652 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK v. 



elements, never exceeded horse-power. So feeble a mechanical effort, 

 developed by so energetic a current, discouraged the inventor com- 

 pletely, who since then has always considered this application of 

 electricity as impracticable for industrial purposes." 



We shall divide, as M. Verdet has done, the electro-motors 

 into two classes, corresponding to two distinct types, that of the 

 oscillating engines and that of the rotating engines, and we shall give 

 an example of each of these types. 



We shall first describe, in the words of M. Verdet, the prin- 

 cipal characteristics of these two types of engines. In the oscillating 

 engines, a coil or fixed electro-magnet attracts, when it is traversed 

 by an electric current in the proper direction, either another coil, or an 

 electro-magnet, or a magnetized bar, or even a simple piece of soft 

 iron. When the movable piece comes nearly into contact with the 

 fixed piece, the action of the engine moves a commutator, by which 

 the attraction is changed into a repulsion, or replaced by the attraction 

 of another piece situated on the opposite side. The direction of the 

 motion is thus reversed, and these attractions being repeated indefi- 

 nitely, we derive from them the same result as from the reciprocating 

 motion of the piston of the steam-engine. In rotating engines the 

 movable and fixed pieces are arranged on the radii of two concentric 

 wheels, the passage of the current makes the movable wheel turn into a 

 position of stable equilibrium, but at the moment this is attained the 

 action of a commutator changes the direction of the action of 

 the forces, and the motion of rotation is continued indefinitely in 

 the same direction. 1 



M. Bourbouze's electro-motor belongs to the first type. The 

 following are its essential arrangements : 



Two magnetising coils, EE, E' E'(Fig. 425), are arranged in pairs on 

 each side of a vertical shaft surmounted by a beam, as in a steam- 

 engine, and play the part of the cylinders, or body of a pump. In 

 the inside, and up to half the height of the bobbins, are cylinders of 

 soft iron, which become magnetised when the current from the battery 

 passes through the wires of each coil. To the ends of the beam two 

 rods are jointed, each of which carries two cylinders of soft iron, which 

 move freely within the bobbins, and which are alternately attracted by 



1 Verdet, Expose de la Theorie Mecanique de la Chaleur, lectures delivered in 

 1862 before the Chemical Society of Paris. 



