tions in which the cannon might be pointed, upwards and downwards, every one would fail, but what was exactly or nearly horizontal. The same thing holds true of the planets: of our own amongst the rest. We are entitled therefore to ask, and to urge the question, Why

sufficient to carry the ball off into infinite space, it will move in the curve of an ellipse, of which one of the foci is situated in the centre of the earth. Now a body moving uninterruptedly in an ellipse must return in time to the same point from which it sat out. The body therefore which, when projected from A, Fig. 6. comes down to the earth at C, would have continued its course along the dotted line and returned to A, if the mass of matter in the earth had been collected together at its centre, so as not to interfere with the motion of the projectile. Let us now conceive the body to be projected back from C, with the velocity which it had acquired in its fall, and with the direction in which it reached the earth, it would then pass through A, and come down on the other side of AI, in just the same curve, in which it had fallen from A to C. The same would apply to bodies projected upwards from B or D; and if the velocities of projection were less or greater than what would have been acquired in falling from A, the bodies would still turn, but at some less or more distant point. The longest diameter, however, of the ellipsis in which they move must always pass through the earth's centre, and if the bodies rise on one side of this diameter they must fall down on the other. Now it will be seen that the curves at B, C, and D, make the angles ABI, ACI, ADI less, as the body is supposed to go farther and farther before it falls, and that the curves, in which the body can complete a revolution near the surface, will in all its parts be nearly parallel to it. Hence the cannon ball fired upwards will come back again to the ground and not be able completely to go round the earth upon any other supposition excepting that of its being fired in nearly an horizontal di rection.

did the projectile velocity and projectile direction of the earth happen to be nearly those which would retain it in a circular form? Why not one of the infinite number of velocities, one of the infinite number of directions, which would have made it approach much nearer to, or recede much farther from, the sun ?

The planets going round, all in the same direction, and all nearly in the same plane, afforded to Buffon a ground for asserting, that they had all been shivered from the sun by the same stroke of a comet, and by that stroke projected into their present orbits. Now, besides that this is to attribute to chance the fortunate concurrence of velocity and direction which we have been here noticing, the hypothesis, as I apprehend, is inconsistent with the physical laws by which the heavenly motions are governed. If the planets were struck off from the surface of the sun, they would return to the sun again. Nor will this difficulty be got rid of, by supposing that the same violent blow which shattered the sun's surface, and separated large fragments from it, pushed the sun himself out of his place; for the consequence of this would be, that the sun and system of shattered fragments would have a progressive motion, which indeed may possibly be the case with our system; but then each fragment would, in every revolution, return to the surface of the sun again. The hypothesis is also contradicted by the vast difference which sub

sists between the diameters of the planetary orbits. The distance of Saturn from the sun (to say nothing of the Georgium Sidus) is nearly five-andtwenty times that of Mercury; a disparity, which it seems impossible to reconcile with Buffon's scheme.* Bodies starting from the same place, with whatever difference of direction or velocity they set off, could not have been found, at these different distances from the centre, still retaining their nearly circular orbits. They must have been carried to their proper distances before they were projected.t

To conclude: In astronomy, the great thing is to raise the imagination to the subject, and that

Buffon published his "Theorie de la Terre" in 1744, and afterwards incorporated it in the first volume of his "Histoire Naturelle," which he published in 1749. M. La Place in the last chapter of his "Systeme du Monde," discusses and refutes this hypothesis of the planets having been struck off from the sun by the collision of a comet.

+ "If we suppose the matter of the system to be accumulated in the centre by its gravity, no mechanical principles, with the assistance of this power of gravity, could separate the vast mass into such parts as the sun and planets; and after carrying them to their different distances, project them in their several directions, preserving still the quality of action and reaction, or the state of the centre of gravity of the system. Such an exquisite structure of things could only arise from the contrivance and powerful influences of an intelligent, free, and most potent agent. The same powers, therefore, which at present govern the material universe, and conduct its various motions, are very different from those which were necessary to have produced it from nothing, or to have disposed it in the admirable form in which it now proceeds."-Maclaurin's Account of Newton's Philosophy, p. 407. edit. 3.-Paley.

oftentimes in opposition to the impression made upon the senses. An illusion, for example, must be gotten over, arising from the distance at which we view the heavenly bodies, viz. the apparent slowness of their motions. The moon shall take some hours in getting half a yard from a star which it touched. A motion so deliberate, we may think easily guided. But what is the fact? The moon, in fact, is, all this while, driving through the heavens, at the rate of considerably more than two thousand miles in an hour; which is more than double of that with which a ball is shot off from the mouth of a cannon. Yet is this prodigious rapidity as much under government, as if the planet proceeded ever so slowly, or were conducted in its course inch by inch. It is also difficult to bring the imagination to conceive (what yet, to judge tolerably of the matter, it is necessary to conceive) how loose, if we may so express it, the heavenly bodies are. Enormous globes, held by nothing, confined by nothing, are turned into free and boundless space, each to seek its course by the virtue of an invisible principle; but a principle, one, common, and the same in all; and ascertainable. To preserve such bodies from being lost, from running together in heaps, from hindering and distracting one another's motions, in a degree inconsistent with any

"Held by nothing, confined by nothing," which is material or mechanical.

continuing order; i. e. to cause them to form planetary systems, systems that, when formed, can be upheld, and more especially, systems accommodated to the organized and sensitive natures which the planets sustain, as we know to be the case, where alone we can know what the case is, upon our earth: all this requires an intelligent interposition, because it can be demonstrated concerning it, that it requires an adjustment of force, distance, direction, and velocity, out of the reach of chance to have produced; an adjustment, in its view to utility, similar to that which we see in ten thousand subjects of nature which are nearer to us, but in power, and in extent of space through which that power is exerted, stupendous.

But many of the heavenly bodies, as the sun and fixed stars, are stationary. Their rest must be the effect of an absence or of an equilibrium of attractions. It proves also, that a projectile impulse was originally given to some of the heavenly bodies, and not to others. But farther; if attraction act at all distances, there can be only one quiescent centre of gravity in the universe: and all bodies whatever must be approaching this centre, or revolving round it. According to the first of these suppositions, if the duration of the world had been long enough to allow of it, all its parts, all the great bodies of which it is composed, must have been gathered together in a heap round this point. No changes, however, which have been observed, afford us the smallest reason for