Telegraph engineering : a manual for practicing telegraph engineers and engineering students (1922)
Hausmann, Erich, 1886- · New York : D. Van Nostrand Company · leaf 235
elephone. Numbered keys may be given to responsible citizenswith which they can operate the police signal boxes whenin need of police assistance without opening the outer door,such keys when used being trapped in the locks for iden-tifying the possessors. Incoming signals are usually received at… … Fig. 19. sent out by detachable signal-wheel or special dial trans-mitters. The equipment at the stables and garages usuallyincludes an electromechanical gong and indicator as illus- MUNICIPAL TELEGRAPHS 221 trated in Fig. 13, a register with take-up reel as indicatedin Fig. 14, a tapper and a…
Telegraph
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