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 23rd 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!….).

Man