Georgian Black Glass Artificial Horizon by Thomas Jones of London

For sale, a George III black glass artificial horizon by Thomas Jones of Charing Cross London.

This early example, is contained within a fitted mahogany case with hinged lid and hook and eye catches to the front. The inside of the lid retains its superb and original trade label for, “Thomas Jones (pupil of Ramsden), Astronomical and philosophical instrument maker to His Royal Highness The Duke of Clarence, 62 Charing Cross, London”. The exterior of the lid has a further paper label which contains writing which is now unfortunately obscured but seems to suggest an original owner.

The horizon is comprised of a solid brass tray with three adjustable screw feet for the purpose of levelling the instrument. The central section is routed out and fitted with a rectangular black glass plate which provides the reflective surface required for its operation. The underside is further engraved to, “Thomas Jones, 62 Charing Cross, London”. The bubble level provided with the instrument does not look original but is certainly a contemporary replacement consisiting of a glass cylinder enclosed at the top with sealing wax and a pearl like ball which moves freely within.

The history of the artificial horizon can be traced back to the sixteenth century but developments were largely popularised in the eighteenth century by John Hadley, John Elton and by the famous instrument maker, George Adams, the latter of whom is merited in 1738 with inventing the mercury trough of which this is a development intended to avoid the shake of the mercury encountered during the motion of a ship. It was devised as a means of navigation when the horizon was obscured by darkness or through the effect of inclement weather.

Its principle was based upon the first law of optics, that the angle of reflection from a mirror is equal to the angle of incidence, therefore a sextant would be employed to measure the angle between the sun or the stars and their reflection on mercury or a glass plate.

The maker Thomas Jones (1775 – 1852) was a superior maker of scientific instruments. Apprenticed to eminent maker of the period, Jesse Ramsden from 1789-1796 at a cost of 50 guineas, Jones continued to work for Ramsden until his death in 1800. Most sources have the firm’s working dates as starting in 1806 and references to work undertaken for Edward Troughton during this period would suggest that he worked as a jobbing instrument maker for the six years prior to opening his first premises in Mount Street. The history of the firm of Troughton & Simms also relates that Jones whilst working for Ramsden, provided the young William Simms with a supporting letter to The Royal Society for Simm’s “improved protractor” so we can be sure that a good working relationship existed. His first year of trading brought Jones’s first success in a commission from Mr HC Englefield to manufacture his new portable or “mountain barometer”. Englefield wrote that he had,

“Employed Mr Thomas Jones, of number 120 Mount St, Berkeley Square, pupil of the late Mr Ramsden, and who will furnish them at the price of two guineas and a half with the attached and detached thermometer”.

The barometer (although very rarely found on the market today) proved extremely popular, so much so that Jones wrote a pamphlet eleven years later in 1817 entitled, “A companion to the Mountain Barometer” wherein he states that “since its introduction in 1806 he had sold between 300 and 400 of these instruments”. It is also interesting to note that Jones signs himself off as, “Astronomical and philosophical instrument maker to his Royal Highness the Duke of Clarence” in this publication so he must have held the Royal Appointment for at least twenty years until William IV eventually died.

(Note: I have an Edward Troughton (pre-Troughton & Simms) Mountain Barometer of this type currently for sale if the reader is inte