Antique Barometres
Barometers
The barometer – an instrument for measuring atmospheric pressure – was invented by the Italian philosopher and mathematician Evangelista Torricelli in 1643-4. Torricelli discovered that the height of mercury in a glass tube immersed upside down in a cistern of mercury is dependent on atmospheric pressure. The British scientist Robert Boyle was the first to relate changes in the height of the mercury to variations in the weather, and the first domestic barometers were made from the 1670s. Barometers were often fitted with a thermometer, calibrated with the Royal Society scale from 0 to 90 degrees until c.1725 and the Fahrenheit scale thereafter.
STICK BAROMETERS
The stick barometer, the earliest and simplest type, consists of a long, straight, glass tube of mercury immersed in a glass cistern full of mercury. Late 17th-century British examples are mounted on a wooden walnut-veneered frame, decorated with Baroque-style twist pillars and fretted scrolls, and have a solid walnut cistern cover and a silvered-brass graduated scale (the “register plates”) at the top with a recording pointer. Made by clockmakers, most follow the form of contemporary clocks.
The closed-cistern stick barometer is usually attributed to Daniel Quare (16491724) in 1695: being sealed, it was more easily transportable. Most early 18th-century barometers found today are of this type. Made mainly in London, they are similar to late 17th-century models but tend to have shorter hoods, gilt finials, and plainer cases. Mahogany veneer was used from c.1740.
While earlier barometers followed clock styles, later 18th-century examples were influenced more by furniture. After the mid-18th century cases became plainer, the engraving on the register plates less ornate, and trunks narrower; the influence of long-case clocks disappeared. From c.1750 the Vernier scale, accurate to one-hundredth of an
inch, was used for mercury readings, and the principal weather indications of “fair”, “changeable”, and “rain” were standardized. Hinged glass doors to protect the register plates appeared at the end of the 18th century.
In the early 19th century finely crafted barometers featured stringing in dark ebony or lighter woods. From c.1840 rosewood as well as mahogany was used for cases, and ivory or paper for the register plates. The “Admiral Fitzroy” barometer, a popular design by the British meteorologist Admiral Robert Fitzroy (1805-65), featured a glazed, rectangular oak case, paper register plates, a thermometer, and a storm glass – a bottle of crystals in a camphor solution that supposedly forecast weather changes. Two recording pointers allowed atmospheric pressure to be recorded on successive days.
The stick barometer went out of fashion in favour of the aneroid barometer in the early 20th century, but earlier designs were reproduced on a limited scale.
ANGLE BAROMETERS
The angle or “signpost” barometer uses the same principle as the stick barometer, but the upper part of the tube is bent. Invented in the 1670s and made until c.1880, this design was intended to give a more accurate reading,
as the mercury moved over a greater length in the upper part of the tube. However, it was less accurate than hoped and never widely popular because of its expense and its unwieldy shape. Rarer than other types, angle barometers are particularly collectable today.
Barometer-makers invented new designs to obscure the awkward form: in the early 18th century the maker John Patrick mounted the angle barometer on a square or rectangular wooden frame with a large mirror in the centre and a thermometer on the other side to balance the design. To reduce the horizontal part of the arm without reducing the scale, some makers used two or three tubes, set side by side and angled at different heights, so that the tubes would cover the full scale.
WHEEL BAROMETERS
The wheel barometer, invented in 1663 by Robert Hooke (1635-1703), featured a U-shaped tube with long and short arms. A float resting on the mercury in the short arm is attached to a lighter counterweight by a thread over a pulley wheel, which in turn is connected to a pointer on a dial. The movement of the mercury in the tube raises or lowers the float, rotating the pointer. The wheel barometer was not made in large numbers in Britain until c.1770, when the “banjo” design was introduced by Italian glassblowers and instrument-makers. The “banjo” wheel barometer, [lie most popular type of wheel barometer in the 19th century, consists of a dial and thermometer in a banjo-shaped wooden case. The silvered-brass dial has a blued-steel indicating hand and a brass fixed hand for recording readings. The scale, measured in inches, ranged from
-1 to 79cm (28-31in), the average atmospheric pressure in northern Europe, and was divided into tenths or twentieths of a inch. Later examples are usually equipped with more detailed scales graduated to hundreths of an inch.
Many wheel barometers were also fitted with a spirit lei el at the bottom for checking that the barometer was hung vertically - if it was not level, the float would jam. Another useful device was the hygrometer, indicating
humidity (which, like temperature, affected the height of the mercury): a beard of oats, which curled and uncurled with changes in air moisture, was set on a dial with the indications “moist” (”damp” from c.1800) and “dry”.
Before c.1825 most wheel barometer cases were veneered in mahogany, with the best examples made in Satinwood, maple, or pearwood. From c.1815 to c.1825 “Sheraton shell” inlay, copied from Regency furniture, was especially fashionable as a form of decoration. The mid-19th century saw the appearance of the “onion” or “tulip” top case, and the finest examples were veneered in mahogany or rosewood, inlaid with mother-of-pearl, tortoiseshell, and brass. Later 19th-century cases, influenced by the 1851 Great Exhibition, tended to use solid wood (often oak) cases, with increasingly elaborate carving. The wheel barometer was superseded by the aneroid barometer in the late 19th century.
ANEROID BAROMETERS
Invented by the French engineer Lucien Vidie in 1843, the aneroid (”liquid-free”) barometer completely transformed barometer making. Instead of mercury, it featured a small, vacuumed, metal chamber that rose and fell with atmospheric pressure change. Very accurate and easily portable, by c.1900 it was the most successful type of barometer. Aneroid barometers were initially used by scientists, surveyors, and engineers, but from c.1860 models were made for the home in a wide variety of case designs, from round brass cases to marble mantel ornaments; some were fitted into mantel or carriage clocks. Imitation “banjo” wheel barometers were also Popular. Domestic versions featured silvered-brass or less expensive cardboard dials; marine barometers had enamel or porcelain dials, less likely to corrode in sea air. Pocket aneroid barometers, used by travellers and climbers, were produced c.1860 by the firm of Negretti & Zambra. Most were fitted in leather-covered wooden cases; some also had a scale on the dial for measuring altitude, a curved mercury thermometer, or a compass.
Stick barometers
• DESIGNS the Vernier scale was used from c.1750; register plates were usually made of silvered brass until 1840, bone and ivory thereafter
• COLLECTING ING barometers made in the late 17th to early 18th century are very rare and valuable today
Angle barometers
• DESIGNS some were mounted on a wooden frame with a mirror and thermometer
• COLLECTING few were made after c.1880, and fewer were made than other types, so they highly sought after
Wheel barometers
• DESIGNS the “banjo” shape was the most popular design from the late 18th century; scroll pediments were fairly standard after 1825; “Sheraton shell” inlay was used c.1815-25; convex glass mirrors were put in the centre from c.1840; best later Victorian examples are inlaid with brass, mother-of-pearl, and tortoiseshell
• COLLECTING most British barometers are signed by Italians, who dominated the industry
Aneroid barometers
• DESIGNS case shapes were varied, but the “banjo” style was especially popular; wheel barometer types were made from the 1860s; pocket examples were produced from c.1860