The wooden base is four inches square and the upright one inch and a half square. The stand is twelve inches high over all, and on the bottom a plate of iron or lead must be screwed fast to make it bottom-heavy, so that it will not topple over.
The lever-switch may be arranged at the back of the upright and the push-button at the front near the base, as shown at A. The wall-box contains the buzzer and induction-coil, and within it the wiring is arranged from the portable stand to the batteries and line as shown at C. This illustration is too small, however, to show the complete wiring, and the young electrician is therefore referred to Fig. 22. The battery (B) is composed of as many dry or wet cells as may be required to operate the line. These must be connected in series at both ends. At D a rear view of the upright and transmitter is shown to illustrate the manner in which the wiring can be done. If a hollow upright is made of four thin pieces of wood a much neater appearance may be secured by enclosing the wires.
In all of these telephone systems one wire must lead to the ground, or be connected with a water-pipe, taking care, however, to solder the wire to a galvanized pipe so that perfect contact will be the result. If the wire is carried directly to the ground it must be attached to a plate, which in turn is buried deep enough to reach moist earth, as described in the chapter on Line and Wireless Telegraphs, page 215.
Care and accuracy will lead to success in telephony, but one slip or error will throw the best system out of order and render it useless. This, indeed, applies to all electrical apparatus; there can be no half-way; it will either work or it won’t.
Nearly every boy is interested in telegraphy, and it is a fascinating field for study and experimental work, to say nothing of the amusement to be gotten out of it. The instruments are not difficult to make, and two boys can easily have a line between their houses.
The key is a modified form of the push-button, and is simply a contact maker and breaker for opening and closing an electrical circuit. A practical telegraph-key is shown in Fig. 1, and in Fig. 2 is given the side elevation.
The base-board is four inches wide, six inches long, and half an inch in thickness. At the front end a small metal connector-plate is screwed fast, and through a hole in the middle of it a brass-headed upholsterer’s tack is driven for the underside of the key to strike against. Two [L] pieces of metal are bent and attached to the middle of the board to support the key-bar, and at the rear of the board another upholsterer’s tack is driven in the wood for the end of the bar to strike on and make a click. The bar is of brass or iron, measuring three-eighths by half an inch, and is provided with a hole bored at an equal distance from each end for a small bolt to pass through, in order to pivot it between the [L] plates. A hole made at the forward end will admit a brass screw that in turn will hold a spool-end to act as a finger-piece. The screw should be cut off and riveted at the underside. A short, strong spring is to be attached to the back of the base-block and to the end of the key-bar by means of a hook, which may be made from a steel-wire nail flattened. It is bound to the top of the bar with wire, as shown in Figs. 2 and 3.