other source of power, the
storage battery solves the problem. The storage battery may be likened
to a tank of water which is drawn on when water is needed, and which
must be re-filled when empty. A storage battery, or accumulator is a
device in which a chemical action is set up when an electric current
is passed through it. This is called _charging_. When such a battery
is charged, it has the property of giving off an electric current by
means of a reversed chemical action when a circuit is provided,
through a lamp or other connection. This reversed action is called
_discharging_. Such a battery will discharge nearly as much current as
is required originally to bring about the first chemical action.

There are two common types of storage battery--the lead accumulator,
made up of lead plates (alternately positive and negative); and the
two-metal accumulator, of which the Edison battery is a
representative, made up of alternate plates of iron and nickel. In the
lead accumulator, the "positive" plate may be recognized by its brown
color when charging, while the "negative" plate is usually light gray,
or leaden in color. The action of the charging current is to form
oxides of lead in the plates; the action of the discharging current is
to reduce the oxides to metallic lead again. This process can be
repeated over and over again during the life of the battery.

Because of the cost of the batteries themselves, it is possible (from
the viewpoint of the farmer and the size of his pocketbook) to store
only a relatively small amount of electric current. For this reason,
the storage battery was little used for private plants, where expense
is a considerable item, up to a few years ago. Carbon lamps require
from 3-1/2 to 4 watts for each candlepower of light they give out; and
a lead battery capable of storing enough electricity to supply the
average farm house with light by means of carbon lamps for three or
four days at a time without recharging, proved too costly for private
use.

_The Tungsten Lamp_

With the advent of the new tungsten lamp, however, reducing the
current requirements for light by two-thirds, the storage battery
immediately came into its own, and is now of general use.

Since incandescent lamps were first invented scientists have been
trying to find some metal of high fusion to use in place of the carbon
filament of the ordinary lamp. The higher the fusing point of this
filament of wire, the more econom