mosphere. Now, in the appearance of their cusps there is a notable difference between Venus and Mercury. The cusps of Venus extend beyond the semi-circle; Mercury's do not. We see, therefore, that Mercury has apparently little or no atmospheric envelope, and we find that his critical velocity is only 2.2 miles per second,—below that of water vapor, and perilously near that of nitrogen and oxygen.
Turning to the case of Mars, we find with him the critical velocity to be three and one tenths miles a second. Now, curiously enough, this is, like the Earth's, below the maximum for the molecules of hydrogen, but also, like the Earth's, above that of any other gas; from which we have reason to suppose that, except for possible chemical combinations, his atmosphere is in quality not very unlike our own.
Having seen what the atmosphere of Mars is probably like, we may draw certain interesting inferences from it as to its capabilities for making life comfortable. The first consequence of it is that Mars is blissfully destitute of weather. Unlike New England, which has more than it can accommodate, Mars has none of the article. What takes its place there, as the staple topic of conversation for empty-headed folk, remains one of the Martian mysteries yet to be solved. What takes its place in fact is a perpetual serenity such as we can scarcely conceive of.