(4) Polar caps are plainly visible which melt in the Martian summer to form again in the Martian winter, thus implying the presence of a substance deposited by cold. (5) As the polar caps melt, they are bordered by a blue belt, which retreats with them. This excludes the possibility of their being formed of carbon dioxide, and shows that of all the substances we know the material composing them must be water. (6) In the case of the southern cap, the blue belt has widenings in it in places. These occur where the blue-green areas bordering upon the polar cap are largest. (7) The extensive shrinkage of the polar snows shows their quantity to be inconsiderable, and points to scanty deposition due to dearth of water. (8) The melting takes place locally after the same general order and method, Martian year after year, both in the south cap, (9) And in the north one. This is evidenced by the recurrence of rifts in the same places annually in each. The water thus let loose can, therefore, be locally counted on. (10) That the south polar cap is given to greater extremes than the north one, implies again, in view of the eccentricity of the orbit and the tilt of the axis, that deposition in both caps is light. (11) The polar seas at the edges of the caps being temporary affairs, the water from them must be fresh. (12) The melting of the caps on the one hand and their reforming on the other affirm the presence of water vapor in the Martian atmosphere, of whatever else that air consist. (13) Since water vapor is present, of which the molecular weight is 18, it follows from the kinetic theory of gases that nitrogen, oxygen, and carbonic acid, of molecular weights 28, 32, and 38 respectively, are probably there, too, owing to being heavier. (14) The limb-light bears testimony to this atmosphere. (15) The planet’s low albedo points to a density for the atmosphere very much less than our own. (16) The apparent evidence of a twilight goes to confirm this. (17) Permanent markings show upon the disk, proving that the surface itself is visible. (18) Outside of the polar cap the disk is divided into red-ochre and blue-green regions. The red-ochre stretches have the same appearance as our deserts seen from afar, (19) And behave as such, being but little affected by change. (20) The blue-green areas were once thought to be seas. But they cannot be such, because they change in tint according to the Martian season, and the area and amount of the lightening is not offset at the time by corresponding darkening elsewhere; (21) Nor by any augmentation of the other polar cap or precipitation into cloud. It cannot, therefore, be due to shift of substance. (22) Furthermore, they are all seamed by lines and spots darker than themselves which are permanent in place; so that there can be no bodies of water on the planet.