National Telegraphic Union · New York : N.T.U. · leaf 12
e especially to the subject of insulators it may be re-marked that the first requisite in an insulator is, that itssubstance should not transmit electric currents, and thatafter long exposure its surface should remain in asimilar condition, even when exposed to rain or the moist-ure deposited from… … wmm
Telegraph
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![An illustration from The Telegrapher [microform], 1864, leaf 12](https://img.insideoutlibrary.com/img/1024/ia-telegrapher04nati-12-8.webp)
