[CHAPTER VI.]
The Electric Motor.
[Barlow’s Spur Wheel]—[Dal Negro’s Electric Pendulum]—[Prof. Henry’s Electric Motor]—[Jacobi’s Electric Boat]—[Davenport’s Motor]—[The Neff Motor]—[Dr. Page’s Electric Locomotive]—[Dr. Siemens’ First Electric Railway at Berlin, 1879]—[First Electric Railway in United States, Between Baltimore and Hampden, 1885]—[Third Rail System]—[Statistics Electric Railways and General Electric Co.]—[Distribution Electric Current in Principal Cities].
Although the electric motor of to-day depends for practical value entirely upon the dynamo which supplies it with electric power, nevertheless the motor considerably antedated the dynamo. The genesis of the electric motor began in 1821 with Faraday’s observation of the phenomenon of the conversion of an electric current into mechanical motion. In his experiment a copper wire was supported in a vertical position so as to dip into a cup of mercury, while a small bar magnet was anchored at one end by a thread to the bottom of the cup and floated in the mercury in upright position. The mass of mercury being connected to one pole of a battery, and the vertical wire to the other, it was found that when the circuit was completed by clipping the wire into the mercury, the floating bar magnet would revolve around the wire as a center.
FIG. 26.—BARLOW’S WHEEL.
In 1826 Barlow, of Woolwich, made his electrical spur wheel, [Fig. 26], and in 1830 the Abbe Dal Negro, in Padua, is said to have constructed a sort of vibrating electrical pendulum, both of which devices were crude forms of magnetic engines. Dal Negro’s machine, see [Fig. 27], consisted of a magnet A, movable about an axis situated about one-third of its length, and the upper extremity of which was capable of oscillating between the two branches of an electro-magnet E. A current being sent into the electro-magnet, passed through an eight-cupped mercurial commutator C, which the oscillating magnet controlled by means of a rod t and a fork F. When the magnet had been attracted toward one of the poles of the electro-magnet this very motion of attraction acting upon the commutator changed the direction of the current, and the magnet was repelled toward the other branch of the electro-magnet, and so on.