The reader who has followed me thus far will by this time be in a position to appreciate a remark made in an earlier part of this chapter, that the multitude of facts known to us in connection with the Sun and its spots is so great, as to render it impossible to exhibit in a single chapter anything more than the barest outline of them. The numerous observations of recent eclipses of the Sun, especially since that of 1860, and the extensive application of the spectroscope to the Sun both in connection with these eclipses, and generally, may be said to have completely revolutionised our knowledge of solar phenomena during the present generation; or perhaps it might be more correct to say have enormously increased our knowledge of the facts of the case and have revolutionised in no small degree the conclusions deduced from the facts. CHAPTER III. MERCURY. So far as we know at present, Mercury is the nearest planet to the Sun. The circumstances under which it presents itself to us and a brief general account of its movements have already been stated. In the present chapter, therefore (and this remark applies in substance to each of the succeeding chapters appropriated to particular planets), I shall limit myself to such topics as seem to be of interest to an observer armed with a telescope. Mercury, as already mentioned, exhibits from time to time phases which may be said to be the same as those of the moon; but as the only chance of seeing it is when it is at its greatest distance east or west of the Sun, practically it can only be studied when in, or rather near to, what may be called the half-moon phase; and even then observations on its physical appearance can only be obtained with difficulty. Perhaps its most definite feature is its colour. This, undoubtedly, is more or less pink. Strange to say, in spite of the multiplication of telescopes and observers, comparatively little attention has been paid to this planet, and we really know very little more about it than Schröter told us nearly a hundred years ago. He obtained what he conceived to be satisfactory evidence of the existence of at any rate one mountain, having a height of about 11 English miles—a height which it will be noted, far exceeds, not only relatively but absolutely, any mountain on the earth. What Schröter based this conclusion upon was the fact that when the planet was near inferior conjunction, the southern horn presented a truncated appearance, which might be the result of a lofty projection arresting the Sun’s light. Schröter also announced that Mercury rotated on its axis in 24 hours 5 minutes. Sir W. Herschel failed to satisfy himself that Schröter’s conclusions were well-founded, but it must certainly be admitted that some support for them is furnished by certain observations made within the last few years. It is matter for regret, however, that most of these