Admiralty Compass Observatory, 1842-1971

Record of laboratory experiments and calculations which eventually led to the development of the D-Type Mercury Control for the Admiralty Gyro-Compass, believed to have been written by Mr J C Hereford later in charge of the Gyro Test Room and subsequently the Sperry Gyro-Compass School, carried out under the superintendence of C Chaffer at the Admiralty Compass Observatory.