Michael Faraday, his Life and Works. 161 
continuous movement, and reciprocally that the pole of a magnet 
must in like manner turn round an electric current, He verified 
this double result by experiment ; and Ampére soon showed its 
accordance with his theory, adding to it other facts of the same 
nature. Itis not the less true that the discovery of a continuous 
movement of rotation due to the combined action of a magnet 
and an electric current was quite unforeseen, and at the same 
time very important ; for up to that time there was no example 
of any such action in physics. It was a first step in the course 
which was to lead to the finding of a relation between mechan- 
ical movement and the molecular forces. : 
Arago (in 1824) was the first who directly established this re- 
lation, by his beautiful discovery of magnetism by rotation ; 
for he showed that simple mechanical movement could render a 
body, in itself non-magnetic, capable of acting upon the magnet. 
araday advanced still further in 1831, by discovering that it 
was sufficient to bring toward, or remove from, a metallic wire 
forming a closed circuit another parallel wire traversed by an 
_ electric current, or simply a magnet, in order to develop in the 
former wire an electric current. He discovered induction—that 
phenomenon which so many others had sought in vain, although 
suspecting its existence, but which he alone had succeeded in 
producing, 
Let us dwell for a moment upon his fundamental experiment. 
Two metal wires covered with silk are rolled together round a 
cylinder of glass or wood ; the two wires are thus isolated, and 
ave all their spires approximate and parallel. An electric 
current is passed into one of these wires ; immediately a current 
18 Manifested in an opposite direction in the neighboring wire, 
the extremities of which are united by a galvanometer ; but 
this current only lasts for a moment. The current passing 
through the first wire is interrupted ; immediately another 
current is developed in the second wire, which is momentary, 
as in the former case, but directed in the same way as the pro- 
ucing current, instead of in the contrary direction. The mo- 
mentariness of these two currents, and the fact of their alter- 
hately opposite directions, constitute the two important char- 
acters of this new mode of production of electricity. : 
Faraday did not stop at this. Starting from Ampére’s idea 
that a magnet is only an assemblage of electric currents arranged 
round an axis in a manner very analogous to the circulation of 
an electric current through a metallic wire rolled into a coil, he 
i the replacement, in his fundamental experiment, of the 
wire traversed by the current by a simple magnet. For this 
| he twisted a'single wire instead of two into a coil round 
& glass or wooden tube ; then he introduced a magnet into this 
Am. Jour. Sc1.—Srconp Series, VoL. XLV, No. 134.—Mancu, 1868, 
ll 
