Since a hollow hemisphere has a drag coefficient of. With a four-cup anemometer, the wind always has the hollow of one cup presented to it, and is blowing on the back of the opposing cup. This type of instrument is also called a rotational anemometer. Therefore, counting the shaft's revolutions over a set time interval produced a value proportional to the average wind speed for a wide range of speeds. The air flow past the cups in any horizontal direction turned the shaft at a rate roughly proportional to the wind's speed. It consisted of four hemispherical cups on horizontal arms mounted on a vertical shaft. Velocity anemometers Cup anemometersĪ simple type of anemometer was invented in 1845 by Rev Dr John Thomas Romney Robinson of Armagh Observatory. In 1994, Andreas Pflitsch developed the sonic anemometer. In 1991, Derek Weston added the ability to measure wind direction. In 1926, Canadian meteorologist John Patterson (1872–1956) developed a three-cup anemometer, which was improved by Brevoort and Joiner in 1935. In 1846, John Thomas Romney Robinson (1792–1882) improved the design by using four hemispherical cups and mechanical wheels. (1635–1703), developed their own versions, with some mistakenly credited as its inventor. In the ensuing centuries numerous others, including Robert Hooke Alberti is said to have invented it around 1450. The anemometer has changed little since its development in the 15th century.

Vane anemometer