Fig. 30 a, to engage a catch projecting from one of the drawers. A
special form of lock is sold for the purpose. If the single flap seems to
give a lop-sided effect, place a fellow on the other side, and fit it with
sunk bolts to shoot into the overhanging top and plinth. If you wish to
avoid the expense and trouble of fitting a lock, substitute a padlock and a
staple clinched through the front of a drawer and passing through a slot in
the flap (Fig. 30, e).

Alternative Method.--The fixing of the front bars can be avoided if the
front of each drawer (except the lowest) be made to overhang the bottom by
the depth of the runner. This method, of course, makes it impossible to
stand a drawer level on a level surface.

X. TELEGRAPHIC APPARATUS.

The easily made but practical apparatus described in this chapter supplies
an incentive for learning the Morse telegraphic code, which is used for
sending sound signals, and for visible signals transmitted by means of
flags, lamps, and heliograph mirrors. Signalling is so interesting, and on
occasion can be so useful, that no apology is needed for introducing
signalling apparatus into this book.

The apparatus in question is a double-instrument outfit, which enables an
operator at either end of the line to cause a "buzzer" or "tapper" to work
at the other end when he depresses a key and closes an electric circuit.
Each unit consists of three main parts--(1) the transmitting key; (2) the
receiving buzzer or tapper; (3) the electric battery.

The principles of an installation are shown in Fig. 33. One unit only is
illustrated, but, as the other is an exact duplicate, the working of the
system will be followed easily.

[Illustration: Fig. 32.--Morse alphabet]

A wooden lever, L, is pivoted on a support, A. Passing through it at the
forward end is a metal bar having at the top a knob, K, which can be
grasped conveniently in the fingers; at the other a brass screw, O, which
is normally pulled down against the contact, N, by the spiral spring, S.
The contact M under K is in connection with the binding post T1 and N with
binding post T3; K is joined up to T2, and O to T4.

T3 and T4 are connected with one of the line wires; T1 with the other wire
through a battery, B; T3 with the other wire through the buzzer, R. [1]

[Footnote 1: For the buzzer may be substituted the tapper, described on a
later page.]

Assuming both keys to be at rest, as in Fig. 33, the two buzzers are