History, theory, and practice of the electric telegraph (1866)
Prescott, George B.(George Bartlett),1830-1894 · Boston, Ticknor and Fields · leaf 40
copper disc, upon which is placed a zinc disc; thecomposition of these two superposed discs forms a pair. Over thisfirst pair a second similar pair is placed, care being taken thatthe copper is always below the zinc: the second pair is separatedfrom the first by a circular piece of cloth or… … Fig. 3. 22 PRELIMINARY NOTIONS. similar to that which preceded. In this manner a greater or les9number of pairs are superposed one upon auother, care beingtaken to retain them in their position by means of vertical rodsof brass; if the precaution has been taken to insulate the pile byresting its…
Telegraph
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