[Electric engineering.] . he bell was rung are operated byprimary batteries, which are of low voltage, and no firehazard is introduced if the bell wires are kept well separatedand insulated from electric light and power wires. THE ELECTRIC BELL. 31. The electric bell is a very simple piece of apparatus. In Fig. 5 is shown a type of skeleton bell, in which all theparts are visible. The battery wiresare connected at the terminals /, t,and the course of the current is asfollows: From the terminal t to theadjustment screw s, which is tippedwith platinum in order to preventoxidation of the contact
[Electric engineering.] . he bell was rung are operated byprimary batteries, which are of low voltage, and no firehazard is introduced if the bell wires are kept well separatedand insulated from electric light and power wires. THE ELECTRIC BELL. 31. The electric bell is a very simple piece of apparatus. In Fig. 5 is shown a type of skeleton bell, in which all theparts are visible. The battery wiresare connected at the terminals /, t,and the course of the current is asfollows: From the terminal t to theadjustment screw s, which is tippedwith platinum in order to preventoxidation of the contact surface,through the spring / and the end pof the armature to the coils of themagnets m, m, and out at the ter-minal f. When no current is pass-ing, the armature is held away fromthe poles of the electromagnets, asin the position shown, but as soon asa battery circuit is closed and a cur-rent sent through the coils, the mag-FlG- 5. nets become energized and attract the armature a, which swings about the pivot/, causing the. § 28 INTERIOR WIRING. 25 hammer h to strike the bell. This movement breaks thecircuit between .? and /, and the iron cores being therebydemagnetized, the spring c draws the armature away, whenthe spring / again touches the screw s, completing the cir-cuit. As long, then, as the battery current is free to flow,this vibration of the armature and hammer will tension of the release spring c may be changed to suitthe strength of the battery by means of the regulatingscrew r, which is provided with nuts for this purpose on eachside of the supporting pillar. The bell mechanism is usuallyenclosed to prevent entrance of dust or insects, which mayinterfere with the working of the bell by lodging on thecontact points, thereby preventing the current from passingthrough the magnets. 32. The bell just described is of the common vibratingclass. When a bell is required to give a single stroke eachtime the circuit is closed, that is, for each pulsation of cur-re
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