The Airy Transit Circle was installed under the direction of George Airy to supersede the separate transit instruments and the mural circles still in use in the 1850s. The new instrument allowed the observer to obtain measurements of both right ascension and declination of a celestial object on the same meridian transit. The purpose of these observations was the production of raw data for the compilation of the star catalogues. The Airy Transit Circle was in operation from 1851 to 1954 although much work done began to be done on alternative instruments from 1920-30s. The principal one of these was the Cooke Reversible Transit Circle which was dismantled and reinstalled to continue work at Herstmonceux whilst the Airy Transit circle remained as museum piece at Greenwich. It appears the CRTC was being used consistently from 1936 and the Airy TC was last used regularly in 1954. Detailed information about the construction of the transit circles and process of making the observations may be found in ''Greenwich Observatory: Volume 3: The Buildings and Instruments'' (Taylor and Francis; London, 1975).