CHAPTEE VI. 



DYNAMO-ELECTRIC MACHINES. 



General Characteristics of Dynamo-Electric Machines Gramme Machine 

 Siemens Machine Schuckert Machine Mather Machine Wilde Ma- 

 chine Weston Machine Elmore Machine Superiority of Dynamo- 

 Electric Machines over Batteries. 



GENERAL CHARACTERISTICS OP DYNAMO-ELECTRIC MACHINES. 

 The use of batteries has, in a large number of electroplating 

 and electro-metallurgic works, been superseded by that of 

 dynamo-electric machines. These are much simpler of in- 

 stallation, they occupy less room, generate electric currents 

 cheaply, and do not give off any smell. 



These apparatuses are all based on Faraday's experiments. 

 Faraday was the first to demonstrate that electric currents 

 could be produced by means of magnets and conductors having 

 a relative motion to each other. It was already known, from 

 Ampere and Arago's discoveries, that a bar of iron could be 

 magnetised by an electric current. Faraday reciprocally 

 demonstrated that a magnet could generate an electric current. 



A dynamo-electric machine is any machine capable of 

 giving rise to an electric current in a closed metallic circuit, 

 by the fact of the displacement of a portion of the said circuit 

 in the field of action of a magnet.* 



The displacement is relative in this respect, that if the 

 magnet is moving and the wire stationary, there is equally 

 production of electricity. 



The current so generated resulting only from the displace- 

 ment of a metallic wire in the vicinity of a magnet, it was 

 perceived that by increasing the magnetic action, the length of 



* This definition, as precise as it is short, is due to Antoine Breguet. 



