MICHAEL FAEADAY — HIS LIFE AND WORKS 237 



and render more precise the cliemicul theory of the voltaic }iile. But I cannot 

 but admit that we are indebted to Faraday for having based this theory upon 

 irrefutable proofs, not only by the great numljer and variety of his researches, 

 but especially by his beautiful disct)very of the definite decomposing action of 

 the electric cunent — a discovery which established between the external chemical 

 action of the voltaic pile and the chemical action which takes j)lace in the interior 

 of tliis a}t]iaratus. a relation so intimate that it is impossible not to see in the 

 latter the cause of tlie former. 



III. In 1831 Faraday discovered electrical induction ; it is the most important, 

 although perhaps not the most brilliant of his discoveries. I'en years before 

 (in 1S21) he had observed a perfectly new phenomenon in the science of elec- 

 tro-dynamics — that science which issued complete, as we may say, from the brain 

 of Ampei-e, after Oersted's discovery. Struck by the experiments of the great 

 French physicist upon the mutual attractions and repulsions of electrical cuiTents 

 and magnets, Faraday was led, by theoretical ideas which were rather disputable 

 and not very comfonnalde to the principles of mechanics, to assume that an electric 

 cuiTcnt must turn round the pole of a magnet with a continuous movement, and 

 reciprocally that the pole of a magnet must in like manner turn round an electric 

 current. He verilied this double result by experiment ; and Ampere soon showed 

 its accordance witJi his theory, adding to it other facts of the same natui'e. It is 

 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 jdiysics. It Avas a first step in the course which was to 

 lead to the finding of a relation between mechanical movement and tho mole- 

 adar forces. 



Arago (in 1824) was the first who directly established this relation 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. Faraday advanced still further in 1831 by discover- 

 TTjg that it w3« sufficient to bring towards, or remove from, a metallic wire I'onn- 

 ing 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 cuiTcnt. He 

 discovered induction — that phenomenon which so many others had sought iu 

 vain, although suspecting its existence, but wliich he alone had succeeded iu 

 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 ; 

 tlie two wires are thus isolated, and have all their spires approximate and par- 

 allel. An electric ciuTeut is -passed into one of these wires; imujediately a cur- 

 rent is manifested in an opposite direction in the neighboring wire, tho extremi- 

 ties of which are united by a galvanometer; but this current only lasts for a 

 moment. The cuiTent passing through tho first wire is intemipted ; immedi- 

 ately another current is developed in the second wire, which is momentary, as 

 in the former case, but directed in the same way as the producing current, 

 instead of in the contrary direction. The momeutarincss of these two currents, 

 and the fact of their alternately opposite directions, constitute the two impoitant 

 cliaracters of this new mode of production of electricity. 



Faraday did not stop at this. Starting from Ampdre'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 cun-ent through a metallic wire 

 rolled into a coil, he tried the replacement, in his fundamental experiment, of 

 the wire traversed by the current by a simple magnet. For this purpose he 

 twnsted a single wire instead of two into a coil round a glass or wooden tube ; 

 then he introduced a magnet into this tube, and ascertained thai a^ this moment 

 a momentary current is developed in the coil of wire, and that a seo->nd, equally 



