84 DYNAMO-ELECTRIC MACHINES. 



induction was discovered, made a machine for generating electric 

 currents, which consisted of a horse-shoe electro-magnet suspended 

 from a wooden frame, and a permanent magnet of similar form, the 

 ends of which were turned upward, and were as close as possible, 

 without touching, to the ends of the suspended electro-magnet. On 

 rotating the lower magnet, so that its poles passed rapidly before the 

 poles of the other, a current was generated in the coils of the electro- 

 magnet, from the magnetic influence communicated to them from 

 the revolving magnet. At every revolution the poles of the electro- 

 magnet were changed twice, which induced a corresponding reverse 

 current in the coils. The machine was not on a sufficiently large 

 scale to be of much practical use. Following Pixii were Saxton, 

 Clarke, Nollet, Siemens, Wheatstone, Ruhmkorff, and others, a de- 

 tailed description of whose experiments and machines would occupy 

 too much space for this paper. All the machines spoken of were 

 magneto-electric, that is, they were machines whose currents were 

 generated by permanent magnets. One only of those was put to 

 public use, that of The Alliance Company, of France, and Holmes of 

 England. Each of these two types of machines were used for light- 

 house purposes. They were very cumbersome and costly, so much 

 so, that they never came into general use. 



About the year 1867, Messers Ladd & Wilde introduced the 

 first Dynamo-Electric Machine, or rather a combination of magneto 

 and dynamo, that is, a machine consisting of both permanent and 

 electro-magnets combined. The permanent magnets were used 

 to excite a small current, which traversed the electro magnets, which 

 were of great size, and they in their turn induced a current in the 

 revolving armature. Shortly afterwards, Wilde brought out a self- 

 exciting machine, that is, the current that was generated was sent 

 around the electro magnets, and became thus its own exciter. To 

 this class of machines which is now nearly the only kind in use, Dr. 

 Siemens gave the name of Dynamo-Electric, or self-exciting machines, 

 to distinguish them from Magneto-Electric, or those in which cur- 

 rents were induced by permanent magnets. Some French writers 

 state that the names are not distinctive, because each class is both a 

 Magneto and a Dynamo machine. Each class generates its current 

 through the inductive influence of magnets, the first from permanent, 

 the other from electro or temporary magnets — and each is driven or 



