3808 Professors Avrton and Perry on the most Econonucal 
Diagram for a. 16-candle 100-volt Edison Lamp. 
103 104 lua 106 
but a small fraction of the total yearly cost, as long as we are 
using potential-differences of not more than about 100 volts ; 
so that when using, with these lamps, this or a lower potential- 
difference, the actual sum paid for the lamps is not so very 
serious an item in the yearly lighting bill. But if, on the 
other hand, we maintain a potential-difference of, say, 104 
