A sympiesometer is a compact and lightweight type of
barometer
A barometer is a scientific instrument that is used to measure air pressure in a certain environment. Pressure tendency can forecast short term changes in the weather. Many measurements of air pressure are used within surface weather analysis ...
that was widely used on ships in the 19th century. The sensitivity of this barometer was also used to measure altitude.
The sympiesometer consists of two parts. One is a traditional
mercury thermometer
Mercury commonly refers to:
* Mercury (planet), the nearest planet to the Sun
* Mercury (element), a metallic chemical element with the symbol Hg
* Mercury (mythology), a Roman god
Mercury or The Mercury may also refer to:
Companies
* Mercury ...
that is needed to calculate the expansion or contraction of the fluid in the barometer proper. The other is the barometer, consisting of a J-shaped tube open at the lower end and closed at the top, with small reservoirs at both ends of the tube. The lower end of the J and its associated reservoir were filled with colored almond oil, while the upper portion and its reservoir were filled with
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
gas.
Increasing air pressure would cause the oil to be pushed out of the lower reservoir and into the tube, compressing the hydrogen gas into the upper reservoir. The pressure was indicated by the position of the top of the oil. To correct for temperature, a sliding scale was used; the operator would first use the thermometer to set the scale and then measure the pressure from it.
The basic idea is similar to the common
weather glass that had been in use for some time, but the use of highly compressible hydrogen in a long, thin tube allowed much more accurate measurements, as changes in pressure resulted in much more movement of the liquid. The basic concept was initially demonstrated by
Robert Hooke
Robert Hooke FRS (; 18 July 16353 March 1703) was an English polymath active as a scientist, natural philosopher and architect, who is credited to be one of two scientists to discover microorganisms in 1665 using a compound microscope that ...
, which he referred to as the Otheometer. However it remained unused until it was re-introduced by
Alexander Adie
Alexander James Adie FRSE MWS (1775, Edinburgh – 4 December 1858, Edinburgh) was a Scottish maker of medical instruments, optician and meteorologist. He was the inventor of the sympiesometer, patented in 1818.
Life
He was born the son of Jo ...
.
References
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Pressure gauges
Meteorological instrumentation and equipment
Scottish inventions