[Illustration:  Fig. 31.—­Divisions of drawer notched to cross each other.]

Lock and Key.—­If a cabinet is intended for storage of articles of any value it should be provided with lock and key.  One lock will secure all the drawers if attached to a flap hinged on one side to the cabinet, as shown in 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.]