NO. 2 



HISTORY OF ELECTRIC LIGHT SCHROEDER 



63 



circuits being connected in multiple across the 1200 volts. The 

 number of lamps on each series circuit depended upon their size, as 

 the voltage of each lamp was different for each size, being about ih 

 volts per cp. 



A popular size was the 32-candlepower unit, which therefore 

 required about 45 volts and hence at 3 amperes consumed about 135 

 watts. Allowing 5 i)er cent loss in the wires of each circuit, there 

 was therefore 1140 of the 1200 volts left for the lamps. Hence 

 about 25 32-candlepower or 50 i6-candlepower lamps could be put on 

 each series circuit. Different sizes of lamps could also be put on the 



Edison Municipal Lamp, 1885. 



Inside the base was an arrangement by which the lamp was auto- 

 matically short circuited when it burned out. 



same circuit, the number depending upon the aggregate voltage of the 

 lamps. 



A device was put in the base of each lamp to short circuit the lamp 

 when it burned out so as to prevent all the other lamps on that circuit 

 from going out. This device consisted of a piece of wire put inside 

 the lamp bulb between the two ends of the filament. Connected to 

 this wire was a very thin wire inside the base which held a piece of 

 metal compressed against a s]:)ring. The spring was connected to one 

 terminal of the base. Should the lamp burn out, current would jump 

 from the filament to the wire in the bulb, and the current then flowed 

 through the thin wire to the other terminal of the liase. The thin 

 wire was melted by the current, and the spring pushed the piece of 

 metal up short circuiting the terminals of the base. This scheme was 



