Chemical Science. 417 



netic pole, it was easy, by applying the information gained 

 above, to deduce beforehand the direction the motions would 

 probably take : for, assuming that the dipping-needle, if it 

 does not point to the pole of the earth, points at least in the 

 direction in which that pole is active, it is evident that a 

 straight electro-magnetic wire, affected by the terrestrial as 

 by an artificial pole, would move laterally at right angles to 

 the needle ; that is to say, it would endeavour to describe a 

 cylinder round the pole, the radius of which may be represented 

 by the line of the needle prolonged to the pole itself. As these 

 cylinders, or circles, would be of immense magnitude, it was 

 evident that only a very minute portion of them could be 

 brought within the reach of experiment; still, however, that 

 portion would be sufficient to indicate their existence, inasmuch 

 as the motions taking place in the part under consideration, 

 must be of the same kind, and in the same direction, as in 

 every other part. 



Reasoning thus, I presumed that an electro-magnetic wire 

 should move laterally, or in a line perpendicular to the current 

 of electricity passing through it, in a plane perpendicular to the 

 dipping-needle ; and the dip being here 72° 30', that plane 

 would form an angle with the horizon of 17° 30', measured 

 on the magnetic meridian. This is not so far removed from the 

 horizontal plane, but that I expected to get motions in the 

 latter, and succeeded in the following manner : — A piece of 

 copper wire, about .045 of an inch thick, and fourteen inches 

 long, had an inch at each extremity bent at right angles, in the 

 same direction, and the ends amalgamated ; the wire was then 

 suspended horizontally, by a long silk thread, from the ceiling. 

 A basin of clean pure mercury was placed under each extremity 

 of the wire, and raised till the ends just dipped into the metal. 

 The mercury in both basins was covered by a stratum of diluted 

 pure nitric acid, which dissolving any film, allowed free motion. 

 Then connecting the mercury in one basin with one pole of 

 Hare's Calorimotor, the instrument mentioned page 74, the 

 moment the other pole was connected with the other basin, the 

 suspended wire moved laterally across the basins till it touched 

 the sides: on breaking the connexion, the wire resumed its 

 first position ; on restoring it, the motion was again produced. 

 On changing the position of the wire, the effect still took place ; 

 and the direction of the motion was always the same relative to 

 the wire, or rather to the current passing through it, being at 

 right angles to it. Thus when the wire was E and W, the E end 

 to the zinc, the W end to the copper plate, the motion was 

 towards the north; wiien the connexions were reversed, the 

 motion was towards the south. When the wire hung N and S, 

 the N end to the zinc plate, the S end to the copper plate, the 

 motion was towards the W ; when the connexions were reversed, 



