In this experiment, Torricelli used mercury which is more than 13
times as heavy as water.
A water barometer would require a tube more than 30 feet long and the
water, of course, would freeze at winter temperatures.
Furthermore, water and most other common liquids release vapor which
would decrease the vacuum at the top of the tube, whereas cold mercury
releases very little vapor.
A glass tube, sealed at one end, is filled with mercury. Then a glass
dish is partially filled with mercury.
Cover the open end of the tube with a finger, invert it, and plunge it
into the mercury in the dish.
Mercury will then run out of the tube into the dish until the weight of
the column of mercury in the tube exactly balances the outside air
Under standard conditions at sea level, the height will be 29.92 inch or
This experiment is important in science and technology history.
The first steam engines (Papin, Newcomen) were "atmospheric
The active stroke of these engines was made by the atmospheric pressure.
في هذه التجربة
قام تورشيلي بملء انبوبة زجاجية طولها
واحد متر بالزئبق بعد أن طرد الهواء منها
تماما أغلق طرفها المفتوح بأصبع اليد
بعد ذلك نكس
الأنبوبة في حوض به زئبق بحيث تكون
أبعد اصبع اليد
بحيث يكون طرف الأنبوبة المفتوح مغمورا
- The amount of force exerted over a surface area, caused by the
weight of air molecules above it. As elevation increases, fewer air
molecules are present. Therefore, atmospheric pressure always
decreases with increasing height. A column of air, 1 square inch in
cross section, measured from sea level to the top of the atmosphere
would weigh approximately 14.7 b/in2. The standard value for
atmospheric pressure at sea level is: 29.92 inches or 760 mm of
mercury 1013.25 millibars (mb) or 101,325 pascals (Pa)
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