A RARE AMERICAN WALNUT CASED MERCURY 'UNION' BAROMETERCURRIER AND SIMPSON, THIRD QUARTER OF THE 19th CENTURYThe ogee moulded rectangular glazed case enclosing syphon tube with large mercury bulb reading against a scale calibrated in barometric inches with Vernier with up-down adjtment in tandem with the entire Fahrenheit scale mercury thermometer positioned to the left hand side via a knob to the base of the case, the upper margin stamped CURRIER & SIMPSON, PAT'D JAN 31. 1880 the top of the case with valve for closing the top of the mercury tube to the atmosphere, the rear with pasted paper label providing instructions for e.39cm (15.5ins) high, 13cm (5ins) wide.Provenance: The exhibition collection of Barometer World Meum, Merton, Devon.Surprisingly little appears to be recorded regarding Simpson and Currier, however the current lot was apparently devised as a small portable form of mercury barometer no doubt targeted to frontiersmen amongst others. The instrument utilises a sealed bulb cistern part filled with air connected to a short column. Change in barometric pressure will naturally cae the mercury column to move but also will a change in temperature. In order to allow for the effect of temperature the level of mercury in the thermometer tube has to be first aligned with that of the barometer tube; the Vernier (which is directly connected to the movement of thermometer) will then provide the reading in barometric inches.