The most important discovery for which we have to thank Faraday is that of induction. This discovery was made by him in the year 1831, and intimated to the philosophical world in a paper read on the 24th November, 1831, appearing in the Transactions of the Philosophical Society in the year 1832.
Faraday’s first induction apparatus consisted of two coils of wire, the one being slid over the other. As he was passing the current from a battery through one of these, he made the discovery that each time the circuit of the coil was opened or closed an electromotive force was created in the second coil, which caused a short gush of current or induction current to flow, provided the circuit of this coil was closed, as might be through a galvanometer. The peculiarity of this induced current was, that it only flowed in the second coil during the time the current in the first coil took to reach its normal strength after closing the circuit, or on breaking the circuit during the time the current took to decrease from its normal strength to zero.
This discovery undoubtedly belongs to the domain of the transformer, induction being the physical precedent upon which the transformer is based; indeed, a transformer is in principle an induction apparatus.
Fig. 1.
Fig. 1 represents the arrangement of this fundamental experiment. The primary coil is connected with the battery, the secondary with the galvanometer. The primary coil, in order to obtain the best effect, is placed inside the secondary, and on opening and closing its circuit the needle of the galvanometer is thrown to the one or the other side respectively.
Fig. 2.
