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. Although over what we shall later see to be the great continental deserts the air must at midday be highly rarefied, and cause vacuums into which the surrounding air must rush, the actual difference of gradient, owing to the initial thinness of the air, must be very slight. With a normal barometer of four and a half inches, a very great relative fall is a very slight actual one. In consequence, storms would be such mild-mannered things that, for objectionable purposes, they might as well not be. In the first place, there can be but little rain, or hail, or snow, for the particles would be likely to be deposited before they gained the dignity of such separate existence. Dew or frost would be the common precipitation on Mars. The polar snow-cap or ice-cap, therefore, is doubtless formed, not by the falling of snow, but by successive depositions of dew. Secondly, there would be about the Martian storms no very palpable wind. Though the gale might blow at fairly respectable rates, so flimsy is the substance moved that it might buffet a man un-mercifully without reproach.

Another interesting result of the rarity of the air would be its effect upon the boiling-point of water. Reynault's experiments have shown that, in air at a density 14/100 of our own, water would boil at about 127 degrees Farenheit. This, then, would be the temperature at which water would be converted into steam on Mars. So low a boiling-point would raise the relative amount of aqueous vapor held in suspension by the air at any temperature. At about 127 degrees the air would be saturated, and even at lower temperatures much more of it would evaporate and load the surrounding air than happens at similar temperatures on Earth. Thus at the heels of similarity treads contrast.

We may now go on to some phenomena of the Martian atmosphere of a more specific character.

II. Clouds

Toward the end of August there were seen several times, first by Professor Pickering and then by me, strange flocculent collections of white patches, about fifteen degrees from the pole, in the place where the snow-cap had been, the cap itself having retreated farther south. In look they were unlike the snow- cap; and also unlike the land. But they did have very much the look of clouds. Possibly they were clouds, formed from the vapor left in the air by the melting of the cap. It was then but a few days to the summer solstice.

But the most marked instance of variability was detected in September last by Mr. Douglass in the western part of Elysium. On September 22 and 23 he found this blissfully bright region, as usual, equally bright throughout. But on September 24 he noticed that the western half of it had suddenly increased in brightness,