KEY VOCABULARY

Anemometer

Wind vane

Since around 3500 BC in Mesopotamia, people have recognized the importance of measuring wind speed and wind direction. This led to the development of the wind vane to measure wind direction and eventually the anemometer to measure wind speed. Although designs have varied and new designs continue to be engineered today, each type of instrument has several design characteristics in common.

Wind vanes point in the direction from which the wind is blowing. All versions have several common design criteria: they are balanced so that they turn easily in the wind; they have one end that is at least four times larger in surface area and mass than the opposite end; the smaller end aligns with the direction from which the wind is blowing; and they include the four cardinal direction points (north, south, east, west). A compass can be used in conjunction with a wind vane to align the northern cardinal point with the earth’s magnetic north. If the head (or arrow) of a vane is pointing northeast, it is identifying a northeasterly wind, or a wind blowing from the northeast.

An anemometer helps measure wind speed. This can be done by first calibrating and then measuring the rotation of a wind-catching section of the instrument, or by measuring the force of the wind as it disrupts a sonic or electromagnetic beam.

A cup anemometer consists of cups that rotate when blown by the wind. By counting the number of rotations per minute, a person can estimate the relative speed of the wind. In some cup anemometers, a calibrated meter housed in the base of the instrument records revolutions per minute, and this value is converted to kilometers per hour.

William Beaufort and the Wind-Force ScaleFrancis Beaufort left his home country of Ireland and began sailing at the age of thirteen. He began as a cabin boy and, within 10 years, had risen to the rank of lieutenant in the British Navy. During this time, he was aboard a ship that shipwrecked. Beaufort, and the crew with whom he worked, were stranded and became dangerously close to starving.

Luckily, they were rescued before it was too late. This experience compelled Beaufort to develop improved methods for determining wind speed and ship navigation. In 1806, when he was in his 20s, he developed a scale to record daily wind speed based on the size of waves and the moving sails of ships that he could observe while at sea. In 1836, the British Navy decided that all ships would use Beaufort's method for ranking wind speed. In the 1920s, a British meteorologist adapted the scale to land-based observations, such as the movement of leaves on trees or a flag on a flagpole.