American telegraphy and encyclopedia of the telegraph; systems, apparatus, operation (1909)
Maver, William, jr. [from old catalog] · New York, Maver publishing company · leaf 611
cedat any point along the route of the block. I^ormally, the contacts c at tlie block instrument are closed. At ct the contacts c are normally open. At such times emand R are in the one circuit, part of which is completed through the armature a of r.Consequently, the disc d is at safety ; the… … THE HALL RAILWAY BLOCK S STEM. 501 to separate them.
Telegraph
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