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35 Engine-Turned Silver Box Sextant

image of Engine-Turned Silver Box Sextant

I collect guilloche snuffboxes in gold and silver, often set with precious and semi-precious stones, frequently having enamelling over the guilloche. When I saw this instrument, I realised how well it would complement items in my collection, as the method of manufacture is the same.

Private Collection, West Midlands, UK

The outer case of this of this silver and gunmetal box sextant is remarkable in that it has been expensively decorated with a design produced by an ornamental turning lathe, such as those made in London by John Jacob Holtzapffel (fl.1793-1835). With its luxury, velvet-lined, gilt-tooled red Morocco case it is in marked contrast to the more utilitarian example exhibited nearby. It was clearly specially made to order, and was intended as a gift for either a dilettante or a lady.

It is also unusual in another respect: the scale is conventionally divided from 0º to 120º but above it is another scale divided from 210º to 120º. The index mirror, within the box, moves with the index arm, and coaxially below this is a fixed mirror. The instrument is furnished with two sighting holes on opposite sides, which can be alternately covered with a dark filter by sliding a pin on the side of the case. Although it measures angles by means of double reflection in the conventional manner, it can also measure much larger angles by using the ‘back sight’ method.

This unique instrument was made about 1810 and is signed ‘Troughton London’ and numbered ‘40’. When the noted instrument maker Edward Troughton (1756-1835) retired in 1826, he took into partnership William Simms (1793-1860).

The instrument maker William Jones (1762-1831) bought from the widow of George Adams (1750-1795) the rights to his Geometrical and Graphical Essays, and edited and republished it in 1797. On page 40 he describes the box sextant and gives the impression that its use in civil and military surveying was quite common although it had not been mentioned in the 1791 edition.


Objects lent by Anonymous Lender II, West Midlands, UK:

04. Beam Compass, by George Adams, London, 1757-60

13. Waywiser, by George Adams jr, London, between 1784 and 1796

37. Sextant, by Jesse Ramsden, London, c.1765

42. Hydrostatic Balance, by George Adams, London, c. 1760

50. Three Early Forms of Electro-Magnetic Demonstration Motor, English, c. 1835-40

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