§ 52. Sometimes the gong or "dome" of the ordinary bell is replaced by a coil spring, as in the American clocks; sometimes quaint forms are given to the parts covering the "movement," so as to imitate the head of an owl, etc. But bells with these changes in outward form will not present any difficulty, either in fixing or in management, to those who have mastered the structural and working details given in this chapter.
[10] "Amateur Work."
[11] Insula in Latin means an island, hence an electrified body is said to be insulated when surrounded by non-conductors, as an island by the sea.
[12] A "push," of which several forms will hereafter be described and figured, consists essentially in a spring carrying a stud, standing directly over, but not touching, another stud, fixed to a base. The lower stud is connected to one terminal of battery, the spring is connected to the bell. When the spring is pressed down, the two studs come into contact, the current flows, and the bell rings.
[14] See "Electrical Instrument Making for Amateurs." Whittaker & Co. Second edition.
CHAPTER IV.
ON CONTACTS, PUSHES, SWITCHES, KEYS, ALARMS, AND RELAYS.
§ 53. All the appliances which have hitherto been described, would be utterly useless for the purposes intended, had we not at hand some means of easily, certainly and rapidly completing and breaking the circuit between the bell or bells, on the one hand, and the battery on the other. This necessary piece of apparatus, which is simply a contact maker, receives different names, dependent on its application. When it is intended to be actuated directly by hand, it is known as a "push," a "pressel," or "pull," according to the mode in which the contact is made. At [Fig. 45], A, B, C, D, and E, show the outward forms of various "pushes," in wood and china, as sent out by the leading makers. (The ones figured are from Messrs. Binswanger & Co.) At F is a sectional view of one of these pushes, and G shows the interior when the cover has been removed. From these two latter illustrations it will be easily understood that the "push" consists essentially in two pieces of