Sweet’s indexed catalogue of building construction for the year 1906 (1906)
New York : Chicago : Architectural Record · leaf 744
and provides a very efficientmeans by which tenants can display a signal on the outside of thebuilding without leaving their floor, thereby notifying the expresscall driver, without any unnecessary delay, of the room requiringhis service. DESCRIPTION—The system consists of a tube or conduit running… … SIGNAL FOR THE OUTSIDE OFA BUILDING
Building materials
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