CERES.

This planet was discovered by Piazzi, astronomer royal at Palermo, January 1, 1801. It appears like a star of the eighth magnitude, being according to some about the extent of the moon; but according to Dr. Herschel, its diameter is thirteen times less than that of the moon.

The planet Ceres is of a colour ruddy, though not very deep. When examined with a magnifying power of about 200, it plainly exhibits a disk, surrounded with an extended and dense atmosphere. By many observations, Mr. Schroeter found this atmosphere 675 miles high, and subject to numerous changes. The visible hemisphere, sometimes overshadowed, at others clear, gives but little opportunity of discovering its diurnal rotation. The atmosphere of Ceres, very dense at the planet and rarer at a distance, like that of the earth, produces very singular variations in its apparent diameter. When the planet is approaching the earth, the disk seems to enlarge much faster than ought to be expected from diminution of distance.

"Mr. Schroeter accounts for the remarkable difference between his measurements and those of Dr. Herschel by maintaining, that the projection-micrometer, used by the English astronomer, was placed at too great a distance from the eye, and that he measured only the middle clear part of the nucleus of the planet."

PALLAS.

Pallas was discovered by Dr. Olbers on the 28th of March, 1802. It is nearly of the same magnitude as Ceres; but of a less ruddy colour. It is surrounded with a nebulosity, similar to that of Ceres, and almost equally extended. It resembles Juno in the eccentricity of its orbit. This planet is distinguished from all the rest of the primary planets, by the great inclination, of its orbit to the ecliptic, being about 35°; nearly five times greater than that of Mercury.

From this inclination and a difference of position in the line of their apsides, while their mean distances are nearly equal, the orbits of these planets intersect each other; phenomena anomalous in the solar system, except in the newly discovered planets. The orbits of these four, says Dr. Brewster, appear to intersect each other in various places. The points of intersection must be perpetually shifting, according to the changes in the aphelia of the planets.

These small planets, discovered in the present century, are called by Dr. Herschel asteroids. Some think the term not very properly applied, as they are really planets. The general name seems not perfectly proper. This however is an object of small moment. But every friend to Christianity must regret that proper names of heathen mythology are applied to the discoveries of Christian countries.

Some have laboured to show, that these four small planets formerly constituted but one body, and that they were separated by some vast explosion. The arguments in support of the hypothesis are not conclusive. They take Juno and Pallas to be the smaller fragments, a supposition not corroborated by observation. A similarity in the inclination of, orbits, in the position of the nodes, and in the place of the perihelia are relied on as principal grounds. These deserve consideration. But circumstances like these might take place in original planets. The nodes and perihelia of all the planets, so far as observed, are not stationary, but continually revolving. They may be together now. But this proves nothing; for we cannot suppose the separating explosion, if ever, was recent. Had the asteroids constituted one planet, since any attention has been paid to astronomy, being sufficiently large for observation by the naked eye, it would have been seen by ancient astronomers, and enumerated among the planets.

The most extravagant idea in the separating hypothesis is the explosion. How vast must this have been, when it could so overcome the mutual attraction of the parts separated, that they should fly asunder forty millions of miles; or

so far as afterwards to revolve in orbits, differing by a mean distance of forty millions of miles! We think the explosive force of Hecla immense, when it can throw lava or cinders one hundred and fifty miles. But how diminutive !— How annihilated in the comparison are all the explosions of Vesuvius and Hecla, of Ætna and Cotopaxi !

Pallas is supposed to have been hurled to the greatest distance from the parent body. But the atmosphere and nebulosity, with which Pallas is surrounded, seem incompatible with the idea of a volcanic origin. For, if we conceive the original planet surrounded with an atmosphere and nebulosity equally dense with that of Pallas, we cannot suppose such atmosphere and nebulosity would have followed that planet in its flight, a flight of inconceivable velocity. Darting through the fluid matter, it would have left it all, or nearly all, behind, with the original planet. The atmospheres of the earth and other planets, it is granted, follow them in their annual revolution. But here the same impulse was, without doubt, originally given to the surrounding fluids, as to the bodies which they accompany.

SECTION X.-OF JUPITER.

Next to the asteroids in the solar system is Jupiter, the largest of the planets. The form of Jupiter is an oblate spheroid, his equatorial diameter being to his polar, as 14 to 13. Next to Venus, Jupiter is the most brilliant of the planets.

Sometimes he evens surpasses her in brightness. The surface of Jupiter is remarkable, being encompassed with a number of belts or stripes of various shades. These appear different at different times, and even at the same time through telescopes of different powers. The weather being very favourable, they sometimes seem formed of a number of curved lines, like the strokes of an engraving. Sometimes sev

en or eight belts have been seen at the same time. "So many changes appear in these belts," says Mr. Ferguson, "that they are generally thought to be clouds; for some of them have been first interrupted and broken, and then have vanished entirely. They have sometimes been observed of different breadths, and afterwards have all become nearly of the same breadth. Large spots have been seen in those belts, and when a belt vanishes, the contiguous spots disappear." Some of these spots, however, seem to make periodical returns. The spot, first observed by Cassini, re-appeared eight times between the years 1665 and 1708.

It again re-appeared in 1713, in the same form and position. May 28, 1780, Dr. Herschel observed the whole disk of Jupiter covered with small curved belts, or rather lines not contiguous, as in Plate III. Fig. 18 and 19. Parallel belts, however, are most common, as represented in Plate III. Fig. 20 and 21. Hence, some suppose, that the clouds of Jupiter, partaking of the great velocity of his diurnal motion, are formed into strata, parallel to his equator ; that the body of Jupiter reflects less light than the clouds; and that the belts are the body of the planet, seen through the parallel interstices of the clouds.

Jupiter has four satellites, reckoned 1, 2, 3, 4, beginning with the nearest to the primary. The satellites often pass between Jupiter and the sun. They then cause eclipses of the primary, resembling our solar eclipses. The shadow of the secondary is seen passing over the disk of Jupiter in a well defined dark line, forming a chord to the disk.

The satellites are themselves eclipsed by falling into the shadow of Jupiter. They often disappear at some distance from the disk of the planet. The third and fourth sometimes re-appear on the same side of the disk. The shadow of Jupiter is not then on the right line between that planet and the earth, produced beyond the planet, but forms an angle with it, by the relative position of the earth, the sun, and Jupiter.

The eclipses of Jupiter and his satellites, exactly similar to those of the earth and moon, are a full proof, that those distant luminaries are in themselves opaque, and shine only by light derived from the sun.

The eclipses of these satellites are of great utility to the inhabitants of the earth. By these it is found, that light is progressive, which, before their discovery, was thought instantaneous. By them the relative distances between Jupiter, the earth, and the sun, can be ascertained with suffi cient accuracy. But their greatest utility is to navigation and geography, by affording one of the best methods, yet known, of ascertaining the longitude of places.

Little, probably, did Galileo think, when he first saw these satellites in 1610, he was making a discovery of so much importance. Here as often is verified the remark of a celebrated traveller, that the Deity every where brings the greatest events from causes apparently the smallest.