hear the ingenious remarks of Dr. S. on this subject in the diffusive language of their author:

When two objects, however unlike, have often been observed to follow each other, and have constantly presented themselves to the sense in that order, they come to be so connected together in the fancy, that the idea of the one seems, of its own accord, to call up and introduce that of the other. If the objects are still observed to succeed each other as before, this connection, or, as it has been called, this association of their ideas, becomes stricter and stricter, and the habit of the imagination to pass from the conception of the one to that of the other, grows more and more rivetted and confirmed. As its ideas move more rapidly than external objects, it is continually running before them, and therefore anticipates, before it happens, every event which falls out according to this ordinary course of things. When objects succeed each other in the same train in which the ideas of the imagination have thus been accustomed to move, and in which, though not conducted by that chain of events presented to the senses, they have acquired a tendency to go on of their own accord, such objects appear all closely connected with one another, and the thought glides easily along them, without effort and without interruption. They fall in with the natural career of the imagination; and as the ideas which represented such a train of things would seem all mutually to introduce each other, every last thought to be called up by the foregoing, and to call up the succeeding; so when the objects themselves occur, every last event seems, in the same manner, to be introduced by the foregoing, and to introduce the succeeding. There is no break, no stop, no gap, no interval. The ideas excited by so coherent a chain of things seem, as it were, to float through the mind of their own accord, without obliging it to exert itself, or to make any effort in order to pass from one of them to another.

"But if this customary connection be interrupted, if one or more objects appear in an order quite different from that to which the imagination has been accustomed, and for which it is prepared, the contrary of all this happens. We are at first surprised by the unexpect edness of the new appearance, and when that momentary emotion is over, we still wonder how it came to occur in that place. The imagination no longer feels the usual facility of passing from the event which goes before to that which comes after. It is an order or law of succession to which it has not been accustomed, and which it therefore finds some difficulty in following, or in attending to. The fancy is stopped and interrupted in that natural movement or career, according to which it was proceeding. Those two events seem to stand at a distance from each other; it endeavours to bring them together, but they refuse to unite; and it feels, or imagines it feels, something like a gap or interval betwixt them. It naturally hesitates, and, as it were, pauses upon the brink of this interval; it endeavours to find out something which may fill up the gap, which, like a bridge, may so far at least unite those seemingly distant ob jects, as to render the passage of the thought betwixt them smooth,

C 3

and

and natural, and easy. The supposition of a chain of intermediate, though invisible, events, which succeed each other in a train similar to that in which the imagination has been accustomed to move, and which link together those two disjointed appearances, is the only means by which the imagination can fill up this interval, is the only bridge which, if one may say so, can smooth its passage from the one object to the other.'

It is hence the proper business of philosophy to tranquillize the imagination, by tracing that hidden chain which binds together the seemingly disjointed events of Nature. Waiving the history of science among the Indians, the Chaldeans, and the Egyptians, (of which our accounts were at best imperfect,) Dr. Smith directs his attention to the Greek colonies planted in the islands in Italy, and in Lesser Asia; which, enjoying many advantages both physical and political, early attained a flourishing condition and lettered elegance. The Ionian school, founded by Thales, made small advances in the study of Nature-but the Italic school of Pythagoras was a nursery of brilliant discoveries; it produced the divine Secrates, who reformed and humanized those abstruse speculations in which his predecessors indulged; and the pursuit of natural knowlege was continued with ardour by the two rival sects instituted by his disciples, Plato and Aristotle.

The most obvious opinion, derived immediately from the information of the senses, pictured the habitable world as a vast irregular plane, vaulted by the solid canopy of the sky, and encircled by an ocean of fathomless depth and unbounded expanse, out of which the luminaries of heaven ascended, climbed the empyreal arch, and then sunk to their repose. It was a very considerable step in the progress of the mind to discover the globular form of our earth. The transitions hence was easy to the theory of cœlestial spheres. The stars were supposed to be fixed like gems to the concave surface of a crystalline shell, which rolled on its axis with perfect uniformity. A distinct sphere was appropriated to the sun and to the moon, and the former had a gentle oblique motion. Other spheres were assigned to carry the planets. This hypothesis, however rude, was not devoid of beauty, was simple, and was calculated to sooth and to charm the imagination:-but, as observations grew more precise, the insufficiency of the system was felt. It was then improved at the expence of its simplicity. Eudoxus bestowed four spheres on each of the planets, and to one of those he ascribed an oscillatory motion. As new anomalies were perceived, the number of coelestial spheres was continually augmented; till, by the successive additions of Callippus, Aristotle, and others, it amounted in the hands of Fracastorio, its last adherent

9

adherent in the sixteenth century, to seventy-four. The hypothesis had become as intricate as the appearances themselves,. and no longer afforded relief to the embarrassed imagination. Another system was, for that reason, invented by Apollonius, was afterward improved by Hipparchus, and was transmitted. to us with the authority of Ptolemy-it was the more artificial system of Epicycles and Eccentric Circles. The idea of circular and equable motion was not abandoned: but, while each of the heavenly bodies revolved in its own orb, the centre of that. orb was supposed to be carried at the same time round the cir-, cumference of another circle. The more obvious inequalities were thus explained with a geometrical precision. With all its nice combination of circles, however, it was soon found to have defects; to remove which, the fine contrivance of the, Equant or Equalizing Circle was introduced. Though the an-, gular motion of a planet viewed from the earth was confessed, to be unequal, a point could be assigned from which it would, be seen to move with perfect uniformity. That point was made the centre of the Equant, and lay at the same distance from the centre of the Eccentricity on the one side as the earth was removed on the other. Nothing (says Dr. Smith) can more evidently shew, how much the repose and tranquillity of the imagination is the ultimate end of philosophy, than the invention of this Equalizing Circle.'

Besides these two systems of Concentric and Eccentric, none ever acquired any durable nor extensive reputation. The Stoics, indeed, appear to have adopted an hypothesis distinct from either: but, though justly renowned for their skill in dia-. lectic, and for the purity and sublimity of their moral doctrines, those sages made feeble efforts in the cultivation of natural science. The system of Eccentric corresponded most exactly with the phænomena, and was therefore very generally received by astronomers and mathematicians; and, from the accumulated observations of centuries, it gained stability and perfection. It seems not, however, to have obtained much credit with the philosophers; who, from the height of their towering speculations, were too apt to regard the geometers with ignorant and supercilious contempt. It is worthy of remark that the name of Hipparchus, the great founder of astronomical science, and one of the brightest geniuses of all antiquity, is only casually mentioned by Cicero, without any note of approbation, and is wholly omitted by Seneca and Plutarch. It was the destiny of Rome never to excel in the abstruser studies. Pliny, indeed, a man of universal learning, frequently bears testimony to the merit of Hipparchus, in terms of the highest admiration.

On the extinction of the Western Empire, the sun of science again rose in those regions of the East, which, under Mohammed, had felt the glow of revolutionary impulse. The reign of his successors the Califfs was mild, equitable, liberal, and beneficent. Unfortunately, that period on which humanity dwells without a sigh was of short duration. The Arabians were occupied in studying the writings of their Grecian masters; and though they enriched the stock of astronomical observations, they made few original improvements on the theory.

When learning again began to dawn in Europe, the Ptolemaic system was adopted. Alphonso, king of Castile, employed some Jewish astronomers in the xiiith century to rectify and enlarge the tables of the cœlestial motions. Its perplexed complication of Epicycles and Eccentric Circles, which their corrections required, now fatigued the imagination; and they drew from that philosophic prince the famous exclamation which the bigotry of the age represented as impious. The revival of astronomical science, however, is chiefly due to the ardour of Purbach and his continuator Muller of Koningsberg, who both' lived in the fifteenth century. Their career of genius was lamentably terminated by premature death. To them succeeded Copernicus, a name familiar to every person who is in any degree imbued with literature. We shall gratify ourselves and our readers by extracting the passage which explains the motives and procedure of that eminent theorist:

The confusion, in which the old hypothesis represented the notions of the heavenly bodies, was, he tells us, what first suggested to him the design of forming a new system, that these, the noblest works of nature, might no longer appear devoid of that harmony and proportion which discover themselves in her meanest productions. What most of all dissatisfied him, was, the notion of the Equalizing Circle, which, by representing the revolutions of the Celestial Spheres, as equable only, when surveyed from a point that was different from their centers, introduced a real inequality into their motions; contrary to that most natural, and indeed fundamental idea, with which all the authors of astronomical systems, Plato, Eudoxus, Aristotle, even Hipparchus and Ptolemy themselves, had hitherto set out, that the real motions of such beautiful and divine objects must necessarily be perfectly regular, and go on, in a manner as agreeable to the imagination, as the objects themselves are to the senses. began to consider, therefore, whether, by supposing the heavenly bodies to be arranged in a different order from that in which Aristotle and Hipparchus had placed them, this so much sought for uniformity might not be bestowed upon their motions. To discover this arrangement, he examined all the obscure traditions delivered down to us, concerning every other hypothesis which the ancients had invented, for the same purpose. He found, in Plutarch, that

He

some

some old Pythagoreans had represented the Earth as revolving in the center of the universe, like a wheel round its own axis; and that others, of the same sect, had removed it from the center, and represented it as revolving in the Ecliptic like a star round the central fire. By this central fire, he supposed they meant the Sun; and though in this he was very widely mistaken, it was, it seems, upon this interpretation, that he began to consider how such an hypothesis might be made to correspond to the appearances. The sup posed authority of those old philosophers, if it did not originally suggest to him his system, seems, at least, to have confirmed him in an opinion, which, it is not improbable, he had before-hand other reasons for embracing, notwithstanding what he himself would affirm to the contrary.

It then occurred to him, that, if the Earth was supposed to revolve every day round its axis, from west to east, all the heavenly bodies would appear to revolve, in a contrary direction, from east to west. The diurnal revolution of the heavens, upon this hypothesis, might be only apparent; the firmament, which has no other sensible motion, might be perfectly at rest; while the Sun, the Moon, and the Five Planets, might have no other movement beside that eastward revolution, which is peculiar to themselves. That, by suppos ing the Earth to revolve with the Planets, round the Sun, in an orbit, which comprehended within it the orbits of Venus and Mercury, but was comprehended within those of Mars, Jupiter, and Saturn, he could, without the embarrassment of Epicycles, connect together the apparent annual revolutions of the Sun, and the direct, retrograde, and stationary appearances of the Planets: that while the Earth really revolved round the Sun on one side of the heavens, the Sun would appear to revolve round the Earth on the other; that while she really advanced in her annual course, he would appear to advance eastward in that movement which is peculiar to himself. That, by supposing the axis of the Earth to be always parallel to itself, not to be quite perpendicular, but somewhat inclined to the plane of her orbit, and consequently to present to the Sun, the one pole when on the one side of him, and the other when on the other, he would account for the obliquity of the Ecliptic; the Sun's seemingly alternate progression from north to south, and from south to north, the consequent change of the seasons, and different lengths of days and nights in the different seasons.

If this new hypothesis thus connected together all these appearances as happily as that of Ptolemy, there were others which it connected together much better. The three superior Planets, whea nearly in conjunction with the Sun, appear always at the greatest distance from the Earth, are smallest, and least sensible to the eye, and seem to revolve forward in their direct motion with the greatest rapidity. On the contrary, when in opposition to the Sun, that is, when in their meridian about midnight, they appear nearest the Earth, are largest, and most sensible to the eye, and seem to revolve backwards in their retrograde motion. To explain these appearances, the system of Ptolemy supposed each of these Planets to be at the upper part of their several Epicycles, in the one case; and at the

lower,