ch is used for sending sound signals, and for visible signals transmitted by means of flags, lamps, and heliograph mirrors. Signalli

e a "buzzer" or "tapper" to work at the other end when he depresses a key and closes an electric circuit. Each unit

unit only is illustrated, but, as the other is an exact du

: Fig. 32.-Mo

be grasped conveniently in the fingers; at the other a brass screw, O, which is normally pulled down against the contact, N, by the spira

es; T1 with the other wire through a battery, B;

may be substituted the tappe

ery, B, forms part is completed, and the buzzer at the other end of the lines comes into action. Since the depression of K raises O off N, the "home" buzzer's connection with the line wires is broken, to prevent the current being sho

egraphic apparatus; sendi

g the

ure is that of the screw terminals for connecting the keys with the lines and buzzers. These cost only a penny each, and, i

a piece of 3/16-inch brass rod; O a 1-1/2-inch brass screw; A a piece of sheet brass 3-1/2 inches long, marked off carefully, drilled 1/8 inch from the centre of each end for the pivot screws, and in

-Telegraphic apparatus

end and by T1 at the other. K was drilled near the end to take the short co

s hole through the lever hole for a pin, and cut a slot across the base hole for a pin to hold the bottom of the spring. Adjust the lever by means of screw O so that there is a space of about 1/4-inch betw

c purposes, I cut off the hammers to reduce the inertia, and so adjusted the contact screw that the armature had to move less than one hundredth of an inch

Tapper o

r." The principle of this simple device is illustrated by the working diagrams in Fig. 35. M is a horseshoe magnet fixed to a base, A. Close to it is an armature, AR, of soft iron, attached to a lever, L, which works on a pivot and is held up against a regulating screw, P1, by the pull of the spring SP. When c

.-Elevation and plan o

t in a cheap form. If these are available, expense will be limited to a few pence. Oak or walnut are the best woods to use for the

m the stop end. The hole should be bored through it as squarely as possible, so that it may lie centrally

n the manner already described on p

e pivot hole through this requires care. The screw S2 should be so adjusted as to prevent the armature actually touching the cores of the mag

are connected up with the keys, batteries, a

ter

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 d

FIG. 36.-Standa

. The three parts are interconnected with one another, and the line wire terminals as sketched in Fig. 34. This arrangement makes the apparatus very compa

he posts be quite dry. In wet weather there will be leakage. (Fencing with metal posts is, of course, unsuitable, as every post short-cir

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 a