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Object Overview
Before us is the famous Early Commercial Vidie Aneroid, manufactured approximately around 1850 and bearing the serial number 4264. The instrument belongs to the first generation of practically usable aneroid barometers based on the system of the French engineer and inventor Lucien Vidie, who created the first truly successful non-liquid barometer.
The particular historical significance of this example is connected with the name of the famous English clockmaker and chronometer maker . Dent played one of the key roles in transforming Vidie’s invention from a technical novelty into a commercially successful instrument. Beginning in 1847, Dent sold Vidie-system aneroids in England. His reputation as a maker of marine chronometers, astronomical regulators, and complex precision clocks gave the new type of barometer the confidence of the British public and scientific community. In 1849, Dent even published a separate work — — which effectively became one of the first specialised guides to the new instrument.
4264
early Vidie
brass, cast iron, copper, glass, mercury, silvered brass, steel
The engraving “E.J. DENT / Paris.” on the dial is also interesting. It does not indicate the existence of Dent’s principal workshop in Paris: the documented commercial premises of the firm during this period were located in London. The word Paris here most likely emphasised the French origin of the aneroid itself and its connection with Vidie’s workshop.
The barometer is housed in a round, drum-shaped brass case characteristic of the earliest commercial aneroids. Its form is still very close to the appearance of a large pocket or marine chronometer: a comparatively small diameter, substantial depth of the case, a perfectly circular profile, and a massive suspension ring at the top give the instrument both a portable and an instrumental character.
Cases of this kind were not cast as a single massive piece. The main shell was made from sheet non-ferrous metal by the process of rotational forming — metal spinning, in which the blank was pressed with a tool against a rotating former and gradually drawn into the required drum-like shape. After this, the individual parts were turned, trimmed, and given their final finish. For early Vidie/Dent instruments, this method of manufacture is well documented; surviving comparable instruments are specifically described as being housed in spun brass or spun copper-alloy cases.
The front of the case is finished with a thin, elegant brass bezel especially characteristic of early instruments. Unlike the considerably heavier profiled bezels of later Victorian aneroids, here it appears visually light and almost jewellery-like. Around its circumference runs a fine repeating ornament produced by machine knurling.
The bezel retains a flat mineral glass, on the inner side of whose centre is mounted the brass hand of the manual tendency indicator — the tell-tale or reference pointer. It is not connected with the barometer mechanism and is positioned by the user by means of a small knurled brass knob in the centre of the glass.
At the top of the case is a substantial brass neck with a large movable suspension ring. Its dimensions correspond well with the original conception of the aneroid as a portable instrument: the barometer could be suspended vertically or transported in its case without requiring the precautions necessary when transporting a mercury barometer.
It is particularly significant that this example has survived together with its original box. This is a rigid rectangular hinged case with a dark exterior finish and a fabric lining inside; the lid is lined with dark burgundy material, while the base incorporates a shaped recess for the instrument itself. In addition to providing practical protection for the relatively thin brass case and glass, such a case emphasises the original status of the aneroid as an expensive precision instrument intended for travel, shipboard use, scientific observation, or a wealthy private owner.
The dial is made of brass with a silvered surface. This technique made it possible to obtain both a bright, highly legible background and exceptionally fine engraving: the divisions, inscriptions, and numerals were cut directly into the metal plate and then filled with a dark compound.
The upper half is occupied by a semicircular barometric scale in London inches of mercury, covering the range from 28 to 31 inHg. Each full inch is divided into twenty parts, meaning that the value of each small division is 0.05 inches of mercury. This is a scale characteristic of early Vidie aneroids — relatively narrow in range, but sufficiently finely divided for ordinary meteorological observations.
Along the outside of the scale is a sequence of traditional English weather indications:
STORMY — Much Rain — Rain — CHANGE — Fair — Set Fair — VERY DRY.
This is a traditional system of verbal interpretation of pressure. The typographical arrangement is especially expressive: the two extreme indications and the central one — STORMY, CHANGE, and VERY DRY — are emphasised in capital letters, while the intermediate conditions are set in a lighter typeface using upper- and lower-case letters. In this way, the scale performs both a measuring and a visual interpretative function.
Below the barometric scale is the name of the instrument — “Aneroid Barometer” — engraved in a large decorative typeface. This is a characteristic Victorian variety of Old English / blackletter, that is, a romanticised Gothic script with strongly calligraphic capital letters.
At the centre is the arbor of the working hand; above it runs the blued-steel barometer hand with a long narrow point and a crescent-shaped tail.
The lower part of the dial is occupied almost entirely by the built-in arcuate mercury thermometer. The curved glass tube follows the circumference of the dial, making it possible to incorporate a sufficiently long mercury column without increasing the overall diameter of the instrument. The graduation is engraved directly onto the silvered brass and is marked in degrees Fahrenheit; the principal numerals are placed at 20-degree intervals, from 20 to 140 °F. Above the scale, on either side of its centre, is engraved the inscription “FAHRENHEIT’S THERMOMETER”.
Immediately above the thermometer is the concise retailer’s signature:
E. J. DENT
Paris.
Still lower, between the thermometer inscriptions, is engraved the serial number 4264.
As is well known, the principle of Vidie’s barometer is as follows: a vacuum is created inside a small metal box formed by two flexible corrugated diaphragms; a coiled spring, opposing the weight of the atmosphere, keeps these diaphragms at the same distance from one another as they would be if no vacuum existed inside. For each value of barometric pressure there corresponds a particular position of equilibrium of this opposing spring, and this is transmitted as rotation of the hand, to which the motion is conveyed by an amplified lever transmission mechanism. The movements are transmitted by means of articulated links, allowing each part of the instrument to be adjusted; all rotations take place around pivots mounted in fixed bearings; all the parts are balanced in such a way that the readings of the instruments do not depend in any way upon changes in the position of the apparatus, nor upon shocks that may be imparted to them during transport.
Detailed images of this barometer clearly show that the basis of the mechanism is an evacuated copper box — the aneroid capsule — formed by two membranes with characteristic toroidal corrugations and a rigid centre. From below, the box is screwed to the main cast-iron plate. From above, the aneroid capsule is suspended from a two-armed cast-iron lever, which performs a rocking movement in the vertical plane around a fixed axis. The support of this lever consists of two knife-edge uprights in order to minimise friction. These uprights define the line that forms the rocking axis.
The aneroid capsule is located on the short arm of the two-armed lever — the central boss of the upper wall of the capsule engages with the projecting beam; thus, at the input of this lever arm, the entire atmosphere pressing upon the walls of the capsule effectively hangs as the load.
At the same time, at the end of the long arm of the two-armed lever is a steel coil spring, which balances the load — the atmosphere.
The atmosphere tends to crush the evacuated box, while the spring, acting through the lever, supports its movable bottom and opposes this force. Thus, this antagonistic spring functions like the weight in the second pan of a balance: it is the calibration reference, and its stiffness determines how far the entire two-armed lever will tilt for a given unit change in pressure. It also holds the capsule open and prevents the upper and lower walls from collapsing together.
At the end of the long arm of the lever there is a small rod which, by means of a linkage, is connected to a pivoting mechanism, where an angular lever, also with unequal arms, rotates by means of a trunnion connection. The vertical arm of this angular lever transmits the motion further to the hand arbor by means of a fusee chain. The hand arbor is held between the characteristic trapezoidal brass plate seen in early Vidie mechanisms above and a brass angle bracket screwed to it from below.
Today, a barometer of this type can easily be mistaken simply for an early variety of the extremely widespread Victorian aneroid. However, at the time of its appearance, the very idea of a small metal instrument capable of replacing a bulky and fragile mercury barometer was still almost entirely new.
Before Vidie, a reliable portable non-liquid barometer had for decades remained more of an engineering dream. His metallic sensing element made possible for the first time a compact instrument that could be carried, taken aboard ship, used during travel, or employed for the approximate determination of altitude without the risk of breaking a long glass tube and losing the mercury. For this reason, the aneroid very quickly developed from a scientific novelty into one of the most widespread meteorological instruments of the nineteenth and twentieth centuries.
Consequently, Early Commercial Vidie Aneroid No. 4264 is of interest not only because of its age or its unusual early mechanism. It belongs to the briefest and most important period in the history of the aneroid — the time when Lucien Vidie’s invention was only beginning to make the transition from an experimental construction to a commercial instrument. The large copper chamber, external coil spring, thin ornamental bezel, silvered dial, arcuate mercury thermometer, E.J. Dent, Paris signature, and original carrying case together form an almost textbook example of the first generation of aneroid barometers.
It was precisely instruments of this kind, sold by Dent in England in the late 1840s and early 1850s, that laid the foundations for the design which, in various forms over the following century and a half, became the most widespread mechanical method of measuring atmospheric pressure without the use of a mercury column.