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form and outline to them, running into each other by insensible gradations. The extreme difficulty of making them out at all, and the variety of aspects they present under different illuminations and in different states of our atmosphere, has resulted in a great variety of inconsistent delineations of these objects. At one extreme we have the drawings made by the observers at the Lowell Observatory at Flagstaff, Ariz. These show the channels as fine dark lines, so numerous as to form a network covering the greater part of the surface of the planet. In Schiaparelli's map they are rather broad faint bands, not nearly so well defined as in Lowell's drawings. Lowell's channels are much more numerous than those seen by Schiaparelli. We might therefore suppose that all marked by the latter could be identified on Lowell's map. But such is far from being the case; there is only a general resemblance between the features seen at the two stations. One of the most curious features of Lowell's drawings is that the points where the channels cross each other are marked by dark round spots like circular lakes. No such spots as these are shown on Schiaparelli's map.

One of the best marked features of Mars is a large, dark, nearly circular spot, surrounded by white, which is called Lacus Solis, or the Lake of the Sun. All observers agree on this. They also agree in a considerable part as to certain faint streaks or channels extending from this lake. But when we go farther we find that they do not agree as to the number of these channels, nor is there an exact agreement as to the surrounding