The telegraph manual: a complete history and description of the semaphoric, electric and magnetic telegraphs of Europe, Asia, Africa, and America, ancient and modern.

MR COOKE'S TELEGRAPH IMPROVED. 197
had been adopted in the mechanical instrument, in conjunction
with the secondary circuit; this was an important improvement, and it was suggested by the permutating keys and the
second mechanical telegraph. The principles of the two were
adopted in the use of one common blank wire, which was in
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