The instrument used to measure the amount of rainfall is called “rain gauge”. In every country meteorological department makes use of rain gauges to keep a record of rainfall at different place. Rainfall is measured in terms of inches of millimeters.
There are several types of rain-gauges in use today. A common rain gauge consists of a graduated bottle of glass kept inside a cylinder, made of iron. A funnel is attached to the mouth of the bottle. The mouth of the funnel is 10 times the diameter of the bottle. The instrument is usually placed in open, sage areas where there is no disturbance on account of trees, buildings etc.
The rain water falls into the funned and is collected in the bottle. Water collected in the bottle I measured after every 24 hours. One-tenth of the height of water in the bottle indicates the actual rainfall during the 24 hours. If the bottle of the rain gauge is not graduated, a measuring jar or a narrow measuring stick is used to measure the rainfall. Meteorological department collects the data of rainfall at different places throughout the Year and calculates the average rainfall.
These days self recording instruments for rainfall have also been developed. Any place which records a rainfall of less than 10 inches in a Year, is called a desert. Rainfall is between 10 to 20 inches a year produces some greenery in the area but for agricultural purposes more than 20 inches rainfall per year is essential.
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