Revolution of Astronomy by Copernicus

A.D. 1543

SIR ROBERT STAWELL BALL

The promulgation of the accepted system of astronomy, called the Copernican system, which represents the earth as revolving on its axis and considers the sun as the centre of motion for the earth and other planets, marked the greatest of scientific revolutions.

Copernicus, whose name, thus Latinized, was Koppernigk or Koper-nik, was born at Thorn, Prussia, February 19, 1473, and died at Frau-en- burg, Prussia, May 24, 1543. The founder of modern astronomy was probably of German descent: according to some authorities his father was a Germanized Slav, his mother a German; and the honor of produc-ing him is claimed by both Germany and Poland.

With equal conciseness and lucidity, in the following pages the emi-nent British astronomer furnishes important particulars concerning the life of Copernicus; and he gives an account, no less interesting than in-structive, of the evolution of the Copernican astronomy in its founder’s mind.

Copernicus, the astronomer, whose discoveries make him the great predecessor of Kepler and Newton, did not come from a noble family, as certain other early astronomers have done, for his father was a tradesman. Chronicie~ are, however, careful to tell us that one of his uncles was a bishop. We are not acquainted with any of those details of his childhood or youth which are often of such interest in other cases where men have risen to exalted fame. It would appear that the young Nicolaus, for such was his Christian name, received his education at home until such time as he was deemed sufficiently advanced to be sent to the University at Cracow. The education that he there obtained must have been in those days of very primitive de-scription, but Copernicus seems to have availed himself of it to the utmost. He devoted himself more particularly to the study of medicine, with the view of adopting its practice as the pro-fession of his life. The tendencies of the future astronomer were, however, revealed in the fact that he worked hard at math- ematics, and for him, as for one of his illustrious successors, Gal-ileo, the practice of the art of painting had a very great Interest, and in it he obtained some measure of success.

By the time he was twenty-seven years old, it would seem that Copernicus had given up the notion of becoming a medical practitioner, and had resolved to devote himself to science. He was engaged in teaching mathematics, and appears to have ac-quired some reputation. His growing fame attracted the notice of his uncle the Bishop, at whose suggestion Copernicus took holy orders, and he was presently appointed to a canonry in the Cathedral of Frauenburg, near the mouth of the Vistula.

To Frauenburg, accordingly, this man of varied gifts re-tired. Possessing somewhat of the ascetic spirit, he resolved to devote his life to work of the most serious description. He es-chewed all ordinary society, restricting his intimacies to very grave and learned companions, and refusing to engage in con-versation of any useless kind. It would seem as if his gifts for painting were condemned as frivolous; at all events, we do not learn that he continued to practise them. In addition to the dis-charge of his theological duties, his life was occupied partly in ministering medically to the wants of the poor, and partly with his researches in astronomy and mathematics. His equipment in the matter of instruments for the study of the heavens seems to have been of a very meagre description. He arranged aper-tures in the walls of his house at Allenstein, so that he could ob-serve in some fashion the passage of the stars across the merid-ian. That he possessed some talent for practical mechanics is proved by his construction of a contrivance for raisIng water from a stream, for the use of the inhabitants of Frauenburg. Relics of this machine are still to be seen.

The intellectual slumber of the Middle Ages was destined to be awakened by the revolutionary doctrines of Copernicus. It may be noted, as an interesting circumstance, that the time at which he discovered the scheme of the solar system coincided with a remarkable epoch in the world’s history. The great as-tronomer had just reached manhood at the time when Columbus discovered the New world.

Before the publication of the researches of Copernicus, the orthodox scientific creed averred that the earth was stationary, and that the apparent movements of the heavenly bodies were real movements. Ptolemy had laid down this doctrine fourteen hundred years before. In his theory this huge error was asso-ciated with so much important truth, and the whole presented such a coherent scheme for the explanation of the heavenly movements, that the Ptolemaic theory was not seriously ques-tioned until the great work of Copernicus appeared. No doubt others before Copernicus had from time to time in some vague fashion surmised, with more or less plausibility, that the sun, and not the earth, was the centre about which the system really re-volved. It is, however, one thIng to state a scientffic fact; it is quite another thing to be in possession of the train of reasoning, founded on observation or experiment, by which that fact may be established. Pythagoras, it appears, had indeed told his dis-ciples that it was the sun, and not the earth, which was the centre of movement, but it does not seem at all certain that Pythagoras had any grounds which science could recognize for the belief which is attributed to him. So far as Information is available to us, it would seem that Pythagoras associated his scheme of things celestial with a number of preposterous notions in natural philosophy. He may certainly have made a correct statement as to which was the most important body in the solar system, but he certainly did not provide any rational demonstration of the fact. Copernicus, by a strict train of reasoning, convinced those who would listen to him that the sun was the centre of the system. It is useful for us to consider the arguments which he urged and by which he effected that Intellectual revolution which is always connected with his name.

The first of the great discoveries which Copernicus made re-lates to the rotation of the earth on its axis. That general diur-nal movement, by which the stars and all other celestial bodies appear to be carried completely round the heavens once every twenty-four hours, had been accounted for by Ptolemy on the supposition that the apparent movements were the real move-ments. Ptolemy himself felt the extraordinary difficulty involved in the supposition that so stupendous a fabric as the celestial sphere should spin in the way supposed. Such movements re-quired that many of the stars should travel with almost Incon-ceivable velocity. Copernicus also saw that the daily rising and setting of the heavenly bodies could bc accounted for either by the supposition that the celestial sphere moved round and that the earth remained at rest, or by the supposition that the celestial sphere was at rest while the earth turned round in the opposite direction. He weighed the arguments on both sides as Ptolemy had done, and as the result of his deliberation Copernicus came to an opposite conclusion from Ptolemy. To Copernicus it ap-peared that the difficulties attending the supposition that the celestial sphere revolved were vastly greater than those which appeared so weighty to Ptolemy as to ~rce him to deny the earth’s rotation.

Copernicus shows clearly how the observed phenomena could be accounted for just as completely by a rotation of the ~rth as by a rotation of the heavens. He alludes to the fact that, to those on board a vessel which is moving through smooth water, the vessel itself appears to be at rest, while the objects on shore appear to be moving past. If, therefore, the earth were rotating uniformly, we dwellers upon the earth, oblivious of our own movement, would wrongly attribute to the stars the displace-ment which was actually the consequence of our own motion.

Copernicus saw the futility of the arguments by which Ptol-emy had endeavored to demonstrate that a revolution of the earth was impossible. It was plain to him that there was nothing whatever to warrant refusal to believe in the rotation of the earth. In his dear~sightedness on this matter we have specially to admire the sagacity of Copernicus as a natural philosopher. It had been urged that, if the earth moved round, its motion would not be imparted to the air, and that therefore the earth would be uninhabitable by the terrific winds which would be the result of our being carried through the air. Copernicus convinced himself that this deduction was preposterous. He proved that the air must accompany the earth, just as one’s coat remains round him, notwithstanding the fact that he is walking down the street. In this way he was able to show that all a priori objec-tions to the earth’s movements were absurd, and therefore he was able to compare together the plausibilities of the two rival schemes for explaining the diurnal movement.

Once the issue had been placed in this form, the result could not be long in doubt. Here is the question: Which is it more likely-that the earth, llke a grain of sand at thc ~entre of a mighty globe, should turn round once in twenty-four hours, or that the whole of that vast globe should complete a rotation in the opposite direction in the same time? Obviously, the former is far the more simple supposition. But the case is really much stronger than this. Ptolemy had supposed that all the stars were attached to the surface of a sphere. He had no ground whatever for this supposition, except that otherwise it would have been wellnigh impossible to devise a scheme by which the rotation of the heavens around a fixed earth could have been arranged. Copernicus, however, with the just instinct of a philosopher, considered that the celestial sphere, however convenient, from a geometrical point of view, as a means of representing apparent phenomena, could not actually have a material existence. In the first place, the existence of a material celestial sphere would require that all the myriad stars should be at exactly the same distances from the earth. Of course, no one will say that this or any other arbitrary disposition of the stars is actually impossible; but as there was no conceivable physical reason why the dis-tances of all the stars from the earth should be identical, it seemed in the very highest degree improbable that the stars should be so placed.

Doubtless, also, Copernicus felt a considerable difficulty as to the nature of the materials from which Ptolemy’s wonderful sphere was to be constructed. Nor could a philosopher of his penetration have failed to observe that, unless that sphere were infinitely large, there must have been space outside it, a consid-eration which would open up other difficult questions. Whether infinite or not, it was obvious that the celestial sphere must have a diameter at least many thousands of times as great as that of the earth. From these considerations Copernicus deduced the important fact that the stars and other important celestial bodies must all be vast objects. He was thus enabled to put the ques-tion in such a form that it would hardly receive any answer but the correct one: Which is it more rational to suppose, that the earth should turn round on its axis once in twenty-four hours, or that thousands of mighty stars should circle round the earth in the same time, many of them having to describe circles many thousands of times greater in circumference than the circuit of the earth at the equator? The obvious answer pressed upon Co-pernIcus with so much force that he was compelled to reject Ptolemy’s theory of the stationary earth, and to attribute the diurnal rotation of the heavens to the revolution of the earth on its axis.

Once this tremendous step had been taken, the great difficulties which beset the monstrous conception of the celestialsphere vanished, for the stars need no longer be regarded as situ-ated at equal distances from the earth. CopernIcus saw that they might lie at the most varied degrees of remoteness, some being hundreds or thousands of times farther away than others. The complicated structure of the celestial sphere as a material object disappeared altogether; it remained only as a geometrical con-ception, whereon we find it convenient to indicate the places of the stars. Once the CopernIcan doctrine had been fully set forth, it was impossible for anyone, who had both the inclina-tion and the capacity to understand it, to withhold acceptance of its truth. The doctrine of a stationary earth had gone forever.

Copernicus having established a theory of the celestial move-ments which deliberately set aside the stability of the earth, it seemed natural that he should inquire whether the doctrine of a moving earth might not remove the difficulties presented in other celestial phenomena. It had been universally admitted that the earth lay unsupported in space. CopernIcus had further shown that it possessed a movement of rotation. Its want of stability being thus recoguized, it seemed reasonable to suppose that the earth might also have some other kinds of movements as well. In this, CopernIcus essayed to solve a problem far more difficult than that which hitherto occupied his attention. It was a com-paratively easy task to show how the diurnal rising and setting could be accounted for by the rotation of the earth. It was a much more difficult undertaking to demonstrate that the plane-tary movements, which Ptolemy had represented with so much success, could be completely explained by the supposition that each of these planets revolved uniformly round the sun, and that the earth was also a planet, accomplishing a complete circuit of the sun once in the course of a year.

It would be impossible, in a sketch like the present, to enter into any detail as to the geometrical propositions on which this beautiful investigation of Copernicus depended. We can only mention a few of the leading principles. It may be laid down in general that, if an observer is in movement, he will, if uncon-scious of the fact, attribute to the fixed objects around him a movement equal and opposite to that which he actually possesses. A passenger on a canal-boat sees the objects on the banks ap-parently moving backward with a speed equal to that by which he himself is advancing forward. By an appllcation of this prin-ciple, we can account for all the phenomena of the movements of the planets, which Ptolemy had so ingeniously represented by his circles. Let us take, for instance, the most characteristic feature in the irregularities of the outer planets. Mars, though generally advancing from west to east among the stars, occa-sionally pauses, retraces his steps for a while, again pauses, and then resumes his ordinary onward progress. Copernicus showed clearly how this effect was produced by the real motion of the earth, combined with the real motion of Mars. When the earth comes directly between Mars and the sun, the retrograde move-ment of Mars is at its highest. Mars and the earth are then ad-vancing in the same direction. We, on the earth, however, be-ing unconscious of our own motion, attribute, by the principle I have already explained, an equal and opposite motion to Mars. The visible effect upon the planet is that Mars has two move-ments, a real onward movement in one direction, and an appar-ent movement in the opposite direction. If it so happened that the earth was moving with the same speed as Mars, then the ap-parent movement would exactly neutralize the real movement, and Mars would seem to be at rest relatively to the surrounding stars. Under the actual circumstances considered, however, the earth is moving faster than Mars, and the consequence is that the apparent movement of the planet backward exceeds the real movement forward, the net result being an apparent retrograde movement.

With consummate skill, Copernicus showed how the appli-cations of the same principles could account for the character-istic movements of the planets. His reasoning in due time bore down all opposition. The supreme importance of the earth in the system vanished. It had now merely to take rank as one of the planets.

The same great astronomer now, for the first time, rendered something like a rational account of the changes of the seasons. Nor did certain of the more obscure astronomical phenomena escape his attention.

He delayed publishing his wonderful discoveries to the world until he was quite an old man. He had a well-founded apprehension of the storm of opposition which they would arouse. However, he yielded at last to the entreaties of his friends, and his book¹

was sent to the press. But ere it made its appearance to the world, Copernicus was seized with mortal illness. A copy of the book was brought to him on May 23, 1543. We are told that he was able to see it and to touch it, but no more; and he died a few hours afterward.

¹De Orbium Caelestium Revolutionibus.