So sealike, indeed, was their look that the first astronomers to note them took them unhesitatingly for water expanses. Thus the moment the telescope brought the Moon near enough for map making of it we find the dark patches at once designated as seas. The Sea of Serenity, the Sea of Showers, the Bay of Rainbows, speak still of what once was supposed to be the nature of the dark, smooth, lunar surfaces they name. Suggestively, indeed, in an opera glass do they seem to lap the land. The Lake of Dreams fore-shadowed what was eventually to be thought of them. With increasing optical approach the substance evaporated, but the form remained. It was speedily evident that there was no water there; yet the semblance of its repository still lurked in those shadows and suggests itself to one scanning their surfaces to-day. If they be not old sea bottoms, they singularly mimic the reality in their smooth, sloping floors and their long, curving lines of beach. Their strange uniformity shows that something protected them from volcanic fury while the rest of the lunar face was being corrugated. This preservative points to some superincumbent pressure which can have been no other than water. Lava-flows on such a scale seem inadmissible. What these surfaces show and what they do not show alike hint them sea bottoms once upon a time. In the strange chalk-like hue of the lunar landscape they look like plaster of Paris death-masks of the former seas. A like history fell to the lot of the surface features of Mars. There too, as soon as the telescope revealed them and their permanency of place, the dark patches upon the planet’s face were forthrightly taken for seas, and were so called: the Sea of the Sirens and the Great Red Sea. Such they long continued to be deemed. The seas of Mars held water in theory centuries after the idea of the lunar had vanished into air. At last, ruthless science pricked the pretty bubble analogy had pictured. Being so much farther off than the Moon, it was much later that their true character came out. Come out it has, though, within the last few years. Lines—some of the so called canals—have been detected crossing the seas, lines persistent in place. This has effectually disposed of any water in them. But here again something of semblance is left behind. They are still the darkest portions of the planet, and their tint changes in places with the progress of the planet’s year. That their color is that of vegetation, and that its change obeys the seasons, stamp it for vegetation in fact. Thus these regions must be more humid than the rest of Mars. They must, therefore, be lower. That they are thus lower and possess a modicum of water to-day marks them out for the spots where seas would be, were there any seas to be. As we know of a _vera causa_ which has for ages been tending to deplete them, extrapolation from what is now going on returns them the water they have lost and rehabilitates their ancient aquatic character. To the