Watkin Patent barometer having finely engraved and silvered 3½” brass dial with tri-concentric altitude and barometric scales, reading indicator set at 6 o’clock, calibrations from 24-31 inches of mercury and from 0–7,000ft, “Watkin Patent” in an arc above the centre with “Compensated” and serial “No 934,” the lower dial signed by the maker “J. Hicks, 8, 9, & 10 Hatton Gardens, London.” Fine blued-steel index, the bezel with very fine telltale spring anchored to arbour. The plain aluminium case with turned pillar and suspension ring, the rear having compensation adjustment port set at 4 o’clock as viewed.

Aluminium-constructed instruments of this period are very unusual.  Aesthetically, they lack the visual attraction of those constructed in lacquered brass, and they were produced at significant additional cost and to special order only. Though aluminium offered the advantage of lower weight, it presented some problems to the maker. Normally the aneroid movement is held into the back of the case by three screws engaged in three corresponding ferrules with internal threads soldered into the back of the case. It is not possible to solder aluminium so a means of fixing the movement with dome-headed engineering screws was used – the domes of those screws are visible on the case rear. It is likely this Watkin Patent extended scale barometer was manufactured c1890 – it is an example of one of the earliest applications of aluminium in scientific instruments and must be viewed as of great significance in technological terms.

Major (later Colonel) Henry Samuel Spiller Watkin of the Royal Artillery was granted a British patent no. 3425 for a rotary indicator and dial scale on 11 March 1886.