But fortunately for progress, this sense of satisfaction was to be rudely disturbed. As Mars, in its progress round the Sun, receded from the Earth, or rather as the Earth moved away from it, the astronomers who observed so diligently during the autumn of 1877 turned their attention to other objects. One of them, however, Schiaparelli, the most distinguished astronomer on the continent of Europe, still continued to watch the planet, and, as the result of his labours, he published some months later the first of a magnificent series of _Memoirs_, bringing to light what appeared to be a new feature. His drawings not only showed the "lands" and "seas," that is to say the bright and dark areas, that Green and his predecessors had drawn, but also a number of fine, narrow, dark lines crossing the "lands" in every direction. These narrow lines are the markings which have since been so celebrated as the "canals of Mars," and the discussion as to the real nature of these canals has focussed attention upon Mars in a way that, perhaps, nothing else could have done. Before 1877 the study of planetary markings was left almost entirely to the desultory labours of amateurs, skilled though many of them were; since 1877, the most powerful telescopes of the great public observatories of the world have been turned upon Mars, and the most skilful and experienced of professional astronomers have not been ashamed to devote their time to it. There is no need to pass in review the whole of the immense mass of observations that have been accumulated since Schiaparelli brought out the first of his great Memoirs. That Memoir gave rise to an immediate controversy, for many astronomers of skill and experience had observed the planet in 1877 without detecting the network of lines which Schiaparelli had revealed, and it was natural that they should feel some reluctance in accepting results so strange and novel. But little by little this controversy has passed. We now know that the "canals" vary much in their visibility, and "curiously enough the canals are most conspicuous, not at the time the planet is nearest to the Earth and its general features are in consequence best seen, but as the planet goes away the canals come out. The fact is that the orbital position and the seasonal epoch conspire to a masking of the phenomena." This was the chief reason why Schiaparelli's discoveries seemed at first to stand so entirely without corroboration; the "canals" did not become conspicuous until after most observers had desisted from following the planet. Another reason was that, in 1877, Mars was low down in the sky for northern observatories, and good definition is an essential for their recognition. But the careful examination of drawings made in earlier oppositions, especially those made by Dawes and Green, afforded confirmation of not a few of Schiaparelli's "canals"; even in 1877 a few of the easiest and most conspicuous had been delineated by