watchmaker's transit

Datecirca 1870

Inventory Number1997-1-1933

ClassificationTransit

Subject

Maker J. Short fl. 1870

Cultural Region

Place of Origin

Place of Use

Dimensions33 × 26.5 × 11.5 cm (13 × 10 7/16 × 4 1/2 in.)

Material

DescriptionThis small brass transit is supported by a cast iron base. The base consists of two fixed feet and a leveling screw. Two columns rise from it, supporting a tube on which is fixed the telescope (optics missing) at one end and a vertical, divided circle and vernier in the center. The scale is made of four 0-90° quadrants divided in degrees and half degrees. Under the vernier a bubble level (missing) would have been attached with the two screws.

On the center column are two thumb screws used to finely adjust the level. A tangent screw is used to finely move the divided circle (and hence the telescope). A thumb screw is also used to clamp in place the divided circle. Towards the telescope, two screws are used to finely adjust the horizontal position of the supporting tube.

In Collection(s)

Exhibit 2008--The Matter of Fact

Signedon the top of the barrel, engraved: J. SHORT, LONDON

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 (like this one) 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.

ProvenanceFrom the Agassiz station, Harvard University (Harvard, Mass.)