A MAHOGANY CASED ADIE-TYPE SYMPIESOMETERPHILIP COLLINS, MERTON, LATE 20th CENTURYThe glazed rectangular case with ogee-moulded pediment above rectangular silvered scale inscribed Adie's Sympiesometer over applied central siphon tube filled with red-stained almond 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 0 and 160 set behind slide with scale annotated for barometric inches and with the ual 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 sliding adjtment via a brass knob to the exterior of the case, the lower edge with recessed circular level recording disc labelled Yesterday, engraved with barometric scale visible through an arched aperture in the plate and manually adjted via projecting rim to the left hand side of the case, the lower margin inscribed Made by, P. Collins, Merton over conforming inverted ogee moulded base.65cm (25.5ins) high, 8cm (3.25ins) wide.Provenance: The retail stock of Barometer World Meum, Merton, Devon.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 ed in later sympiesometers). As barometric pressure increases the liquid will be forced down the tube caing the gas to bepressed, 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 adjting 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 sceptible to the motion of a vessel at sea.