CHAP. XI. other year, when it comes to the meridian near midnight, it is then most conspicuous; and the next year it is scarcely noticed by the common observer.

Apparent im

the system.

arises from a dense atmosphere which surrounds him, of the existence of which there is other proof depending on the appearance of stars as they approach him; they grow dim and are sometimes wholly extinguished as their rays pass through that medium,"

(139.) The next planet, as known to ancient astronomers, perfection in is Jupiter; but its distance is so great beyond the orbit of Mars, that the void space between the two had often been considered as an imperfection, and it was a general impression among astronomers that a planet ought to occupy that vacant space.

Bode's law.

why it should

a law.

Professor Bode, of Berlin, on comparing the relative distances of the planets from the sun, discovered the following remarkable fact that if we take the following series of numbers: 0, 3, 6, 12, 24, 48, 96, 192, &c.,

and then add the number 4 to each, and we have,

4, 7, 10, 16, 28, 52, 100, 196, &c.,

The reason and this last series of numbers very nearly, though not exnot be called actly, corresponds to the relative distances of the planets from the sun, with the exception of the number 28. This is sometimes called Bode's law; but remarkable as it certainly is, it should not be dignified by the term law, until some better account of it can be given than its mere existence; for, at present, all that can be said of it is, "here is an astonishing

coincidence." But, mere accident as it may be, it suggested CHAP. XI. the possibility of some small, undiscovered planet revolving A bold hy in this region, and we can easily imagine the astonishment of pothesis. astronomers, on finding four in place of one, revolving in orbits tolerably well corresponding to this law, or rather coincidence. Had they even found but one, it would seem to indicate something more than mere coincidence; but finding four, proves the series to be simply accidental - unless the four or more planets there discovered were originally one planet; and then came the inquiry, is not this the case? Thus originated the idea that these new and newly discovered small planets are but fragments of a larger one, which formerly circulated in that interval, and was blown to pieces by some internal explosion — and we shall examine this hypothesis in a text note, under physical astronomy.

The names of these planets, in the order of the times of their discovery, are, Ceres, Pallas, Juno, Vesta. The order of their distances from the sun, is Vesta, Juno, Ceres, Pallas.

If a planet has really burst, it is but reasonable to suppose that it separated into many fragments; and, agreeably to this view of the subject, astronomers have been constantly on the alert for new planets, in the same regions of space; and every Recert discovery of the kind greatly increases the probability of the discoveries theory. The following very recent discoveries are said to have this hypothebeen made, but the elements of the orbits are not regarded as sufficiently accurate to demand a place in the table.

favorable to

sis.

New plan.

On the 8th of December, 1845, Mr. Hencke, of Dreisen, claims to have discovered a planet which he calls Astrea; and the same observer also claims another, discovered in 1847, called Hebe. His success induced others to a like exa- ets discovermination, and a Mr. Hind, of London, within the past year, and 1846.

ed in 1845

CHAP. XI. 1848, claims a seventh and eighth asteroid, named Iris and

Flora.

Thus we have eight miniature worlds, supposed to have once composed a planet; and if the four last named are veritable discoveries, we shall soon have the elements of their orbits in an unquestionable shape.

The elements of the orbits of the four known asteroids, as given for the epoch 1820, are not as accurate as the following, which were deduced from the Nautical Almanac for 1846 and 1847; which have been corrected from more modern, extended, and accurate observations. (Epoch Jan., 1847.)

On account of the small magnitude of these new planets, and their recent discovery, nothing is known of them save the following tabular facts, and these are only approximation to the truth.

Object of Fig. 29.

(140.) With the two elements, the longitude of the ascending nodes, and the inclination of the orbits to the ecliptic, we are enabled to give à general projection of these orbits around the celestial sphere, in relation to the ecliptic, as represented on page 37; and our object is to show that there are two points in the heavens, nearly opposite to each other, near to which all these planets pass. One of these points is about the longitude of 185 degrees, and the latitude of 15 degrees north; and the other is the opposite point on the celestial sphere. If these planets are but fragments of one original planet, which burst or exploded by its internal fires, from that

moment they must have started from the same point, and the orbits of all have one common distance from the sun; and for ages after such a catastrophe, these fragments must have had nearly a common node; and the fact that they do not, at present, pass through a common point, nor have a common node, does not prove that they were not originally in one body; for, owing to mutual disturbances, and the disturbances of other planets, the nodes must change positions; and the longer axis of the orbits, especially the very eccentric ones, must change positions; and now (after we know not how many ages), it is not inconsistent with the theory of an explosion, that we find the orbits as they

The hypothesis that these planets were originally one, and must, therefore, have two common points in the heavens near which they must all pass, led to the discovery of Juno and

L

CHAP. XI. Vesta, by carefully observing these two portions of the

belts.

Jupiter's

heavens.

The apparent diameters of these planets are too small to be accurately measured; and therefore we have only a very rough or conjectural knowledge of their real diameters.

All of these planets are invisible to the naked eye, except Vesta, which sometimes can be seen as a star of the 5th or 6th magnitude.

(141.) Jupiter. We now come to the most magnificent planet in the system-the well-known Jupiter-which is nearly 1300 times the magnitude of the earth.

The disc of Jupiter is always observed to be crossed, in an eastern and western direction, by dark bands, as represented in Fig. 30.

Fig. 30. Telescopic View of Jupiter.

"These belts are, however, by no means alike at all times; they vary in breadth and in situation on the disc (though never in their general direction). They have even been seen broken up, and distributed over the whole face of the planet: but this phenomenon is extremely rare. Branches running out from them, and subdivisions, as represented in the figure, as well as evident dark spots, like strings of clouds, are by no means uncommon; and from these, attentively watched, it is concluded that this planet revolves in the surprisingly Diurnal re short period of 9 h. 55 m. 50 s. (sid. time), on an axis perpendicular to the direction of the belts. Now, it is very remarkable, and forms a most satisfactory comment on the reasoning by which the spheroidal figure of the earth has been deduced from its diurnal rotation, that the outline of Jupiter's disc is evidently not circular, but elliptic, being considerably flattened in the direction of its axis of rotation.

volution.