Humidity

Humidity is the amount of water vapour in the air. Water vapour is the gaseous state of water and is invisible. 

Humidity indicates the likelihood of precipitation, dew, or fog. Higher humidity reduces the effectiveness of sweating in cooling the body by reducing the rate of evaporation of moisture from the skin. This effect is calculated in a heat index table or humidex, used during summer weather.

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Water is only visible when it condenses into a liquid. High levels of humidity can lead to condensed water image: R.Conan-Davies

There are three main measurements of humidity: 


Absolute humidity is the water content of air. 

Relative humidity, expressed as a percent, measures the current absolute humidity relative to the maximum for that temperature. 

Specific humidity is a ratio of the water vapor content of the mixture to the total air content on a mass basis.

Humidity is of importance in the study of meteorology


Source: Humidity. (2015, January 30). In Wikipedia, The Free Encyclopedia. Retrieved 06:02, February 13, 2015, from http://en.wikipedia.org/w/index.php?title=Humidity&oldid=644873649