ribed on p. 89
in connection with the "buzzer."

The plate P2 should be stout enough not to spring under the impact of the
lever. Fig. 36 is an end view of the standard B. The drilling of the pivot
hole through this requires care. The screw S2 should be so adjusted as to
prevent the armature actually touching the cores of the magnets when
attracted. The ends of the magnet winding wire, after being scraped, are
clipped tightly against the base by the binding posts T1 T2.

If sounders are used in place of buzzers they are connected up with the
keys, batteries, and line wires in the manner shown in Fig. 33.

Batteries.

The dry cells used for electric bells are the most convenient batteries to
use. They can now be purchased at all prices from a shilling upwards, and
give about 1-1/2 volts when in good condition. One cell at each end will
suffice for short distances, or for considerable distances if large
conductors are used. If a single cell fails to work the buzzer strongly
through the circuit, another cell must be added.

[Illustration: FIG. 36.--Standard for sounder.]

For ease in transport it will be found advisable to mount key, buzzer, and
battery on a common baseboard, which should be provided with a cover and
handle. The three parts are interconnected with one another, and the line
wire terminals as sketched in Fig. 34. This arrangement makes the apparatus
very compact and self-contained. As a finishing touch fit the lid inside
with clips for holding a stiff-backed writing pad and pencil for the
recording of messages.

Lines.--Fencing made of stout galvanized iron wires strung on wooden
posts supplies excellent conductors for practice purposes, provided the
posts be quite dry. In wet weather there will be leakage. (Fencing with
metal posts is, of course, unsuitable, as every post short-circuits the
current.) The two wires selected for land lines must be scraped quite
bright at the points where the connections are to be made.

It is an easy matter to rig up a telegraph line of galvanized wire 1/12 to
1/8 inch in diameter, strung along insulators (the necks of bottles serve
the purpose excellently) supported on trees, posts, or rough poles. The
length of the line will be limited by the battery power available, but a
6-volt battery at each end will probably suffice for all experimental
purposes. A second wire is not needed if one terminal at each end is
connected with a copper plate sunk in the ground, or wi