Y A WILLIAM IV ROSEWOOD CASED SYMPIESOMETERDOLLOND, LONDON, ...

Estimate

£500 - £700

Y A WILLIAM IV ROSEWOOD CASED SYMPIESOMETERDOLLOND, LONDON, CIRCA 1830The glazed rectangular case with concave upstand and cavetto cornice to pediment above rectangular silvered scale inscribed Improved Sympiesometer nest to the applied central siphon tube filled with pink-stained oil incorporating low cistern bulb to the left limb beside tube terminating with a further sealed bulb at the top, the left hand margin with mercury tube Fahrenheit scale thermometer, opposing vertical scale for degrees Fahrenheit ranging between 10 and 110 set behind slide with scale annotated for barometric inches 27-31 and with the usual weather observations to the right, the upper edge of the slide fitted with angled brass pointer for calibration against the temperature scale behind and with rack-and-pinion screw adjustment via a brass knob to the exterior of the case, the lower edge with recessed circular level recording disc labelled Register, engraved with barometric scale visible through an arched aperture in the plate and manually adjusted via projecting rim to the left hand side of the case, the lower margin signed DOLLOND, LONDON.59cm (23ins) high, 7.5cm (3ins) wide. Provenance:The Dr. Castle Collection of barometers and other weather instruments. Purchased at Bonhams, London sale of FINE CLOCKS Wednesday 7th July 2016 (lot 7) for £1,820.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 surname to Dollond. George Dollond became instrument maker to William IV and Queen Victoria, exhibited at the Great Exhibition in 1851 and died 1856. The firm became one of the largest makers and suppliers of scientific and optical instruments and continued trading under various guises throughout the 19th and 20th centuries.The sympiesometer was invented by Alexander Adie of Edinburgh in 1818 and is essentially an improved version of Robert Hooke's thermobarometer which was subject of a paper presented to the Royal Society in 1668. The instrument works by having a syphon tube filled with liquid open to the air at one end and with trapped gas at the other (sulphuric acid and hydrogen were used in later sympiesometers). As barometric pressure increases the liquid will be forced down the tube causing the gas to be compressed, resulting in a change in level in the tube; however the volume of the gas changes with temperature so before a reliable reading can be taken the instrument would first need to be calibrated by adjusting the position of the movable barometer scale in relation to the temperature scale behind to reflect the reading provided by the thermometer. The sympiesometer was conceived by Adie as an alternative to the mercury marine barometer as it was smaller and believed to be less susceptible to the motion of a vessel at sea.

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