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 color 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 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 color of the beam therefore when it reaches the eye, must partake of the color 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 color, when near the horizon, and that every luminous object seen through a mist, is of a ruddy hue. There is a great difference of color among the planets, we are therefore, (if the preceding observations be correct,) under the necessity of concluding, that those in which the red color predominates, 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 equatorial 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.

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. Olders, 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. Olders examined thrice every year all the little stars in the opposite constellations of the Virgin, and the Whale, till his labors 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, & 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 color, and is free from that nebulosity which surrounds Pallas. It is distinguished from all the other planets by the great excentricity 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 dif ference 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. Riazzi, an ingenious observer, who has since distinguished himself by his Astronomical labors. It was however again discovered by Dr. Olders, 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 color, and appears about the size of a star of the 8th 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 Olders, 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 color. 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 orbits of these two planets mutually intersect each other; 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

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