A fine very scarce light oak cased barothermograph of Bourdon tube design by Negretti & Zambra No 4311 c1910

Barograph of conventional design driven from a 7 cell pressure sensor acting through levers, a drop link and spindle with micro adjustment for gain, polished aluminium recording arm and standard nib. Chassis mounted calibration stem. The 3¾” x 7¼” recording drum with 7 day movement, platform escapement, captive long tail key and regulation adjustment.

The thermograph driven from a single alcohol filled ¼ bourdon tube retained by an open oxidised brass sub frame and acting through a drop link  and primary lever, finely pivoted spindle with gain adjustment, polished aluminium recording arm with nib. Chassis mounted calibration stem.

All assembled over and between twin chassis raised upon turned columns.

Presented in a five glass light oak case, the hinged lid having bevelled top glass and securing hook. The inner case with maker’s plate marked “Negretti & Zambra, London.” Frieze drawer below.

Condition: The subject of a full service, conservation, and calibration under laboratory conditions, see performance chart from dynamic test. 

About fine, both instruments working correctly and well within the limits of accuracy required by domestic users. The metalwork retaining virtually all its original lacquered golden finish with little sign of oxidation or wear. The chassis with minor marks and an ink stain immediately below the recording arms and just below the drum. Replacements include both nibs and one recording arm. The oak case cleaned and re-polished, remains structurally sound with some fading to colour, and minor marks and abrasions.

Comments: Aesthetically by far the most interesting instrument of its class and era, this is a truly wonderful object, functionally very good and exceptionally hard to find.

This instrument has not only been serviced but completely disassembled to component parts, re-built to exacting standards including re-ground and burnished pivots, re-alignment of all moving parts setting the train for optimum resolution. This is reflected in the very accurate test results.

The glass removed from the timber case, cleaned and re-fitted. In all this is a beautifully re-conditioned instrument remaining virtually completely original condition.

The serial numbers are confusing since the oak case carries serial no. 1320 and the chassis no. 4311 – in common with a similar instrument in the Vavasseur Archive there is a number mismatch. The timber case is a bespoke case specifically intended for this instrument – in my view this is a much more accurate reflection of the numbers of these instruments built. The number applied to the chassis is far more likely to have been applied in series and to have included other types of instruments. Numbers noted for the almost identical instrument in the Vavasseur Archive are case 284 and chassis 2698, and a later version of this barothermograph, dating to around 1915-1920 with bi-metallic strip thermograph has no case number but chassis no. 30293. Clearly Negretti & Zambra did not build 30,000 or more of these instruments. Since the serial no. 1320 almost certainly included other instruments, perhaps standard barographs, thermographs, and others, it is not possible to properly deduce actual numbers produced.

At a listed selling price of £ 12 and 12 shillings, this was, for the catalogue year of 1910, a very expensive instrument and certainly not one for the mass market. The best guide to numbers produced might be made from other surviving instruments for which we know the volumes originally manufactured. Based on that data, I may conclude that probably total numbers of this instrument produced were in the low 100s.

As a collector’s piece and a fine example of this type of instrument, especially in a market which has become ever more selective, this piece is absolutely one to consider.