Of all the planets, Venus appears, to the unassisted eye, by far the loveliest. When seen in the early morning before sunrise--its "western elongation"--or after sundown in the evening--its "eastern elongation"--and still more as it attains its greatest brilliancy, it has attracted attention everywhere and in all ages. It then shines with brilliance ten times as great as Jupiter in opposition, and the brightest members of the heavenly host look pale and dim beside it. It is emphatically the morning or the evening star, Lucifer, or Vesper, herald or follower of the Sun; it can even assert itself in the presence of the Lord of Day, for it has often been seen at noonday by watchers who knew where to look; sometimes by the general crowd. But in the telescope Venus appears less satisfying. It is a pretty spectacle indeed to watch the phases of the gleaming little globe of silver, for, like the Moon under varying illumination from the Sun, it undergoes change of apparent shape. But the surface of the planet yields little detail, and that little is illusive and ill-defined. The clear-cut outlines and black shadows of the Moon have no place here, nor do the ruddy plains and blue-grey "seas" of Mars find any analogues. All that can be observed beyond the changes of phase are a few faint, ill-defined patches, where the molten silver of the general surface is slightly dimmed and tarnished, and perhaps one or two spots, not less evasive and difficult to fix, that exceed the rest of the surface in brightness. This very difficulty in making out the markings on Venus is hopeful for our search; it points to a veiling over the planet, a veiling by an atmosphere. And the statistics of the Table show that Venus closely resembles our Earth in size and mass, and therefore probably in atmospheric equipment. If we assume that the atmosphere of any planet is in direct proportion to its mass--and as Venus is so nearly the twin of the Earth there is no reason to expect any great difference between the two in this respect--the atmosphere of Venus would have a pressure of about 11·2 lb. on the square inch, and the level of half pressure would be nearly four miles above the surface. In other words the atmosphere would be both thinner and deeper than that of the Earth, but the difference would not be important in amount.