THE ELECTRIC TELEGRAPH. 



suspension, and since the rotation of the magnet may be made 

 with any desired rapidity, it follows that the pulsations will 

 succeed each other with such celerity, and the intervals of 

 suspension will be so brief that for all practical purposes the 

 current will be continuous. 



165. Such are the principles on which is founded the construction 

 of magneto-electric machines, one form of which is represented in 

 fig. 64 (page 1). The purpose of this apparatus is to produce by 

 magnetic induction an intermitting current constantly in the same 

 direction, and to contrive means by which the intervals of inter- 

 mission shall succeed each other so rapidly that the current shall 

 have practically all the effects of a current absolutely continuous. 



A powerful compound horse-shoe magnet, A, is firmly attached 

 by bolts and screws upon a horizontal bed, beyond the edge of 

 which its poles a and b extend. Under these is fixed an electro- 

 magnet x Y, with its legs vertical, and mounted so as to revolve 

 upon a vertical axis. The covered wire is coiled in great 

 quantity on the legs x Y, the direction of the coils being reversed 

 in* passing from one leg to the other. 



The two extremities of the wire proceeding from the legs x and 

 Y are pressed by springs against the surfaces of two rollers, c and 

 dj fixed upon the axis of the electro-magnet. These rollers them- 

 selves are in metallic connection with a pair of handles p and M", 

 to which the current evolved in the wire of the electro-magnet 

 x Y will thus be conducted. 



If the electro -magnet x Y be now put in rotation by the handle 

 m, the handles P and N being connected by any continuous con- 

 ductor, a system of intermitting and alternately contrary currents 

 will be produced in the wire and in the conductor by which the 

 handles p and N are connected. But if the rollers c and d are 

 so contrived that the contact of the ends of the wire, with them 

 shall be only maintained during a semi-revolution in which the 

 intermitting currents have a common direction, or so that the 

 direction during the other semi-revolution shall be reversed, then 

 the current transmitted through the conductor connecting the 

 handles P and N" will be intermitting, but not contrary ; and by 

 increasing the velocity of rotation of the electro -magnet x Y, the 

 intervals of intermission may be made to succeed each other with 

 indefinite celerity, and the current will thus acquire all the 

 character of a continuous current. 



The forms of commutators by which the rollers c and d are 

 made to break the contact, and re-establish it with the necessary 

 regularity and certainty, or to reverse it during the alternate 

 semi-revolutions are various. 



166. All the usual effects of voltaic currents may be produced 

 4 



