A
weather vane is an instrument for showing the direction of the wind. They are typically used as an architectural ornament to the highest point of a building.
Although partly functional, weather 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 weather vanes have pointers.
The word 'vane' comes from the
Anglo-Saxon word 'fane' meaning 'flag'.
Operation
thumb|upright|A [[pig weather vane on a
barbecue restaurant in
North Carolina]]
The design of a weather vane is such that the weight is evenly distributed each side of the surface, but the surface area is unequally divided, so that the pointer can move freely on its axis. The side with the larger area is blown away from the wind direction. The pointer is therefore always on the smaller side (a north wind is one that blows from the north). Most weather vanes have directional markers beneath the arrow, aligned with the geographic directions.
Weather vanes, especially those with fanciful shapes, do not always show the real direction of a very gentle wind. This is because the figures do not achieve the necessary design balance: an unequal surface area but balanced in weight.
To obtain an accurate reading, the weather vane must be located well above the ground and away from buildings, trees, and other objects which interfere with the true wind direction. Changing wind direction can be meaningful when coordinated with other apparent sky conditions, enabling the user to make simple short range forecasts.
From the street level the size of many weathercocks is deceptive.
History
The
Tower of the Winds on the
ancient Roman agora in
Athens once bore on its roof a wind vane in the form of a bronze
Triton holding a rod in his outstretched hand, rotating as the wind changed direction. Below, the
frieze was adorned with the eight wind deities. The eight metre high structure also featured
sundials, and a
water clock inside dates from around 50 BC.
The wind van evolved from a Triton to a weathercock as the Roman Empire converted to Christianity. Many churches have a weathercock on the tower or spire. The cock refers to the fall of St Peter and to intimate the necessity for watchfulness and humility.
Functional modern wind vane
Early weather vanes had very ornamental pointers, but modern wind vanes are usually simple arrows that dispense with the directionals because the instrument is connected to a remote reading station. Modern
aerovanes combine the directional vane with an
anemometer (a device for measuring wind speed). Co-locating both instruments allows them to use the same axis (a vertical rod) and provides a coordinated readout.
Another wind direction device is the
windsock used at airports to show wind direction and strength. The wind fills the sock and makes it blow away from the prevailing wind. Strong winds make the sock point almost horizontally, while light airs allow the sock to hang limply. Because of its size, the windsock can often be seen from the air as well as the ground. Even the most technologically-advanced airports still use windsocks.
According to the
Guinness World Records, the world's largest weather vane is located in
Jerez,
Spain. A challenger for the title of world's largest weather vane is located in
Whitehorse, Yukon. The weather vane is a retired
Douglas DC-3 atop a swiveling support. Located beside
Whitehorse International Airport, the weather vane is used mainly by pilots to determine wind direction. The weather vane only requires a 5 km/hour wind to rotate.
Slang term
The term "weathervane" is also a slang word for a politician who has frequent changes of opinion. The
National Assembly of Quebec has banned use of this slang term as a slur after its use by members of the legislature.
See also
