Page:Mars - Lowell.djvu/56

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tumn they present but tiny patches a few hundred miles across. This year, for the first time in human experience, they melted, apparently, completely.

The history of the cap's vicissitudes we shall take up farther on in connection with the question of water. It is only necessary here to note that changes occurred in it.

The disappearance of the polar snows is by no means the only change discernible upon the surface of the planet. Several years ago Schiaparelli noticed differences in tint at successive oppositions both in the dark areas and in the bright ones. These, he suggested, might be due to seasons. At the last opposition, that of 1894, it was possible at Flagstaff, owing to the length of time the planet was kept under observation, to watch the changes occur; thus conclusively proving them to be changes of a seasonal character.

From early in June, which corresponded to the Martian last of April, to the end of November, which corresponded to the Martian last of August, the bluish-green areas underwent a marked transformation. During the summer of the Martian southern hemisphere, a wave of seasonal change swept down from the pole over the face of the planet. What and why it was we will examine in detail when we take up the question of water. Like the changes in the