4 Inch Miniature Vernier sextant by Jesse Ramsden
Very small 4 inch vernier sextant by Jesse Ramsden. London
Type of object:
Sextant
Time period:
Britain rules the waves + France
Place:
London
Date:
1792
Maker / Author:
Jesse Ramsden ( 1735-1800)
Publisher / Printer:
idem
Dimensions:
18 cm
Material:
Brass and glass
Graduation:
0-140°
Inscription:
Ramsden London, upside down
Provenance:
England
References:
Letter from Piazzi to Lalande 'on the instruments of Ramsden' in Jérôme de la Lande, Description d'une machine pour diviser les instruments de mathématiques par M. Ramsden...traduite... par M. de la Lande, Paris 1790.
W. F. J. Morzer Bruyns, Sextants at Greenwich..., Oxford & Greenwich 2009. See pag 173
McConnell, Anita, 2007, 'Jesse Ramsden (1735 – 1800) London's Leading Scientific Instrument Maker', Hampshire, Ashgate Publishing Ltd.
Description
A MINIATURE 4IN. RADIUS SEXTANT BY RAMSDEN, LONDON,
CIRCA 1795 constructed from lacquered brass, signed on the T-frame
as per title (upside down!), the arc divided to 140°, vernier with magnifier,
secondary mirror adjustment switch, index mirror and two shades, brass pin feet, contained within fitted keystone box with detachable lid and containing two sighting tubes.
According to Piazzi, Ramsden made sextants from 15inches radius down to 1.5 inches, but very few of the smaller sizes are known. A 5. 25 inches radius instrument employing a similar simple crossed-strut frame however is conserved in the Royal Museums of Greenwich (see Morzer Bruyns, 173 N° 150). Particularities of the present instrument are its lack of shades for the horizon mirror, the removable index shades, the absence of a handle or provision for attaching one or otherwise mounting the instrument, and the use of Peter Dollond's 1772 extended lever and rising piece for adjusting the horizon glass. The small size of the instrument and these peculiarities suggest that it may have been intended for non-marine use, but since it is currently without parallel in the corpus of Ramsden's sextants, there can only be speculation as to what this use might have been.
Additional information
Jesse Ramsden FRS (1735 – 1800) was one of the leading manufacturers of scientific instruments in the latter part of the eighteenth century, apprenticed unusually late to the industry at the age of 21, to Mark Burton, mathematical instrument maker in Denmark Street, in the Strand. Ramsden had previously been apprenticed to a cloth worker, although abandoned this trade when he apprenticed himself to Burton in 1756.
Swiftly gaining a reputation, Ramsden began trading under his own name by 1763. It was at this time that he developed a life long association with the Dollond family. Ramsden was undoubtedly influenced by and learnt from John Dollond, who had famously invented and patented 'the achromatic lens'. When Ramsden married Dollond's daughter, Sarah, he subsequently acquired a profitable share in this patent. Opening a shop in Haymarket, near Little Suffolk Street, Ramsden traded under the sign of the Golden Spectacles
