we spend our time to better purpose, now and then, than in harkening to a demonstration by Alemæon.

In many works on Astronomy I find it distinctly stated that the laws of Kepler are the basis of the great principle, Gravitation. This idea must have arisen from the fact that the suggestion of these laws by Kepler, and his proving them à posteriori to have an actual existence, led Newton to account for them by the hypothesis of Gravitation, and, finally, to demonstrate them à priori, as necessary consequences of the hypothetical principle. Thus so far from the laws of Kepler being the basis of Gravity, Gravity is the basis of these laws-as it is, indeed, of all the laws, of the material Universe which are not referable to Repulsion alone.

The mean distance of the Earth from the Moon-that is to say, from the heavenly body in our closest vicinity-is 237,000 miles. Mercury, the planet nearest the Sun, is distant from him 37 millions of miles. Venus, the next, revolves at a distance of 68 millions-the Earth, which comes next, at a distance of 95 millions --Mars, then, at a distance of 144 millions. Now come the eight Asteroids (Ceres, Juno, Vesta, Pallas, Astræa, Flora, Iris, and Hebe) at an average distance of about 250 millions. Then we have Jupiter, distant 490 millions; then Saturn, 900 millions; then Uranus, 19 hundred millions; finally Neptune, lately discovered, and revolving at a distance, say of 28 hundred millions. Leaving Neptune out of the account-of which as yet we know little accurately and which is, possibly, one of a system of Asteroids-it will be seen that, within certain limits, there exists an order of interval among the planets. Speaking loosely, we may say that each outer planet is twice as far from the Sun as is the next inner one. May not the order here mentioned—may not the law of Bode-be deduced from consideration of the analogy suggested by me as having place between the solar discharge of rings and the mode of the atomic irradiation?

The numbers hurriedly mentioned in this summary of distance, it is folly to attempt comprehending, unless in the light of abstract arithmetical facts. They are not practically tangible ones. They convey no precise ideas. I have stated that Neptune, the planet farthest from the Sun, revolves about him at a distance of 28

hundred millions of miles. So far good :—I have stated a mathematical fact; and, without comprehending it in the least, we may put it to use-mathematically. But in mentioning, even, that the Moon revolves about the Earth at the comparatively trifling distance of 237,000 miles, I entertained no expectation of giving any one to understand-to know-to feel-how far from the Earth the Moon actually is. 237,000 miles! There are, perhaps, few of my readers who have not crossed the Atlantic ocean; yet how many of them have a distinct idea of even the 3,000 miles intervening between shore and shore? I doubt, indeed, whether the man lives who can force into his brain the most remote conception of the interval between one milestone and its next neighbor upon the turnpike. We are in some measure aided, however, in our consideration of distance, by combining this consideration with the kindred one of velocity. Sound passes through 1100 feet of space in a second of time. Now were it possible for an inhabitant of the Earth to see the flash of a cannon discharged in the Moon, and to hear the report, he would have to wait, after perceiving the former, more than 13 entire days and nights before getting any intimation of the latter.

However feeble be the impression, even thus conveyed, of the Moon's real distance from the Earth, it will, nevertheless, effect a good object in enabling us more clearly to see the futility of attempting to grasp such intervals as that of the 28 hundred millions of miles between our Sun and Neptune; or even that of the 95 millions between the Sun and the Earth we inhabit. A cannon-ball, flying at the greatest velocity with which such a ball has ever been known to fly, could not traverse the latter interval in less than 20 years; while for the former it would require 590.

Our Moon's real diameter is 2160 miles; yet she is comparatively so trifling an object that it would take nearly 50 such orbs to compose one as great as the Earth.

The diameter of our own globe is 7912 miles-but from the enunciation of these numbers what positive idea do we derive?

If we ascend an ordinary mountain and look around us from its summit, we behold a landscape stretching, say 40 miles, in every direction; forming a circle 250 miles in circumference; and including an area of 5000 square miles. The extent of such a

prospect, on account of the successiveness with which its portions necessarily present themselves to view, can be only very feebly and very partially appreciated:-yet the entire panorama would comprehend no more than one 40,000th part of the mere surface of our globe. Were this panorama, then, to be succeeded, after the lapse of an hour, by another of equal extent; this again by a third, after the lapse of an hour; this again by a fourth after lapse of another hour-and so on, until the scenery of the whole Earth were exhausted; and were we to be engaged in examining these various panoramas for twelve hours of every day; we should nevertheless, be 9 years and 48 days in completing the general survey.

But if the mere surface of the Earth eludes the grasp of the imagination, what are we to think of its cubical contents? It embraces a mass of matter equal in weight to at least two sextillions, two hundred quintillions of tons. Let us suppose it in a state of quiescence; and now let us endeavor to conceive a mechanical force sufficient to set it in motion! Not the strength of all the myriads of beings whom we may conclude to inhabit the planetary worlds of our system-not the combined physical strength of all these beings-even admitting all to be more pow erful than man—would avail to stir the ponderous mass a single inch from its position.

What are we to understand, then, of the force, which under similar circumstances, would be required to move the largest of our planets, Jupiter? This is 86,000 miles in diameter, and would include within its periphery more than a thousand orbs of the magnitude of our own. Yet this stupendous body is actually flying around the sun at the rate of 29,000 miles an hour—that is to say, with a velocity forty times greater than that of a cannon-ball! The thought of such a phænomenon cannot well be said to startle the mind:-it palsies and appals it. Not unfrequently we task our imagination in picturing the capacities of an angel. Let us fancy such a being at a distance of some hundred miles from Jupiter-a close eye-witness of this planet as it speeds on its annual revolution. Now can we, I demand, fashion for ourselves any conception so distinct of this ideal being's spiritual exaltation, as that involved in the supposition that, even by this

immeasurable mass of matter, whirled immediately before his eyes, with a velocity so unutterable, he-an angel-angelic though he be is not at once struck in. nothingness and overwhelmed?

At this point, however, it seems proper to suggest that, in fact, we have been speaking of comparative trifles. Our Sun-the central and controlling orb of the system to which Jupiter belongs— is not only greater than Jupiter, but greater by far than all the planets of the system taken together. This fact is an essential condition, indeed, of the stability of the system itself. The diameter of Jupiter has been mentioned: it is 86,000 miles :—that of the Sun is 882,000 miles. An inhabitant of the latter, travelling. ninety miles a day, would be more than eighty years in going round a great circle of its circumference. It occupies a cubical space of 681 quadrillions, 472 trillions of miles. The Moon, as has been stated, revolves about the Earth at a distance of 237,000 miles-in an orbit, consequently, of nearly a million and a half. Now, were the Sun placed upon the Earth, centre over centre, the body of the former would extend, in every direction, not only to the line of the Moon's orbit, but beyond it, a distance of 200,000 miles.

And here, once again, let me suggest that, in fact, we have still been speaking of comparative trifles. The distance of the planet Neptune from the Sun has been stated: it is 28 hundred millions of miles the circumference of its orbit, therefore, is about 17 billions. Let this be borne in mind while we glance at some one of the brightest stars. Between this and the star of our system, (the Sun,) there is a gulf of space, to convey any idea of which, we should need the tongue of an archangel. From our system, then, and from our Sun, or star, the star at which we suppose ourselves glancing is a thing altogether apart :-still, for the moment, let us imagine it placed upon our Sun, centre over centre, as we just now imagined this Sun itself placed upon the Earth. Let us now conceive the particular star we have in mind, extending, in every direction, beyond the orbit of Mercury—of Venus— of the Earth :-still on, beyond the orbit of Mars-of Jupiterof Uranus-until, finally, we fancy it filling the circle-seventeen billions of miles in circumference-which is described by the revo lution of Leverrier's planet. When we have conceived all this, we shall have entertained no extravagant conception. There is the

very best reason for believing that many of the stars are even far larger than the one we have imagined. I mean to say, that we have the very best empirical basis for such belief:—and, in looking back at the original, atomic arrangements for diversity, which have been assumed as a part of the Divine plan in the constitution of the Universe, we shall be enabled easily to understand, and to credit, the existence of even far vaster disproportions in stellar size than any to which I have hitherto alluded. The largest orbs, of course, we must expect to find rolling through the widest vacancies of Space.

I remarked, just now, that to convey an idea of the interval between our Sun and any one of the other stars, we should require the eloquence of an archangel. In so saying, I should not be accused of exaggeration; for, in simple truth, these are topics on which it is scarcely possible to exaggerate. But let us bring the matter more distinctly before the eye of the mind.

In the first place, we may get a general, relative conception of the interval referred to, by comparing it with the inter-planetary spaces. If, for example, we suppose the Earth, which is, in reality, 95 millions of miles from the Sun, to be only one foot from that luminary; then Neptune would be forty feet distant; and the star Alpha Lyra, at the very least, one hundred and fifty-nine.

Now I presume that, in the termination of my last sentence, few of my readers have noticed anything especially objectionableparticularly wrong. I said that the distance of the Earth from the Sun being taken at one foot, the distance of Neptune would be forty feet, and that of Alpha Lyræ, one hundred and fifty-nine. The proportion between one foot and one hundred and fifty nine, has appeared, perhaps, to convey a sufficiently definite impression of the proportion between the two intervals-that of the Earth from the Sun, and that of Alpha Lyræ from the same luminary. But my account of the matter should, in reality, have run thus:— The distance of the Earth from the Sun being taken at one foot, the distance of Neptune would be forty feet, and that of Alpha Lyræ, one hundred and fifty-nine- -miles :-that is to say, I had assigned to Alpha Lyræ, in my first statement of the case, only the 5280th part of that distance which is the least distance possible at which it can actually lie.