u expect to use it for a line. In that case make a regular gravity
battery like the cell of App. 9. See Fig. 99 for line connections, and
Fig. 98 for plan view of this sounder.

APPARATUS 124.

_209. Telegraph Line; Connections._ Fig. 99 shows the complete
connections for our telegraph line, with two complete outfits. The
capital letters are used on the right side, R, and small letters are on
the left side, L. The batteries, B, b, are like App. 9. The keys, K, k,
are like App. 119. The sounders, S, s, are like App. 121 or 122.

[Illustration: Fig. 99.]

210. The two stations, R and L, may be near each other, or in different
houses. The return wire, R W, passes from the copper of b to the zinc of
B. This is important. If the cells are not joined properly, they will
not work. It is better to have the cells together, on a short line,
joined in series. The line wire, L W, and the return wire, R W, may be
made of insulated copper wire for short lines in the house. Ordinary
annunciator wire, No. 20, is good and cheap. The kind that is double
cotton wrapped, waxed, and paraffined, has about 235 ft. to the pound.
You should get at least 5 ft. for 1 cent. If your line stretches from
one house to another you will find it better to use iron wire.
Galvanized iron or steel wire No. 14 is good. This size weighs about
100 lbs. to the mile. The return and line wires must not touch each
other at any point; they must not touch any pipe or other piece of metal
that will short circuit your batteries. It is best to use porcelain or
glass insulators to support your wires if the line is long; but for
short lines, where you use a return wire, you may support the wires upon
poles or trees by means of loops made of strong cord or wire.

211. Operation. Suppose R (right) and L (left) have a line. By studying
Fig. 99 you will see that R's switch, E, is open while e is closed. The
whole system, then, has but one place where the circuit is open. As soon
as R presses his key, K, the circuit is closed, the current from both
cells rushes around through K, S, L W, s, k, b, R W, and B. This
magnetizes the bolts of both S and s, and their armatures come down with
a click upon the regulating-screws, where they remain as long as the
current passes. As soon as R raises his key the armatures rise, making
the up-click. R can, in this way, regulate the time between the two
clicks. If he presses K down and lets it up quickly, the two clicks that
his frien