CONDITIONS OF MAGNETO-ELECTRIC INDUCTION. 
193 
ordinary magnetic powers, but none of any electric current occasioned in the 
metal by the approximation and recession of the magnet. I therefore venture 
to arrange substances in three classes as regards their relation to magnets; 
first, those which are affected when at rest, like iron, nickel, &c. being such as 
possess ordinary magnetic properties ; then, those which are affected when in 
motion, being conductors of electricity in which are produced electric currents 
by the inductive force of the magnet; and, lastly, those which are perfectly 
indifferent to the magnet, whether at rest or in motion. 
256. Although it will require further research, and probably close investi¬ 
gation, both experimental and mathematical, before the exact mode of action 
between a magnet and metal moving relatively to each other is ascertained; 
yet many of the results appear sufficiently clear and simple to allow of expres¬ 
sion in a somewhat general manner. If a terminated wire move so as to cut 
a magnetic curve, a power is called into action Avhicli tends to urge an elec¬ 
tric current through it; but this current cannot be brought into existence un¬ 
less provision be made at the ends of the wire for its discharge and renewal. 
257- If a second wire move in the same direction as the first, the same power 
is exerted upon it, and it is therefore unable to alter the condition of the first: 
for there appear to be no natural differences among substances when connected 
in a series, by which, when moving under the same circumstances relative to 
the magnet, one tends to produce a more powerful electric current in the whole 
circuit than another (201. 214.). 
258. But if the second wire move with a different velocity, or in some other 
direction, then variations in the force exerted take place ; and if connected at 
their extremities, an electric current passes through them. 
259. Taking, then, a mass of metal or an endless wire, and referring to the 
pole of the magnet as a centre of action, (which though perhaps not strictly 
correct may be allowed for facility of expression, at present,) if all parts move 
in the same direction, and with the same angular velocity, and through 
magnetic curves of constant intensity, then no electric currents are produced. 
This point is easily observed with masses subject to the earth’s magnetism, and 
may be proved with regard to small magnets ; by rotating them, and leaving 
the metallic arrangements stationary, no current is produced. 
260. If one part of the wire or metal cut the magnetic curves, whilst the other 
2 c 
MDCCCXXXII. 
