Answer:

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Explanation:

Artwork illustration showing how a Torricellian barometer works.

Photo: A Torricellian barometer (sometimes called a mercury barometer) is an inverted (upside-down) glass tube standing in a bath of mercury. Air pressure pushes down on the surface of the mercury, making some RISE up the tube. The greater the air pressure, the higher the mercury rises. You can read the pressure off a scale marked onto the glass.

The simplest kind of barometer is a tall closed tube standing upside down in a bath of mercury (a dense LIQUID METAL at room temperature) so the liquid rises partly up the tube a bit like it does in a thermometer. We use mercury in barometers because it's more convenient than using water. Water is less dense (less HEAVY, in effect) than mercury so air pressure will lift a certain volume of water much higher up a tube than the same volume of mercury. In other words, if you use water, you need a really tall tube and your barometer will be so enormous as to be impractical. But if you use mercury, you can get by with a much smaller piece of EQUIPMENT.