CHAP. VIL] ELECTRIC MOTORS. 651 



CHAPTER VII. ' 



ELECTRIC MOTORS AND ELECTRO-MAGNETIC MACHINES. 



. 1. OSCILLATING ELECTRIC MOTORS. 



IN telegraphy and in electrical horology the energy of the current 

 of a battery or of induction currents is the source of the 

 motions by which signals are made and transmitted in one word, 

 electricity is there employed as a mechanical agent or motor. But 

 the employment of this force is not for the purpose of obtaining 

 power, and indeed, it is generally only intended to regulate the play 

 of another force, that of gravitation for example, whose influence it 

 allows us to suspend and re-establish periodically. 



But can electricity be employed directly as a prime mover ? that is, 

 take the place of steam in engines, which, having produced and stored 

 a certain quantity of motion, distribute it to other engines, where it 

 is transformed according to the needs of industry ? This question 

 has received several positive and practical answers, but we shall see 

 in what way they are restricted. 



Although different early attempts have been recorded, such 

 as that of Salvator del Negro, of Padua, who in 1831 constructed 

 a machine in which a magnet oscillated between the poles of an 

 electro-magnet, and that of a German, Jedlick, wno invented an electro- 

 motive engine for direct rotation, it is to Jacobi of St. Petersburg, that 

 the first serious invention of this kind must be ascribed. In 1839 a trial 

 of his engine on a grand scale was made. " It was applied," says M. 

 du Montcel, " to move a little boat with twelve persons on board, and 

 having paddle-wheels for this purpose. He was able certainly to 

 navigate the waters of the Neva for several hours, but the energy 

 developed, although coming from a battery of 128 large Grove's 



