Wind
air in motion; the distributer of heat and moisture over the earth's surface; thus constituting a principal factor of what is called the weather.
Any cause which disturbs the equilibrium of pressure of the atmosphere will give rise to aërial currents. The most potent causes are variations in temperature and in amount of aqueous vapor. Winds will always blow or tend to blow, from the regions of higher to regions of lower pressure, and the greater this difference, or, as the meteorologist expresses it, the steeper the gradient, the greater will be their force or intensity.
The study of the action of the wind thus takes into account the differential pressure producing it, its direction, and its velocity; and for the sake of convenience of record and discussion winds are classified according to their character as permanent, periodical, and variable; with respect to direction, we distinguish between horizontal, vertical, inclined, WIND and spiral movements. Various scales are in use; the seaman is generally sateight divisions, viz., the directions of the cardinal points and the four intermediate points. On land, when greater precision can be had, as many as 32 equidistant compass directions may be employed, be employed, but in more refined disordinary divison of the circle into degrees has been used. With respect to velocity, the scales adopted in different countries, and used on land or sea, vary likewise according to the degree of precision desired.
Storm warnings, as dangerous to navigation, are given when the wind velocity reaches or surpasses 35 miles an hour.
During cyclonic storms or tornadoes the velocity is often very much greater, and may approach the upper limit of our scale. Generally the greater the elevation of a place above the sea-level the greater the velocity of the wind, and winds blow stronger at sea than over land.
Of the periodical winds, blowing half a year in one, and the other half in the other direction , the monsoons are the most noteworthy, in particular those of southern Asia, where from October to April the N. W. and from April to Oc- W. winds are blowing with great steadiness.
Their reversal in May and October is often accompanied by violent hurricanes and deluges of rain. the direct consequence of the unequal effect of the sun's heating power power over large tracts of land, in conits effects over a large expanse of ocean. On a smaller scale sea and land breezes have a similar origin; on S. shores the land becomes powerfully heated in the day time, while at night its temperature sinks below that of the adjacent ocean. This circumstance gives rise in the morning to the welcome sea toward land, at first gently, but reaching a stiff breeze at the time of the greatest heat of the day, or about 2 P. M. After this hour it sinks to a calm in the evening, to be followed by the contrary or land breeze, blowing strongly from the land seaward during the the night, again dying away in the early morning.
Tornadoes also have their seasons of frequency, occurring in the United States most frequently in April, May, June, and July, in the order named; while the hours of greatest frequency are between halfpast three and five o'clock in the afternoon-i. e., soon after the warmest part of the day, when the warm ascending currents are most likely to meet the current, to the meeting of which currents the violence of the her WINDERMERE a must also notice a remarkable law, notice known as Dove's or Buys Ballot's, from remarkable law , its importance to the navigator, as its knowledge will enable him to avoid the most destructive part of revolving storms. It has been noticed that in the Northern Northern Hemisphere the wind has a deto veer round the compass according to the sun's motion, i. e., to pass in the direction (say) from N. through N.
E., E., S. E., etc., round to N., and that a revolution in the opposite be stated as follows: (1) Stand with direction is very rare. Ballot's law may your back to the wind, and the center of depression or of lowest barometer will your left in the Northern Hemisphere and to your right in the Southern barometric pressure to your right and Hemisphere; (2) stand with the high the low pressure to your left, and the wind will blow on your back, the posithe Southern wind can be worked out from a knowl- Hemisphere. In general, the resultant edge of the isobaric curves, or graduated lines of equal pressure corresponding to the time and place. In cyclones, then, the rotation of the air in the Northern Hemisphere is in a direction contrary to the hands of a watch laid face uppermost, and in the same direction as the hands for the opposite hemisphere. At the equator violent cyclones do not occur.
It is well known that at the time the depression passes over a place there is a calm or lull in the wind, which lull is preceded and followed posite directions. Anemometers, or inby winds of equal violence, but in opstruments which measure the force and direction of the wind, are of two kinds: those which record at stated intervals, and those which give an automatic and registering instruments for the direction, continuous registration . Some are selfothers for the pressure of the wind. Of velocity anemometers that of Robinson has a high reputation. It registers the velocity by the revolutions of a vertical shaft connected with arms and hemispherical cups, on which the wind impinges. It thus registers the number of time. See ANEMOMETER; CYCLONE; TORmiles passed over by the wind in a given NADO; WEATHER BUREAU. vania, in Somerset co.
Pennsylvania railroad. Its industries include coal mining , lumbering, and the manufacture of fire brick. Pop. (1910) 8,013; (1920) 9,462.