This planet, with the exception of the asteroids, is the smallest of the system. It is the nearest to the Sun, and, in consequence, can not be seen (on account of the Sun's superior light), except at its greatest eastern and western elongations, which occur in March and April, August and September, when it may be seen for a short time immediately after sunset and shortly before sunrise. It then appears like a star of the first magnitude, having a white twinkling light, and resembling somewhat the star Regulus in the constellation Leo. The day in Mercury is about ten minutes longer than ours, its year is about equal to three of our months. It receives six and a half times as much heat from the Sun as we do; from which we conclude that the climate must be very similar to that of Fort Yuma, on the Colorado River. The difficulty of communication with Mercury will probably prevent its ever being selected as a military post; though it possesses many advantages for that purpose, being extremely inaccessible, inconvenient, and, doubtless, singularly uncomfortable. It receives its name from the God, Mercury, in the Heathen Mythology, who is the patron and tutelary Divinity of San Diego County. VENUS This beautiful planet may be seen either a little after sunset or shortly before sunrise, according as it becomes the morning or the evening star, but never departing quite forty-eight degrees from the Sun. Its day is about twenty-five minutes shorter than ours; its year seven and a half months or thirty-two weeks. The diameter of Venus is 7,700 miles, and she receives from the Sun thrice as much light and heat as the Earth. An old Dutchman named Schroeter spent more than ten years in observations on this planet, and finally discovered a mountain on it twenty-two miles in height, but he never could discover anything on the mountain, not even a mouse, and finally died about as wise as when he commenced his studies. Venus, in Mythology, was a Goddess of singular beauty, who became the wife of Vulcan, the blacksmith, and, we regret to add, behaved in the most immoral manner after her marriage. The celebrated case of Vulcan _vs._ Mars, and the consequent scandal, is probably still fresh in the minds of our readers. By a large portion of society, however, she was considered an ill-used and persecuted lady, against whose high tone of morals and strictly virtuous conduct not a shadow of suspicion could be cast; Vulcan, by the same parties, was considered a horrid brute, and they all agreed that it served him right when he lost his case and had to pay the costs of court. Venus still remains the Goddess of Beauty, and not a few of her _proteges_ may be found in California. THE EARTH