Theory and practice of the electric telegraph; a manual for operators and students (1875)
Churchill, Charles Henry, d. 1904. [from old catalog] · Oberlin, Ohio, Sherman & bros. · leaf 142
OF THE LINE. 121 … In Brooks stoneware insulator, (Fig.56) a stone cap is saturated with para-ffine and screwed to an iron pin whichis itself screwed into the crossbar orbent up and screwed directly into thepost. This affords a far better insula-tion than any glass cap, and is cheap. 14. What precautions are…
Telegraph
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