Bell Telephone Company, America. Top left: Winding and inspecting coils. Top right: Experimental deparment. Centre right: First Bell telephone and First Boston telephone exchange with 5 lines (1877). Centre: Inspecting department. Centre right: Hand telephone department. Bottom left: Boston telephone exchange, 1884. Bottom right: Assembling transmitters. Engraving from Scientific American (New York, 20 September 1884).