French Scientific Pocket Barometer Altimeter c1890
Silvered and engraved 6cm dial, the reflector ring with settable index (reference to standard pressure 76 cmHg or Torr), the outer ring with meteorological terms “Tempête, Pluie, Vble, Beau, Très Sec”, the dial with dual concentric scales, the outer calibrated in cmHg (Torr) with a range from 57 to 79, approximately 22.4 – 31.1″ of mercury, the inner altitude scale marked “HECTOM.” (ie. 100s metres) having a range from 0 – 2800m, stations marked at 200m intervals and further divided to 20m increments. Rotating bezel with fine index. All set beneath a fine bevelled crystal.
Highest quality single capsule driven cantilevered movement with rack and pinion transmission, the chassis marked “746.” The whole contained within a high gloss japanned finish drum barrel-formed case fitted with extension and suspension loop. Together with its original black leather over timber red satin and velvet fitted case, the lid bearing initials “AB” in gold block, snap closure on a button release.
A very unusual instrument with a movement of superb quality, not an ordinary pocket barometer and probably intended for a scientific application. There are a number of aspects to this instrument that set it apart from the vast majority of others. The dial, though not especially remarkable, is fitted with twin indexes: the outer one actuated from the bezel is standard and enables a reference to be made to a starting pressure or altitude; it is the second or inner one that is most notable, this one is clearly designed for longer term pressure reference, here set at standard pressure 76cmHg. It may though be moved to any position, the operation is a simple one of removing the bezel and simply re-positioning the ring and index. The reader will note that the annotations are not centred for the instrument as one might normally expect, this is due entirely to the positioning of the standard pressure index.
The particularly high quality movement fitted to this instrument is of the type much more common in continental-made instruments. This pattern offers some real advantages over the type of standard movement found in the vast majority of English-made instruments, notably a reduction in friction. To be made to work well, though, requires finer making and that of course means a higher price. This movement might be consider amongst the most refined of its type that we have examined.
The japanned case finish, though not indicative of any particular application, is however noteworthy – this is expensive making and finely executed, almost certainly a special order.
Condition is generally good with only minor signs of handling and age related patination, the dial is crisp and vibrant in appearance, slight oxidation at the 77cm position, very minor marks radiating from centre to toward 61cm, only visible in critical lighting. The crystal remains clean and almost entirely free of marking, no chips or noticeable scratches. The case retains virtually all its original high gloss finish and depth of hue, minor marks to verso and circumference. The travel case with losses to finish at top and bottom, the circumference with much original lustre. The fabric interior clean, intact with good colour and vibrancy.
Dismantled, cleaned, serviced and calibrated under laboratory test conditions (see performance graph below).
In all, this is a very unusual and particularly fine instrument, very much a collector’s piece.
Dimensions: 3¼” diameter x 1⅜” height
Stock No: PB1521
Price: Not currently for sale – in Vavasseur Archive