1200 GBP ($1495 USD)

An amazingly accurate double framed brass sextant by Thomas Jones c.1816


12 x 12 x 5 inches (30 x 30 x 12.5 cm.)




Thomas Jones

Country of manufacture

UK and Ireland

Categories: Navigational instruments, Calculating, Engineering antiques, Office Antiques, Patent & Salesmans Samples


A good double frame brass sextant in case with three eyepieces, 7 light filters (three round and four square), 2 solar filters (black and red), adjustment key and rare micrometer fine focusing to the vernier  (with lens and frosted glass).

Having an 8 inch radius arm with an 11 inch arc circle, the platinum scale runs out to 135 degrees in 0.2 degree increments using the patented dividing engine of “Thomas Jones, 62 Charing Crofs, London” (scripted signature) c.1816. 

Cleaned but NOT polished, this instrument has every screw and nut in place and has not been abused in any way. Locking radius arm with worm and screw fine tuning, the divisions of the scale are a marvel of engineering for the era c.1811. Sitting atop three tapering brass legs with a boxwood handle and harp shaped braces, the double frame is straight and true.

The entire instrument is intact and tight with it’s original keystone, mahogany case measuring 12 x 12 x 5 inches deep. All hardware intact, functional lock and key. Mirrors are in excellent condition, as are the filters. Three height adjustable eyepieces (sighting, low power and high power with cross hairs intact). The micrometer divided vernier (0-10 in twos ) can be read using the built in magnifying lens (on bridge with worm and screw adjustment)  to an incredible 1 arc second (100 feet or 30 m.- a boat length, or so the boast).

Thomas Jones was at 62 Charing Cross from 1816-1850, apprenticed to Jesse Ramsden in 1798, had numerous patents (including the dividing engine used for this instrument) and was instrument maker to the Duke of Clarence ( later George IV).

The instrument has a platinum scale because silver is too soft to cut such fine degree increments. This would have been the finest, most accurate instrument of it’s day, giving latitude and longitude to within 100 feet (like a modern GPS), anywhere in the world.


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CA ScientificaOpticae

Scientifica Opticae

Mark Hacking (Scientifica Opticae Inc.) has been an avid collector/dealer for over 30 years. A former Science teacher, he has an innate love for anything natural or mechanical. Specializing in optical (microscopes, telescopes), surveying, medical, weighing and drawing instruments, he is an active participant of the Scientific Instrument Fair in London. Living in Stratford, Ontario, Canada, with his wife and two children; Mark looks forward to meeting as many fellow collectors as possible, and has a worldwide following on eBay (Sciopti).

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