NO. 2 



HISTORY OF ELECTRIC LIGHT SCHROEDER 



45 



an intensive study of gas distribution and reasoned that a constant 

 pressure electrical system could be made similar to that of gas. 



The first problem was therefore to design a dynamo that would 

 give a constant pressure instead of constant current. He therefore 

 reasoned that the internal resistance of the armature must be very 

 low or the voltage would fall as current was taken from the dynamo. 

 Scientists had shown that the most economical use of electricity from 



Constant Current DLjnamo 



o — o — o 



o — o — o 



Diagram of Constant Current Serif.s System. 

 This, in 1878. was the only method of distribnting electric current. 



i^ 



^Consfan-l- Voltaqe Dynanrxj 



a ^o ^ ^ ^ ^^r^ 



Diagram of Edison's Multiple System, 1879. 



Edison invented the multiple system of distributing electric current, 

 now universally used. 



a primary battery was where the external resistance of the load was 

 the same as the internal resistance of the battery, or in other words, 

 50 per cent was the maximum possible efficiency. 



When Edison proposed a very low resistance armature so that the 

 dynamo would have an efficiency of 90 per cent at full load, he was 

 ridiculed. Nevertheless he went ahead and made one which attained 

 this. The armature consisted of drum-wound insulated copper rods, 

 the armature core having circular sheets of iron with paper between 

 to reduce the eddy currents. There were two vertical fields above and 



