Accession No
6538
Brief Description
fox-type dip circle, by William Wilton, plus manuscript letter from John George Children to Robert Were Fox, English, c. 1850
Origin
England; Cornwall; St. Day
Maker
William Wilton [maker] Robert Were Fox [designer]
Class
magnetism; earth sciences; metrology
Earliest Date
1846
Latest Date
1860
Inscription Date
Material
metal (brass, mercury, steel); glass; ivory; paper
Dimensions
173mm wide x 173mm deep x 205mm tall
Special Collection
Provenance
Purchased from Christie’s South Kensington, 85 Old Brompton Road, London, SW7 3LD. From the Travel Science and Natural History sale, 10/10/2013, lot 64.
Inscription
W. Wilton, St. DAY, Cornwall.
Description Notes
Fox-type dip circle, by William Wilton, plus manuscript letter from John George Children to Robert Were Fox, English, c. 1850.
6538.1: Dip circle. Circular box in vertical plane attached by neck to horizontal circular base. All brass. Tripod screw feet, inscription, nonius and vernier, bubble level all on base. Brass scale outer concentric ring 80o-0o-80o-0o divided to 10o, internal ring with dip circle attachment may be rotated with respect to outer scale, and read off using vernier 15o-25o-0o-15o divided to 1/4o. Circle box features tightly machined door with double glazed window. Half depth into circle box, concentric silvered scale 90o-0o-90o-0o divided to 10’. Full depth, blackened circular face with curved mercury thermometer across upper half. Thermometer ivory scale graduated from 10oF to 160oF and centigrade equivalents. Brass screw at each end and apex. Ivory thermometer scale chipped where screw has been inserted at apex. Steel magnetic needle at centre, resting in jewel cup bearing. Bearing held in place by 3 screws, small amount of solder on bottom left screw. Pointed needle, approximately 100mm, likely balanced by Fox [Royal Society Manuscripts, MS 257/574-577]. Brass pulleys on axis. Back of circle box, brass outer scale 90o-0o-90o-0o divided to 10o. Vernier 15o-25o-0o-25o-15o divided to 1/4o . Centre, brass wheels for adjusting needle position.
6538.2: manuscript, John George Children to Robert Were Fox, 17/**/1835, Falmouth. Letter concerning terrestrial magnetism observations taken with Fox-type dip circle, Ireland and Cumberland. Mentions D. Gilbert, Professor Barlow, Professor Christie, Sir John Franklin, Captain Sabine. See OHF for transcript.
Condition: good, complete.
References
Events
Description
Dip circles measure ‘magnetic dip’, the angle between the horizon and the earth’s magnetic field. The Fox-type was designed by Cornish industrialist, geologist, and physicist Robert Were Fox (1789-1877) and first set out in print in 1834. Fox’s design emerged from experiments into terrestrial magnetism in Cornish mines. Changes in magnetic dip also had practical value in the field of navigation, and in the 1840s the Fox-type became the standard instrument for Admiralty observations of dip at sea. The design was widely recommended for its stability and portability. Fox worked with a number of instrument makers but encouraged the production and development of his instrument by Cornish makers such as William Wilton - to the frustration of those outside Cornwall, keen to commission an instrument. Fox placed particular emphasis on balancing the needles himself.
This instrument’s maker, William Wilton (1801-1860), established in St Day, Cornwall in the 1830s and specialised in adapting mathematical instruments for use in mines. Fox was among the judges of a series of Royal Cornwall Polytechnic Society panels which awarded Wilton prizes for the quality of his work through the 1830s. From 1845 Fox and Wilton worked together on the Fox-type design, Fox describing Wilton as ‘ingenious’ and Wilton’s work ‘even beyond [his] expectations’. A Wilton Fox-type was exhibited at the 1851 Great Exhibition alongside mine-surveying instruments by the same maker. Despite Wilton’s parochial location in the little town of St Day his mining instruments can be found all over the world following in the wake of Cornish émigré miners and Admiralty navigators.
09/06/2014
Created by: Jenny Bulstrode on 09/06/2014
FM:47050
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