Constructed principally in brass and in two finishes, clear lacquer and contrasting oxidised brass. The clock with silvered and die-struck 5” dial, roman chapter ring, winding square blued steel pear hands, signed by the maker “Negretti & Zambra,” London, eight day single chain fusee movement with pendulum having regulation adjustment, dead beat escapement, mechanically linked to the drum recorder, chart marker and barometer progression hammer. The 2½” diameter drum recorder moved at the base by a clock-driven helical gear acting on a circumferential gear at the drum base, spring loaded chart clips, the chart marking mechanism comprising a vertical guide bar with sliding marker carriage raised and lowered on a fusee chain driven from the barometer arbour, associated barometric scale calibrated in inches of mercury and mounted upon spring steel leaves to the top and bottom, the whole being caused by the clock to rotate through approximately 30 degrees bringing the marker into contact with the chart twice hourly.
The barometer with silvered and die-struck 5” dial, calibrated in inches of mercury with a range from 28 -31, marked principally to the upper portion in standard meteorological terms, “Stormy,” “Rain,” “Change,” “Fair,” “Set Fair,” signed by the maker “Negretti & Zambra,” the lower portion further marked “Scientific Instrument Makers, London.” Blued steel pointer driven by four 2¾” capsules, conventional C spring design.
The case with oblong slot accommodating the arbour driven fusee running on a pulley positioned on a crane. Timber base chassis with lacquered brass facings. The whole contained within an oak case, glazed drop-down front with lock and key. The rear backboards with opening door affording access to the clock. The entire mechanism retained in the case on four side mounted screws which, when removed, allows the mechanism to be withdrawn to the rear.
The larger or full size version of this instrument is often seen attributed to different makers and retailers. Given the obvious similarity in these large instruments it is reasonable to suggest manufacture by one maker, probably given the complication a clock maker. The names of many different makers and retailers appear on the dials, as yet the manufacturer remains unknown. This, the smaller variant, when it appears is invariably signed by Negretti & Zambra. It is interesting to note a number of changes made from the larger version, changes which arguably are improvements. Notably the drum being a smaller diameter and therefore less stable if left freestanding, is steadied by a spring-loaded top,
Essentially the clock drives three systems: the drum continuously, the barometer progression hammer twice hourly, and the marker system brought to the chart twice hourly. Timing of these operations is critical since the mechanical effort required for each is reasonably high. The complication in marking charts creates friction for the barometer, thus an arrangement driven by the clock causes a hammer to strike the chassis immediately below the pen rail – this ensures the barometer and marker pen follow any changes in barometric pressure. It is noteworthy that the standard type of barograph mechanism might have been easier to engineer.
The marking system originally was achieved using special paper easily marked by a bright brass pen housed in the sliding carrier. The original paper charts are now obsolete so an alternative had had to be found without altering the originality of the instrument. Trials with graphite were successful but a modified barograph nib cut to precisely the correct size has also been developed – this modification produces a clearly marked chart with good reliability. The ink nib is offered as an alternative to the graphite marker.
For all its complication, these are magnificent instruments. This one remains in essentially original condition having had the benefit of a complete service. The surface finishes to dials, metal parts and oak case are all original and in exceptional condition. This version by Negretti & Zambra is very rarely encountered – it is very much a collector’s piece.
Dimensions: 18″ wide x 12″ high x 8″ deep
Stock No: CP0609