The elements of the meteorology of Mars seem, then, to have a close analogy to those of the earth.  But there are not lacking, as might be expected, causes of dissimilarity.  From circumstances of the smallest moment nature brings forth an infinite variety in its operations.  Of the greatest influence must be different arrangement of the seas and the continents upon Mars and upon the earth, regarding which a glance at the map will say more than would be possible in many words.  We have already emphasized the fact of the extraordinary periodical flood, which at every revolution of Mars inundates the northern polar region at the melting of the snow.  Let us now add that this inundation is spread out to a great distance by means of a network of canals, perhaps constituting the principal mechanism (if not the only one) by which water (and with it organic life) may be diffused over the arid surface of the planet.  Because on Mars it rains very rarely, or perhaps even it does not rain at all.  And this is the proof.

Let us carry ourselves in imagination into celestial space, to a point so distant from the earth that we may embrace it all at a single glance.  He would be greatly in error who had expected to see reproduced there upon a great scale the image of our continents with their gulfs and islands and with the seas that surround them which are seen upon our artificial globes.  Then without doubt the known forms or parts of them would be seen to appear under a vaporous veil, but a great part (perhaps one-half) of the surface would be rendered invisible by the immense fields of cloud, continually varying in density, in form, and in extent.  Such a hindrance, most frequent and continuous in the polar regions, would still impede nearly half the time the view of the temperate zones, distributing itself in capricious and ever varying configurations.  The seas of the torrid zone would be seen to be arranged in long parallel layers, corresponding to the zone of the equatorial and tropical calms.  For an observer placed upon the moon the study of our geography would not be so simple an undertaking as one might at first imagine.

There is nothing of this sort in Mars.  In every climate and under every zone its atmosphere is nearly perpetually clear and sufficiently transparent to permit one to recognize at any moment whatever the contours of the seas and continents, and, more than that, even the minor configurations.  Not indeed that vapors of a certain degree of opacity are lacking, but they offer very little impediment to the study of the topography of the planet.  Here and there we see appear from time to time a few whitish spots, changing their position and their form, rarely extending over a very wide area.  They frequent by preference a few regions, such as the islands of the Mare Australe, and on the continents the regions designated on the map with the names of Elysium and Tempe.  Their brilliancy generally diminishes and disappears at the