Accession No
0386
Brief Description
portable universal equatorial instrument, by W. and S. Jones, English, 1800 (c)
Origin
England; London; 30 Holborn
Maker
W. and S. Jones
Class
astronomy
Earliest Date
1800
Latest Date
1800
Inscription Date
Material
metal (brass, oxidised brass); glass; liquid
Dimensions
height 239mm; telescope length 200mm; breadth of base 129mm
Special Collection
Robert Whipple collection
Provenance
Purchased by Robert Stewart Whipple from Gertrude Hamilton (trading as 'Mercator'), Paris, on 09/04/1927.
Inscription
‘W & S, Jones, 30 Holborn, London’ (base)
Description Notes
Portable universal equatorial instrument or “Portable Observatory”. Brass. Telescope with crosshairs, held in bearings by arms secured by screws. Eye-piece in draw tube. Bearing mounts secured by knurled screws to support which pivots concentrically with declination semicircle, and carries clamping screw and central-zero vernier. Declination semicircle divided 90˚ - 0 - 90˚, numbered by 10˚, subdivided to 1˚, vernier gives reading to 5´; supported on bevelled ring which rotates on open right ascension circle, divided I - XII twice, numbered by I, subdivided to 4 minutes, vernier giving division to 1 minute. Right ascension circle carried by latitude arc, divided 90˚ - 0 - 90˚, numbered by 10˚, subdivided to 1˚, vernier giving reading to 5´; mounted on semi-column with clamping screw and central zero vernier. All mounted on horizontal circle, divided 0 - 180˚ - 0, numbered by 10˚, subdivided to 1˚, with 2 bubble levels, which rotates on flat tripod base with 3 levelling screws amd central zero vernier giving reading to 5´.
Condition good; complete
References
Events
Description
An equatorial instrument is a telescope set on a mounting that can rotate parallel to the earth’s rotation: this allows it to be turned with a single motion to track the movement of a star across the sky. This instrument was made around 1800 and is known as a ‘portable observatory’. It has crosshairs on the viewfinder for measuring the position of celestial objects.
Equatorial mountings are more complicated to manufacture than altazimuth mountings (which move separately in the horizontal and vertical axes). But equatorial mountings have the advantage that you can train the telescope on a particular celestial object and keep the telescope fixed on it for many hours as the earth revolves, only needing to adjust the mount in one axis of movement. Many equatorial telescopes had a mechanism to turn the mount automatically, powered by running water or, later, electricity. This one, however, needed to be turned by hand.
02/05/2008
Created by: Dr. Jenny Downes on 02/05/2008
FM:40160
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