CHAPTER V.
ABOUT PUSH-BUTTONS, SWITCHES AND BINDING-POSTS.
60. Electrical Connections. In experimental work, as well as in the everyday work of the electrician, electrical connections must constantly be made. One wire must be joined to another, just for a moment, perhaps, or one piece of apparatus must be put in an electric circuit with other apparatus, or the current must be turned on or off from motors, lamps, etc. In order to conveniently and quickly make such connections, apparatus called push-buttons, switches and binding-posts are used.
| Fig. 51. | Fig. 52. |
61. Push-Buttons. The simple act of pressing your finger upon a movable button, or knob, may ring a bell a mile away, or do some other equally wonderful thing. Fig. 51 shows a simple push-button, somewhat like a simple key in construction. If we cut a wire, through which a current is passing, then join one of the free ends to the screw A and the other end to screw C, we shall be able to let the current pass at any instant by pressing the spring B firmly upon A.
Push-buttons are made in all sorts of shapes and sizes. Fig. 52 gives an idea of the general internal construction. The current enters A by one wire, and leaves by another wire as soon as the button is pushed and B is forced down to A. The bottom of the little button rests upon the top of B.
Fig. 53 shows a Table Clamp-Push for use on dining-tables, card-tables, chairs, desks, and other movable furniture. Fig. 54 shows a combination of push-button, speaking-tube, and letter-box used in city apartment houses. Fig. 55 shows an Indicating Push. The buzzer indicates, by the sound, whether the call has been heard; that is, the person called answers back.
| Fig. 53. | Fig. 54. |
Modifications of ordinary push-buttons are used for floor push-buttons, on doors, windows, etc., for burglar-alarms, for turning off or on lights, etc., etc. (See "Apparatus Book," Chapter III., for home-made push-buttons.)