¹ In Crow's Liquid Compass of 1813 the card was constructed as a float.Google Scholar

² Dry card compasses were still widely used in the Merchant Navy during the Second World War.Google Scholar

³ Commander (later Captain) the Honourable Chetwynd, L. W. P. was Superintendent of the Admiralty Compass Department from 1904 to 1912. There is a photograph of the instrument in this Journal 41, 328.Google Scholar

⁴ Webster's Third New International Dictionary, 1971 edition.Google Scholar

⁵ Although airship and balloon compasses are air navigation systems they are not discussed in this paper because of the virtual extinction of the species. Airship compasses were generally more akin to marine compasses than aeroplane compasses.Google Scholar

⁶ The abbreviation ACO is used in this paper to describe the Admiralty Compass Department, the Admiralty Compass Establishment, the Admiralty Compass Observatory, the Admiralty Research Establishment (Slough).Google Scholar

⁷ Samuel Franklyn Cody became, in 1908, the first man to fly in Great Britain. Born in the USA, he was a naturalized British subject.Google Scholar

⁸There is a photograph of the instrument in this Journal 41, 328.Google Scholar

⁹ Large numbers of British compasses were supplied to Britain's allies during the First World War but it was Germany which provided the nicest compliment. German aircraft shot down behind the allied lines were sometimes found to have a standard British compass acquired from an allied aircraft shot down behind the German lines. In 1918 the ACO was invited to advise the US army and navy on aircraft compasses. In 1913 the ACO designed a compass especially for the flying boat America which, but for the outbreak of war, would have been the first aeroplane to essay the Atlantic crossing. This instrument was one of the few aircraft compasses fitted with soft iron spheres to correct coefficients D and E. There is a photograph of it in this Journal 41, 329.Google Scholar

¹⁰ Lord Kelvin's company Kelvin and James White became Kelvin Bottomley and Baird in 1913. Many years later it merged with the other leading British compass manufacturer of that period, Henry Hughes and Son, to become Kelvin Hughes which is today a subsidiary of Smiths Industries plc.Google Scholar

¹¹ The Royal Aircraft Establishment at Farnborough was formerly the Royal Aircraft Factory and produced compasses designated with the letters RAF. To avoid confusion with the Royal Air Force (formed in 1918) the factory is herein designated RAE.Google Scholar

¹² See McMullen, J. A. (1933). Simplified Aerial Navigation. Charles Griffin and Co.Google Scholar

¹³ Tests on the Pro compass showed that it could be read at angles at which the parallax was 6°.Google Scholar

¹⁴ See Hughes, A. J. (1946). History of Air Navigation. Allen & Unwin.Google Scholar

¹⁵ More common than was realized as this anecdote shows. At the time of the Salerno landing the writer was flying to the north of Sicily when a Spitfire pilot who sounded very close broke radio silence to request a vector to the nearest allied airfield. He was given a vector of I85° but the D/F station seemed concerned that he was going further away. It was late afternoon. D/F: Is the Sun to your left or your right? Pilot: To my left. D/F: Steer reciprocal. The D/F station's quick recognition of the problem, its adept handling of it, shows how familiar it was.Google Scholar

¹⁶ Air Vice Marshal Oulton (see acknowledgements) writes ‘I do not agree - taking the whole span of fighter operations - that the vertical card would have been better. We changed from the vertical card to the P₄ because for many operations, such as reinforcing flights, photographic reconnaissance and flights involving a rendezvous, it was necessary to steer more accurately than was possible with a P₃ which in the circumstances of stress and discomfort to which you refer would be useless anyway’.Google Scholar

¹⁷ Photoelectric systems were employed during the Second World War in German and Italian compasses intended primarily for small fast surface vessels.Google Scholar

¹⁸ In 1944 a British requirement was stated for a compass capable of driving an Air Position Indicator in aircraft too small for a DRC (Section 7). The Magnesyn developed insufficient torque and was otherwise unsuitable. An aeronautical version of the Admiralty Transmitting Magnetic Compass was developed around a P8 (section 1) as master unit and some installations were made in Fleet Air Arm aircraft of the ATMC Mk III as it was known.Google Scholar

¹⁹ However, Alfred Hine, in his magisterial Magnetic Compasses and Magnetometers attributes the basic patent of the Fluxgate (Pioneer) and Flux valve (Sperry) to H. Antranikian in 1936. U.S. patent 2047609.Google Scholar

²⁰ Graphically illustrated in Calvert's, B. J. Presidential Address of 1984. This Journal 38, 2.Google Scholar

²¹ Without a visible horizon, pitch or attitude still could only be inferred from a comparison of tachometer and air speed indicator readings.Google Scholar

²² The setting of the screws, spaced at intervals of 15°, distort a flexible metal strip which acts as a kind of cam, the contour of which determines the deviation of then needle from the uncorrected heading.Google Scholar

²³ AP 1275B Vol 1 Sec 3. Chapter 7 para 17 (amended to AL 111).Google Scholar

²⁴ In some models the precession control was d.c., replaced by an a.c. system because of the undesirability of steady magnetic fields on the flight deck.Google Scholar

²⁵A typical modern standby compass, the E2B, is illustrated in this Journal 41, 334.Google Scholar