Automatic block signals and signal circuits: American practice in the installation and maintenance of signals electrically controlled, and operated by electric or other power, with descriptions of the accessories now regarded as standard

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McGraw publishing company, 1908 - Transportation - 243 pages
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Page 4 - D^ sition approximating thirty degrees from the vertical it will indicate the same as though at the full horizontal position. This is effected by using several spectacles, each held in place by independent bezel rings, or by so-called continuous light spectacles. Semaphores vary in length from four to five feet, about four and one-half being regarded as standard.
Page 3 - If thsee be automatic track relays properly interconnected, they can be readily arranged to give the protection desired. If they be semi-automatic, electric interlocking will be introduced to prevent confliction of routes. Thus, when signal 3 is at clear, to allow a south bound train to pass, 2, and 4, must be locked in the normal or stop position when electric locking or interlocking is used and prevented moving to clear if the ordinary automatic system be employed.
Page 5 - The post, B, consists of two lengths of channel iron strengthened by a lattice structure, the base being bolted to, or incorporated with, a foundation of concrete, A.

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