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Object Overview
This Ivory Register-Plate Cistern Barometer, made by the London firm of Carpenter & Westley around 1850, is a mercury cistern instrument also known, from the form of its case, as a stick barometer. The company, established at 24 Regent Street, became known not only as a manufacturer of optical and scientific instruments but also for its phantasmagoria lanterns, kaleidoscopes, microscopes and projection apparatus. This barometer clearly demonstrates that the firm’s range extended far beyond optics and included precision meteorological instruments.
The case is made of solid oak and has the elongated vertical form characteristic of English stick barometers. Its upper section widens and terminates in a rounded arch containing the register plates, thermometer and upper end of the barometer tube. Below, the case gradually narrows to form a long, straight stem supporting the glass tube along almost its entire length. The warm brown colour of the timber and the clearly visible linear grain of the oak emphasise the restrained character of the construction. Ornamentation is kept to a minimum, and the visual appeal of the instrument derives chiefly from its proportions and from the contrast between the wood, pale ivory and polished brass.
n/a
cistern
brass, glass, ivory, leather, mercury, wood
At the lower end of the case is a spherical, turned wooden cover protecting the mercury cistern. Formed as a projecting hemisphere against the circular backplate of the case, it visually balances the enlarged head of the barometer. In addition to its decorative function, it protects the relatively fragile cistern and its leather base from accidental knocks and handling.
Two separate ivory register, or scale, plates are mounted in the upper part of the instrument. The material is identifiable by the characteristic intersecting Schreger lines visible on their surfaces. The inscriptions, graduations and numerals are engraved directly into the ivory and filled with a dark compound, making them clearly legible against the pale background.
The right-hand plate carries the barometric scale. It is calibrated in London inches of mercury and covers a range from 27 to 31 inches Hg. The principal values are indicated by large numerals, with smaller subdivisions representing tenths of an inch between them, allowing changes in atmospheric pressure to be read with considerably greater precision.
Beside the scale is a movable index with a small numbered scale from 1 to 10 and a brass pointer. This assembly functions as a vernier, permitting a more accurate determination of the height of the mercury column. It can also be used to mark a previous reading, enabling the observer to judge not only the absolute pressure but also its tendency—whether rising or falling.
The barometric scale is supplemented by the traditional verbal indications of expected weather conditions: FAIR, CHANGE, RAIN, STORMY
The inscriptions are engraved in several different typefaces, ranging from a restrained upright Roman letter to more decorative outlined forms. This typographical variety gives the plate the characteristic appearance of an English instrument of the mid-nineteenth century. As with most antique barometers, these words should not be understood as independent forecasts: the direction and rate of change in pressure are more significant than the position of the mercury column opposite any particular word.
The maker’s signature is engraved at the top of the right-hand plate:
CARPENTER & WESTLEY
24 REGENT STᵀ
London
The company name is arranged in an arc around the street number, while the word London is executed in a decorative Gothic typeface. The inscription served not merely as a trade signature but also as an indication that the instrument originated from one of London’s best-known centres of optical and scientific-instrument manufacture and retailing.
The left-hand register plate carries the glass tube of a mercury thermometer. Its lower bulb is protected by a shaped brass fitting composed of a central collar and horizontal decorative bands. This fitting secures the thermometer, shields the most vulnerable section of the glass and gives the assembly a visually finished appearance.
The thermometer is provided with two parallel systems of temperature measurement. The scale on the left is graduated in degrees Fahrenheit, approximately from 20 to 120 degrees, while the scale on the right is centigrade, later known as the Celsius scale. This combination was particularly convenient for an instrument intended both for British users and for customers familiar with the Continental system of measurement.
The principal glass barometer tube runs between the two ivory plates. Its sealed upper end is covered by a hemispherical decorative brass cap secured by two small screws. This fitting protects the glass from impact and conceals the technical junction between the tube and the upper part of the case. Below, the tube is held by brass clips and follows the central axis of the oak board down to the cistern.
The glass tube is approximately 86 cm long, with an external width of about 15 mm and an internal diameter of approximately 8 mm. It contains the mercury column, whose height varies according to atmospheric pressure. The estimated volume of mercury within the working section of the tube is approximately 25 ml, with a further 10 ml or so contained in the cistern.
The cistern is made of boxwood, a dense, fine-grained timber well suited to precision turning and threaded components. It consists of two principal parts: an upper reservoir connected to the barometer tube and a screw-on lower cap. The inside of the cap is closed by a flexible leather membrane forming the movable base of the cistern.
The removable section has a wooden exterior and an internal brass thread. This arrangement allowed the reservoir to be dismantled for maintenance, inspection or replacement of the leather base. The surviving leather has a dense, fibrous texture and was originally intended to maintain a seal while remaining sufficiently flexible to permit the volume of the cistern to be altered.
Beneath the spherical protective cover is a vertical brass screw operated by a turned, knurled handle. As the screw is rotated, it moves upwards and presses against the leather base of the cistern. The volume of the reservoir is thereby reduced, forcing mercury out of the cistern and upwards through the glass tube.
This mechanism forms the instrument’s safe-transport system. Before the barometer was removed from the wall, the screw was tightened until the mercury rose to the sealed upper end of the tube. In this condition there was virtually no space in which the mercury column could move freely and strike the glass with force. Once the barometer had been installed in its new position, the screw was slowly released, increasing the volume of the cistern and returning the mercury to its normal working level.
The impact of the mercury—commonly known as hammering—was one of the principal hazards involved in transporting long cistern barometers. The considerable mass of the liquid metal could break the tube even when subjected to a relatively moderate jolt. The adjustable leather base transformed an ordinary wall instrument into a barometer that, after proper preparation, could be transported with a reasonable degree of safety.
Brass fittings for securing the instrument to the wall are mounted on the reverse of the oak case. At the top is a broad hanging plate with a circular aperture, fixed by three screws. The lower fitting was intended to secure the case after levelling, ensuring that the barometer remained perfectly vertical and did not swing while readings were being taken.
A paper instruction label issued by the firm also survives on the reverse, although on this example it is heavily worn and partly lost. The instructions state that, when the instrument was received, the mercury should be locked at the upper end of the tube. Before releasing it, the barometer was to be fixed to a perfectly vertical wall at a height that placed the word CHANGE approximately level with the observer’s eye. Once suspended, the case was to be additionally secured by a screw through the lower brass plate.
The brass screw at the base of the instrument was then turned from right to left as far as it would go. This released the leather base of the cistern and allowed the mercury to assume its working position, after which the barometer would indicate the actual atmospheric pressure. Before the instrument was subsequently removed or transported, the procedure had to be reversed: by turning the screw in the opposite direction, the mercury was once again forced towards the sealed upper end of the tube.
The instructions therefore described not only the correct method of installation but also the essential procedure for securing the mercury column before every movement of the barometer. The label served an important practical purpose, since improper handling could result in both breakage of the glass tube and the escape of mercury.
The term portable barometer, used by the firm itself in the surviving instructions, does not denote a small travelling instrument intended to be carried by hand. It refers instead to a full-sized wall barometer whose construction allowed the mercury to be safely secured within the tube and cistern before transportation, preventing the heavy column of mercury from striking and breaking the sealed end of the glass tube.
This portable cistern barometer by Carpenter & Westley is a particularly expressive example of London scientific instrument-making from the mid-nineteenth century. Its construction combines a precise mercury system, a dual-scale thermometer, ivory register plates, a vernier for refining the reading and a carefully devised transport mechanism. The restrained exterior of the oak case contrasts with the delicacy of the engraving, the variety of typefaces and the finely executed brass fittings.
The instrument possesses additional historical significance through its association with Carpenter & Westley, a firm more widely known for optical entertainments, phantasmagoria lanterns and projection equipment. This barometer reveals another aspect of the company’s activities and demonstrates that Carpenter & Westley was a comprehensive supplier of scientific, meteorological and measuring instruments. The surviving signed plates, transport mechanism, boxwood cistern and remains of the original instruction label make it not merely a functional meteorological instrument, but also a well-documented witness to the culture of precision measurement and the London scientific-instrument trade of the Victorian period.