NO. 2 HISTORY OF ELECTRIC LIGHT — SCHROEDER 4I 



carbon a larger crater at the vaporizing point of carbon. This source 

 furnishes the largest proportion of light, the smaller crater in the 

 negative carbon much less. With the alternating current arc, the 

 large crater is formed first on the upper and then on the lower carbon. 

 On account of the cooling between alternations, the mean temperature 

 falls below the vaporizing point of carbon, thus accounting for the 

 lower efBciency of the alternating current arc. 



For this reason all these systems used direct current and the 10 

 ampere ultimately displaced the 20 ampere system. The 10 ampere 



Maxim Dynamo. 

 This dynamo is in the collection of the Smithsonian Institution. 



circuit was later standardized at 9.6 amperes, 50 volts per lamp. The 

 lamp therefore consumed 480 watts giving an efificiency of about 15 

 lumens per watt. This lamp gave an average of 575 candlepower 

 (spherical) in all directions, though it was called the 2000 cp (candle- 

 power) arc as under the best possible conditions it could give this 

 candlepower in one direction. Later a 6.6 ampere arc was developed. 

 This was called the " 1200 cp " lamp and was not c^uite as efficient as 

 the 9.6 ampere lamp. 



