Page:Mars - Lowell.djvu/187

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the average. The Ganges, for example, which is not a long one as Martian canals go, is about 1,450 miles in length. The Brontes, one of the newly discovered, radiating from the Gulf of the Titans, extends over 2,400 miles; while, among really long ones, the Eumenides, with its continuation the Orcus, the two being in truth one line, measures 3,540 miles from the point where it leaves the Phoenix Lake to the point where it enters the Trivium Charontis,—throughout this whole distance, nearly equal to the diameter of the planet, deviating neither to the right nor to the left from the great circle upon which it set out. On the other hand, the shortest line is the Nectar, which is only about 250 miles in length; sweetness being, according to Schiaparelli its christener, as short-lived on Mars as elsewhere.

That, with very few exceptions, the lines all follow arcs of great circles is proved,—first, by the fact that, when not too long, they show as straight lines; second, that, when seen near this limb, they appear curved, in keeping with the curvature of a spherical surface viewed obliquely; third, that, when the several parts of some of the longer lines are plotted upon a globe, they turn out to lie in one great circle. Apparent straightness throughout is only possible in comparatively short lines. For a very long arc upon the surface of a revolving globe