A RARE VICTORIAN EBONISED MITCHEL PATENT BAROMETER OR 'DIFFERENTIAL BAROMETER'R.H.C. WILSON, LONDON, CIRCA 1875The oil filled tube with sealed cistern formed as a radially corrugated capsule set behind a panel inscribed with monogram HB over inscription DIFFETRENTIAL BAROMETER the upper section with slightly enlarged scale calibrated in barometric inches incorporating rack-and-pinion adjting recording pointer set beside a FAHREN'T and CENTIG'E scale mercury thermometer, the upper margin inscribed R.H.C. WILSON, 12 WILSON ST, GRAYS INN, LONDON and the case with Greek style shallow triangular pediment opposing cavetto moulded underside. 32cm (12.5ins) high, 11cm (4.25ins) wide.Provenance: The exhibition collection of Barometer World Meum, Merton, Devon.Robert Henry Capel Wilson is recorded in Banfield, Edwin BAROMETER MAKERS AND RETAILERS 1660-1900 as working from 12 Wilson Street, Gray's Inn, London 1873-91 and 37 Gough Street, London 1871-80; he joined the firm of Pastorelli and Rapkin in 1893.The design of the current barometer utilises the effect that a change of barometric pressure would have on a sealed disc-shaped corrugated metal chamber. Although the chamber resembles that of an aneroid barometer the instrument utilises fluid (oil) which, via a glass tube rising from the chamber, provides a level from which readings can be taken. It is thought that the patent for this type of barometer was filed in 1863.