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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



carbons, while lasting about 50 hours, were not uniform in density, 

 so the arc would flare up and cast off soot and sparks. 



Edward Weston of Newark, New Jersey, also developed an arc 

 lighting system. His commercial lamp had carbon rods, one above the 

 other, and the arc was also differentially controlled. An oil dash pot 



Brush's Dynamo, 1877. 

 This dynamo was used for many years for commercial arc lighting. 



Diagram of Brush Armature. 



The armature was not a closed circuit. For description of its opera- 

 tion, see text. 



prevented undue pumping of the carbons. His dynamo had a drum- 

 wound armature, and had several horizontal field coils on each side of 

 one pair of poles between which the armature revolved. The system 

 was designed for about 20 amperes, each arc taking about 35 volts. 



Charles F. Brush made a very successful arc lighting system in 

 1878. His dynamo was unique in that the armature had eight coils, 



