In 1894 Percival Lowell erected at Flagstaff, Arizona, an observatory for the specific purpose of observing Mars and its canals in good and steady air. He was assisted by W. H. Pickering and by _Andrew Ellicott Douglass_ (born 1867). During a year’s study Douglass measured the Martian atmosphere and discovered canals crossing the dark regions of the planet, finally disproving the idea of their aqueous character. Lowell recognised all Schiaparelli’s canals, and discovered many more. He also attentively studied the south polar cap of Mars, which disappeared entirely on October 12, 1894. Lowell noticed, also, that as the cap melted the canals became darker, as if water was being conveyed down; and accordingly he adopted the view put forward by Schiaparelli, that the canals are waterways lined on either side by banks of vegetation. His observations were published in the end of 1895 in his work ‘Mars.’ He is of opinion that the reddish-ochre regions or “continents” are deserts, and the greenish areas marshy tracts of vegetation. The lakes are named by him “oases,” and, as Miss Clerke observes, he “does not shrink from the full implication of the term.” He regards the canals as strips of vegetation fertilised by a small canal, much too small to be seen, an idea which originated with W. H. Pickering. The canals are believed by Lowell to be waterways down which the water from the melting polar cap is conveyed to the various oases. He considers, in fact, that the canals are constructed by intelligent beings with the express purpose of fertilising the oases, regarded by him as centres of population. He remarks that water is scarce on the planet, owing to its small size, and as a consequence the inhabitants are forced to utilise every drop. The canal system is the result.