A rare Air Ministry flameproof Morse key with spark indicator S.G. Brown Limited, London, No. 1969 circa 1910 The beam fitted with Bakelite knob and yoke-shaped cast aluminium alloy applied to pivot within inverted U-shaped frame and opposing connector assembly comprising twin contact breakers incorporating spark gap a two sets of connectors, with cast aluminium alloy cover incorporation mica window to view the spark and on rectangular brown Bakelite base stamped S. G. BROWN LTD, LONDON W and REF No. 1969, the base 10cm (4ins) long; 15cm (6ins) long overall. S.G. Brown Ltd was established in 1903 at an address on Dukes Lane, Chiswick by Sidney George Brown as manufacturers of scientific instruments. During WWI they were contracted to produce instruments for the war effort including gyroscopic compasses. During the inter war period the firm became well known for making radios, headphones, amplifiers etc. On the outbreak of WWII S.G. Brown Limited were contracted and financed for expansion by the Admiralty to produce of military instruments in particular gyroscopic compass assemblies. After the war the government retained control of the firm due to the importance of gyroscopic instruments in postwar defence programmes. In 1948 the principal operations were moved from Acton to a new site in Watford, Hertfordshire before being bought-out by the De Havilland division of Hawker Siddeley. S.G. Brown was later owned by Vosper Thornycroft which merged it with another of its companies, TSS (motion sensor and subsea pipe/cable tracker specialist) in April 2000 to develop underwater gyros. The current lot was designed for use on aircraft and is unusual in both having a spark-gap contact indicator and two sets of contacts. The enclosure of the assembly and provision of a window so that the spark can be seen suggests that the key was designed to be used in an application where a spark could be dangerous i.e. a hydrogen-filled balloon or airship. It has also been suggested that the second set of contacts may have served to allow indication of (and protection of the key from) static build-up within the aircraft or may have been an indicator of an incoming message as the key is in receive mode when at rest.