MERCURY is the first planet in the order of the system; about 3498 miles diameter: he moves round the Sun with the greatest velocity of any of the Planets familiar to our system (as being nearest the Sun) in about 88 of our days; at the rate of 110,680 English miles every hour, but the angle of his distance from the Sun, as seen by us, is so small, that unless by the telescope, we can seldom discern him[2]; (and even then an equatorial instrument to direct to its place, as indicated by the Ephemeris, will be requisite;) and when we do, it is for so short a time, and in twilight, that we can discover no spots on his face, and therefore to this hour know nothing of the length of his days and nights: we see him partially enlightened like the Moon, sometimes like a small crescent, in other situations half enlightened, and sometimes gibbous or oval, and are therefore certain he derives his light from the Sun, as she does: so that no doubt he is a fellow world, with inhabitants adapted to the heat of his situation: altho’ this heat is seven times as great as that of the Earth. He is not much larger than the Moon. Our Earth, viewed from Mercury, must appear much larger and more luminous than any of the Planets, except Venus, appears to us. VENUS is the next planet in the order of the system, and distinguished by her _superior brilliancy_, as the Sun’s light is twice as great to this planet as to the Earth; from this cause she is sometimes visible to the naked eye in full day-light. She is about 70 millions of miles from the Sun, or about twice the distance of Mercury; and like him, but much longer and more conspicuously, appears under the different phases of the Moon. These, as we have said, are proofs that both planets borrow their light from the Sun. The orbits of these planets (as well as those of the rest of the system) are inclined to the orbit of the Earth. Hence when Venus and Mercury are found in the nodes of their orbits between the Earth and Sun, they are transferred upon the Sun’s face like small round black spots, and which in fact are partial Eclipses of the Sun; these are called the TRANSITS of Mercury, or Venus.