lower, in the other. But it afforded no satisfactory principle of con-, nection, which could lead the mind easily to conceive how the Epicycles of those Planets, whose spheres were so distant from the sphere of the Sun, should thus, if one may say so, keep time to his motion. The system of Copernicus afforded this easily, and like a more simple machine, without the assistance of Epicycles, con nected together, by fewer movements, the complex appearances of the heavens. When the superior Planets appear nearly in conjunction with the Sun, they are then in the side of their orbits, which is almost opposite to, and most distant from the Earth, and therefore appear smallest, and least sensible to the eye. But, as they then revolve in a direction which is almost contrary to that of the Earth, they appear to advance forward with double velocity; as a ship, that sails in a contrary direction to another, appears from that other, to sail both with its own velocity, and the velocity of that from which it is seen. On the contrary, when those Planets are in opposition to the Sun, they are on the same side of the Sun with the Earth, are nearest it, most sensible to the eye, and revolve in the same direction with it; but, as their revolutions round the Sun are slower than that of the Earth, they are necessarily left behind by it, and therefore seem to revolve backwards; as a ship which sails slower than another, though it sails in the same direction, appears from that other to sail backwards. After the same manner, by the same annual revolution of the Earth, he connected together the direct and retrograde motions of the two inferior Planets, as well as the stationary appearances of all the Five.' Thus far did this new account of things render the appearances of the heavens more completely coherent than had been done by any of the former systems. It did this, too, by a more simple and intelligible, as well as more beautiful machinery. It represented the Sun, the great enlightener of the universe, whose body was alone larger than all the Planets taken together, as established immoveable in the center, shedding light and heat on all the worlds that circulated around him in one uniform direction, but in longer or shorter periods, according to their different distances. It took away the diurnal revolution of the firmament, whose rapidity, upon the old hypothesis, was beyond what even thought could conceive. It not only delivered the imagination from the embarrassment of Epicycles, but from the difficulty of conceiving these two opposite motions going on at the same time, which the system of Ptolemy and Aristotle bestowed upon all the Planets; I mean, their diurnal westward, and periodical eastward revolutions. The Earth's revolution round its own axis took away the necessity for supposing the first, and the second was easily conceived when by itself, The Five Planets, which seem, upon all other systems, to be objects of a species by themselves, unlike to every thing to which the imagination has been ac customed, when supposed to revolve along with the Earth round the Sun, were naturally apprehended to be objects of the same kind with the Earth, habitable, opaque, and enlightened only by the rays of the Sun. And thus this hypothesis, by classing them in the same species of things, with an object that is of all others others the most familiar to us, took off that wonder and uncertainty which the strangeness and singularity of their appearance had excited; and thus far, too, better answered the great end of Philosophy. Neither did the beauty and simplicity of this system alone recommend it to the imagination; the novelty and unexpectedness of that view of nature, which it opened to the fancy, excited more wonder and surprise than the strangest of those appearances, which it had been invented to render natural and familiar, and these sentiments still more endeared it. For, though it is the end of Philosophy to allay that wonder, which either the unusual or seemingly disjointed appearances of nature excite, yet she never triumphs so much, as when, in order to connect together a few, in themselves, perhaps, inconsiderable objects, she has, if I may say so, created another constitution of things, more natural indeed, and such as the imagination can more easily attend to, but more new, more contrary to common opinion and expectation, than any of those appearances themselves. As, in the instance before us, in order to connect together some seeming irregularities in the motions of the Planets, the most inconsiderable objects in the heavens, and of which the greater part of mankind have no occasion to take any notice during the whole course of their lives, she has, to talk in the hyperbolical language of Tycho-Brache, moved the Earth from its foundations, stopt the revolution of the Firmament, made the Sun stand still, and subverted the whole order of the Universe. Such were the advantages of this new hypothesis, as they appeared to its author, when he first invented it. But, though that love of paradox, so natural to the learned, and that pleasure, which they are so apt to take in exciting, by the novelty of their supposed discoveries, the amazement of mankind, may, notwithstanding what one of his disciples tells us to the contrary, have had its weight in prompting Copernicus to adopt this system; yet, when he had completed his Treatise of Revolutions, and began coolly to consider what a strange doctrine he was about to offer to the world, he so much dreaded the prejudice of mankind against it, that, by a species of continence, of all others the most difficult to a philosopher, he detained it in his closet for thirty years together. At last, in the extremity of old age, he allowed it to be extorted from him, but died as soon as it was printed, and before it was published.' This noble theory, however, being repugnant to the prejudices of habit and education, was at first coldly received, or utterly rejected, by every class of men. The astronomers alone favoured it with their notice, though rather as a convenient hypothesis than an important truth. By the vulgar it was considered as a chimæra, belied by the clearest evidence of our senses; while the learned beheld it with disdain, because it militated against the fanciful distinctions, and the vague erroneous tenets, of the Peripatetic Philosophy, which no one had ventured to call in question; and it is amusing to observe with what what dexterity the Copernicans, still using the same weapons, endeavoured to parry the blows of their antagonists. Its real merits and blemishes appear to have been overlooked by both parties. Brahé framed a sort of intermediate system: but this Danish astronomer was more remarkable for his patience and skill in observing the heavens, than for his talents of philosoTowards the commencement of the phical investigation. sixteenth century, a new order of things emerged. The system of Copernicus became generally known, and daily made conIts reception alarmed the ever-watchful authority of the church, roused her jealousy, and at length provoked her vindictive artillery. The ultima ratio theologorum was pointed at the head of the illustrious Galileo, whose elegant genius discovered the laws of motion, extended the science of mechanics, and added lustre and solidity to the true system of the universe. From the storms of persecution, Copernicus himself had been exempted only by a timely death. verts. Germany gave birth to Kepler, a man of extraordinary genius, ardour, and application. His laborious computations from the register of Brahé dissolved that spell which, for many ages, had enchanted the world; and the notion of circular and equable motions now received a fatal blow. He demonstrated that the planets revolve in elliptical orbits, which no combination of Epicycles can describe; and he pursued, with incredible perseverance, every figurate analogy that his exuberant fancy could suggest. At length he obtained the full measure of success, and laid open those immortal laws which connect the motions, the distances, and the periods of the heavenly bodies. The importance of Kepler's discoveries was not yet fully perceived. Gassendi, Ward, and Bonillaud attempted to combine his corrections with the antient doctrines :-but it requir ed a lofty genius to demolish the structure of Aristotelian phiJosophy. To Des Cartes is mankind indebted for that inestimable service; and the magnitude of the atchievement may well excuse the temerity of attempting to rear a new and unstable edifice. The French philosopher accurately understood the science of mechanics, and was the first to transfer its principles to the explication of the appearances of the heavens. As the system of vortices is now exploded, it has been the fashion of late to undervalue the original author :— but, if the system of Des Cartes, for nearly a century, maintained its reputation over a large portion of enlightened Europe, it had surely much intrinsic merit. We make, therefore, no apology for quoting the following very clear and copious exposition of it: • According According to that ingenious and fanciful philosopher, the whole of infinite space was full of matter, for with him matter and exten sion were the same, and consequently there could be no void. This immensity of matter, he supposed to be divided into an infinite num ber of very small cubes; all of which, being whirled about upon their own centers, necessarily gave occasion to the production of two differ ent elements. The first consisted of those angular parts, which, hav ing been necessarily rubbed off, and grinded yet smaller by their mutual friction, constituted the most subtile and moveable part of matter. The second consisted of those little globules that were formed by the rubbing off of the first. The interstices betwixt these globules of the second element were filled up by the particles of the first. But in the infinite collisions, which must occur in an infinite space filled with matter, and all in motion, it must necessarily happen, that many of the globules of the second element should be broken and grinded down into the first. The quantity of the first element having thus been encreased beyond what was sufficient to fill up the interstices of the second, it must, in many places, have been heaped up together, without any mixture of the second along with it. Such, according to Des Cartes, was the original division of matter. Upon this infinitude of matter thus divided, a certain quantity of motion was originally impressed by the Creator of all things, and the laws of motion were so adjusted as always to preserve the same quantity in it, without increase, and without diminution. Whatever motion was lost by one part of matter, was communicated to some other; and whatever was acquired by one part of matter, was derived from some other: and thus, through an eternal revolution, from rest to motion, and from motion to rest, in every part of the universe, the quantity of motion in the whole was always the same. But, as there was no void, no one part of matter could be moved without thrusting some other out of its place, nor that without thrusting some other, and so on. To avoid, therefore, an infinite progress, he supposed, that the matter which any body pushed before it, rolled immediately backwards, to supply the place of that matter which flowed in behind it; as we may observe in the swimming of a fish, that the water, which it pushes before it, immediately rolls backwards, to supply the place of what flows in behind it, and thus forms a small circle or vortex round the body of the fish. It was in the same manner, that the motion originally impressed by the Creator upon the infinitude of matter, necessarily produced in it an infinity of greater and smaller vortices, or circular streams and the law of motion being so adjusted as always to preserve the same quantity of motion in the universe, those vortices either continued for ever, or by their dissolution give birth to others of the same kind. There was, thus, at all times, an infinite number of greater and smaller vortices, or circular streams, revolving in the universe. • But, whatever moves in a circle, is constantly endeavouring to fly off from the center of its revolution. For the natural motion of all bodies is in a straight line. All the particles of matter, therefore, in each of those greater vortices, were continually pressing from the center to the circumference, with more or less force, according to the different different degrees of their bulk and solidity. The larger and more solid globules of the second element forced themselves upwards to the circumference, while the smaller, more yielding, and more active particles of the first, which could flow, even through the interstices of the second, were forced downwards to the center. They were forced downwards to the center, notwithstanding their natural tendency was upwards to the circumference; for the same reason that a piece of wood, when plunged in water, is forced upwards to the surface, notwithstanding its natural tendency is downwards to the bottom; because its tendency downwards is less strong than that of the particles of water, which, therefore, if one may say so, press in before it, and thus force it upwards. But there being a greater quantity of the first element than what was necessary to fill up the interstices of the second, it was necessarily accumulated in the center of each of these great circular streams, and formed there the firey and active substance of the Sun. For, according to that philosopher, the Solar Systems were infinite in number, each Fixed Star being the center of one: and he is among the first of the moderns, who thus took away the boundaries of the Universe; even Copernicus and Kepler, themselves, having confined it within, what they supposed, the vault of the Firmament • The center of each vortex being thus occupied by the most active and moveable parts of matter, there was necessarily among them, a more violent agitation than in any other part of the vortex, and this violent agitation of the center cherished and supported the movement of the whole. But, among the particles of the first element, which fill up the interstices of the second, there are many, which, from the pressure of the globules on all sides of them, necessarily receive an angular form, and thus constitute a third element of particles less fit for motion than those of the other two. As the particles, however, of this third element were formed in the interstices of the second, they are necessarily smaller than those of the second, and are, therefore, along with those of the first, urged down towards the center, where, when a number of them happen to take hold of one another, they form such spots upon the surface of the accumulated particles of the first element, as are often discovered by telescopes upon the face of that Sun, which enlightens and animates our particular system. Those spots are often broken and dispelled, by the violent agitation of the particles of the first element, as has hitherto happily been the case with those which have successively been formed upon the face of our Sun. Sometimes, however, they encrust the whole surface of that fire which is accumulated in the center; and the communication betwixt the most active and the most inert parts of the vortex being thus interrupted, the rapidity of its motion immediately begins to languish, and can no longer defend it from being swallowed up and carried away by the superior violence of some other like circular stream; and in this manner, what was once a Sun, becomes a Planet. Thus, the time was, according to the system, when the Moon was a body of the same kind with the Sun, the firey center of a circular stream of ether, which flowed continually round her; but her face having been crusted over by a congeries of angular particles, the |