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A fine and rare George III mahogany mercury mountain stick barometer, Dollond, London, late 18th century The slender square section mahogany case comprising full-height lift-off front section secured by sprung clasps to the sides, the interior with slender silvered brass Vernier scale calibrated in barometric inches from 17 inches to over 32 inches divided into twentieths and annotated 18-32 to right hand margin, the left hand side with engraved signature Dollond, London over glass tube terminating with a cylindrical glass cistern with fixed ivory stopper to upper edge and threaded ivory tube-height adjustment screw to base engaging with a decoratively-turned threaded eye secured via an adjustable slide to the rear of the case, the exterior with chamfered slot behind the scale for viewing the tube from the rear, 98.5cm (38.75ins) high. Provenance: Private collection Hampshire (ref. B30); purchased from Asprey, London, 16th December 1987 for £1,500. Peter Dollond is recorded in Banfield, Edwin BAROMETER MAKERS AND RETAILERS 1680-1860 as born 1730 and died 1820. He was the son of John Dollond, a Huguenot silk weaver and started business as an optician in 1750. He was joined by his father in 1752 until his death in 1761, and then by his brother, John, until his death in 1804. The family business was continued by Peter Dollond's nephew, George Huggins, who changed his name to Dollond. George Dollond became instrument maker to William IV and Queen Victoria, exhibited at the Great Exhibition in 1851 and died 1856.Soon after the invention of the barometer in the 17th century it was observed that air pressure decreased with altitude. However, it was not until the latter part of the 18th century before an accurate mathematical relationship between height and drop in air pressure had been devised allowing barometers to be made with the intention of measuring altitude. The current lot is of relatively lightweight construction and the design of the cistern allows a degree of portability. This, coupled with the elongated scale (potentially allowing a range of around 15,000 feet to be observed), indicates that the instrument was clearly designed for mountain use and as such is a relatively early example of a mercury barometer made for this purpose.

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