An important, very early, fine, silver-cased pocket barometer by Negretti & Zambra, London, No 575, hallmarked for 1863

Pocket barometer with finely engraved 2” silvered dial signed “Negretti & Zambra, London,” with instrument serial no. “575,” single scale 16-31 inches of mercury, equating to approximately 18,000ft altitude, and fine blued-steel pointer. Rotating bezel with fine index point. Bevelled crystal. Substantial deep open-faced English silver case with compensation port to rear having sliding dust guard. The bow with hallmarks for London and date letter “h” for 1863. Fine first quality movement.

This is an extraordinary instrument in almost all respects. Manufactured in 1863 it represents one of the very first of its type. Negretti & Zambra had only just filed the patent (1861) for the pocket watch-sized barometer, and this is one of the first. The movement exhibits some very early characteristics: the primary lever is loaded with a Vidi-style coil spring; provision is made for three adjustments – rate of deflection, temperature compensation and, most unusually, capsule tension; the secondary lever clearly is fitted with a bi-metallic compensation device though this is not stated on the dial (the principle of temperature compensation was very much in its infancy at this time). The chassis is most unusual in that it is milled to accommodate the close proximity of certain component parts – presumably this afforded a lower profile for the movement as a whole. There are many and extensive embellishments not present in most other movements: a finely cut and contoured primary lever; blued set screws; extensive gilding of components; and decoration of the chassis. The dial must also be mentioned, since this is not of the traditional flat plate form.  It has a deep circumferential return locating it snugly into the silver case.

The dial almost perfect, save two very slight marks only visible in oblique light; the case with minor hazing overall, essentially dent-free; crystal with a very small chip to the bevelled edge; very clean and crisp overall.  Clear, well-struck silver hallmarks. This pocket barometer is in excellent and completely original condition, with good sensitivity and progression.

Precise use for this instrument is unclear as the extensive barometric range is calculated only in inches of mercury.  It might be considered a special order placed with the maker for use in scientific research.

Negretti & Zambra, founded in 1850 as makers of scientific instruments, were the most prolific and leading makers of all types of barometers during the second half of the 19th century and into the early 20th century. The partnership exhibited at the Great Exhibition at the Crystal Palace in 1851 and won a Prize Medal. Negretti & Zambra held the appointment of instrument-makers to Her Majesty Queen Victoria, Prince Albert and Edward VII, the Royal Observatory and the British Admiralty (see Banfield, Edwin, Barometer Makers and Retailers, 1660-1900).