hat have been used
up must be renewed from time to time, in order to obtain a continued
supply of electric current.

The storage battery also generates electric current through chemical
action, but without involving the constant repriming with active
materials to replace those consumed and exhausted as above mentioned.
The term "storage," as applied to this species of battery, is,
however, a misnomer, and has been the cause of much misunderstanding
to nontechnical persons. To the lay mind a "storage" battery presents
itself in the aspect of a device in which electric energy is STORED,
just as compressed air is stored or accumulated in a tank. This view,
however, is not in accordance with facts. It is exactly like the primary
battery in the fundamental circumstance that its ability for generating
electric current depends upon chemical action. In strict terminology it
is a "reversible" battery, as will be quite obvious if we glance briefly
at its philosophy. When a storage battery is "charged," by having an
electric current passed through it, the electric energy produces a
chemical effect, adding oxygen to the positive plate, and taking oxygen
away from the negative plate. Thus, the positive plate becomes oxidized,
and the negative plate reduced. After the charging operation is
concluded the battery is ready for use, and upon its circuit being
closed through a translating device, such as a lamp or motor, a
reversion ("discharge") takes place, the positive plate giving up its
oxygen, and the negative plate being oxidized. These chemical actions
result in the generation of an electric current as in a primary battery.
As a matter of fact, the chemical actions and reactions in a storage
battery are much more complex, but the above will serve to afford the
lay reader a rather simple idea of the general result arrived at through
the chemical activity referred to.

The storage battery, as a commercial article, was introduced into the
market in the year 1881. At that time, and all through the succeeding
years, until about 1905, there was only one type that was recognized as
commercially practicable--namely, that known as the lead-sulphuric-acid
cell, consisting of lead plates immersed in an electrolyte of dilute
sulphuric acid. In the year last named Edison first brought out his new
form of nickel-iron cell with alkaline electrolyte, as we have related
in the preceding narrative. Early in the eighties, at Menlo Park, he had
giv