Rare Hypsometer Aneroid Barometer by Negretti & Zambra

For sale, an extraordinarily rare hypsometer aneroid barometer by Negretti & Zambra, London.

Contained within a six-inch circular oak case, the five-inch silvered dial measures 28 to 31 inches of barometric pressure around the outer circumference and has a highly unusual secondary inner scale reading for 209 to 213.5 degrees of Fahrenheit.

The makers name, Negretti & Zambra, London is at the centre with the registered design number of R/3877 and the company logo beneath.

It is completed with blue steel pointer and hand operated brass pointing hand with knurled turn through the thick bezelled glass dial front.

This is the first I have ever seen of this Negretti product. The logo and the style certainly date it to the early Twentieth Century, and it is fortunate that it is listed also in their engineering and industrial catalogues of the 1920’s. It is described as follows:

“It is not always fully appreciated that the boiling point of water is not necessarily 212F (100C). The boiling point of water may differ from this temperature by many degrees depending upon the atmospheric pressure, purity of the water, nature of the vessel, rate of boiling etc.

The Hypsometer aneroid is an aneroid with the dial graduated in both inches barometric pressure and degees Fahrenheit. The pointer indicates the temperature of the free steam (commonly termed the boiling point of water), together with the barometric pressure.”

An unusual instrument which can form direct links to the equally uncommon hypsometer instrument first invented by the eminent scientist William Hyde Wollaston in the early Nineteenth Century. Its predecessor was used as a means to measure elevation using boiling water. Its principle is based upon the fact that the boiling point of water becomes lower as atmospheric pressure becomes reduced and as such, thermometers were used to measure boiling point during an ascent which would subsequently measure the level of elevation.

This instrument is essentially the same in reverse where atmospheric pressure may be used to accurately calculate the expected boiling point of water and steam for industrial use.

Negretti & Zambra’s diversity of ideas for the application of barometric pressure rarely fail to impress. Most examples from this period are domestic products which seek to make weather prediction as simple as possible for the owner, but this rare example shows that the company continued to work hard in making the aneroid barometer relevant to industrial application during this period.

Negretti & Zambra were a leading name in the production of meteorological and scientific instruments and have a company history dating back to 1850. Throughout their long and esteemed history they exhibited at British industrial fairs throughout and became makers to both Queen Victoria and Edward VII. Owing to changes in the business, the firm ceased the public retailing of scientific instruments sometime around the late 1960’s and continued with a focus on the aviation industry in numerous guises until its eventual liquidation in the year 2000. A sad end to a hundred and fifty years of quality manufacturing.

Circa 1920