127
as in the case assumed in Fig. 4. The minimum total cost in this case is $444, and to make this cost a minimum we must use lamps having an efficiency of 3.5 watts per candle.
Lamps $1.00 each—Life 300 hrs. at 3 Watts per candle.
Current costs 2.5 cts. per ㏋. per hour.
Fig. 6.
In this case shown in Fig. 6 the lamps cost the same as in the last, but are only half as good; the current costs just half as much as in the last case. The minimum total cost in this case is $273, and
