or lower efficiency in small engines). That
would be 3.125 pints of gasoline per hour. Allowing a ten per cent
loss of current in wiring, we have 900 watts of electricity to use,
for this expenditure of gasoline. This would light 900 / 25 = 36 lamps
of 25 watts each, a liberal allowance for house and barn, and
permitting the use of small cooking devices and other conveniences
when part of the lights were not in use. With gasoline selling at 12
cents a gallon, the use of this plant for an hour at full capacity
would cost $0.047. Your city cousin pays 9 cents for the same current
on a basis of 10 cents per kilowatt-hour; and in smaller towns where
the rate is 15 cents, he would pay 13-1/2 cents.

Running this plant at only half-load--that is, using only 18 lights,
or their equivalent--would reduce the price to about 3 cents an
hour--since the efficiency decreases with smaller load. It is
customary to figure an average of 3-1/2 hours a day throughout the
year, for all lights. On this basis the cost of gasoline for this
one-kilowatt plant would be 16-1/2 cents a day for full load, and
approximately 10-1/2 cents a day for half-load. This is extremely
favorable, as compared with the cost of electric current in our cities
and towns, at the commercial rate, especially when one considers that
light and power are to be had at any place or at any time on the farm
simply by starting the engine. A smaller plant, operating at less cost
for fuel, would furnish ample light for most farms; but it is well to
remember in this connection plants smaller than one kilowatt are
practical for light only, since electric irons, toasters, etc., draw
from 400 to 660 watts each. Obviously a plant of 300 watts capacity
would not permit the use of these instruments, although it would
furnish 10 or 12 lamps of 25 watts each.

CHAPTER XI

THE STORAGE BATTERY

What a storage battery does--The lead battery and the Edison
battery--Economy of tungsten lamps for storage batteries--The
low-voltage battery for electric light--How to figure the capacity
of a battery--Table of light requirements for a farm
house--Watt-hours and lamp-hours--The cost of storage battery
current--How to charge a storage battery--Care of storage
batteries.

For the man who has a small supply of water to run a water wheel a few
hours at a time, or who wishes to store electricity while he is doing
routine jobs with a gasoline engine or