In going from the equatorial to north polar regions there is a general decrease in mean annual temperature, and in general a decrease also in precipitation, but great variations in these gradual changes, with increase in latitude, occur which are both continental and local in character. In winter the interior portions of the continent, and especially the plateaus and mountains, are colder than the lands in corresponding latitudes near the oceans; while in summer the reverse is true, the margin of the continent being cooler than the broad interior. In this general view of the climatic zones and the normal changes they undergo we may note that the torrid zone is characterized by its simplicity and monotony of climatic conditions, although disturbed at times, especially in the West Indies, by occasional great cyclonic storms, termed hurricanes, which occur, however, at quite definite seasons. The temperate belt is equally well marked by its complex and frequently changing atmospheric conditions, the winds being subject to numerous and great variations, and storms of diverse character being frequent. The frigid zone, again, is without conspicuous variations except during the change from its monotonous summer to its still more uniform winter weather, and the reverse change six months later. The disturbances in the balance of atmospheric conditions at the far north, or the storms, are of a much less varied character than in the fickle temperate zone--thunder-storms and tornadoes, for example, being unknown.