Mercury is the smallest of the seven primary planets, and nearest to the sun; he appears as a small star, and emits a very vivid white light. He was called by the Greeks Στιλβων, plainly alluding to his brightness. Costard observes, “ברק אור Bark-oor, ברק אורי Bark-oori, or, changing the letter ב into מ as letters of the same organ frequently are, מרק אורי Mark-oori, we have in another dialect, with a Latin termination us, another name of this planet, Mercurius; and from whence comes Mercury, as he is called by us.” This planet never goes to a greater distance from the sun than about 27° 50ʹ; so that he appears only a little after sunset, and again a little before sunrise; he is never longer in setting after the sun than an hour and fifty minutes nor does he ever rise more than an hour and fifty minutes before that luminary: he is then about as far as the moon appears to be from the sun on the second day after the change. His mean distance from the sun says Dr. O. Gregory, is to that of the earth from the sun as 387 to 1,000: hence his distance is about thirty-seven millions of miles. To an inhabitant of Mercury, the sun appears almost three times broader than we see him from the earth; because the planet is almost three times nearer to the sun than the earth. Whence also the solar disk, seen from Mercury, is seven times greater than the disk as it appears to us, and Mercury has seven times more light than the earth.

“——Mercury the first,

Near bordering on the day, with speedy wheel

Flies swifter on, inflaming where he comes

With seven-fold splendor.”

The diameter of this planet is more than one-third of the diameter of the earth, or 3,180 miles. Hence his surface is about 1/7th; and his magnitude 1/16th of that of the earth. His period of revolution round the sun is 87 days, 23 hours, 14 minutes, 33 seconds, which is his year, and falls short of three of our months: hence he moves in his orbit round the sun at the rate of more than 95,000 miles in an hour. According to some astronomers, it has not been ascertained by observation, whether Mercury turns upon his own axis, and therefore it cannot be certainly affirmed that he has the vicissitude of day and night, neither the return of summer and winter: because they depend upon the inclination of the axis of his rotation, which is unknown, to the plane of the orbit which he describes about the sun; though there is very little doubt entertained on the subject. But Schroëter affirms that he “has distinguished spots and mountains, which he has assiduously followed, till he has arrived at the subsequent conclusions: that the apparent diameter of the planet is about 6ʺ; that it does not present any sensible ellipticity; that the mountains it contains are proportionably larger than those of Venus and the Earth; that the highest are, as in these two bodies, in the southern hemisphere; that the angle which the equator makes with its orbit is very considerable; that the difference of days and seasons ought to be much greater in Mercury than it is on the earth; that its atmosphere, like that of Venus, is very dense; and lastly, that its rotation about its axis is 24 hours, 5 minutes, 30 seconds.” When examined by means of a telescope magnifying about 200 or 300 times, he appears equally luminous throughout his whole surface, without the least dark spot. He exhibits the same difference of phases with the moon, being alternately horned, gibbous, and shining almost with a round face, though not entirely full because his enlightened side is never turned directly toward us; but at all times perfectly well defined without any ragged edge, and completely bright; and, like the moon, the crescent is always turned toward the sun. Mercury has no inferior planet known to us, and if that be actually the case, a spectator on his body will want the argument taken from the horned phases of the planets, to establish the true system of the world. But though we do not see any planets inferior to Mercury, it does by no means follow that there are none: for we seldom see Mercury himself, he being buried in the rays of the sun; and a planet much nearer the sun could never be seen from the earth. The first observation that was ever made of a transit, was by Gassendi, who saw Mercury on the sun, A.M. November 7, 1631. Since his time there have occurred seventeen other transits of this planet, the last of which was at his ascending node on the 9th of November, 1802. The ascending and descending nodes are in the 16° of Taurus, and 16° of Scorpio. Other transits are expected in the years 1822, 1832, 1835, 1845, and 1848.

Venus, the second planet from the sun in the order of the system, is the most beautiful star in the heavens, being easily distinguished by her brightness and whiteness, which exceeds that of all the other planets, and is so considerable, that in a dusky night she projects a sensible shadow. Concerning her name, Costard remarks, “From the Chaldee הן Han, or Hen, which signifies gratia, decor, elegantia, with the Æolic digamma Ϝ, comes Fen, or Ven, and with the additional termination us, Venus; the name by which this planet was known among the Romans, and by which, from them, it has been transmitted to us.” The mean distance of Venus from the sun is about 69,000,000 miles; her diameter is 7,630 miles; she performs her revolution round the sun in 224 days, 16 hours, 41 minutes, 27 seconds; her diurnal motion on her axis, according to some observations accurately made by Schroëter, is performed in 23 hours, 21 minutes; and she moves at the rate of 81,398 miles an hour.

This planet constantly attends the sun, and never departs from him more than forty-seven degrees, and consequently is never seen at midnight, nor in opposition to that luminary; being visible only for three or four hours in a morning or evening, according as she is before or after the sun. Venus is a morning star when she appears westward of the sun, for she then rises before him, and is among poets called Phosphorus or Lucifer——

“——Fair morning star,

That leads on dawning day to yonder world,