Accession No

2123

Brief Description

reflecting circle, Troughton.E, 1805 (c)

Origin

London; England

Maker

Troughton.Edward

Class

navigation

Earliest Date

1805

Latest Date

1805

Inscription Date

Material

metal (brass, silver); glass; wood

Dimensions

box 1 length 345mm; breadth 240mm; height 142mm box 2 length 355mm; breadth 345mm; height 147mm; reflecting circle height 530mm; diameter of circle 317mm

Special Collection

Provenance

Transferred from Institute of Astronomy, University of Cambridge, Cambridge, England.

Inscription

‘Troughton London’
‘163’
‘CAMB OBS Refl:Circ:’ (on limb)
‘Camb Obs. Refl Circ’ (on telescope)
‘Camb. Obs. Refl. Circ’ (on pillar)
‘Camb: Obs: Refl: Circ.’ (on foot)

Description Notes

Brass reflecting circle, lattice type frame. Index mirror. Telescope sights. Horizon glass. Two sets of 3 shades. Three index arms, each with mount for reading microscope and type-B vernier on silver, one with clamp and tangent screws. Reading microscope. Silver scale, 720˚ divided by degrees, subdivided to 20’, and part numbered 160-0-160. Wooden handles. Brass pillar stand, with counter-weights, three radial feet with levelling screws. Instrument may be mounted on stand from either side. (Found later:) 2 fitted wooden boxes, 2 additional eyepieces, 1 telescope, 1 dark tube, 1 brass piece.

Condition: good.

References

Events

Description
As made by Edward Troughton from 1796, the reflecting circle is a modification of the repeating circle developed earlier in France. The optical arrangement is similar to that of the sextant, where the image seen directly through the telescope is brought to coincide with the same image seen by reflection in the mirror fixed to the index arm then in the half-silvered horizon mirror. The index is then clamped and the bearing read off to great precision, with the aid of the vernier and the small microscope.

Presented to the Whipple Museum by the Institute of Astronomy, University of Cambridge.
04/08/2008
Created by: Dr Anita McConnell on 04/08/2008

FM:39662