SOME three years ago, M. Camille Flammarion's classical book on the “Planet Mars” was noticed in these columns (NATURE, vol. xlvii. p. 553). This work was a compilation of all the observations made up to that period from the very earliest record, and a thorough discussion of them was given, as was to be expected, in a masterly way. Since that time, however, the planet's surface has been studied by observers in numerous parts of the world, and their observations have been published n various journals and in different languages. Perhaps the most important, or at any rate the most consecutive series, of such observations hails from Flagstaff, Arizona, Mr. Percival Lowell having, at great expense, equipped himself with some fine instruments, and set out for that region to make a systematic study of the surface markings during the opposition of the planet in the year 1894.