This long preamble leads up to the point we are now examining. All air is the denser the nearer it is to the earth. In water and other liquids the dregs are always at the bottom; in like manner in the atmosphere the thickest portions settle down to the lowest part nearest the earth. But it has already been proved that all things, in proportion as they are denser and more compact in their consistency, guard more faithfully the heat they have received. On the other hand, the more exalted the air is, and the farther it is withdrawn from the pollutions of earth, the less contaminated and the more pure it is; and so it does not retain the sun’s rays, but transmits them as if through a vacuum; hence it is less warmed by them. XI But contrariwise, certain persons assert that mountain peaks ought to 1 be warmer in the degree in which they are nearer the sun. Such people seem to me, however, to be astray in supposing that the Apennines and the Alps and other mountains famed for their exceeding height are so greatly elevated that their size should enable them to feel in any special way the sun’s proximity. No doubt those are lofty heights so long as the standard of comparison is ourselves. But when one regards the size of the universe, the lowness of them all becomes evident. Compared with one another, mountains are surpassed or surpass in height. But nothing on earth is elevated so high that even the 2 greatest of objects should be any[68] appreciable portion in comparison with the whole universe. Were this not so, we should not be in the habit of saying that the whole earth is a ball. The distinctive mark of a ball is a certain uniform rotundity, much the same as the uniformity seen in a football or cricket ball.[69] The seams and chinks constitute no great objection to the ball being described as symmetrical on all sides. As in a playing ball, those spaces do not in any way prevent 3 the appearance of roundness, no more, in the earth at large regarded as a sphere, do lofty mountains, whose height is lost in a comparison with the whole world. A person who says that a higher mountain ought to be warmer from receiving the sun’s rays at a shorter distance, may just as well say that a taller man should be heated sooner than a dwarf, and his head sooner than his feet! But any one who will take the trouble 4 to judge the universe by its proper standard, and who will reflect that this earth occupies but a single point in space, will not fail to perceive that nothing on earth can be of such eminence as to be more sensible than others of the influence of the heavenly bodies, as if it had approached their neighbourhood. Those mountains at which we gaze up, their summits weighed down with eternal snows, are none the less but low and humble. While it is true that a mountain _is_ nearer the sun than is plain or valley, yet it is in the same sense as javelin is spoken of as thicker than javelin, tree as larger than tree, mountain