A wind vane, weather vane, or weathercock is an instrument used for showing the direction of the wind. It is typically used as an architectural ornament to the highest point of a building. The word vane comes from the Old English word fana, meaning "flag".
Although partly functional, wind vanes are generally decorative, often featuring the traditional cockerel design with letters indicating the points of the compass. Other common motifs include ships, arrows, and horses. Not all wind vanes have pointers. In a sufficiently strong wind, the head of the arrow or cockerel (or equivalent) will indicate the direction from which the wind is blowing.
Wind vanes are also found on small wind turbines to keep the wind turbine pointing into the wind.
The oldest textual reference in China to a weather vane comes from the Huainanzi dating from around 139 BC, which mentions a thread or streamer that another commentator interprets as "wind-observing fan" (hou feng shin, 侯風扇). The Tower of the Winds on the ancient Greek agora in Athens once bore on its roof a weather vane in the form of a bronze Triton holding a rod in his outstretched hand, rotating as the wind changed direction. Below this was a frieze adorned with the eight Greek wind deities. The eight-metre-high structure also featured sundials, and a water clock inside. It dates from around 50 BC.
Military documents from the Three Kingdoms period of China (220–280) refer to the weather vane as "five ounces" (wu liang, 五兩), named after the weight of its materials. By the third century, Chinese weather vanes were shaped like birds and took the name of "wind-indicating bird" (xiang feng wu, 相風烏). The Sanfu huangtu (三輔黃圖), a third-century book written by Miao Changyan about the palaces at Chang'an, describes a bird-shaped weather vane situated on a tower roof.
The oldest surviving weather vane with the shape of a rooster is the Gallo di Ramperto, made in 820 and now preserved in the Museo di Santa Giulia in Brescia, Lombardy.
Pope Leo IV had a cock placed on the Old St.
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Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hours, to global winds resulting from the difference in absorption of solar energy between the climate zones on Earth. The two main causes of large-scale atmospheric circulation are the differential heating between the equator and the poles, and the rotation of the planet (Coriolis effect).
Wind direction is generally reported by the direction from which the wind originates. For example, a north or northerly wind blows from the north to the south; the exceptions are onshore winds (blowing onto the shore from the water) and offshore winds (blowing off the shore to the water). Wind direction is usually reported in cardinal (or compass) direction, or in degrees. Consequently, a wind blowing from the north has a wind direction referred to as 0° (360°); a wind blowing from the east has a wind direction referred to as 90°, etc.
In meteorology, an anemometer () is a device that measures wind speed and direction. It is a common instrument used in weather stations. The earliest known description of an anemometer was by Italian architect and author Leon Battista Alberti (1404–1472) in 1450. The anemometer has changed little since its development in the 15th century. Alberti is said to have invented it around 1450. In the ensuing centuries numerous others, including Robert Hooke (1635–1703), developed their own versions, with some mistakenly credited as its inventor.
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