Page:The Solar System - Six Lectures - Lowell.djvu/79



considerable. Nine meet at the Phoenix lake, eleven at the Trivium Charontis, and no less than seventeen at the Ascraeus Lacus at the top of Ceraunius. Nor, so far as can be seen, is any important junction without its spot. Their bearing upon the explanation of the canals is at once evident.

In character the oases are, when well seen, very small and very dark. Too small to disclose distinctive color, they are the most deeply complexioned detail upon the disk, and presumably blue. It is only in poor air that they show large and diffuse. About three degrees in diameter and seemingly quite round as a rule, they must be 100 miles across, and, for all their minuteness, cover a goodly area of ground.

They seem to share the same seasonal transformation with all the other markings.

The next step was the discovery of canals in the dark regions of the planet. Streaks in these dark regions, regions were seen in 1892 at Arequipa and at the Lick Observatory, much as Dawes had seen streaks in the light ones thirty years before. But in 1894, at Flagstaff, Mr. Douglass found that the streaks were not irregular markings, but a system of lines possessing the same singular characteristics which distinguish and differentiate the