ness.

no solid argument, and rapidly sunk into forgetfulThis philosopher is said to have fixed the sun in the centre of his planetary system, and to have taught the revolution of the earth in an orbit; but to sustain this bold conjecture, the only reason assigned, was, that fire which composes the sun, was more dignified than earth, and hence should hold the more dignified position in the centre. We are not surprised that Hipparchus and Ptolemy, the true astronomers among the Greeks, should have rejected a doctrine sustained by so futile and absurd a reason. Nicetas, a follower of Pythagoras, is said to have gone farther than his master, and to have adopted the idea that the revolution of the heavens, was an appearance produced by an actual rotation of the earth on an axis, once in twenty-four hours. This extraordinary and almost prophetic announcement, unfortunately was not sustained by any solid argument. It was regarded as a vain dream, and soon was lost in oblivion.

A crowd of theoretic philosophers filled for a long time the schools of Greece, contributing little to science, and diverting the mind from the only train of research which could lead to any true results. At length a philosopher arose who restored investigation to its legitimate channel. Hipparchus, abandoning, for the present, all vain effort to explain the phenomena of the heavens, gave himself up to close, continuous, and accurate observation. He began with the movements of the sun in his annual orbit. By the construction of superior brazen circles, he measured the daily motion of the sun during the entire year. He confirmed the discovery of the ancients. of the irregular or unequal progress of this luminary,

and fixed that point in the sun's orbit where it moved with greatest velocity. Year after year, did this devoted astronomer follow the sun, until finally he discovered that the point on the orbit, where its motion was swiftest, did not remain fixed, but was advancing in each revolution, at a very slow rate along the orbit. Having thus demonstrated and characterised the irregularity of the sun's motion, he directed his attention to minute examinations of the moon, and reached results precisely similar. From these discoveries, it became manifest, that in case the motions of the sun and moon were circular and uniform, the earth did not occupy the exact centres of their orbits; for on this hypothesis any irregularity of motion would have been impossible. Here was a point gained. The exact central position of the earth was disproved in two instances, and even the amount of its eccentricity, or distance from the true centre, determined. Retaining the circular and uniform motion of the sun and moon, the discovered irregularities were tolerably well represented by the eccentric position of the earth, from whose surface these motions were measured.

While pursuing these important researches, Hipparchus resolved upon a work of extraordinary difficulty, which had never before been attempted, and which fully attests the grandeur and sagacity of his views. This enterprise was nothing less than numbering the stars and fixing their positions in the heavens. This he actually accomplished, and his catalogue of 1081 of the principal stars, is perhaps the richest treasure which the Greek school has transmitted to posterity. We cannot too much admire the

disinterested devotion to science, which prompted this great undertaking, and the firmness of purpose which sustained the solitary observer, through long years of toil. It was a work for posterity, and could yield to its author no reward during his life.' Conscious of this, his resolution never faltered, and grateful posterity crowns his memory with the well-earned title of Father of Astronomy. The noble example thus set by Hipparchus, was not lost on Ptolemy, justly the most distinguished among his immediate successors. An ardent student, a close observer, a patient and candid reasoner, Ptolemy collected and digested the discoveries and theories of his predecessors, and transmitted them, in connection with his own, successfully to posterity. Rejecting the absurd doctrine of the solid crystal spheres of Eudoxus, and the unsustained notions of Pythagoras, this bold Greek undertook the resolution of the great problem, which Plato had long before presented, and to accomplish which, so many unsuccessful efforts had been made.

After a careful examination of all the facts and discoveries, which the world then possessed, adding his own extensive observations, Ptolemy promulged a system which bears his name, and which endured for more than fourteen hundred years. He fixed the earth as the great centre, about which the sun, the moon, the planets, and the starry heavens revolved. Retaining the doctrine of uniform circular motion, he accounted for the irregularity in the movements of the sun and moon by the eccentric position of the earth in their orbits.—To explain the anomalous movement of the planets, he devised the system of cycles and epicycles. Every planet moved uniformly in the cir

cumference of a small circle, whose centre moved uniformly in the circumference of a large circle, near whose centre the earth was located. By this ingenious theory, it was shown that a planet moving in the circumference of its small circle might appear to retrograde, to become stationary, and finally to advance among the fixed stars. Thus were all the phenomena known to the Greek astronomer, so satisfactorily ac counted for, that it even became possible from this singular theory, to compute tables of the planetary motions, from which their places could be predicted with such precision, that the error, if any existed, escaped detection by the rude instruments then in use.

While the explanation of the 'celestial phenomena had constituted the principal object of the Greek astronomers, some rude efforts were commenced to determine the magnitude of the earth, and the relative distances of the sun and moon. The process adopted

by Eratosthenes, two thousand years ago, to determine the circumference of the earth, and its diameter, is essentially the same now employed by modern science. The results reached by the Greek astronomer, owing to an ignorance of the exact value of his unit, are lost to the world.

When astronomy was banished from Greece, it found a home among the Arabs. When darkness and gloom wrapped the earth through ten long centuries, and human knowledge languished, and art died, and genius slumbered, it is a remarkable fact, that astronomy during that long period of ignorance, instead of being lost, was actually slowly advancing, and when the dawn of learning once more broke on Europe, the astronomy of the Greeks, improved by the Arabs and

the Persians, was preserved in the great work of Ptolemy, and transmitted to posterity.

It is true that no change had been wrought in the Greek theory, but observations had been multiplied and slow changes measured, which prepared the way for the discoveries which were soon to succeed. On the revival of learning in Europe, the literature and science of the Greeks and Romans rapidly spread, and gained an astonishing ascendancy over the human mind. Indeed, theirs was the only science, the only wisdom. Time honored, and venerable with age, the philosophy of Aristotle, the geometry of Euclid, and the astronomy of Ptolemy, filled the colleges and uni· versities, and fastened itself upon the age, with a tenacity, which permitted no one to question or doubt, and which seemed to defy all further progress.-Such was the state of science and the world, when Copernicus consecrated his genius to the examination of the heavens.

To a mind singularly bold and penetrating, Copernicus united habits of profound study and severe observation. Deeply read in the received doctrines of science, he examined with the keenest interest, every hint which the philosophers of antiquity had left on record concerning the system of nature. For more than thirty years he watched, with unceasing perseverance, the movements of the heavenly bodies. By the construction of superior instruments, he compared the observed places of the sun, moon and planets, with their positions computed from the best tables founded on the theory of Ptolemy. The hy pothesis of uniform circular motion, had originally been adopted, to preserve the simplicity of nature