54,000 miles every hour, he goes round the Sun in 686 of our days, 23 hours, and 30 minutes, which is the length of his year, equal to 667 and 3-4ths of his days; and every day and night together, being nearly 40 minutes longer than with us. His diameter is computed at 4,189 miles, and by his diurnal rotation, the inhabitants at his equator are carried 528 miles every hour.--The Sun appears to the inhabitants of Mars, nearly twothirds the size that it does to us.

His mean apparent diameter, as seen from the earth, is 27 seconds, and as seen from the Sun, ten seconds of of a degree. His axis is inclined to his orbit 59 degrees and 22 minutes.

To the inhabitants of the planet Mars, our Earth and Moon appear like two Moons; the one being 13 times as large as the other; changing places with each other, and appearing sometimes horned, sometimes half or three-quarters illuminated, but never full, nor at most above one-quarter of a degree from each other; although they are in fact 240,000 miles asunder.

This Earth appears almost as large from Mars as Venus does to us. It is never seen above 48 degrees from the Sun, at that planet. Sometimes it appears to pass the disk of the Sun, and likewise Mercury and Venus. But Mercury can never be seen from Mars by such eyes as ours (unless assisted by proper instruments,) and Venus will be as seldom seen as we see Mercury. Jupiter and Saturn are as visible to Mars as to us. His axis is perpendicular to the ecliptic, and his inclination to it is one degree and 51 minutes. The planet Mars is remarkable for the redness of its light, the brightness of its polar regions, and the variety of spots which appear upon its surface. The atmosphere of this planet, which Astronomers have long considered to be of an extraordinary height and density, is the cause of the remarkable redness of its appearance. When a beam of white light passes through any medium, its colour inclines to redness, in proportion to the density of the medium; and the space through which it has travelled. The momentum of the red, or at least refrangible rays being greater than that of the violet, or most refrangible, the former will make their way through the resisting medium, while the latter are either reflected or absorbed. The colour of the beam therefore when it reaches the eye, must partake of the colour of the least refrangible rays, and must consequently increase with the number of those of the violet, which have been obstructed. Hence we discover, that the morning and evening clouds are beautifully tinged with red, that the Sun, Moon and Stars appear of the same colour, when near the horizon, and that every luminous object seen through a mist, is of a ruddy hue. There is a great difference of colour among the planets, we are therefore, (if the preceding observations be correct,) under the necessity of concluding, that those in which the red colour pre dominates, are surrounded with the most extensive and dense atmospheres. According to this idea, the atmosphere of Saturn, must be the next to that of Mars, in density and extent.

The planet Mars is an oblate spheroid, whose equa torial diameter is to the polar as 1,355 is to 1,272, or nearly as 16 to 15. This remarkable flattening at the poles of Mars, probably arises from the great variation in the density of his different parts. To the inhabitants of the earth Mars appears sometimes gibbous, sometimes full, but never horned. Figures 4, 5, 6 and 7, of plate third, represent different telescopic appearances of Mars. At figure 5 he appears gibbous.

VESTA.

Some Astronomers supposed that a planet existed between the orbits of Jupiter and Mars; judging from the regularity observed in the distances of the former discovered planets from the Sun. The discovery of Ceres confirmed this conjecture, but the opinion which it seemed to establish respecting the harmony of the Solar System, appeared to be completely overturned, by the discovery of Pallas and Juno. Dr. Olbers, however, imagined that these small celestial bodies were merely the fragments of a larger planet which had burst asunder by some internal convulsion, and that several more might yet be discovered between the orbits of Mars and Jupiter. He therefore concluded that though the orbits of all these fragments might be inclined to the ecliptic, yet as they must have all diverged from the same point. they ought to have two common points of reunion, or two nodes in opposite regions of the Heavens, through which all the planetary fragments must sooner or later pass. One of these nodes he found to be in Virgo, and the other in the Whale, and it was actually in the latter of these regions, that Mr. Harding discovered the planet Juno. With the intention therefore of detecting other fragments of the supposed planet, Dr. Olbers examined thrice every year all the little stars in the opposite constellations of the Virgin and the Whale, till his labours were crowned with success on the 29th of March, 1807. by the discovery of a new planet in the constellation Virgo, to which he gave the appropriate name of Vesta. The planet Vesta is the next above Mars, and is in appearance of the fifth or sixth magnitude, and may be seen in a clear morning by the naked eye. Its light is more intense, pure and white, than either of the three following, Ceres, Juno, or Pallas. Its distance from the Sun is computed at 225 millions of miles, and its diameter at 238: its revolutions have not hitherto been sufficiently ascertained.

ON JUNO.

The planet Juno, the next above Vesta, and between the orbits of Mars and Jupiter, was discovered by Dr. Harding, at the Observatory near Bremen, on the evening of the 5th of September, 1804. This planet is of a reddish colour, and is free from that nebulosity which surrounds Pallas. It is distinguished from all the other planets by the great eccentricity of its orbit, and the effect of this is so extremely sensible, that it passes over that half of its orbit which is bisected by its perihelion in half the time that it employs in describing the other half, which is further from the Sun: from the same cause its greatest distance from the Sun is double the least. The difference between the two being about 127 millions of miles. Its mean distance from the Sun is computed at 252 millions of miles, and performs its tropical revolution in 4 years and 128 days. Its diameter is estimated at 1,425 miles, and its apparent diameter as seen from the Earth, three seconds of a degree, and its inclination of orbit twenty-one degrees.

ON CERES.

The planet Ceres was discovered at Palermo, in Sicily, on the first of January, 1801, by M. Piazzi, an ingenious observer, who has since distinguished himself by his Astronomical labours. It was however again discovered by Dr. Olbers, on the first of January, 1807, nearly in the same place where it was expected from the calculations of Baron Zach. The planet Ceres is of a ruddy colour, and appears about the size of a star of the Sth magnitude. It seems to be surrounded with a large dense atmosphere of 675 miles high, according to the calculations of Schroeter, and plainly exhibits a disk, when examined with a magnifying power of 200.

Ceres is situated between the orbits of Mars and Jupiter. She performs her revolution round the Sun in four years, 7 months and ten days; and her mean distance is estimated at 263 millions of miles from that luminary. The observations which have been hitherto made upon this celestial body, do not appear sufficiently correct to determine its magnitude with any degree of accuracy.

ON PALLAS.

The planet Pallas was discovered at Bremen, in Lower Saxony, on the evening of the 28th of March, 1802, by Doctor Olbers, the same active Astronomer who re-discovered Ceres. It is situated between the orbits of Mars and Jupiter, and is nearly of the same magnitude and distance with Ceres, but of a less ruddy colour. It is seen surrounded with a nebulosity of almost the same extent, and performs its annual revolution in nearly the same period. The planet Pallas, however, is distinguished in a very remarkable manner from Ceres and all the primary planets, by the immense inclination of its orbit. While these bodies are revolving round the Sun in almost circular paths, rising only a few degrees above the plane of the ecliptic, Pallas ascends above this plane, at an angle of about 35 degrees, which is nearly five times greater than the inclination of Mercury. From the eccentricity of Pallas being greater than that of Ceres, or from a difference of position in the line of their apsides, where their mean distances are nearly equal, the oroits of these two planets mutually intersect each other: see Frontispiece:] a phenomenon which is altogether anomalous in the Solar System.

Pallas performs its tropical revolution in four years, 7 months, and 11 days. The distance of this planet from the Sun, is estimated at 265 millions of miles. It is surrounded with an atmosphere 468 miles high.

OF JUPITER.

Jupiter, the largest of all the planets, is still higher in the Solar System, being four hundred and ninety millions of miles from the Sun, and by performing his annual revolution round the Sun in 11 years, 314 days, 20 hours, and 27 minutes, he moves in his orbit at the rate of 29,000 miles in an hour. The diameter of this planet is estimated at 89,170 miles, and performs a revolution on its own axis in nine hours, 55 minutes, and 37 seconds; which is more than 28,000 miles every hour, at his equator, the velocity of motion on his axis being nearly equal to the velocity with which he moves in his annuat orbit.

This planet is surrounded by faint substances called belts, in which so many changes appear, that they have been regarded by some, as clouds or openings in the at mosphere of the planet; while others imagine that they are of a more permanent nature, and are the marks of