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A very nice mahogany cased sympiesometer. The case with ogee moulded top and flat bottom has a deeply bevelled glass to the front.
The silvered brass scale plate is signed for the maker ‘J R Cameron, 54 South Castle Street, Liverpool’. It has an unusual U shaped thermometer which gives added interest to the instrument. It has the usual sympiesometer tube which, since it is of the improved variety, has a restricted capillary, and is filled with blue coloured acidic oil. At the bottom is a knurled dial which can be set to the last reading thus showing the movement of pressure between readings. There is a slide to the right which can be moved up via the brass knob to the temperature shown by the thermometer. The level of the liquid can then be read off against the scale which goes from 28 to 31 showing rain, change and fair.
Length: 19.5″ (50 cm)
The maker John R Cameron is noted as a chronometer and watchmaker working from 54 Castle Street which was near the Customs in Liverpool.
The sympiesometer was an instrument patented and perfected by Adie and was considered to be a better instrument for marine use than a mercury filled marine barometer. The rise and fall of the liquid in the sympiesometer tube is affected both by temperature and barometric pressure, hence the need for a movable scale to take out the effect of temperature movement. The liquid used varies, but is normally almond oil with dilute acid. The improved sympiesometer with the restricted capillary are more accurate than the original early examples. These instruments have the advantage of small size, an impressive looking scale plate and a useful thermometer.
More detail can be found in Barometers Stick or Cistern Tube, chapter 12, page 214, by Edwin Banfield.