NOTE: Sid Lethbridge 2020 - No. 492 applies to only the green lamp. The ruby lamp is No. 456 and we do not know what the numbers are for the blue or amethyst lamps. (ref. Dugan/Diamond by Heacock, Wiggins and Measell, pp. 48-9) "The Dugan/Diamond book indicates that the lamp appears in 1903 Butler Bros. catalogues. Given that Dugan did not take over the National factory until January 1904, the initial production of the lamp predated their ownership. Production of the lamps continued under Dugan."