324 MAGNETO-ELECTRIC APPARATUS. SECT. XXXII. 



magnetic and electric fluids by producing the spark, 

 heating metallic wires, and accomplishing chemical 

 decompositions, 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 horseshoe magnet, formed of twelve 

 steel plates in close approximation, is placed in a hori- 

 zontal 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 compound 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 connection 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 

 temporaiy magnetism to the helices which concentrate 

 it ; and while one set conveys a current to the disc, the 

 other set conducts the opposite current to the copper slip. 

 As the edge of the revolving disc is always immersed in 

 the mercury, one set of wires is constantly maintained 

 in contact with it, and the circuit is only completed 

 when a point of the copper slip dips in the mercury 

 also ; but the circuit is broken the moment that point 

 rises above it. Thus, by the rotation of the armature, 

 the circuit is alternately broken and renewed ; and as 

 it is only at these moments that electric action is mani- 



