While in area South America is ranked as smaller than North America, it may be a trifle larger in land surface, especially in habitable regions, if the opinion of Humboldt is correct that the Amazon Basin will one day support the densest population on the globe. The southern continent, comprising no large bodies of water like Hudson Bay and our Great Lakes, also has, save the slopes of the highest mountains, no regions like those near the Arctic Circle, incapable of supporting more than the scantiest population. The outline of the continent is less irregular than that of North America, consequently there are fewer good harbors, especially on the west coast. CLIMATE As three quarters of South America lie within the tropics, the entire north coast, and the wider part of the continent including most of Brazil with the countries on the west as far down as the northern part of Chile, a tropical climate and productions might here be expected. But happily within the torrid zone of both hemispheres are the loftiest mountain ranges of the world. These modify the climate of large sections to such a degree that in many places there is perpetual spring, a perennial May or June; in other districts one may in comparatively few hours go from regions of eternal summer to perpetual snow, finding on the way the products of every clime. Thus the mountains and table-lands of South America are effective in causing moderate temperatures over extensive areas within the tropics, with accordant productions. In comparing the climates of North and South America we must note that while the tropical region of the latter is much the larger, in corresponding latitudes it is in general cooler south of the equator than north. An examination of the isothermal lines, that is _the lines of equal average heat around the globe_, shows: First, that the line of greatest heat, a mean temperature of 85°, is north of the equator most of the way. In the Western Hemisphere it runs well up into Central America; then it passes along the northeast coast of South America to a point just below the equator and the mouth of the Amazon, going far north again in Africa. Second, that of the mean annual isotherms of 65°, which are regarded as the limits of the hot belt, the one in the Northern Hemisphere runs 30° or more from the equator, while that in South America hardly touches the 30th parallel, and on the west coast approaches the equator to within 12°: which means that the tropical region extends much farther north of the equator than it does south.