NO. 2 



HISTORY OF ELECTRIC LIGHT SCHROEDER 



35 



which lasted much longer than rods. When the edges had burned 

 away so that the arc then became unduly long, the carbon plates were 

 brought closer together by hitting them with a hammer. Wallace 

 became associated with Moses G. Farmer, and they improved this 

 crude arc by fastening the upper carbon plate to a rod which was held 

 by a clutch controlled by a magnet. This magnet had two coils in one, 

 the inner winding in series with the arc, and outer one in shunt and 

 opposing the series winding. The arc was therefore dififerentially 

 controlled. 



Weston's Arc Lamp, 1876. 

 This lamp is in the collection of the Smithsonian Institution. 



They also developed a series wound direct current dynamo. 

 The armature consisted of a number of bobbins, all connected 

 together in an endless ring. Each bobbin was also connected to 

 a commutator bar. There were two sets of bobbins, commutators and 

 field poles, the equivalent of two machines in one, which could be 

 connected either to separate circuits, or together in series on one 

 circuit. The Wallace-Farmer system was commercially used. The 

 arc consumed about 20 amperes at about 35 volts, but as the carbon 

 plates cooled the arc, the efficiency was poor. The arc flickered back 

 and forth on the edges of the carbons casting dancing shadows. The 



