Electro-Magnetic Apparatus atid Experiments. 257 



Experiment 3d. — Bring one extremity of the magnet used in 

 the foregoing experiment in contact with one pole of the magnet 

 of a common magneto-electric machine. As this disguises a por- 

 tion of the magnetism, the amount of electricity developed by 

 the revolution of the armature will of course be diminished. 

 While working the machine the magnetic state of the electro- 

 magnet will vary with the approximation and recession of the 

 armature, and a current of electricity in its wires will be the con- 

 sequence. When the current from the armature is broken or not 

 suffered to flow at all, the current from the electro-magnet will be 

 much stronger than when the circuit from the armature is con- 

 stantly complete. When the armature is leaving the magnet, 

 the flowing current or closed circuit magnetizes the armature and 

 consequently disguises more of the power of the inducing mag- 

 net, than when the armature leaves without the closing of the 

 circuit. The consequence is a detraction of magnetic power 

 from the electro-magnet. Also, breaking the circuit from the 

 armature under ofl, increases the current from the electro-mag- 

 net. 



Experiment Ath. — Join the ends of the wire coiled on one leg 

 of the curved armature of a common magneto-electric machine, 

 and ^llow the coil from the other leg to be connected with the 

 break piece, as usual. As long as the circuit of the first coil is 

 closed, the second coil will furnish scarcely any electricity ; but 

 when the circuit of the first coil is opened, the second furnishes 

 nearly as much electricity as the combined current from both 

 coils. This singular fact first called my attention to the great 

 advantage of short, straight armatures, for the magneto-electric 

 machine. Obviously, the best arrangement for straight arma- 

 tures, would be that wherein they revolved between the ends of 

 the magnetic poles, the axis or shaft being parallel to the legs of 

 the magnets. The points gained by this plan would be, a more 

 uniform and powerful current, and an exact division by the Uni- 

 trep of the semicircular routes through which the alternating 

 currents are developed. In the machine described in Vol. 

 XXXIV, p. 164, of this .Tournal, and in all others where the axis of 

 motion is perpendicular to the plane of the magnet, if the two 

 routes in which the opposite currents are developed be represented 

 by two arcs of a circle drawn through the two neutral -points, 

 that arc towards the bend of the magnet will be nmch the longer, 

 Vol. XXXV.— No. 2. 33 



