An electric motor, as the name indicates, is an engine for convert-~ng electricity into mechanical force. This is done most efficiently through the medium of electro-magnetism, and the honor of inaugurating the movement which has led to the utilization of this force as a motive power belongs to our own Professor Henry. His first paper on this subject appeared in 1831. In the following year Salvatore dal Negro constructed his motor and described it in detail. The first electric motors were rude machines, about as efficient as Hero's steam engine, but it hardly took the world more years to perfect the one than it required centuries to complete the other. Dal IN~egro's motor consisted of a fixed electro-magnet, which, by suitable interruptions of the electric current, alternately attracted and released a level" by which the mechanism was driven.
In 1835 Prof. Jacobi, of St. Petersburg, constructed an electric engine at the expense of the Czar Nicholas, with which, after four years of' further experiment, he was able to drive a twelve-oared boat against the swift current of the Neva at the rate of three miles an hour. His enormous batter3" consisted of sixty-four cells, containing twenty square fee~ of platinum.
This was in all respects an apparent failure, and the i)hilosol)her was thoroughly disheartened while standing unwittingly on the threshold of a brilliant success. In the first place, he attempted the impossible in twing to get a great power economically iron, any bat-teD" , and in the second place no powerful battery had yet been invented. But his engine was an excellent one, and the subsequent inventors thiled to equal it until Gramme, of Paris, discovered that one of his own dynamo-electric generators would act in the reverse direction '~s an admlral)le motor.
The interval 1)etween 1839, When Jacobi's motor was abandoned, and 1870, when Gramme's nmehines came into notice , was occupied by a large re,tuber of inventors, who 1)rought to their work a world of ingemdty, and all the learning ()f all the sciences save one, but that