battery the long thin line is supposed to represent the positively
charged plate and the short thick line the negatively charged plate.
The number of pairs may indicate the number of cells in the battery.
Frequently, however, a few pairs of such lines are employed merely for
the purpose of indicating a battery without regard to its polarity or
its number of cells.

[Illustration: Fig. 67. Battery Symbols]

In Fig. 67 the representation at _A_ is that of a battery of a number
of cells connected in parallel; that at _B_ of a battery with the
cells connected in series; and that at _C_ of a battery with one of
its poles grounded.




CHAPTER VIII

MAGNETO SIGNALING APPARATUS


Method of Signaling. The ordinary apparatus, by which speech is
received telephonically, is not capable of making sufficiently loud
sounds to attract the attention of people at a distance from the
instrument. For this reason it is necessary to employ auxiliary
apparatus for the purpose of signaling between stations. In central
offices where an attendant is always on hand, the sense of sight is
usually appealed to by the use of signals which give a visual
indication, but in the case of telephone instruments for use by the