VOL1AIC ELECTEICITY. 623 



foundest and most sagacious philosophers, and perpetually verified and 

 illustrated, by unforeseen discoveries in unguessed forms, through the 

 labors of the most skilful experimenters. 



Magneto-electric Machines. 



The discovery that a voltaic wire moved in presence of a magnet, 

 has a current generated in it, was employed as the ground of the con- 

 struction of machines ^to produce electrical effects. In Saxton's 

 machine two coils of wire including a core of soft iron revolved oppo- 

 site to the ends of a horseshoe magnet, and thus, as the two coils came 

 opposite to the N. and S., and to the S. and N". poles of the magnet, 

 currents were generated alternately in the wires in opposite directions. 

 But by arranging the connexions of the ends of the wires, the success- 

 ive currents might be made to pass in corresponding directions. The 

 alternations or successions of currents in such machines are governed 

 by a contrivance which alternately interrupts and permits the action ; 

 this contrivance has been called a rkeotome. Clarke gave a new form 

 to a machine of the same nature as Saxton's. But the like effect may 

 be produced by using an electro-magnet instead of a common magnet. 

 When this is done, a current is produced which by induction produces 

 a current in another wire, and the action is alternately excited and 

 interrupted. When the inducing current is interrupted, a momentary 

 current in an opposite direction is produced in the induced wire ; and 

 when this current stops, it produces in the inducing wire a current in 

 the original direction, which may be adjusted so as to reinforce the 

 resumed action of the original current. This was pointed out by M. 

 De la Rive in 1S43. U Machines have been constructed on such prin- 

 ciples by him and others. Of such machines the most powerful hitherto 

 known is that constructed by M. Ruhrnkorff. The effects of this 

 instrument are exceedingly energetic. 



Applications of Electrodynamic Discoveries. 



The great series of discoveries of which I have had to speak have 

 been applied in many important ways to the uses of life. The Elec- 

 tric Telegraph is one of the most remarkable of these. By wires 

 extended to the most distant places, the electric current is transmitted 



14 Traiti de 1'Elcct. i. 391. 



