NICOLAUS, an eminent astronomer, was born at Thorn in Prussia, Jan. 1° 1472. He was taught the Latin and Greek languages at home; and afterwards sent to Cracovia, where he studied philosophy and physic. His genius in the mean time was naturally turned to mathematics, which he pursued through all its various branches. He set out for Italy when he was 23 years of age; but staid at Bologna some time, for the sake of being with the celebrated astronomer of that place, Dominicus Maria: whose conversation, however, and company, he affected, not so much as a learner, as an assistant to him in making his observations. From thence he passed to Rome, where he was no sooner arrived than he was considered as not inferior to the famous Regiomontanus; and acquired, in short, so great a reputation, that he was chosen professor of mathematics, which he taught for a long time with great applause. He also made Copernicus made some astronomical observations there about the year 1520. Returning to his own country some years after, he began to apply his vast knowledge in mathematics to correct the system of astronomy which then prevailed. He set himself to collect all the books which had been written by philosophers and astronomers, and to examine all the various hypotheses they had invented for the solution of the celestial phenomena, to try if a more symmetrical order and constitution of the parts of the world could not be discovered, and a more just and exquisite harmony in its motions established, than what the astronomers of those times so easily admitted. But of all their hypotheses none pleased him so well as the Pythagorean, which made the sun to be the centre of the system, and supposed the earth to move not only round the sun, but round its own axis also. He thought he discerned much beautiful order and proportion in this; and that all that embarrassment and perplexity from epicycles and eccentricities, which attended the Ptolemaic hypothesis, would here be entirely removed.

This system, then, he began to consider, and to write upon, when he was about 35 years of age. He employed himself in contemplating the phenomena carefully; in making mathematical calculations; in examining the observations of the ancients, and in making new ones of his own; and after more than 20 years chiefly spent in this manner, he brought his scheme to perfection, and established that system of the world which goes by his name, and is now universally received, (see Astronomy Index). His system, however, was then looked upon as a most dangerous heresy; for which he was thrown into prison by Pope Urban VIII. and not suffered to come out till he had recanted his opinion; that is, till he had renounced the testimony of his senses. He died the 24th of May 1543, in the 70th year of his age.

This extraordinary man had been made canon of Worms by his mother's brother, Lucas Watzelrodius, who was bishop of that place. He was not only the greatest of astronomers, but a perfect master of the Greek and Latin tongues; to all which he joined the greatest piety and innocence of manners.

The following is the account of the discoveries of Copernicus by Dr Smith, in his Essays on Philosophical Subjects.

"The confusion (says Dr Smith) in which the old hypotheses represented the heavenly bodies, was, as Copernicus himself 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 centres, 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. He 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 some Pythagoreans had represented the earth as revolving in the centre of the universe, like a wheel round its own axis; and that others, of the same sect had removed it from the centre, 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 supposed 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 beforehand 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 supposing 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, when 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, Copernicus, 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 in the other. But it afforded no satisfactory principle of connection, 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, connected 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 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 immovable in the centre, 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 accustomed, 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 clasping them in the same species of things, with an object that is of all 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 surprize 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 hyperbolic language of Tycho Brahe, 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.

name of an astronomical instrument, invented by Mr Whiston, to exhibit the motion and phenomena of the planets, both primary and secondary. It is built upon the Copernican system, and for that reason called by his name.