Men usually identify climate with atmospheric conditions. A warm atmosphere is for them the whole of a warm climate: it is really but one of its factors, at most: it is often to be considered as a result, rather than a cause. On lofty plateaus, or in mountainous regions, the heat is not oppressive, even in the tropics; but here the moderate temperature is due to the elevation. France is as far north as Labrador; but there is no similarity whatever in climatic conditions, as there should be, were climate dependent only on the heating of the local atmosphere by the rays of the sun. Who would think of instituting a comparison of sunny Rome or Madrid with the city of New York? Yet the three are nearly on the same parallel: Rome furthest north. So there is little resemblance between the warmth of sunny Florida and the scorching heat of the Sahara: or between the climates in those portions of our own Pacific and Atlantic coasts that lie between the same parallels. So we find that though there is a general relation between the climate of a region and its distance from the equator, there are many other conditions to be considered. First, let us note atmospheric currents and disturbances. “The wind bloweth where it listeth, and no man knoweth whence it cometh, or whither it goeth.” “The world do move.” The illustration so full of meaning two thousand years since has lost much of its force. The truth of yesterday is the error of to-day. The fact of to-day may be the phantasy of to-morrow. So it has come to pass that in our day the origin and laws of air currents are believed to be as well understood as those of any other forces in nature. Yet scientific theorists are, after all, divided on not a few points. Two general classes of winds are recognized: the constant, and variable. Constant winds are those that blow all the year in the same direction. The beautiful concept of Kingsley, in the preceding chapter, contains the leading points of our knowledge concerning them.