440 



WELLS'S NATURAL PHILOSOPHT. 



place in the secondary wire ; but the current now arising 

 has the same direction as the primary one. 



The passage of an electrical current, therefore, develops other currents iu 

 its neighborhood, which flow in the opposite direction as the primary ona 

 first acts, but in the same direction as it ceases. Whenever a magnet, also, 

 is moved in the neighborhood of a conducting wire, these currents are also 

 induced. 



818. Magneto-electric machines, arranged for developing 

 electricity by the reaction of a magnet, are constructed in a 

 great variety of forms. In some, permanent steel magnets are 

 used ; in others, temporary soft iron ones, brought into ac- 

 tivity by a galvanic current. A common form of magneto- 

 electric machine is represented in Fig. 372. 



What is tbe 

 Ifeneral con- 

 Btruction of 

 magneto-elec- 

 tric machines ? 



Fig. 372. 



It consists of a compound horse- 

 shoe magnet, S, Fig. 372, bolted 

 to a mahogany stand, arranged in 

 such a manner that an electro- 

 magnet, or armature, A B, mount- 

 ed on an axis, revolves in front of 

 its poles, by turning a multiplying 

 wheel, W. This electro-magnet, 

 or armature, consists of two cores 

 of soft iron wound about with fine 

 insulated copper wire. The ends 

 of the wire in these coils are kept 

 pressed, by means of springs, 

 against a good conducting metal plate, which in turn is connected by wires 

 with the screw-caps at the end of the base board. When the iron cores, or 

 axes of the coils are in firont of the poles of the magnet, they become mag- 

 netic by induction. This sets in motion the natural electricity of the coil, or 

 helices, which flows in a certain direction, and is conveyed through the 

 springs and wires to the screw-caps. 



If the armature be turned half round, the magnetism of the iron is reversed, 

 and a second current is excited in the opposite direction. 



By turning the armature very rapidly, a constant current 

 passes through the wires, and by connecting a small piece of 

 platinum wire in the circuit, it is rapidly rendered red hot. 

 By conveying connecting wires from the magneto-electric 

 machine into acidulated water, its decomposition is effected; 

 and many chemical compounds may in like manner be resolved into their 

 ultimate constituents: machmesalso of this character maybe used for electro- 

 plating. 



The effects of electricity thus generated on the human system are peculiar. 

 If the two handles connected with the screw-caps of the machine are grasped 

 by the hands, slightly moistened, and the armature is made to revolve rap- 



What effects 

 may be pro- 

 duced by the 



action of elec- 

 tro-magnetic 

 machines? 



