Airy's Transit Circle. There are parts marked AST0991.1-66 which can be found via the Whole/Part toggle. Object glass 8.1 inches aperture, 11 feet 7 inches focal length, magnification 195 (180 for the Sun). Eye-end: originally 7 vertical fixed wires & 1 horizontal wire movable by micrometer; 6 additional vertical wires added in 1854 with introduction of chronograph to give 9 wires for galvanic registration & 7 for 'eye-and-ear': in 1891 a 10-wire galvanic system was introduced to simplify arithmetic: travelling wire micrometer fitted in 1915. Bohenberger nadir eyepiece for ascertaining level errors. Handle by window replaced by conservation department.