The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 414
Fig. 382.—GlazedEarthenware Duct UNDERGROUND WORK 3B5 over both the concrete and cast-iron conduits, as the shortlengths used allow of slight curves being negotiated to avoidvarious obstructions met with. It has also the advantage overconcrete conduits of being practically gas and water proof.It… … Fig. 383.—Method of laying Earthenware Ducts is to use cast-iron pipes where only 5 ducts or under are requiredand earthenware ducts for more than that number, as this isfound to be the economic dividing line. American Practice.—In America wooden ducts of variouskinds are much used, the wood being…
Telephone
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