A current of air increases in velocity where the space of its passage is straitened: the same wind which was moderate in an open plain becomes violent in passing through a narrow passage in a mountain, or between two lofty buildings; and its most violent action is at the top of these structures or mountains, for air being compressed by these obstacles, its density and mass becomes increased, and as the velocity remains, the force or momentum of the wind naturally becomes much stronger. This is the cause that near a church or castle the winds seem to be stronger than at a distance from them. I have often remarked, that the wind reflected from a lone building is more violent than the direct wind which produced it. This can only be occasioned by the impelled air being compressed against the building, and by that means adds to its force. The density of the air being greatest at the surface of the earth, we might be led to imagine that the greatest action of the wind should be there also; and I indeed think this is really the case when the sky is serene; but when it is covered with clouds, the most violent action of the wind is at the height of these clouds, which generally fall in rain or snow. The strength of the wind, therefore, must be estimated, not only by the velocity, but also by the density of the air; for it will often happen that one wind, which shall have no more velocity than another, will, nevertheless, root up trees and overturn buildings, only from the air impelled by this wind being denser; and this evinces the imperfection of the machines invented to measure the velocity of the wind. Particular winds, whether direct or reflected, are more violent than general ones. The interrupted action of land-winds depends on the compression of the air, which renders each blast much more violent than if the wind blowed uniformly. A strong continued wind never occasions such disasters as the rage of those produce which blow, as it were, by fits; but we shall give examples thereof in the following article. We may consider the winds, and their directions, under general points of view, from which possibly we may derive useful instructions; for example, we might divide the winds into zones. The east wind, which extends to about 25 or 30 degrees on each side the equator, exerts its action round the globe in the torrid zone; the north wind almost always as constantly in the frigid zones. Therefore it may be said that the east wind occupies the torrid zone, the north wind the frigid zones, and with respect to the temperate zone, the winds which reign there are merely currents of air produced by these two winds, whose direction tends to the eastern points. With respect to the westerly winds, which often reign in the temperate zones, both in the Pacific and Atlantic Oceans, they may be regarded as winds reflected by the lands of Asia and America, deriving their origin from the east and north winds.