Signedon wind rose: A. J. FROST / 6, WESTMINSTER CHAMBERS, LONDON
Inscribedon wind rose: LATIMER CLARK'S / PATENT
on wind rose: No. 1036
FunctionAn astronomical transit is used with a clock to measure the altitude and time that a star or celestial body crosses the meridian at a specific location. This gives the declination and right ascension of the star, which are that star's coordinates in the sky. The information can also be used to find the longitude of a location if one has knowledge of when the meridian crossing would happen at the zeroth longitude.
If one has a table listing when a particular star is to cross the meridian at a given location, one can use the transit to find the time at that location at that moment. For this reason, small table top transits were often used by watchmakers to check the running of their watches and clocks.
Medium-sized and larger portable transits were used in the field by astronomers when they went on expeditions to observe an eclipse or Transit of Venus.
Historical AttributesLatimer Clark, F.R.A.S. developed his patent transit to make timefinding by the sun or stars simple for people who wanted to check their watches and clocks. He published a "A Treatise on the Transit Instrument as Applied to the Determination of Time" in 1882. The instrument was manufactured and advertised by A. J. Frost. It came in two sizes: a 19-inch and an 18-inch. This is the larger one, which retailed for £14 13s 0d in 1886.
The Harvard College Observatory acquired the transit in the late 19th century. In 1950 the instrument was being used in the Students' Astronomical Lab at Harvard. It later went to Harlow Shapley, director of the Observatory from 1921-1952. It was transferred to CHSI from Shapley's office in 1969.
Primary SourcesLatimer Clark, The Transit Instrument (London: Latimer Clark, 1882).