120 



GALVANIC ELECTRICITY. 



is therefore a south pole. The other end 

 attracts the south pole of a magnetic nee- 

 dle, and is therefore, itself, a north pole- 

 But the direction in which the current 

 moves round in the helix, determines 

 which shall be north, and which south.. 

 As the current is represented to move 

 in the first of the two coils in the figure, the up- 

 per end of the coil is north, and the lower end south. 

 If it is made to move in the other direction, as in 

 the second figure, the poles are reversed. 



287. CONSEQUENT MOTION or A sus- 



Hoio may we 



obtain motion FENDED COIL. To obtain motion of the 

 /eif ke C d li ~ coil itself > as a consequence of its magne- 

 tism, it is necessary to suspend it ; and in 

 order to suspend it with perfect freedom of motion, it is 

 necessary to suspend the battery 

 with it. Such a suspended coil 

 and battery is represented in the 

 figure. In preparing it, the wire 

 is wound forty or fifty times 

 round a test-tube, (which is afterward removed,) and 

 copper and zinc plates then attached to the ends. 

 The plates are tied together with several layers of paper 

 between them, then dipped in acid, and the apparatus 

 carefully suspended by an untwisted silk fibre. The 

 acid absorbed by the paper, suffices to maintain for 

 some time the action of the battery. On approaching 

 a magnet to either pole of the suspended coil, it is at- 

 tracted or repelled precisely as if it were a magnet. In- 

 stead of suspending the apparatus by a thread, it may 



