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TELEGRAPHS.
91
space, which is a great desideratum in the smaller signal cabins.
The one-wire system differs from the three-wire, in so far as the indicator of the instrument is moved over to the different positions by a momentary current, and is
Fig. 15.
One-Wire Block Telegraph Instrument.
afterwards held there by induced magnetism, the wire being left free for any succeeding signals. The mode of working is about the same, only that there are but two positions, viz., "Line clear," and "Train on line," and no vertical position, (See Fig. 15.)
