ELECTRO-MAGNETISM, 



49 



Faraday succeeded in obtaining this 

 effect in the following manner*. A 

 piece of copper wire, about .045 of an 

 inch thick, and fourteen inches long, has 

 an inch at each extremity bent at right 

 angles in the same direction, as shown 

 at W tv, in fig. 88, and the ends amal- 

 gamated ; the wire is then to be sus- 



Fiff. 88. 



\v 



ponded horizontally, by a long silk 

 thread *, from the ceiling. Two grooves 

 G g are cut in the sides of a rectangular 

 piece of hard wood, parallel to the sides, 

 and about half an inch in depth, and 

 filled with mercury. P and N are wires 

 fixed in the board, passing each into its 

 respective groove, so as to come in con- 

 tact with the mercury, and terminating 

 at their other ends in cups for making 

 the connexions with the voltaic battery. 

 The points of the wires are now to be 

 slightly immersed in the mercury con- 

 tained in the respective grooves ; and in 

 order to obviate the inconvenience aris- 



ing from the film of oxide which is apt 

 to form upon the surface of the mercury, 

 and impede the motion of the wires, it is 

 advisable to cover the surface with a 

 stratum of diluted nitric acid, which, by 

 dissolving the oxide, removes this ob- 

 stacle to free motion. As soon as the 

 connexions are made with the battery, 

 and the electric current passes along the 

 wire, it will be seen to move laterally, 

 being carried across the field until the 

 points strike against the ends of the 

 grooves. On breaking the connexion, 

 the wire resumes its first position ; on 

 restoring it, motion is again produced. 

 On changing the position of the appa- 

 ratus with respect to the points of the 

 compass, the same effect still takes 

 place ; and the direction of the motion 

 is always the same relatively to the wire, 

 or rather to the current passing through 

 it, being at right angles to it. Thus, 

 when the wire is east and west, and the 

 electric current flowing from west to 

 east, the motion is towards the north ; 

 when the current passes from east to 

 west, the motion is towards the south. 

 When the wire hangs north and south, 

 and the current moves from north to 

 south, the wire is directed towards the 

 east, and when the current is reversed, 

 towards the west. In intermediate posi- 

 tions the motions of the wire are in in- 

 termediate directions. 



(138.) These different motions cor- 

 responding to the different positions of 

 the wire, and directions of the current, 

 are exhibited by the lines in Jigs. 89, in 

 which N and S express the north and 



Figs. 69. 



Quarterly Journal of Science, &e., Vol. XII. n. 117. 



