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BAROMETERS
They are used to measure the atmospheric pressure. A common and simple instrument is the mercury barometer where atmospheric pressure is counterbalanced by the pressure exerted by a mercury column whose height is proportional to the atmospheric pressure. Mercury is 13.6 times heavier than the air and, therefore, a mercury column of about only 76cm height counterbalances the atmospheric pressure at the sea level (this is the famous Torricelli experiment).
Another, more synchronous instrument is the vacuum spring barometer which can measure small changes of the atmospheric pressure.
In this instrument, the small deformation of one, almost empty, airtight metal drum, which is caused by the atmospheric pressure, is amplified via a system of levers and is indicated on a marked scale by an indicator.
VACUUM PUMPS
They are used for pumping the air out from the inside of an enclosed space. They are normally used in laboratory applications but also in other practical applications as, for example, in order to fill-up the cooling fluid in air conditioners and refrigerators.
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