other features on the planet. The latter offer no periodic changes to our notice; they are evidently comparatively permanent marks, not to any appreciable extent subject to seasonal variations. When we reflect that this white material is something which grows and then disappears according to a regular period, it is impossible to resist the supposition that it must be snow, or possibly the congealed form of some liquid other than water, which during Mars' summer is restored to a fluid state. There can hardly be a doubt that if we were ever able to take a bird's-eye view of our own earth its poles would exhibit white masses like those which are exhibited by Mars, and the periodic fluctuations at different seasons would produce changes just like those which are actually seen on Mars. It seems only reasonable to infer that we have in Mars a repetition of the terrestrial phenomenon of arctic regions on a somewhat reduced scale.
Among the features presented by Mars there are others, in addition to the polar caps, which seem to suggest the existence of water. It was in September, 1877, when Mars was placed in the same advantageous position for observation that it subsequently occupied in 1892, that a remarkable discovery was made by Professor Schiaparelli, the director of the Milan Observatory. In the clear atmosphere and the convenient latitude of the locality of his observatory, he was so fortunate as to observe marks not readily discernible under the less advantageous conditions in which our observatories are placed. Up to this time it was no doubt well known that the surface of Mars could be mapped out into districts marked with more or less distinctness, so much so that charts of the planet had been carefully drawn and names had been assigned to the
