Wright, Mark R., 1854- · London : Longmans · leaf 233
urrent; thus the wire between cu and G might be removed,the ends being inserted in the earth. (See also fig. 227.) For the purposes of signalling it is convenient to have thepower of turning the needle either to the right or left—that is,it must be possible to cause the current to pass from… … Z» ICaFig. 225.
Physics
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