A thick, gray ring or belt has been noticed round the small, black disk of Mercury, while it has passed between us and the sun. The edge of Mercury, seen against the bright photosphere beyond, would, if there were no atmosphere, be sharp and clear as the edge of the airless moon. This surrounding haze seems to show that Mercury has an atmosphere. The sunlight reflected from Mercury’s envelope of clouds shines at least as brightly as if it were reflected from his solid body. The small size of Mercury makes attraction on his surface much less than on earth. A lump of iron weighing on earth one pound, would weigh on Mercury only about seven ounces, or less than half as much. So a man would be a very light leaper indeed there, and an elephant might be quite a frolicsome animal. If there are star-gazers in Mercury, and if the cloud-laden atmosphere allows many clear views of the sky, the earth and Venus must both be beautiful to look upon. Each of the two would shine far more brightly than Jupiter, as seen at his best from earth. Like Mercury, Venus, the next planet, has an orbit lying inside our orbit. Mercury and Venus are always nearer to the sun than we are; and if Mercury and Venus traveled round the sun in orbits, the planes of which were exactly the same as the plane of the earth’s orbit, we should very often see them creeping over the surface of the sun. Not that they really “creep over” it; only, as they journey between the sun and us, we can see them pass like little black dots across the sun’s disk. This is the same thing as when the moon passes across the sun’s disk and eclipses it. But Mercury and Venus are too far away from us to cause any eclipse of the sun’s light. Mercury has given more trouble to astronomers than any other member of the system; for, owing to his proximity to the sun, he is usually lost in the solar glory, and is never seen in a dark part of the heavens, even at the time of his greatest distance. This circumstance, together with a small mass and an immense velocity, renders it difficult to catch and watch him. In high latitudes, where the twilight is strong and lengthened, while mists often overhang the horizon, the planet can seldom be seen with the naked eye. Hence an old astro-meteorologist contemptuously describes him as “a squirting lacquey of the sun, who seldom shows his head in these parts, as if he was in debt.” Copernicus lamented that he had never been able to obtain a sight of Mercury; and the French astronomer Delambre saw him not more than twice with the naked eye.