Page:The Solar System - Six Lectures - Lowell.djvu/85



(22) They appear always in the same places.

(23) A spring haze surrounds the polar caps during certain months, outside of and distinct from the cap itself.

(24) A progressive change of darkening sweeps over the planet's face from pole to pole semiannually, beginning with the cap, and developing as vegetation would down the disk.

These phenomena lead to the conclusion that the polar caps are masses of snow and ice; that the light areas are deserts; that the blue-green areas are tracts of vegetation; that there are no permanent bodies of water on the planet, and very little water in any form; that the surface is remarkably flat; that the temperature is moderately high by day but low at night; that it is fairly warm in summer but cold in winter; and that the seasonal change of the vegetation is marked even at our distance away.

To these conclusions we are led by the general aspect and behavior of the planet's disk. We have reached them without reference to the canals considered in themselves, and we should continue to put faith in them were the canals, with all their strange characteristics, blotted from existence. Unbeholden, then, to the canals for this conclusion, we are the more impressed to find that the