A rare and potentially important mahogany cased balloonists barometer Henry Negretti, London, cir

A rare and potentially important mahogany cased balloonists barometer Henry Negretti, London, circa 1845. The shallow arch top glazed front case with cavetto moulded edge to front door enclosing a Guy-Lussac type of wide bore syphon tube with a Bunten air trap mounted against an adjustable ivory scale calibrated from 5 to 31 inches, with manual vernier and signed H. NEGRETTI, 19 Leather Lane, HOLBORN to upper edge, 97cm high overall, B.C. Ref. 100. Illustrated in Banfield, Edwin BAROMETERS Stick or Cistern Tube page 201 and described on page 203. Henry or Enrico Negretti is recorded by Banfield as working from his 19 Leather Lane, Holborn address in London 1845-9 after which he formed a partnership with Joseph Warren Zambra establishing the prolific firm of Negretti & Zambra which operated throughout the second half of the 19th and into the 20th century. This barometer has a scale calibrated from 5 to 31 inches which could record altitudes up to 40,000 feet. The scale is adjustable via an ivory knob half way up the scale in order to zero it against the mercury level in the cistern via a brass pointer before a reading can be taken. The vernier only covers the normal 27-31 inch range of barometric pressure. Banfield suggests that this barometer, due to its ability to measure very high altitudes, was probably used for early balloon experiments and comments that Negretti was an acquaintance of James Glaisher the well known balloon pioneer. Glaisher was known to have run an experiment to compare two of Negretti & Zambras aneroid barometers with a syphon tube mercury barometer at pressures down to 7 inches and Banfield conjects that the current example could well have been used for these experiments.