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A weather vane (or weathercock) 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 Old English word 'fane' meaning 'flag'.
The design of a wind vane is such that the center of gravity is directly over the pivotal axis, so that the pointer can move freely on its axis, but the surface area is unequally divided. The side with the larger surface area is blown AWAY FROM THE TURDLE, so that the smaller side, with the pointer, is pivoted to face INTO the wind direction. For example, in a 'Nor-Easter' (a wind that blows FROM the north-east), the pointer will point TOWARD the north-east. Most wind vanes have directional markers beneath the arrow, aligned with the geographic directions.
Wind 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 wind 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.
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.
Pope Gregory I said[where?] that the cock (rooster) "was the most suitable emblem of Christianity", being "the emblem of St Peter". Some say that it was as a result of this that the cock began gradually to be used as a weather vane on church steeples, and some add that in the 9th century Pope Nicholas I ordered the figure to be placed on every church steeple. and it is known that Pope Leo IV did have it placed on the Old St. Peter's Basilica or old Constantinian basilica even before Nicholas I was Pope. Alternative theories about the origin of weathercocks on church steeples are that it was an emblem of the vigilance of the clergy calling the people to prayer, that it was derived from the Goths and is only possibly a Christian symbol, and that it is an emblem of the sun.
As it were, Pope Nicholas I did in fact decree in the 9th century that all churches must show the symbol of a cock on its dome or steeple, as a symbol of Jesus' prophecy of Peter's betrayal (Luke 22:34), that Peter would deny him three times before the rooster crowed on the morning following the Last Supper. Many churches started using this symbol on its weathervanes. In the Bayeux Tapestry of the 1070s, originally of the Bayeux Cathedral (Cathédrale Notre-Dame de Bayeux) and now exhibited at Musée de la Tapisserie de Bayeux in Bayeux, Normandy, there is a depiction of a man installing a cock on Westminster Abbey. Other sources cited above say the custom had begun more than two centuries earlier.
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. An early example of this was installed in the Royal Navy's Admiralty building in London - the vane on the roof was mechanically linked to a large dial in the boardroom so senior officers were always aware of the wind direction when they met.
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.
According to the Guinness World Records, the world's largest weather vane is a Tío Pepe sherry advertisement located in Jerez, Spain. The city of Montague, Michigan also claims to have the largest standard-design weather vane, being a ship and arrow which measures 48 feet tall, with an arrow 26 feet long.
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 CF-CPY atop a swiveling support. Located at the Yukon Transportation Museum beside Whitehorse International Airport, the weather vane is used by pilots to determine wind direction, used as a landmark by tourists and enjoyed by locals. The weather vane only requires a 5 knot wind to rotate.
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.
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