. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . ally a brake and holds theratchet wheel, preventing any backwardmotion. The quick impulses work thepawl which appears at the top of theselector and step the ratchet wheelaround the proper number of teeth, atwhich point the two contacts make,and the bell in the station is rung. Theoperation of the selector bell at any waystation automatically sends a distinctivesignal out on the telephone circuit. Thisis familiarly known as the answer-back,and serves to inform the dispatcherthat the bell he ca
. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . ally a brake and holds theratchet wheel, preventing any backwardmotion. The quick impulses work thepawl which appears at the top of theselector and step the ratchet wheelaround the proper number of teeth, atwhich point the two contacts make,and the bell in the station is rung. Theoperation of the selector bell at any waystation automatically sends a distinctivesignal out on the telephone circuit. Thisis familiarly known as the answer-back,and serves to inform the dispatcherthat the bell he called actually rang. Itis one of the features peculiar to the tele-phone method of dispatching. The remainder of the revolution ofthe key, after the signaling impulsesare complete, keeps the contact closedand, therefore, keeps battery on theline during a period of about five sec-onds. As long as this battery is on theline, the bell at the way station installing a simple strap key, thedispatcher can hold this down andmake the way station bell ring as longas !u pleases, this strap key merely. SELECTOR AND BELL IN ST.\ taking the place of the key contactsand keeping the circuit closed. The selector requires approximatelythree seconds to call the thirtieth sta-tion on the line, and any one of the firstten stations will be called in one second October, 1910. RAILWAY AND LOCOMOTIVE ENGINEERING. 413 or less. The selectors which we aredescribing are equipped for fifty sta-tions, which would cover the majorityof train dispatching districts. As we pointed out before the selectoris wired across the circuit. Retardationcoils are employed to choke back anylightning which may get past the pro-tectors at a station. A variable re-sistance is required at each selector,since each must receive approximately I ^ DISP.^TCHERS INDniDLAL KEY, SETFOR STATION 7. the same current and voltage, and ifthis were not used, the high voltagenear the dispatcher would give the sta-tions adja
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