calculated to balance and counteract disturbing forces, even although other considerations should prove that the system was not intended to be eternal. It is this principle which secures the equal and salutary working of the system, while it lasts, and which bestows upon it properties suited for the habitation of organized existencies, during that period; and this is the whole extent of the view for which we have been contending.

Is there, then, a resisting medium,—a fluid in which our system floats? or are our planetary spheres wheeled in empty space? The diffusion of light throughout the universe, might, of itself, form a powerful argument for the existence of such a medium, on whatever theory its properties are accounted for. Light is either an emanation from the great central body, and then that emanation must be something material; or it is an exciting cause of vibratory motion; and, in that case, the vibrations must, apparently, be conveyed through some material substance. In either case, the theory of an absolute vacuum seems to be untenable. But, independent of this view, some facts have been very recently discovered, which cannot well be accounted for, but on the supposition of a resisting medium. I allude to certain circumstances occurring in the motion of one of the comets belonging to our solar system, to which the importance of Encke's observations have justly caused that astronomer's name to be attached. The revolution of this body round the sun, is found to be completed in a period of about three years and four months, while its orbit is so eccentric and elongated, that it is more than ten times nearer the sun in one part of its course, than in another. The materials of which it is composed, seem to be exceedingly thin and transparent, so much so, indeed, that the stars may be seen through the most condensed part of its nucleus, without any apparent diminution of their brilliancy. In 1786, this comet was first observed; but it was not till 1822, that its periods were accurately determined; and then Encke, on comparing the calculated with the observed places, perceived a differ

ence, which he attributed to the effect of a resisting medium. It was again the subject of observation in 1825, in 1828, and still more recently; and the conclusion has become general, that the obvious and constant disturbance of its course, arises from no other cause than that of its being affected by its motion in an ethereal fluid.

This fluid, however, must be of inconceivable rarity, and would probably not produce any apparent effect in its velocity, were it not from the small quantity of matter contained in the vapoury sphere, which, as will easily be perceived, must increase the power of resistance of the medium through which it moves. Light and loose, however, as the body is, it has been found to be acted on by the solar and planetary attraction, in the same manner with the other heavenly bodies; and the result having been accurately calculated, what Sir J. Herschel calls a residual phenomenon, has been discovered, which has given rise to the inference of a resisting medium.

The effect, however, though something very discernable, is yet but trifling; and, what may appear strange, this retardation of the motion, causes the body to perform its revolutions round the sun more quickly. The reason is, that the increasing slowness of the motion, has the effect of augmenting the relative power of the sun's attraction, thus drawing the comet nearer to himself, and shortening its orbit. Within the last fifty years, in which its course has been observed, it has been found, that, while it has advanced about ten days farther in its path, than would otherwise have been the case, the time of its revolution has been diminished by about two days.

Now, the very same power of resistance, which acts so perceptibly on this unsubstantial body, must act also on every other body which passes through the same medium; and, however small the effect produced may be, it must be something, which, though not, perhaps, sufficient to produce any sensible effect on those more solid bodies, for many centuries, must yet, in reference to a period of eternal duration, be sufficient to derange, and finally to destroy,

the whole system. As yet, no retardation of the planetary bodies has been observed, which could be referred to the existence of a resisting medium, because our observations extend to a period too limited; but this may only prove the extreme remoteness of the final catastrophe. "It may be millions of millions of years," says the interesting author, whom we chiefly follow in this part of our work, "before the earth's retardation may perceptibly affect the apparent motion of the sun; but still the day will come (if the same Providence, which formed the system, should permit it to continue so long), when this cause will entirely change the length of the year, and the course of our seasons, and finally stop the earth's motion round the sun altogether. The smallness of the resistance, however small we choose to suppose it, does not allow us to escape this certainty. There is a resisting medium; and therefore the movements of the solar system cannot go on for ever. The moment such a fluid is known to exist, the eternity of the movements of the planets becomes as impossible as a perpetual motion on the earth.”*

The obvious use to be made of the fact now stated, is, that our present system of things, which must have an end, must also have had a beginning. We have not yet

arrived at that end; and therefore an eternal revolution of ages has not passed. A period of commencement implies a Cause; the order and regularity of the system implies an Intelligent Cause; and thus the idea of a Creator is forced upon us; and, instead of an eternal operation of mechanical powers, and an eternal succession of organized existences, which is the dream of the atheist, we see a system, glorious with the impress of a Divine hand, and rejoicing in the smile of a present Deity.

* Whewell's Bridgewater Treatise, p. 200.

THIRD WEEK-SATURDAY.

VII. THE STARRY HEAVENS.-THE SATELLITES.

We have considered the arrangements of the planetary system, in reference to its stability, and to the diffusion of light and heat; but there is a contrivance of a different kind, which seems to require a slight notice. The existence of satellites, or secondary planets, as they are called, is a striking concomitant of the system. These smaller bodies attend the primary planets in their course round the sun, partaking of their motion, and at the same time wheeling round them, in an orbit of their own, at greater or less distances. Now, it has been remarked, that, speaking generally, these moons are bestowed as attendants on the planets, in some relation to their distance from the sun, increasing in number in proportion as we recede from that luminary. The inferior planets, that is, those that are nearer the sun than our earth, have none. The Earth has one; Jupiter, which is five times more distant from the sun than our planet, has four; Saturn, which nearly doubles the distance of Jupiter, has seven, besides the curious anomaly of a ring; Uranus is known to have five, and may, in all probability, have many more, which the extreme remoteness of his situation, at the distance of 900,000,000 of miles, may well render invisible, even with the use of our best instruments. Supposing, however, that this is the case, there are still exceptions to the rule of increase. Mars, and the four other planetary bodies which are stationed between the Earth and Jupiter, have no attendants. As to the ultra-zodiacal planets, the peculiarity of their condition might lead us to expect this deviation; and though it may be more difficult to account for the want of an attendant in the case of Mars, there are few who,

on this account, will withhold their assent to the truth of the general observation.

What purpose, then, do these secondary planets serve? This is a question which has been so well answered by Mr Whewell, in reference to our own moon, and in refutation of the sceptical doubts of Laplace, that I cannot suppose any apology is required for the quotation which follows:

"A person of ordinary feelings," observes this sound philosopher, "who, on a fine moonlight night, sees our satellite pouring her mild radiance on field and town, path and moor, will, probably, not only be disposed to 'bless the useful light,' but also to believe that it was ordained for that purpose; that the lesser light was made to rule the night, as certainly as the greater light was made to rule the day.

He

"Laplace, however, does not assent to this belief. observes, that some partizans of final causes have imagined, that the moon was given to the earth to afford light during the night;' but he remarks, that this cannot be so, for that we are often deprived at the same time of the light of the sun and of the moon, and he points out how the moon might have been placed so as to be always 'full.'

66 "That the light of the moon affords, to a certain extent, a supplement to the light of the sun, will hardly be denied. If we take man in a condition in which he uses artificial light scantily only, or not at all, there can be no doubt that the moonlight nights are for him a very important addition to the time of daylight. And, as a small proportion, only, of the whole number of nights are without some portion of moonlight, the fact, that sometimes both luminaries are invisible, very little diminishes the value of this advantage. Why we have not more moonlight, either in duration or in quantity, is an inquiry, which a philosopher could hardly be tempted to enter upon, by any success which has attended previous speculations of a similar nature. Why should not the