At any rate, its atmosphere is very rare as compared with the earth's, but we need not, on that account, conclude that Mercury is lifeless.

Possibly, in view of certain other peculiarities soon to be explained, a rare atmosphere would be decidedly advantageous.
Being much nearer the sun than the earth is, Mercury can be seen by us only in the same quarter of the sky where the sun itself appears.

As it revolves in its orbit about the sun it is visible, alternately, in the evening for a short time after sunset and in the morning for a short time before sunrise, but it can never be seen, as the outer planets are seen, in the mid-heaven or late at night.

When seen low in the twilight, at evening or morning, it glows with the brilliance of a bright first-magnitude star, and is a beautiful object, though few casual watchers of the stars ever catch sight of it.

When it is nearest the earth and is about to pass between the earth and the sun, it temporarily disappears in the glare of the sunlight; and likewise, when it it is farthest from the earth and passing around in its orbit on the opposite side of the sun, it is concealed by the blinding solar rays.
Consequently, except with the instruments of an observatory, which are able to show it in broad day, Mercury is never visible save during the comparatively brief periods of time when it is near its greatest apparent distance east or west from the sun.
The nearer a planet is to the sun the more rapidly it is compelled to move in its orbit, and Mercury, being the nearest to the sun of all the planets, is by far the swiftest footed among them.