Negretti & Zambra Weather Watch No R/411 c.1920

This is a very good gilt lacquered brass weather watch aneroid pocket barometer forecast prognosticator No R/411 by Negretti & Zambra, London, c1920. Weather watch pocket barometer having 2” tri-concentric silvered and die struck dial, the outer part calibrated in inches of mercury with a range from 28” – 31” and divided down to 1/10th”, the lower part marked Direction of Wind with compass points and “Dead Calm.” The inner part, rotated from the crown, with short altitude compensation scale to top, three apertures for falling, rising and steady pressure revealing the Arabic letter codes, “N&Z” logogram, “Patent 6276/15,” serial no. “R/411,” and signed by the maker at lower part. Blued steel pointer, bevelled glass. Standard Vidie pattern movement driven from a single 1” nickel alloy capsule tensioned on a C spring, contained within a semi barrel form case with engine turned finishers, the verso with interpretation guide and calibration port, the case side with Whiteside-Cook pattern altitude correction scale from sea level to 3,000ft. Pendant and bow. Presented with its correct oxblood leather over timber, green velvet lined case having celluloid interpretation disk within lid. Snap closure on a button release. Condition: The subject of a full service, conservation and calibration under laboratory conditions. The movement working well with good sensitivity and progression, yielding easily acceptable accuracy across the range 28” – 31” inches Hg, see performance chart from dynamic test. The dial clean and bright, some ageing; the brass case retaining a very good proportion of original finish, again some slight ageing and minor losses. The altitude setting working correctly with good resistance, crown operated forecasting dial centre smooth in operation. The instrument mechanically good in all respects. The leather case sound, some play in the hinge though perfectly serviceable. The leather covering intact even across the release button which is unusual, the lid outside marked with impressions, the forecast disc a replacement taken from an original Negretti & Zambra pocket forecaster. Comments: This is the Rolex of the pocket barometer world, probably the single most sought after and iconic instrument of this type. Certainly the had-to-have device of the day though the price probably restricted the market somewhat which might explain the very few that are seen to-day. These instruments were developed from meteorological data collected over 13 years – N&Z claimed around 80% success in an accurate forecast, if the instrument operated correctly. These instruments are occasionally seen and should be considered scarce, particularly complete with correct case, and this condition very hard to find. Overall this is a good instrument and worthy of any collection. Nb: The original instructions shown are in the Vavasseur Archive – a copy will be provided with this instrument. How a Weather Watch Works: You will need to observe the barometer over a few hours to determine rising or falling pressure or if it remains steady. You will need to know the wind direction and the season. Operation is simplicity itself: 1. Set the wind direction by rotating the bezel aligning the small black arrow with the correct compass point 2. Rotate the crown causing the centre upper dial zero point on the semi-circular altitude scale to align with the barometer pointer 3. Read from one of three viewing ports relevant to season, S-Summer/ W-Winter, and pressure condition, Rising, Falling or Steady 4. Refer to interpretation disc in case lid or verso of instrument, the letter denoting one of 26 different prognostications