Philadelphia Instruments & Controls Inc.
4401 North Sixth Street
Philadelphia, PA 19140
USA

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Did you know?
The earliest barometer was the mercury barometer. It is made of a glass tube, open at one end. The tube is filled with mercury, the open end is covered, and the tube is then turned upside down with the covered end placed into a dish of mercury. The end is uncovered, and part of the mercury drains into the dish. Most of the mercury remains in the tube, however. It remains in the tube because of the atmospheric pressure on the surface of the mercury in the dish. That atmospheric pressure is equal to the downward pressure of the mercury in the tube. Since the mercury barometer was the first one invented, atmospheric pressure is often expressed in terms of the height of the mercury in the tube above the mercury in the dish. At sea level, this height averages about 30 inches (760 millimeters).
 

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