Images(3)

astronomical transit

Datecirca 1790

Inventory Number5006

ClassificationTransit

Subject

Maker American

Cultural Region

Dimensionswith telescope horizontal: 29.5 × 44.6 × 42.2 cm (11 5/8 × 17 9/16 × 16 5/8 in.)

Material

AccessoriesLarge brass key for tightening joints

DescriptionThis astronomical transit consist of a brass frame that supports a small transit telescope and a hanging level. The workmanship is extremely high, but the design is rather idiosyncratic.

The brass telescope has 3 parallel cross hairs. The tube is 42 cm long. There is a sliding shutter to protect the objective and a pressure-fitting aperture stop to protect the ocular. The tube is held in two rings that attach to a bracket mounted on a spring, which is attached to the horizontal axis. A counterweight is suspended directly below the telescope. The weight is cylindrical and threaded on a vertical screw.

The horizontal axis also supports a hanging bubble level. The level consists of a brass box with a glass tube inserted. It has fine adjustment screws at one end.

The brass trunions have fine adjustment screws to shift the telescope axis. The clamping bolts are key driven. The brass key has a square socket and a large heart-shaped head.

The brass trunions (20.5 cm high) are mounted on a "I" shaped platform that may rotate on a larger platform (31.5 cm wide) of the same shape. The platforms are cast brass. The smaller platform has a pointer on one side; the larger platform has two arcs below the pointer. The smaller platform is shifted by means of two fine adjustment screws in brackets on the larger platform.

The brass platforms are attached to a thick mahogany base with two semi-cylindrical cut-outs on each end. The base is 5.8 x 45 x 15 cm.

Signedunsigned

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.

ProvenanceDavid Wheatland purchased from Saul Moskowitz, Marblehead, Massachusetts, May 7, 1974. Donated to CHSI May 1977.

Historical AttributesThis appears to be a colonial American piece of work striving for precision and attempting to match English style. Some parts are not necessary, but the workmanship is high.