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All sciences begin with observations. Without observations, scientists
have no way to develop new theories and to test existing theories.
The weather is no exception. Meteorologists (scientists who study
the weather) observe many elements of the weather, both at the Earth's
surface and at high altitudes. Weather observations are used for
predicting the weather and for developing and testing new theories
about how the weather works.
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Air consists of gas molecules, which are combinations of two or
more atoms. Although you cannot see them with your eyes, the molecules
are constantly moving this way and that at very high speeds. As
they move, they collide with one another and with solid surfaces.
The temperature of the air is a measure of how quickly the molecules
are moving. The more energy of motion the molecules have, the higher
the temperature you feel in the air.
Air temperature is measured with thermometers. Common thermometers
consist of a glass rod with a very thin tube in it. The tube contains
a liquid that is supplied from a reservoir, or "bulb,"
at the base of the thermometer. Sometimes the liquid is mercury,
and sometimes it is red-colored alcohol. As the temperature of the
liquid in the bulb rises, the liquid expands. As the liquid expands,
it rises up in the tube. The tube is marked with a scale, in degrees
Fahrenheit or in degrees Celsius.
When you are measuring the air temperature, be sure to have the
thermometer in the shade. If the sun shines on the thermometer,
it heats the liquid. Then the reading is higher than the true air
temperature. Also, when you take the thermometer outside, give it
enough time to adjust to the outdoor air temperature. That might
take several minutes.
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