest by the 

 light evolved. When a powerful magnet was presented to this column, with 

 its pole at a very acute angle to it, the column was attracted or repelled with a 

 rotatory motion, or made to revolve by placing the poles in different positions, 

 in the same manner as metallic wire conducting the current would have been. 

 The electric column was more easily affected by the magnet, and its motion 

 * Phil. Trans., 1823; also Davy's works, vol. vi., p. 258. 



