History of electric light

by Henry Schroeder

INVENTION OF THE DYNAMO

Michael Faraday was an English scientist. Born of parents in poor circumstances, he became a bookbinder and studied books on electricity and chemistry. He finally obtained a position as laboratory assistant to Sir Humphry Davy helping him with his lectures and experiments. He also made a number of experiments himself and succeeded in liquifying chlorine gas for which he was elected to a Fellowship in the Royal Institution in 1824. Following up Oersted’s and Ampère’s work, he endeavored to find the relation between electricity and magnetism. Finally on Oct. 17, 1831, he made the experiment of moving a permanent bar magnet in and out of a coil of wire connected to a galvanometer. This generated electricity in the coil which deflected the galvanometer needle. A few days after, Oct. 28, 1831, he mounted a copper disk on a shaft so that the disk could be rotated between the poles of a permanent horseshoe magnet. The shaft and edge of the disk were connected by brushes and wires to a galvanometer, the needle of which was deflected as the disk was rotated. A paper on his invention was read before the Royal Society on November 24, 1831, which appeared in printed form in January, 1832.

Faraday’s Dynamo, 1831.

Faraday discovered that electricity could be generated by means of a permanent magnet. This principle is used in all dynamos.

Faraday did not develop his invention any further, being satisfied, as in all his work, in pure research. His was a notable invention but it remained for others to make it practicable. Hippolyte Pixii, a Frenchman, made a dynamo in 1832 consisting of a permanent horseshoe magnet which could be rotated between two wire bobbins mounted on a soft iron core. The wires from the bobbins were connected to a pair of brushes touching a commutator mounted on the shaft holding the magnet, and other brushes carried the current from the commutator so that the alternating current generated was rectified into direct current.

Pixii’s Dynamo, 1832.

Pixii made an improvement by rotating a permanent magnet in the neighborhood of coils of wire mounted on a soft iron core. A commutator rectified the alternating current generated into direct current. This dynamo is in the collection of the Smithsonian Institution.

E. M. Clarke, an Englishman made, in 1834, another dynamo in which the bobbins rotated alongside of the poles of a permanent horseshoe magnet. He also made a commutator so that the machine produced direct current. None of these machines gave more than feeble current at low pressure. The large primary batteries that had been made were much more powerful, although expensive to operate. It has been estimated that the cost of current from the 2000-cell battery to operate the demonstration of the arc light by Davy, was six dollars a minute. At present retail rates for electricity sold by lighting companies, six dollars would operate Davy’s arc light about 500 hours or 30,000 times as long.