At one end is a brass plate (B), with a hole for a wood screw (C), this screw being designed to pass through the plate and also into the window-frame, so as to serve as a means of attaching one of the wires thereto. The inner end of the plate has a hole for a round-headed screw (C') that also goes through the base and into the window-frame. It also passes through the lower end of the heart-shaped metal switch-piece (D). The upper end of the base has a brass plate (E), also secured to the base and window by a screw (F) at its upper end. The heart-shaped switch is of such length and width at its upper end that when it is swung to the right with one of the lobes projecting past the edge of the window-frame, the other lobe will be out of contact with the plate (E). [Illustration: _Fig. 58._ NEUTRAL POSITION OF CONTACT] The window sash (G) has a removable pin (H), which, when the sash moves upwardly, is in the path of the lobe of the heart-shaped switch, as shown in Fig. 56, and in this manner the pin (H) moves the upper end of the switch (D) inwardly, so that the other lobe contacts with the plate (E), and establishes an electric circuit, as shown in Fig. 57. During the daytime the pin (H) may be removed, and in order to protect the switch the heart-shaped piece (D) is swung inwardly, as shown in Fig. 58, so that neither of the lobes is in contact with the plate (E). WIRE CIRCUITING.--For the purpose of understanding fully the circuiting, diagrams will be shown of the simple electric bell with two push buttons; next in order, the circuiting with an annunciator and then the circuiting necessary for a series of windows and doors, with annunciator attachments. [Illustration: _Fig. 59._ CIRCUITING FOR ELECTRIC BELL] CIRCUITING SYSTEM WITH A BELL AND TWO PUSH BUTTONS.--Fig. 59 shows a simple circuiting system which has two push buttons, although any number may be used, so that the bell will ring when the circuit is closed by either button. THE PUSH BUTTONS AND THE ANNUNCIATOR BELLS.--Fig. 60 shows three push buttons and an annunciator for each button. These three circuits are indicated by A, B and C, so that when either button makes contact, a complete circuit is formed through the corresponding annunciator. [Illustration: _Fig. 60._ _Annunciators_] [Illustration: _Fig. 61._ WIRING SYSTEM FOR A HOUSE]