=465. Directions.= (A) Arrange as in Fig. 155. Slip a spring connector attached to wire 1 upon the iron strip I, a short distance from its end. Hold the left-hand end of I firmly in one hand, and with the other hold the connector on wire 2 just above that on 1. The right-hand end of I should be just above the core of H. (B) Allow the current to pass through the circuit by touching the two connectors together gently. Does the armature make one click, as in the telegraph sounder, or does it vibrate rapidly? (C) Try the connectors in various positions on I. _=466. Automatic Current Interrupters=_ are used on bells, buzzers, induction coils, etc. The principle upon which they work is shown in the above experiment (Fig. 155). The current, as it comes from the carbon of D C, is obliged to stop when it reaches I, unless the two connectors touch. As soon as the current passes, I is pulled down and away from the upper connector, and this breaks the circuit. I, being held firmly in the hand, immediately springs back to its former position, closing the circuit. The rapidity of the vibrations depends somewhat upon the position of the connectors upon I. In regular instruments, a platinum point is used where the circuit is broken; this stands the constant sparking at that point. [Illustration: Fig. 156.] =EXPERIMENT 196. To study the action of a simple "electric bell," or a "buzzer."= =467. Directions.= (A) Fig. 156 shows the circuit explained in Exp. 195, with a key or push-button put in, so that the circuit can be closed at a distance from the vibrating armature. (B) Have a friend work the key while you hold I and wires 1 and 2 as directed in Exp. 195. The circuit must not be broken at two places, of course, so begin by holding the two connectors together. The armature should vibrate rapidly each time K is pressed. _=468. Electric Bells and Buzzers=_ are very nearly alike in construction; in fact, you will have a buzzer by removing the bell from an ordinary electric bell. Buzzers are used in places where the loud sound of a bell would be objectionable. By placing a bell near the end of the vibrating armature (Fig. 156), so that the bell would be struck by it at each vibration, we should have an electric bell. By making the wires 1 and 3 long, the bell or buzzer can be worked at a distance. (See Apparatus Book, Chapter XV, for Home-made Bells and Buzzers.) [Illustration: Fig. 157.] =EXPERIMENT 197. To study the action of a simple telegraph "recorder."=