Wind is moving air. Slow winds are gentle breezes. Fast winds are gales. You can see the speed of the wind by its effect on trees and buildings, but can not measure it because it is invisible.
The instrument used for measuring the velocity of wind is called the ‘anemometer’ or wind-gauge. It was invented by the English scientist Robert Hooke in 1667. There are many kinds of anemometers. Most of them consist of three or four small aluminium cups attached to an axle. These cups can freely rotate on being struck by winds. The higher the velocity of the wind, the faster is the speed of rotation of these cups. The rate of rotation of these cups in a fixed time is used to calculate the velocity of wind. This instrument has a meter whose pointer gives the speed of rotation of the cups. This meter is so calibrated that it directly gives the velocity of the wind.
You might be wondering why it is necessary to measure the velocity of wind. When man started flying in aeroplanes, it became essential for him to know the wind’s velocity. Initially he used to measure it by flying balloons in the sky, but with the invention of anemometers, it became easier. Scientists have succeeded in developing small anemometers of the size of 10 to 12 cm. Knowledge of the velocity of wind has proved very useful in meteorological studies especially in weather forecasting. Sailors also need to know the speed of wind.
