been entirely forgotten. Instead of consulting the heavens, and collecting the history of nature, succeeding philosophers were ambitious of gratifying their own vanity, by inventing whimsical hypotheses, which had no conformity to fact and experiment. Solid orbs and epicycles were multiplied to answer every appearance, till the universe had lost all its native beauty in their descriptions, and seemed again reduced to a chaos by their unhappy labours.

It was about the middle of the sixteenth century that Copernicus, a bold and original genius, adopted the Pythagorean, or true system of the universe, and published it to the world with new and demonstrative arguments in its favour. (Pl. 1.) Seized with a daring enthusiasm, he laid his hands on the cycles and crystal orbs of Ptolemy, and dashed them to pieces. And, with the same noble phrensy, he took the unwieldy earth, and sent her far from the centre of the system, to move round the sun with the rest of the planets; so that of all the celestial equipage, with which she had been formerly dignified, there only remained the moon to attend and accompany her in her journey.

Europe, however, was still immersed in barbarism and ignorance; and the general ideas of the world were not able to keep pace with those of a refined philosophy. This occasioned Copernicus to have few abettors, but many opponents. Threatened by the persecution of religious bigots on the one side, and with an obstinate and violent opposition from those who called themselves philosophers,

on the other, it was not without the greatest solicitations, that he could be prevailed upon to give up his papers to his friends, with permission to make them public. But, from continual importunities of this kind, he at length complied; and his book De Revolutionibus Orbium cœlestium, after being suppressed for more than thirty-six years, was at length published, and a copy of it brought to him a few hours before his death.

In this treatise he restored the ancient Pythagorean system, and deduced the appearances of the celestial motions from it in the most convincing and satisfactory manner. Every age since has produced new arguments in its favour; and notwithstanding the opposition it met with from the prejudices of sense against the earth's motion, the authority of Aristotle in the schools, the threats of ignorant enthusiasts, and the terrors of the inquisition, it has gradually prevailed ever since, and is now universally received by all the learned throughout Europe.

Towards the end of the same century also, and about the beginning of the next, those great men Galileo and Kepler particularly distinguished themselves in the defence of this doctrine; and by means of the telescope, which was the invention of that time, made many new and surprising dis-. coveries in the heavens. By applying this instrument to the planets, Galileo first observed, that the phases of Venus were like the monthly phases of the moon; and thence inferred that she revolved round the sun as a centre. He also proved the

revolution of the sun on its axis, from the motion of his spots; and by that means rendered the diurnal rotation of the earth more credible. The four satellites which attend Jupiter, in his revolution about the sun, represented, likewise, in miniature, a just image of the great solar system, and rendered it more easy to conceive how the moon might attend the earth, as a satellite, in her annual revolution. In short, by his discovering hills and cavities in the moon, and spots in the sun, he proved, clearly, that there was not so great a difference between celestial and sublunary bodies as philosophers had vainly imagined.

From these discoveries, astronomy began to assume a new form, and most of the celestial phanomena were soon accounted for, according to their real or physical causes. Des Cartes, Gassendus, Cassini, and Newton, employed themselves, with the utmost diligence, in improving and perfecting this science: and the last of these great men, in particular, has established the Copernican system upon such an everlasting basis of mathematical demonstration, as can never be shaken, but must last as long as the present frame of nature continues in existence.

LETTER V.

OF THE SYSTEM OF DES CARTES.

THE active mind of man is naturally fond of investigation; and from contemplating effects, we are insensibly led to enquire into the causes which produced them. After having discovered the vast extent of the creation, and the order, regularity, and harmony of the celestial motions, our next reflections will be, how such a frame began at first to exist, and by what force those prodigious bodies are constantly driven round the sun, and retained in their orbits.

But to prosecute these researches with proper advantage, requires a free and unbiassed mind, invigorated with all the powers of genius and judgment. From the workmanship to trace the Workman; and from viewing the grand machine of the universe, to discover the hidden springs of its motion, and the secret laws of its mechanism and contrivance, is, of all pursuits, the most sublime and interesting, and, perhaps, the highest pitch of knowledge which the human faculties are capable of attaining.

It must not, therefore, be considered as a matter of surprise, that, in the more early ages of the world, when science was yet in its infancy, and the mind of man enslaved and debased by ignorance and a barbarous superstition, a knowledge so exalted and refined should be but imperfectly understood, and but little cultivated.

F

The priests and magi of the east, who are supposed to have been the first masters of the sciences, involved all their notions in ænigmatical and allegorical representations; so that what was plain and simple, was rendered mysterious and doubtful; and mankind, instead of being made acquainted with nature, and the manner in which she conducts her operations, were amused only with absurd fables and chimerical conceits, which were so far from answering the purposes of instruction, that they served only to impede and retard it. To some of their most favoured disciples and followers they unveiled their mysteries, but the people in general were kept in darkness and the grossest ignorance.

From Egypt and Phoenicia philosophy travelled into Greece, and was there more generally cultivated and diffused; but in a manner equally unfavourable to instruction and improvement. The philosophers of those times, disputatious and obstinate, were more fond of victory than truth; and whilst they contended only to show their ablities, and to display a vain ostentation of learning, men were diverted from pursuing real knowledge, and a talkative philosophy was instituted, which was principally upheld by logical quibbles and sophistical subtilties, that had no relation to fact or experiment, the only sure foundations upon which any system of physics can possibly be supported.

Instead of searching into nature, men retired to contemplate their own notions; and, instead of tracing her operations, gave their imaginations full