A barometer is an instrument that measures atmospheric pressure. Barometers are used by weather forecasters to measure air pressure, because rising or falling atmospheric pressure indicates a coming change in weather
Evangelista Torricelli was an Italian physicist. He was born in 1608 and died in 1647. He studied mathematics in Rome, and there became fascinated by the work of Galileo, whom he aided in the preparation of his Discorsi. Toriccelli succeeded Galileo, on the latter's death, in the chair of philosophy and mathematics at Florence. Toriccelli is famous for balancing the weight of a column of mercury against the pressure of the atmosphere, the principle of the barometer. The space above the mercury in a brometer is still called the Torricellian vacuum.
The Torricelli barometer is made by first filling a dish with mercury which is afterwards poured into a long tube. The tube is filled almost to the top, stopped and inverted several times to remove air bubbles. The tube is then completely filled with mercury using a dropper. A finger is placed over the top of the tube and the tube is inverted and placed into the dish below the level of the mercury. When the finger is removed, the level of the mercury inside the tube drops until the pressure at the bottom of the column of mercury is equal to the pressure exerted by the surrounding air. Since no air was allowed to enter the tube, the empty space above the mercury column is a vacuum. We can ...
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