Popular Science Monthly/Volume 68/April 1906/The Earliest Predecessors of Copernicus

by Charles Rochester Eastman

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THE EARLIEST PREDECESSORS OF COPERNICUS

By Dr. CHARLES R. EASTMAN,

HARVARD UNIVERSITY

THE first glimmerings of perception that presage the discovery of great truths, whether coeval with, or long antecedent to complete apprehension, possess for most minds a fascinating interest. Whether it be abstract ideas, epoch-making inventions or discoveries of fundamental laws, such as gravitation or evolution, matters not; the names of those who have contributed largely toward intellectual progress, even if they fell short of the whole truth—if they merely prepared the way for final discovery—become universally reverenced, or acquire at least a romantic interest, by virtue of their heraldry. In natural science, as elsewhere, it is right and fitting that a high place be reserved for the advance prophets who have preceded the great expounders of Nature's truths.

By common consent of mankind, the Copernican cosmogony ranks as one of the immortal triumphs of genius, whence it follows that not only the monk of Frauenburg, and the scarcely less famous defenders of his theory, but also his remote predecessors, are entitled to an exalted position amongst those favored mortals who have been permitted, in one age or another, to wrest from Nature the solution of her deepest mysteries. Yet because of the absolute originality of the great sixteenth-century astronomer's discovery; because, furthermore, the anticipators of his theory failed to convert the world to their belief; and because Copernicus himself knew nothing of his real predecessors, it has come about that too little credit is commonly bestowed upon ancient forerunners of our modern system.

There is abundant and undisputed testimony to show that in the minds of at least two astronomers prior to the Christian era, namely, Aristarchus of Samos, and Seleuchus the Chaldæan, the essential features of our modern system were clearly recognized, and elaborated not only into a working hypothesis, but into a valid explanation of the universe. It is impossible to view this achievement in its manifold relations to human progress, without being impressed with the pathetic and remarkable fact that a ray of divine intelligence should have shone forth for an instant in that far-off period, kindling here and there a momentary spark; sparks that, although revealing the true order of the cosmos, were not finally to illumine the world until after the lapse of centuries.

No demonstration is necessary to show that the beginning of astronomical knowledge is a subject in which all intelligent persons are interested. Indeed, precisely this sort of interest is recognized by Professor Simon Newcomb as one of the characteristics of modern science. The opening words of his presidential address at the St. Louis Congress tell us that "among the tendencies characteristic of the science of our day is one toward laying greater stress on questions of the beginnings of things, and regarding a knowledge of the laws of development of any object of study as necessary to its complete understanding in the form in which we find it."^[1] But interest alone is scarcely sufficient to overcome the difficulties which beset the general reader in quest of information, owing to the exceedingly scattered, and more or less special nature of the literature. The absence, too, of a popular conspectus which treats in satisfactory manner of the origin of the heliocentric hypothesis, is to be regretted.^[2] Hence the present article has been prepared with the idea of affording those who may be inquisitive as to the sources of information with the means of orienting themselves.

In order to keep the relations of the founders of different cosmical systems firmly in mind, the distinguishing features of the latter may be pointed out, with indication of the most prominent names associated with each. Four distinct systems may be recognized, according as the center of the universe is supposed be occupied by (1) a central fire, other than our sun (Philolaus the Pythagorean); (2) by a stationary earth about which the heavens revolve (Eudoxus of Cnidos, Ptolemy, Tycho Brahé); (3) by an earth rotating upon its axis, but otherwise immovable (Heraclides of Pontus); and (4) by the sun, about which the entire planetary system revolves (Aristarchus, Copernicus). As thus outlined, the transition between the third and fourth of these systems appears at first sight abrupt, but examination of the views of Heraclides shows that he too recognized the competency of the modern system as a working hypothesis, and thus helped prepare the way for its rigorous adoption. It is evident, also, that a somewhat remote connection can be traced between the last of these systems and the first, a correspondence which did not escape notice by Copernicus himself.^[3]

Familiar as Copernicus undoubtedly was with Pythagorean doctrines, how are we to explain his silence regarding the system of Aristarchus? The answer lies in the fact that he never had access to the writings of Archimedes, which furnish our chief information in this matter; indeed he could not, for the reason that the editio princeps was not given to the world until the year following his death in 1543.

For a succinct statement of the views of Aristarchus, as reported in the Arenarius of the famous Syracusan, one may refer to an article by Professor Holden in an earlier number of Popular Science Monthly (April, 1904). The original text of the passages, both in the Arenarius and in Copernicus relating to them, together with a variety of precious documents extracted from ancient authors, is appended to the anniversary memoir of Professor Schiaparelli, prepared in honor of the fourth centenary of the birth of Copernicus.^[4]

At the same time it must be admitted as at least curious that the brief sentence in Plutarch (de Placitis Philosophorum, II., 24), in which Aristarchus is represented as having reckoned the sun amongst the category of fixed stars, and to have conceived of the earth revolving around it, should have passed altogether unnoticed by Copernicus. Almost the identical words are repeated by Stobæus in his Eclogæ Physicæ, and in the distorted abridgment of Plutarch's treatise which passes under the name of Historia Philosophica, often erroneously attributed to Galen; but we must suppose that none of these statements attracted the attention of Copernicus, even if he was aware of their existence. The same remark applies to passages concerning Aristarchus which occur elsewhere in Plutarch and amongst other authors, fortunately in considerable number. Those desirous of consulting them in the original, and of comparing the opinions of learned critics, will readily be directed to them by the special literature.^[5]

Contenting ourselves with these brief literary indications, we may pass on to the more intricate questions relating to the predecessors of Aristarchus, and the influence of Pythagorean views upon later thinkers. As has been previously remarked, Heraclides Ponticus acknowledged that the heliocentric theory provided an adequate explanation of celestial phenomena, and even approached so nearly to modern ideas as to maintain the revolution of Mercury and Venus about the sun. This we know from the testimony of numerous authors, chiefly Roman, amongst whom Heraclides was held in high regard. Of interest is the passage in Simplicius ('Commentary on Aristotle's de Cælo,' Karsten's edition, p. 232), which shows Heraclides' correct apprehension of the causes determining the difference in length between the sidereal and ordinary day of twenty-four hours. We are informed, however, by Plutarch (Plac. Philos., III., 13) and later writers (e. g., Simplicius, Hippolytus, Proclus, Chalcidius, and especially Vitruvius and Terentius Varro) that although Heraclides of Pontus and Ecphantus the Pythagorean believed the earth to turn upon its axis from west to east, they distinctly denied to it a movement of translation through space. It is clear also from Aristotle that it was no unheard-of thing to explain the apparent diurnal motion of the heavens upon the hypothesis of the earth's rotation. Plato appears to have accepted this idea as the starting-point of his system, complicated as it was with superadded mechanism. But the great Athenian appears to have elaborated his cosmical theory more as a speculative abstraction than as an orderly induction from observed facts, and it was easy to explain the discrepancy of the latter as due to false appearances.

It has been claimed on the authority of Theophrastus, as reported by Plutarch and Aristotle, that Plato repented in his old age at having placed the earth at the center or 'altar' of the universe, this being deemed too sacred a position for it to occupy (Plutarch, Plat. Quæst., VIII. 1; Aristotle, de Cælo, II. 13, 3). But this is very far from indicating that the heliocentric theory ever fully shaped itself in his mind, although one sees that it required merely a combination of his views and those of the Pythagorean school to arrive at a cosmical system identical with that which we call Copernican. Moreover, if we may trust to a somewhat obscure statement in Simplicius, there lived in the time of Alexander the Great an individual whose name we know not, but who actually did effect a combination of these ideas, and who is therefore worthily entitled to rank as a predecessor of Copernicus. Whether the heliocentric conception was ever presented to Aristarchus in concrete form, or was independently excogitated by him, we are without information; but it is impossible that his mind should not have received some fertile stimulus from the ideas already extant concerning the earth's revolution and rotation. Indeed, the way had been fairly prepared for a realization of the Copernican system; and as a matter of fact it was easier to arrive at this conception in the time of Aristarchus than subsequently, when the scheme of planetary movements had become hopelessly obscured through the invention, by Apollonius of Perga, of eccentrics and epicycles. The transition from Philolaus to Aristarchus is natural and easy as compared with the truly Herculean feat performed by Copernicus, who had first to clear away heaps of Augean refuse before the truth could again become manifest.

A melancholy interest in the fate of Aristarchus bids one inquire the reasons which prevented his theory from obtaining foothold. So far as history tells, it found but a solitary champion in the person of Seleuchus,^[6] who flourished half a century later than Aristarchus. To Archimedes, and presumably to contemporary mathematicians and philosophers, the insuperable objection to this system consisted in its stationing the fixed stars at an infinite distance from the earth. Moreover, as witness the clamant protests against the Sage of Athens—to say nothing of the witty caricatures of him in the 'Clouds'—followed in the end by his martyrdom; and as witness the charges preferred against Aristarchus by Cleanthes, any dislodgment of the earth from its sacred position in the 'hearth of the Universe' was tainted with suspicion of impiety. And when afterwards the Ptolemaic mechanism was introduced, blocking with its devices the brilliant conception of Aristarchus, fourteen centuries were required to roll by before this useless debris could be swept away.

Possibly yet other circumstances conspired to hinder the acceptance of the heliocentric system, the nature of which can not now be ascertained, any more than can the reasons which first carried conviction of its truth. But this much is clear, there can be a tragic history of ideas no less than of individuals: and in meditating on the fate of the many 'struck eagles' of the pagan world, who soared loftily even where we now stumble, one is reminded of that beautiful simile of Byron, which concludes in deepest pathos:

Such is the aspect of this shore;
'Tis Greece, but living Greece no more!

••••••••

1. 'The Evolution of the Scientific Investigator' (opening address of the president of the International Congress of Arts and Science, at the St. Louis Exposition), Science, Vol. XX., p. 385.
2. The treatises by Berry ('A Short History of Astronomy,' London, 1898), and Miss Agnes Clerke (in Appleton's 'Concise Knowledge Library,' New York, 1898), contain but a bare mention of the prior establishment of the Tychonian and Copernican systems amongst the Greeks. Even the elaborate work of Sir George Cornewall Lewis ('An Historical Survey of the Astronomy of the Ancients,' London, 1862) can hardly be said to do justice to the evolution of these systems. The French reading public is more fortunate than ours, having a goodly number of popular works at its disposal. Two only need be mentioned here, each of them being provided with ample bibliographical references. These are: Thirion, J., 'L'evolution de l'astronomie chez les Grecs' (Brussels, 1900); and Bonnel, J. F., 'Étude sur l'histoire de l'astronomie: la Découverte du double Mouvement de la Terre' (Tours, 1886).
3. The system of Philolaus is twice mentioned by Copernicus in his famous work, 'De revolutionibus orbium cœlestium,' first in the dedicatory epistle to Pope Paul III., and again in the fifth chapter of Book I. Upon these passages, which gave rise to heated discussions a few decades after the death of Copernicus, Professor Schiaparelli comments as follows:

   'Neppure qui è possibile inferire, che nella mente di Copernico il sistema di Filolao fosse il sistema eliocentrico. Anzi, le caute e indeterminate espressioni . . . mostrano che le parole di Plutarco più sopra citate non gli sembravano abbastanza decisive per invocare l'autorità di Filolao in favore del sistema da lui [i. e., Copernicus] propugnato."—I Precursori di Copernico, etc., p. 9. note 20.

4. Published in the Memoirs of the Royal Lombardy Institute, Vol. XII., and also in the Publications of the Milan Observatory, No. 3, 1873. A German translation by Curtze exists under the title of 'Die Vorläufer des Copernicus im Alterthum' (Leipzig, 1876). Three other invaluable historical memoirs by the same author have appeared in the Lombardy Memoirs, the latest one (1898) dealing in consummate manner with the 'Origin of the Heliocentric Planetary System amongst the Greeks.' These contributions are absolutely indispensable for students.
5. Besides the writings of Schiaparelli above mentioned, one should not fail to consult H. Martin's works, especially his 'Etudes sur le Timée de Platon,' Vol. II. (Paris, 1841), and Paul Tannery's 'Recherches sur l'Histoire de l'Astronomie ancienne' (Paris, 1893). The fourth essay in Bergk's 'Abhandlungen zur Geschichte der griechischen Philosophic und Astronomie' (Leipzig, 1883) is devoted to Aristarchus. The older work of Schaubach contains some rather adverse estimates, no longer considered tenable. On Pythagorean doctrines, one of the most critical essays in English is by George Grote: 'Plato's Doctrine respecting the Rotation of the Earth, and Aristotle's Comment upon that Doctrine' (London, 1860).
6. Cf. Ruge, S., 'Der Chaldäer Seleukos,' Dresden, 1865.