Voltaic Induction* 25 



probable that they are in a perpetual state of rotation in the magnet, 

 since they exhibit no tendency to neutralize each other, and yet pos- 

 sess so strong an attraction towards the steel as never to depart 

 from it. 



Fig. 1. 



g|T|^g»fg"g VZ&^imSrjL 1* 



s 



N 



*••* 



^V-,' - & v.. 



When a voltaic current passes through a helix, it may be repre- 

 sented as moving in planes at right angles to the axis ; and, as the 

 magnetic forces are known to revolve at right angles to the current, 

 by this arrangement, their planes of revolution pass through that axis. 

 Hence their general direction will be towards the extremities of the 

 helix, the north polar forces all revolving towards one extremity, and 

 the south ones towards the other, both being viewed from the same 

 line, as the axis. Fig. 1 represents the magnetic action of a helix. 

 The positive voltaic current moves from S. to N., and the small 

 arches, n s, around every part of this heliacal current, mark the re- 

 volving magnetic forces; the cross representing the movement of the 

 north pole, and the hook that of the south. It will be seen that sim- 

 ilar poles have the same general direction, throughout the instru- 

 ment, and that a south pole turns from the inside of the helix at the 

 end S., while a north one passes out from the opposite end N. As 

 these poles, in consequence of their issuing more directly from the 

 interior of the extremity, obtain a preponderance of action, they rep- 

 resent the magnetic power of the helix ; N. being its north end, and 

 S. its south one. Along the sides of the helix, these poles have an 

 equally direct action upon bodies in front of them, and hence they 

 neutralize each other* When the extremities S. and N. are bent in- 

 wards along the axis of the helix as far as the middle, the voltaic cur- 

 rent which each thus conveys backwards, compensates nearly for the 

 obliquity of the coil, and makes the resemblance with the magnet 

 more complete. The helix then becomes what Ampere has called 

 the electro-dynamic cylinder and upon the action of which he has 

 founded his hypothesis of magnetism. According to this philoso- 

 pher's views, every substance, even the earth, obtains magnetic prop- 

 erties in consequence of the circulation of voltaic currents, passing 



Vol. XXVL— No. L 4 



