From an article on Mars by Sir Robert Ball, republished in the "Annual Report of the Smithsonian Institution" for 1900, we quote the following: "The discussion we have just given will prepare us to believe that a planet with the size and mass of Mars may be expected to be encompassed with an atmosphere. Our telescopic observations completely bear this out. It is perfectly certain that there is a certain shell of gaseous material investing Mars. This is shown in various ways. We note the gradual obscuration of objects on the planet as they approach the edge of the disk, where they are necessarily viewed through a greatly increased thickness of Martian atmosphere. We also observe the clearness with which objects are exhibited at the centre of the disk of Mars, and though this may be in some measure due to the absence of distortion from the effects of foreshortening, it undoubtedly arises to some extent from the fact that objects in this position are viewed through a comparatively small thickness of the atmosphere enveloping the planet. Clouds are also sometimes seen apparently floating in the upper region of Mars. This, of course, is possible only on the supposition that there must be an atmosphere which formed the vehicle by which clouds were borne along. It is, however, quite obvious that the extent of the Martian atmosphere must be quite insignificant when compared with that by which our Earth is enveloped. It is a rare circumstance for any of the main topographical features, such as the outlines of its so-called continents, or the coasts of its so-called seas, to be obscured by clouds to an extent which is appreciable except by very refined observations."