communities where the lines have a
rather great average length; where a good many subscribers are likely to
be found on some of the lines; where the sources of electrical power
available for charging storage batteries are likely either not to exist,
or to be of a very uncertain nature; and where it is not commercially
feasible to employ a high-grade class of attendants, or, in fact, any
attendant at all other than the operator at the central office.

In large or medium-sized exchanges it is always possible to procure
suitable current for charging the storage batteries required in
common-battery systems, and it is frequently economical, on account of
the considerable quantity of energy that is thus used, to establish a
generating plant in connection with the central office for developing
the necessary electrical energy. In very small rural places there are
frequently no available sources of electrical energy, and the expense of
establishing a power plant for the purpose cannot be justified. But even
if there is an electric light or railway system in the small town, so
that the problem of available current supply does not exist, the
establishment of a common-battery system with its storage battery and
the necessary charging machinery requires the daily attendance at the
central office of some one to watch and care for this battery, and this,
on account of the small gross revenue that may be derived from a small
telephone system, often involves a serious financial burden.

There is no royal road to a proper decision in the matter, and no sharp
line of demarcation may be drawn between the places where common-battery
systems are superior to magneto and _vice versa_. It may be said,
however, that in the building of all new telephone plants having over
about 500 local subscribers, the common-battery system is undoubtedly
superior to the magneto. If the plant is an old one, however, and is to
be re-equipped, the continuance of magneto apparatus might be justified
for considerably larger exchanges than those having 500 subscribers.

Telephone operating companies who have changed over the equipment of old
plants from magneto to common battery have sometimes been led into
rather serious difficulty, owing to the fact that their lines, while
serving tolerably well for magneto work, were found inadequate to meet
the more exacting demands of common-battery work. Again in an old plant
the change from magneto to common-battery equipme