American telegraphy and encyclopedia of the telegraph; systems, apparatus, operation (1909)
Maver, William, jr. [from old catalog] · New York, Maver publishing company · leaf 612
THE HALL RAILWAY BLOCK S STEM. 501 to separate them. … This has the effect of opening tlie prei^-^nt circuit of em and e. Theresult is, tlie disc d fall** to danger, and the arm-ature A of R drops, opoiiug tlie circuit at a secondpoint .r. After the train has passed bt the pistonp falls down, ])ermitting the contacts c to cometoo-ether again. But now…
Telegraph
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