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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



arc voltage (80) and the line voltage (no). On alternating cur- 

 rent, a reactance was used in place of the resistance. 



The efficiencies in lumens per watt of these arcs (with clear glass- 

 ware), all of which have now disappeared from the market, were 

 about as follows : 



6.6 ampere 510 watt direct current (D. C.) series arc, 8^ 1-p-w. 

 5.0 ampere 550 watt direct current multiple (no-volt) arc, 4^ 1-p-w. 

 7.5 ampere 540 watt alternating current (A. C.) multiple (no-volt) 

 arc, 4I 1-p-w. 



Opex Flamk Arc 

 Lamp, 1898. 



Certain salts impregnated in 

 the carbons produced a bril- 

 liantly luminous flame in the 

 arc stream which enormously 

 increased the efficiency of the 

 lamp. 



Enclosed Im.a.me Arc 

 Lamp, 1908. 



By condensing the smoke 

 from the arc in a cooling 

 chamber it was practical to en- 

 close the flame arc, thereby 

 increasing the life of the 

 carbons. 



The reason for the big difference in efficiency between the series 

 and multiple direct-current arc is that in the latter a large amount of 

 electrical energy (watts) is lost in the ballast resistance. While there 

 is a considerable difference between the inherent efficiencies of the 

 D. C. and A. C. arcs themselves, this difference is reduced in the 



