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Object Overview
Sea Level Forecasting Aneroid — an awe-inspiring instrument from circa 1920, crafted by the renowned makers Negretti & Zambra. The 9-centimeter-diameter case is made of gilded brass, featuring a rotating crown at the top that activates a patented mechanism for turning the barometer’s backplate, which also includes a calibration port. Engraved around the entire circumference of the instrument is an altitude scale in feet. The ribbed rotating bezel, fitted with a faceted glass, completes what can only be described as a brass "hamburger," consisting of three interconnected parts. The bezel incorporates a reflective brass ring and is equipped with a trend indicator hand.
The barometer’s dial, stamped from silver-plated brass, displays a barometric scale in London inches of mercury, ranging from 28 to 32 inches, with divisions as precise as 1/20 of an inch. The scale markings are executed in a bold, "Goliath-style" design. Notably, there is no textual weather indication, while the top of the dial bears the engraved title "Forecasting Aneroid." The long, ultra-thin indicator hand, gliding gracefully along the dial, is made of blued steel and features a crescent moon as its tailpiece.
10941
aneroid capsule tensioned on a C-spring
brass, glass, nickel silver, silvered brass, steel
At the heart of the barometer lies a nickel silver capsule with a diameter of 5 cm. The mechanism is temperature-compensated for enhanced accuracy.
This barometer, crafted as part of a custom-ordered, limited-edition set, includes the patented Negretti & Zambra weather forecaster. The forecaster, made of brass with a crackled finish on its reverse side, complements the barometer. An identical Negretti & Zambra forecaster made of celluloid is also known to exist. This explains the absence of standard textual weather indications on the dial. The title engraved at the top of the dial — "Forecasting Aneroid" — further confirms that the barometer was part of a unified set with the weather predictor. Both instruments — the barometer and the weather forecaster — were housed together in a wooden case wrapped in pigskin leather.
Whiteside-Cook’s Patent
The Whiteside-Cook’s Patent, registered under number 14424, represents an innovation in aneroid barometer design, engineered for precise atmospheric pressure measurement at sea level regardless of the current altitude. This was achieved through a specialized mechanism allowing the user to set the current altitude, after which the instrument automatically adjusted the pressure reading to the sea-level equivalent.
In operation, a keyless knob (crown) — similar to the winding action of a watch — is turned counterclockwise, enabling the case back, to which the movement is attached, to rotate. A scale from 0 to 3000 feet is engraved around the case's circumference, and the altitude is set by aligning the engraved index point located on the case back. The crown is then turned clockwise to lock the new value in place.
The Whiteside-Cook’s Patent, registered in the late 19th century (circa 1870), is closely associated with Negretti & Zambra, although it was originally designed and patented by the engineer whose name it bears. The patent essentially described a correction system for barometric pressure readings, enabling adjustments to sea level for greater accuracy. Negretti & Zambra, as one of Britain’s leading meteorological instrument manufacturers, extensively utilized this patent in their barometers, making the technology widely recognized.
The same technology was also employed in barometers by Short & Mason, which featured instructions such as: “For sea level reading, rotate this plate until the arrow on the case points to the altitude of your locality.” This technology was particularly notable in their fisherman’s barometers, produced under the Taylor brand.
Here is how Negretti & Zambra describe the advantages of sea level pattern barometers in their catalog:
1. The difference of altitudes on an ascent is ascertained with facility and without calculation.For example, the observer starts from sea level when the pressure is 30-in. The arrow is opposite 0 on the altitude scale, and before starting the small pointer is placed opposite the index hand. In ascending, the hand falls to, say, 26-in., and on arrival at the top the height is required. The moveable back is unclamped and turned round until the index hand is again opposite the small pointer. On reversing the instrument, it will be seen then that the arrow is opposite 3,750 feet, which is the height in feet of the ascent.
2. The reduction of the reading to that of sea level is ascertained at any moment without calculation. Supposing the instrument is taken into a country, say, 1,000 feet above sea level, the hand will fall about 1-in. of the scale, say, from 29-in. to 28-in., although the atmospheric conditions are practically the same, this difference being due simply to the change of the altitude. To correct this, release the clamp, and turn the back until the arrow points to 1,000 feet on the altitude scale, which brings the hand back again to its proper position on the dial relative to the words "Rain”, "Change," etc.
3. The Aneroid may be set without trouble to read correctly at any altitude. Travellers on the Continent meet with great changes of altitude, and as the Barometer falls or rises accordingly, it is difficult to arrive at the movements of the Barometer as regards the weather. The elevation of the place can nearly always be found in the Guide Book, and by placing the arrow opposite this altitude, the hand will always give the true sea level reading.
4. The advantage of having the altitude scale apart from the pressure scale is very great. Each scale is clearly engraved and legible, whereas on the ordinary Aneroid, the two are so close together as to be somewhat confusing.