discovery was attracting attention, he wrote an Historical Sketch of Electro-Magnetism,[1] as a preparation for which he carefully repeated the experiments described by the writers he was reviewing, and this seems to have been the beginning of the researches to which his fame is chiefly due.
The memoir which stands first in the published volumes of Faraday's electrical work[2] was communicated to the Royal Society on November 24th, 1831. The investigation was inspired, as he tells us, by the hope of discovering analogies between the behaviour of electricity as observed in motion in currents, and the behaviour of electricity at rest on conductors. Static electricity was known to possess the power of "induction"—i.e., of causing an opposite electrical state on bodies in its neighbourhood; was it not possible that electric currents might show a similar property? The idea at first was that if in any circuit a current were made to flow, any adjacent circuit would be traversed by an induced current, which would persist exactly as long as the inducing current. Faraday found that this was not the case; a current was indeed induced, but it lasted only for an instant, being in fact perceived only when the primary current was started or stopped. It depended, as he soon convinced himself, not on the mere existence of the inducing current, but on its variation.
Faraday now set himself to determine the laws of induction of currents, and for this purpose devised a new way of representing the state of a magnetic field, Philosophers had been long accustomed[3] to illustrate magnetic power by strewing iron filings on a sheet of paper, and observing the curves in which they dispose themselves when a magnet is brought underneath.
- ↑ Published in Annals of Philosophy, ii (1821), pp. 195, 274; iii (1822), p. 107
- ↑ Experimental Researches in Electricity, by Michael Faraday: 3 vols.
- ↑ The practice goes back at least as far as Niccolo Cabeo; indeed the curves traced by Petrus Peregrinus on his globular lodestone (cf. p. 8) were projections of lines of force. Among eighteenth-century writers La Hire mentions the use of iron filings, Mém. de l'Acad., 1717. Faraday had referred to them in his electromagnetic paper of 1821, Exp. Res. ii, p. 127.
