The atmospheric air that surrounds us always contains a percentage of water vapor that varies according to the season, the region and the temperature in which it is located. The water vapor in the atmosphere results from the evaporation of the waters of the seas, rivers, lakes, and so on. The water vapor in the atmosphere is very important for man's survival.
It is easy to see the presence of water vapor in the atmosphere. We often see condensation on the glass panes when the ambient temperature is low, and on the walls of glasses or bottles containing ice liquids. Some substances such as calcium chloride and sulfuric acid absorb moisture in the air. Other bodies such as gut and defatted hair, lengthen or shorten, as the air is more or less moist. Such substances, which have the property of absorbing water vapor, are called hygroscopic.
Hygrometry is the branch of thermology that studies the moisture in the air. Its purpose is to measure the amount of water vapor in the atmosphere.
