Accession No

0426

Brief Description

sextant-type navigational instrument, invented by A. Thompson, 1800 (c)

Origin

Maker

Thompson, A. [inventor]

Class

dials

Earliest Date

1800

Latest Date

1800

Inscription Date

Material

metal (brass)

Dimensions

length 308mm; breadth 212mm; thickness 35mm

Special Collection

Robert Whipple collection

Provenance

Purchased by Robert Stewart Whipple from T.H. Court in 05/1927.

Inscription

‘Invented by A.Thompson’
‘O or * Altitude’ (on index arm’s racked companion)
‘C Altitude’ (on fixed arm’s companion)

Description Notes

Unusual sextant-shaped instrument, brass arc divided 0-120o by 1o, subdivided to 20’, on brass. Index arm with clamp, tangent screw and type-B vernier, arm divided 5-90, and has racked arm alongside. Fixed arm, similarly divided, has sliding arm divided 0-60 in linear scale. Three brass feet. Central threaded hole for handle (missing). Instrument for longitude ?

References

Events

Description
Quadrant
A quadrant is a quarter of a circle, and there are different types of instrument that come under that description. The size of quadrants varied hugely from Tycho Brahe’s highly successful huge 2m radius one, to the more portable versions of the 18th century. In all examples it was important to keep movement, wear and flexure to a minimum, especially if results were to form part of an extended research program and to be compared with one another.

The quadrant was the principle measuring instrument of astronomy in the 17th and 18th centuries, being used in all major observatories. Plain sights (where the angle was simply read off by eye) were replaced by telescopic sights in more sophisticated examples.

18/10/2002
Created by: Saffron Clackson on 18/10/2002

FM:43368