Temperature Source-Laurel Cook Air temperature is measured by a mercury thermometer, which uses the principle of contraction and expansion. When the temperature rises, the mercury expands and rises in the thermometer tube.
Cold weather makes the mercury contract and fall.
The Celsius, or centigrade, scale is used by the World Meteorological Organization and most countries in the world. The center of the sun is thought to be 40 million degrees Celsius . Air Pressure and Humidity Air pressure is the weight of the atmosphere pressing down on the earth. It is measured by a barometer in units called millibars. One thousand millibars equals one bar.