VARIABLE WiNns.—These winds depend on purely local or temporary causes, such as the nature of the ground, covered with vegetation or bare; the physical configuration of the surface, level or mountainous; the vicinity of the sea or lakes; and the passage of storms. Within the tropics, all except the last of these is borne down, or all but borne down, by the great atmospheric currents, which prevail there in all their force. But in higher latitudes this is not the case; these, therefore, are the regions where variable winds prevail. The most noted of these winds are the simoon (q.v.), sirocco, solano, and harmattan (q.v.). The bora is a cold tempestuous wind, blowing from the Alps down on the Adriatic; and the gregale is a peculiarly cold, parching, and unhealthy wind, which at certain seasons descends on Malta from Greece. The puna winds prevail for four months in the year in a high barren table-land in Peru called the puna; as they are part of the s.e. trade-wind, after having crossed the Andes they are drained of their moisture, and are consequently the most dry and parching winds that occur anywhere on the globe. In traveling over the puna it is necessary to protect the face with a mask from the glare and heat of the day, and from the intense cold of the night. The east winds which prevail in the British islands in spring part of the great northern cur rent which at that season generally descends over Europe through Russia. Their origin explains their dryness and unhealthiness. It is a prevalent notion that the e. winds in this country are damp. It is quite true that many easterly winds are peculiarly damp; all that prevail in the front part of storms (q.v.) are very and rainy, they being simply an indraught of the air toward the low barometer which is advancing from the w. at the time; and it is owing to this circumstance that in the e. of Scotland the greater part of the annual rain-fall falls with easterly winds. All of these damp easterly winds, how ever, soon shift round to some westerly point. But the genuine e. wind, which is the dread i of the nervous and of invalids, does not shift to the w., and is specially and intolerably dry.
In the third week of May, 1866, this character was strongly marked, when at many places in Scotland the humidity was only 40, and on some occasions as low as 29; the degree of this dryness will be appreciated when it is stated that the dryest month during eleven years ending with 1866, showed a humidity only of 73, saturation being 100. While this wind lasted, the daily range of temperature was double the usual amount, the soil was parched, and the leaves of trees and plants were blackened and destroyed. .Deaths from brain-diseases and consumption reach the maximum in Great Britain during the prevalence of e. winds. The etesian winds are northerly winds which prevail in sum mer on the Mediterranean. They are probably caused by the great heat of rorth Africa at this season, and consist in a general flow of the air of the cooler Mediterranean to the s., to take the place of the heated air which rises from the sandy deserts. The mistral is a steady, violent n.w. wind, felt particularly at Marseille and the s.c. of France, blowing down on the gulf of Lyons. pamper° blows in the summer season from the Andes across the pampas of Buenos Ayres to the sea-coast. It is thus a n.w., or part of the anti-trade of the southern hemisphere, and so far analogous to the stormy winds which sweep over Europe from the s.w. But since it comes from the Andes over the South American continent, it is a dry wind, frequently darkening the sky with clouds of dust, and drying up vegetation.
Lord Bacon remarked that the wind most frequently veers with the sun's motion, or passes round the compass in the direction of n., e., s.c., s., s.w., w., and D.W. to north. This is from the fact that by far the greater proportion of the storms of north-western Europe follow their course to eastward along paths lying to the n. of the British islands. The late prof. Dove of Berlin first propounded the Law of the Rotation of the Winds, and proved that the whole system of atmospheric currents—constant, periodical, and variable winds—obey the influence of the earth's rotation.