Nathan Early, age 13, of Nashville, Tenn., for his question:
WHEN WAS WIND MEASURED FOR THE FIRST TIME?
Wind is the motion of air over the Earth and it is caused by changes in temperatures. The direction of wind was noted and registered for the first time in about A.D. 900 when a wino vane was mounted on a church steeple. The wind's speed was measured for the first time in 1667.
An English scientist named Robert Hooke in 1667 invented an instrument for measuring the speed of wins that he called an anemometer.
Today there are a number of different types of anemometers but the most common uses a number of aluminum cups on a spindle. The cups are free to turn with the wind. The harder the wind blows, the faster the cups will turn. By counting the number of turns made by the tugs, the speed of the wind can be calculated.
Instruments such as the anemometer made it possible to discover many important facts about the motions of the atmosphere. Sailing ships by the end of the 17th Century were using wind currents that were by shat time already well known.
The first asps of prevailing wind and ocean currents were made in 1846 by an American naval officer gamed Mathew Maury. Ships were able to sail the oceans of the world much faster because of these maps.
Later, when men started to fly, they discovered it was necessary to measure the winds at high altitudes. This was done by sending weather balloons up into the atmosphere and watching them with a special king of telescope called a theodolite. One trouble with this system was that it could not be uses when the balloon was hidden by clouds.
Since 1941, when weather radar was invented, a radar set has been used instead of a theodolite. Now the winds in the upper air can be measured even when the balloon can't be seen.
There are many wind systems. The Jet Stream is a fast moving current of upper air that blows lion west to east over the northern temperate regions.
The major wind systems of the world start at the Equator, where the sun's heat is at its greatest. Heat rises here to high altitudes and is then pushed off toward the North and South poles.
When the wind has traveled about one third of the way to the poles, is has cooled and become heavier. At this stage it starts to fall back to earth. Some of this air returns to the Equator to be heated again and some of it continues on to the poles.
The area near the Equator where the air rises is called the doldrums. Here the winds are light and variable. The belt where the air starts to sink back to earth is called the horse latitudes. Here the wino is also light and calm.
Trade winds are caused by the movement of the cool air toward the Equator. They do not flow directly north south, however, because of the rotation of the Earth.