This is one of the earliest forms of electrical transmitting compass. By the early twentieth century, finding good compass positions on ships had become increasingly difficult. One obvious solution seemed to be to design a transmitting compass, with a relatively large master compass held in a position where there was space, but able to transmit its readings to small repeater units placed anywhere in the ship where they might be needed.
Siemens took out a patent for this system in 1902 (patent no. 16979), which seemed to offer a greater hope of success than designs suggested in the previous half-century. The Siemens design operated using a Wheatstone bridge in which resistances were varied according to temperature. The master compass card had a segment cut out of it and had a heat source (an electric glow lamp) placed above it. As the master card moved, the heat from the lamp changed the resistance in circuits placed below the card, thus altering the electrical currents that were trasmitted to repeater units. As a result, the compass cards of the reapeater units aligned with the card of the master unit.
The design was shown at the St Louis Exhibition of 1905, after which the Royal Navy bought one for £1,400 and fitted it into HMS 'Dreadnought'. The master unit was fitted into the lower steering position, with repeaters in the conning tower and at the steering engine. Initial tests were promising, and a second system was bought in 1908 for the 'Bellerophon'. Subsequent testing, however, proved less satisfactory, with the navigating officer of the 'Bellerophon' complaining that he was 'sorely affected by that electrical compass'. By 1913, the Royal Navy had decided against adopting the system.
Siemens had also produced an improved version of the transmitting compass in 1909, which was fitted in German submarines, but the British Admiralty decided against testing the improved system.
Bowl-Dia.105" (26.7cm) Black painted brass with unpainted brass top. Electrical mechanism can be seen through glass top. a black lubber line is engraved on underside of an oval piece of glass set in brass top. Mounted in a black and white painted brass gimbal ring 13" (33cm)
Card-Electrical elements
Binnacle-Dia. of top 17" (43.2cm) Dia. of pillar 13" (33cm) Brown painted metal pillar with brass urn mounted on top. Urn has heavy brass sphere brackets attached with black painted wooden spheres. Hood consists of a heavy brass ring with a large copper top.