Fleming oscillation valve, in wooden mounting frame, marked 15, (RMW/A4 - McVitie Weston number), by The Edison and Swan Electric Light Company Limited, 1905, invented by Sir (John) Ambrose Feming. Marked: “FLEMING OSCILLATION VALVE / 12 VOLTS" and opposite this:

ROYAL EDISWAN.

This valve was used by Marconi and Fleming in their early work at the famous Poldhu radio station in 1905. Carbon loop filament. Cylindrical anode of either nickel or platinum. Bulb diameter 52mm. Height to top of gallows: 80mm.