Detector bar
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De`tect´or bar
| 1. | (Railroads) A bar, connected with a switch, longer than the distance between any two consecutive wheels of a train (45 to 50 feet), laid inside a rail and operated by the wheels so that the switch cannot be thrown until all the train is past the switch. |
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.