Meadowcroft, Wm. H. (William Henry), b. 1853 · New York & London, Harper & brothers · leaf 42
the use of which we willexplain later. The sounder is shown on the followingpage. (Fig. 7.) ^ The part consisting of the two black pil-lars is an electromagnet, and across the topof these pillars is a piece of iron called the armature, which is held up by a spring. 24 THE TELEGRAPH Now let us see… … Fig. 7 to return on. But you will easily see thatif two wires had to be used in telegraphing itwould be a very expensive matter, especiallywhen they had to be carried thousands ofmiles. So, instead of using a second wire,we use the earth to carry back the electricityto the battery, because the…
Electricity
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