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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



ciency, such arcs on account of their color being used only to a limited 

 extent for advertising purposes. 



These arcs were remarkably efficient but their maintenance expense 

 was high. Later, about 1908, enclosed flame arcs with vertical carbons 



Constant Current Transformer, 1900. 



This converted alternating current of constant voltage into constant 

 current, for use on series circuits. 



were made which increased the life of the carbons, the smoke being 

 condensed in cooling chambers. However, their maintenance expense 

 was still high. They have now disappeared from the market, having 

 been displaced by the very efficient gas-filled tungsten filament incan- 

 descent lamp which appeared in 19 13. 



