Push Buttons.—A push button is but a modified structure of a switch, and they are serviceable[p. 69] because they are operating, or the circuit is formed only while the finger is on the button.
In its simplest form (Fig. [48]) the push button has merely a circular base (A) of insulating material, and near one margin, on the flat side, is a rectangular plate (B), intended to serve as a contact plate as well as a means for attaching one of the wires thereto. In line with this plate is a spring finger (C), bent upwardly so that it is normally out of contact with the plate (B), its end being held by a binding screw (D). To effect contact, the spring end of the finger (C) is pressed against the bar (B), as at E. This is enclosed in a suitable casing, such as will readily suggest itself to the novice.
Electric Bell.—One of the first things the boy[p. 70] wants to make, and one which is also an interesting piece of work, is an electric bell.
To make this he will be brought, experimentally, in touch with several important features in electrical work. He must make a battery for the production of current, a pair of electro-magnets to be acted upon by the current, a switch to control it, and, finally, he must learn how to connect it up so that it may be operated not only from one, but from two or more push buttons.
