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. 
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, ns, 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 
Vou. XXVI.—No. 1. 4 
