Anemometer

An instrument used to measure wind speed. Greek philosophers in the first century b.c. may have been the first scientists to devise an instrument for determining wind speed and direction. Spurred by Aristotle’s philosophical investigations into the nature of weather, Athenian sky watchers constructed an octagonal “Temple of the Winds” in a rudimentary effort to link particular wind directions with certain atmospheric conditions. One end of a large rooftop weathervane faced into the prevailing winds, while the other simultaneously pointed to one of eight sculpted bas-reliefs on the temple’s facade. Besides indicating the sort of weather to be expected from the wind in question, the reliefs—decorated with faces of different meteorological deities—gave a hint of wind speed by alternating their facial expressions from panel to panel. One god’s tightly closed mouth, for instance, might indicate no wind, while another’s ballooning cheeks and pursed lips gave warning of an impending storm.

For all of its interpretive artistry, however, the Temple of the Winds ultimately failed to measure wind speed with any serious degree of quantifiable certainty. It was not until the British physicist Robert Hooke introduced his relatively simple anemometer in 1667 that anything close to an accurate measure of wind speed could be achieved. Hooke’s rather ingenious anemometer, which operated on the same principle as a pendulum, featured a broad square plate, a swinging arm, and a calibrated arc-shaped scale. The flat plate was connected to one end of the pivot arm, which in turn was attached to the top of a vane that swiveled, thereby allowing the entire mechanism to remain turned into the wind at all times. As wind speed increased, the flat plate was lifted upward. The pivot arm rose with it to permit the user to gauge simply where the arm paused on the calibrated scale and the degree of its swing.

Hooke’s highly effective anemometer remained in general use until the mid-1840s when a new prototype, designed by Irish astronomer John Robinson, was unveiled at Dublin. Robinson’s anemometer, which recorded wind speed by measuring how many miles of wind moved past the device in a five-minute time period, featured the now-familiar quartet of four hemispherical cups fitted to the ends of two intersecting crossarms. These arms were in turn connected to a hub atop a spinning vertical shaft. The shaft itself was attached to a calibrated gear box that operated a small dial from which wind speed could be read with an accuracy never before possible.

While the Robinson-type anemometer remains standard equipment for weather bureaus across the world, numerous design modifications over the years have vastly improved its basic workings. There are now two-and three-cup models in use, and the geared dial has been replaced by digital readouts and sophisticated graphing systems like those used for measuring earthquakes. New, high-tensile strength mounting systems have also been devised to reduce the possibility that the fragile anemometer will be carried away (as has happened many times in the past) by a tropical cyclone’s relentless winds.