When Schiaparelli began his observations it was generally believed, as we have said, that the dusky areas on Mars were seas, and since Schiaparelli thought that the “canals” invariably began and ended at the shores of the “seas,” the appropriateness of the title given to the lines seemed apparent. Their artificial character was immediately assumed by many, because they were too straight and too suggestively geometrical in their arrangement to permit the conclusion that they were natural watercourses. A most surprising circumstance noted by Schiaparelli was that the “canals” made their appearance _after_ the melting of the polar snow in the corresponding hemisphere had begun, and that they grew darker, longer, and more numerous in proportion as the polar liquidation proceeded; another very puzzling observation was that many of them became double as the season advanced; close beside an already existing “canal,” and in perfect parallelism with it, another would gradually make its appearance. That these phenomena actually existed and were not illusions was proved by later observations, and today they are seen whenever Mars is favorably situated for observation. In the closing decade of the nineteenth century, Mr Percival Lowell took up the work where Schiaparelli had virtually dropped it, and soon added a great number of “canals” to those previously known, so that in his charts the surface of the wonderful little planet appears covered as with a spider’s web, the dusky lines criss-crossing in every direction, with conspicuous knots wherever a number of them come together. Mr Lowell has demonstrated that the areas originally called seas, and thus named on the earlier charts, are not bodies of water, whatever else they may be. He has also found that the mysterious lines do not, as Schiaparelli supposed, begin and end at the edges of the dusky regions, but often continue on across them, reaching in some cases far up into the polar regions. But Schiaparelli was right in his observation that the appearance of the “canals” is synchronous with the gradual disappearance of the polar snows, and this fact has become the basis of the most extraordinary theory that the subject of life in other worlds has ever given birth to.