NO. 2 



HISTORY OF ELECTRIC LIGHT SCHROEDER 



39 



designed to fit the requirements of the series arc lamp. The Thomson- 

 Houston machine was a bipolar, having an armature consisting of 

 three coils, one end of each of the three coils having a common termi- 

 nal, or " Y " connected, as it is called. The other end of each coil 

 was connected to a commutator segment. The machine was to a great 

 extent self-regulating, that is the current was inherently constant with 

 fluctuating load, as occurs when the lamps feed or when the number 

 of lamps burning at one time should change for any reason. This 

 regulation was accomplished by what is called " armature reaction," 

 which is the effect the magnetization of the armature has on the field 

 strength. Close regulation was obtained by a separate electro-magnet. 



0^mi 



Diagram uf T-li Arc Lighting System. 



in series with the circuit, which shifted the brushes as the load 

 changed. As there were but three commutator segments, one for each 

 coil, excessive sparking was prevented by an air blast. 



The " T-H " (Thompson-Houston) lamp employed the shunt feed 

 principle. The carbons were normally separated, being in most types 

 drawn apart by a spring. A high resistance magnet, shunted around 

 the arc, served to draw the carbons together. This occurred on 

 starting the lamp and thereafter the voltage of the arc was held con- 

 stant by the balance between the spring and the shunt magnet. As 

 the carbon burned away the mechanism advanced to a point where 

 a clutch was tripped, the carbons brought together, and the cycle re- 

 peated. Both the T-H and Brush systems were extensively used in 

 street lighting, for which they were the standard when the open arc 

 was superseded by the enclosed. 



