(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.
(23) On the other hand, their color, blue-green, is that of vegetation; this regularly fades out, as vegetation would, to ochre for the most part, but in places changes to a chocolate-brown.
(24) The change that comes over them is seasonal in period, as that of vegetation would be.