SECT, xxxiii.] MAGNETO-ELECTEIC APPARATUS. 367 



which produce the same phenomena with the electrical 

 currents from the Voltaic battery: they, however, differ 

 materially in this respect that time is required for the 

 exercise of the magnetico-electric induction, whereas Volta- 

 electric induction is instantaneous. 



After Dr. Faraday had proved the identity of the magnetic 

 and electric fluids by producing the spark, heating metallic 

 wires, and accomplishing chemical decomposition, it was 

 easy to increase these effects by more powerful magnets and 

 other arrangements. The apparatus now in use is in effect 

 a battery where the agent is the magnetic instead of the 

 Voltaic fluid, or, in other words, electricity, and is thus 

 constructed. 



A very powerful horse-shoe magnet, formed of twelve 

 steel plates in close approximation, is placed in a horizontal 

 position. An armature, consisting of a bar of the purest 

 soft iron, has each of its ends bent at right angles, so that 

 the faces of those ends may be brought directly opposite 

 and close to the poles of the magnet when required. Ten 

 copper wires covered with silk, in order to insulate them 

 are wound round one half of the bar of soft iron, as a com- 

 pound helix: ten other wires, also insulated, are wound 

 round the other half of the bar. The extremities of the 

 first set of wires are in metallic connexion with a circular 

 disc, which dips into a cup of mercury, while the ends of 

 the other ten wires in the opposite direction are soldered to 

 a projecting screw-piece, which carries a slip of copper with 

 two opposite points. The steel magnet is stationary ; but, 

 when the armature, together with its appendages, is made 

 to rotate vertically, the edge of the disc always remains 

 immersed in the mercury, while the points of the copper 

 slip alternately dip in it and rise above it. By the ordinary 

 laws of induction, the armature becomes a temporary magnet 

 while its bent ends are opposite the poles of the steel 

 magnet, and ceases to be magnetic when they are at right 

 angles to them. It imparts its temporary magnetism to 



