Venus would appear from Mercury as much as four times as large as she seems to us--a veritable little moon, and always full, her size varying slightly as Mercury speeded back and forth from the farthest to the nearest point in his orbit, changing the extreme of the distance between them from one hundred and ten million to less than twenty-four million miles. If Mercury needed a moon, he could well find some consolation for his lack of it in the presence of the lovely Venus in his sky. MERCURY’S SIZE AND THE CONSEQUENCES OF IT Mercury is the smallest of all the major planets. His diameter is about three thousand miles. It is only about nine hundred miles greater than that of our moon. The surface of Mercury is only one-seventh that of the earth, and his volume only one-twentieth. Jupiter and Saturn each have a satellite that is considerably larger. Mercury would make a splendid satellite or a giant asteroid, but as a planet seems hardly to have had a fair chance in life. For being a small planet means something more than being constructed on smaller lines than some others are. It means a difference in physical development. It means less power to hold the gases that compose an atmosphere, which is the cover that shields the planets from the too burning rays of the sun and keeps their internal heat from radiating too quickly into space. It means less power to resist the tidal friction that the parent body uses as a brake to retard rotation. It means a shorter time of activity in life, and a long, dull, monotonous old age. The nucleus that was detached from the great spiral, or the portion of nebula that was separated in whatever way from the parent body, to form Mercury chanced to be a small one. Being small, it was unable to add materially to its mass by attracting other particles to it through the power of gravitation, as a larger planet might do, and thus Mercury was doomed to develop with the limitations that nature’s law has decreed as inevitable in the small bodies of our solar system, be they planets, satellites, or asteroids. Of these limitations the first and most far-reaching in its effect is the feebleness of its force of gravity, or power to attract other bodies.