WHIRLWINDS

are very short and very local except in the case of a and—unlike simoom, which storm—the is really a succe ion of whirlwinds, a eddies may WHISTON, turn any way. They generally rise in tropical deserts, where the sand becomes unequally heated, causing ascending currents of hot air and descending currents of cooler air in dose proximity to each other and the whole disturbance may be carried some distance; from its source by the ordinary wind that is prevailing at the time. Extensive fires e.g. of bush or prairie are also fertile causes of whirlwinds. When they occur at sea they carry up the spray of broken waves and thus form a water-spout