Images(6)

astronomical transit

Datecirca 1885

Inventory Number1997-1-1943

ClassificationTransit

Subject

Maker A. J. Frost fl. 1880 - 1890

Inventor Josiah L. Clark 1822 - 1898

User Students' Astronomical Laboratory, Harvard University 1903 - c. 1953

User Harvard College Observatory founded 1839

User Harlow Shapley 1885 - 1972

Cultural Region

Place of Origin

Dimensionsoriented vertically: 52.7 × 37.7 × 15.6 cm (20 3/4 × 14 13/16 × 6 1/8 in.)

Material

Bibliography

The Transit Instrument

DescriptionThis is the large, 18-inch Latimer Clark transit. The base is of cast iron, with 5 large brass leveling screws (and a place for a 6th). The axis is of gun metal, with the trunnions resting on gun-metal bearings. The altitude circle is on the side. It is brass with a silvered scale. The scale runs 0-90-0-90-0 degrees and has a vernier reading to single minutes. A spirit level is attached to the vernier. There is provision for ordinary axial illumination.

The telescope is made of gun metal. It was furnished with a diagonal eye-piece (currently missing). There are three spider-web cross-wires, with colllimating screws. The objective has a dust cap.

Missing are "two dark glasses for solar observation and a delicate striding level" as advertised by the maker. The illumination of the cross-wires at night was effected by a front reflecting diaphragm, and the instrument came with a candle lantern carried on an adjustable support (both missing).

Signedon wind rose: A. J. FROST / 6, WESTMINSTER CHAMBERS, LONDON

Inscribedon wind rose: LATIMER CLARK'S / PATENT on wind rose: No. 1036

Curatorial RemarksA copy of Latimer Clark's treatise is in the CHSI library (4040) and photographs of it are in the file.

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.

ProvenanceHarvard College Observatory, late 19th century; transferred to CHSI 1969.

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.