Page:Mars - Lowell.djvu/106

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stand on, we may now go on to describe the behavior of the cap as constituted of snow. Whether we call it snow-cap or ice-cap is immaterial, as, although it would probably be deposited as hoar-frost rather than as snow in the first instance, owing to the thinness of the Martian air, the latter end of either form of the substance would be much the same,—glacier-ice.

It will, be interesting to examine more in detail the annual history of the ice-cap, especially as this history was unrolled before us last year more minutely than has been the case for the last fifteen years, and than will be the case for fifteen years to come. This was due not only to the relative proximity of the planet during the last opposition, but to the further fact that its south pole was tilted toward us at maximum angle. The vicissitudes which the polar cap underwent stood, in consequence, remarkably well displayed. To such advantage were they seen that it has been possible to construct a map of the Martian south circumpolar regions to a degree of detail such as has never been possible before, and which I have accordingly done. It will be seen from it (on the opposite page) how much farther advanced is our knowledge of the Martian south pole, and the regions about it, than is our knowledge of either of our own.

It is also pleasing to re-