Modern practice of the electric telegraph : a handbook for electricians and operators (1874)
Pope, Frank L., 1840-1895 · New York : D. Van Nostrand · leaf 73
Fig. 35. Fig. 34. 94. Farmers Hard Rubber Insulator.—This isshown in Fig. 34. It is a good insulator when new, INSULATION. 61 but by exposure to the weather its surface becomesrough and spongy, and retentive of moisture. It isscrewed to the under side of the cross-arm or woodenblock, which is…
Telegraph
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