464. Directions. (A) Arrange as in [Fig. 154]. Stick a pin on each side of the N pole of the galvanoscope-needle through the degree-card, so that the needle can make but part of a turn when the circuit is closed.
(B) Touch one lever of the reverser C R, then the other, to see whether connections are right. The needle should be forced against one pin and then against the other. If motions to the left represent dots, and those to the right dashes, combinations of dots and dashes can be used for letters as in the "sounder" ([Exp. 191]).
(C) Arrange the apparatus shown in [Fig. 122] so that messages can be sent.
EXPERIMENT 195. To study the action of a simple automatic "contact breaker," or "current interrupter."
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[197] 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.