American telegraphy and encyclopedia of the telegraph; systems, apparatus, operation (1909)
Maver, William, jr. [from old catalog] · New York, Maver publishing company · leaf 638
r to add strength to the mass andto protect the ducts from mechanical injury, the concrete is applied more thickly onthe bottom, top and sides of tiie conduits, than between the pipes. There is placed,over all, a two-inch yellow pine plankijig, heavily creosoted, to further protect theconduits… … Access is had to the conduits of the drawing in and out system by means ofmanholes placed at an average distance apart of about one tAventy-fiftli of a mile.The manholes are generally of brick or cast iron. Access is had to the manloles fromthe street through a cast iron head, which is provided…
Telegraph
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