Early Victorian Sympiesometer by Charles Baker of 244 High Holborn, London.

For sale, an early Victorian Sympiesometer by Charles Baker of 244 High Holborn, London.

This example is comprised of a 22” rosewood case containing a silvered scale plate with thermometer, glass cistern and setting dial for recording the day’s reading which is hand operated from the under-side of the case. The front right hand side of the sypiesometer case has an adjusting knob to allow for the accompanying scale to be moved up and down to record the temperature and provide the associated reading from the level in the cistern.

To the left side of the bulb, the sympiesometer is engraved to C. Baker, 244 High Holborn, London.

The sympiesometer was patented by the famous Scottish instrument maker, Alexander Adie of Edinburgh around 1816 and it was patented on the 23^rd Dec 1818 (Patent No 4323 –Description of the Patent Sympiesometer or New Air Barometer). The following extract provides a brief explanation and directions for it use.

“My attention was first directed to the improvement of the Barometer, with the view of rendering it susceptible of indicating any of those minute changes in the weight of the atmosphere, which might be supposed to arise from the action of the Sun and Moon. A very sensible instrument was obviously necessary for such a purpose; and I was therefore led to the idea of measuring the pressure of the atmosphere by its effect in compressing a column of common air. Upon constructing an instrument of this kind, however, I found that the air was absorbed by the fluid with which it was enclosed, and that a good and permanent barometer could not be made upon such a principle, till this radical defect was removed. I therefore directed my attention particularly to this object, and succeeded beyond my most sanguine expectations, in freeing the Air Barometer from this great source of inaccuracy.

The name sympiesometer which I have given to this improved instrument, is derived from the Greek words “to compress” and “a measure”, denoting the property it possesses of measuring the weight of the atmosphere by the compression of a gaseous column.

The principle of the Sympiesometer consists in employing an elastic fluid or gas, different from air, and any liquid, excepting quicksilver, which neither acts upon the gas which it confines, nor is perceptibly acted upon by the air, to the contact of which it is in some measure exposed. Hydrogen gas, azotic gas, or any of the gases not liable to be absorbed by the enclosing fluid, may be used; but I prefer hydrogen gas as superior to any other that I have tried. The liquid which answers best is an unctuous oil, or a mixture of unctuous and volatile oils.

The enclosed gas with which the bulb and part of the tube is filled, changes its bulk, or occupies more or less space, according to the pressure of the atmosphere upon the surface of the oil. The scale for measuring the change in the bulk of the gas, occasioned by the change of pressure, is formed experimentally.

As the bulk of the gas is altered by any change that takes place in the temperature of the atmosphere, it is necessary to apply a correction on this account. For this purpose, the principal or barometric scale, is made to slide upon another scale, placed either below it or on one side of it, which is divided into degrees and tenth parts, so as to represent the change of bulk in the gas produced by a change of temperature under the same pressure, and corresponding to the degrees of a common thermometer attached to the instrument, the scale of which is also divided into degrees and tenth parts of a degree.

When the sypiesometer is hung up for observation, the cistern must be opened, by taking out the cork, or pushing up the small slider at its mouth, the only use of either being to prevent the loss of the oil in the cistern, when the instrument is carried horizontally (Note: Not Advised!….).

Manner of Using the Instrument

Observe the temperature by the thermometer, and set the pointer above the top of the sliding scale, opposite to the degree of temperature upon the fixed scale; and then the height of the oil as indicated on the sliding scale, will be the pressure of the air required.

As it is convenient to know what change has taken place since the last observation, the circular register at the bottom of the frame should be set, by turning the division on it corresponding to that indicated by the Sympiesometer to the fleur de luce or index. When the column of oil descends, bad weather may be expected; and when it rises, the weather will in general be fine.”

From 1816 until its eventual patent date, Adie put the sypiesometer through a number of practical tests. The first was a voyage from The Clyde to the East Indies in 1816, it was later taken by Captain Ross in 1818 on a voyage to the Arctic Regions and used extensively by the Scotch Lighthouse Board. All reported very favourable and deemed it more reactive than the standard marine barometers of the time, reporting variations in measurements approximately two hours or more ahead of its competitor.

For example, Captain Ross reported that,

“This instrument acts as a marine barometer and is certainly not inferior in its powers. It has also the advantages of not being affected by the ship’s motion, and of taking up very little room in the cabin. I am of opinion that the instrument will supersede the marine barometer when it is better known”.

Although they proved popular with those that used these instruments, they were not destined to supersede the standard marine barometer. The reasons are probably due to the comparative complications of manufacture and that the aneroid barometer which was invented in the 1840’s eventually overtook them both and which accounts for the relative rarity of these fine instruments.

According to some of the company’s advertising, the Baker firm had roots stretching back to 1765 but Charles Baker (1820-1894) is actively recognised to have been trading by 1851 and presented itself as both opticians and instrument makers.

Baker is more commonly associated with the making of microscopes to most modern collectors, but voluminous catalogues held at The Borthwick Institute in York suggest that he was as prolific as the likes of WF Stanley and Elliotts in the range of instruments available.

The company continued after Baker’s death under the stewardship of the Curteis family until it was finally subsumed by Vickers Instruments Ltd in 1959 although a repair business called “Rekab” continued to be managed by Michael Curteis until his death in 1965.

Circa 1850