metal one or both of which are springs, and one of which is connected with one of the wires from the battery, while the other is attached to the wire proceeding to the bell. When the button is pressed the upper spring comes into contact with the lower metal spring or plate. The circuit is now complete; hence the bell rings. But as soon as the finger is removed from the stud or button of the "push," the spring returns to its old place, contact being thereby broken when the bell ceases to ring, unless it be fitted with a continuous ringing arrangement (see [§ 48]). In fastening the leading wires to these
pushes, care must be taken that the ends of the wires be scraped, and sand papered quite clean and bright, bent into a loop which must be inserted under the head of the screw that holds the wire to the spring pieces; the screws being then tightened up carefully to ensure a good grip and contact with the wires.
Fig. 45.
Fig. 46.
§ 54. A "pressel" ([Fig. 46]) is simply a push which instead of being made a fixture by being fastened in the wall or door, is attached to a metallic wired line, so that it is generally made to resemble somewhat in outward appearance the knob or tassel of the bell-pull of the last generation, the interior arrangement is precisely similar to that of the push; that is to say, the pressel consists in a pear-shaped or acorn-shaped hollow wooden box, with a projecting knob or button below. This button is attached to a spring, the tension of which keeps the knob protruding from the end of the box, and at the same time prevents contacts with the second spring at the bottom of the box. Two insulated wires, one from the battery, the other from the bell, are connected to separate screws at the top of the pressel. One of these screws connects with the lower spring, the other with the upper.