The Gradual Acceptance of the Copernican Theory of the Universe/Part 1/Chapter 1

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The Development of Astronomical Thought to 1400 A. D.

A Preliminary Sketch of Early Theories as a Background.

THE appearances in the heavens have from earliest historic ages filled men with wonder and awe; then they gradually became a source of questioning, and thinkers sought for explanations of the daily and nightly phenomena of sun, moon and stars. Scientific astronomy, however, was an impossibility until an exact system of chronology was devised.[1] Meanwhile men puzzled over the shape of the earth, its position in the universe, what the stars were and why the positions of some shifted, and what those fiery comets were that now and again appeared and struck terror to their hearts.

In answer to such questions, the Chaldean thinkers, slightly before the rise of the Greek schools of philosophy, developed the idea of the seven heavens in their crystalline spheres encircling the earth as their center.[2] This conception seems to lie back of both the later Egyptian and Hebraic cosmologies, as well as of the Ptolemaic. Through the visits of Greek philosophers to Egyptian shores this conception helped to shape Greek thought and so indirectly affected western civilization. Thus our heritage in astronomical thought, as in many other lines, comes from the Greeks and the Romans reaching Europe (in part through Arabia and Spain), where it was shaped by the influence of the schools down to the close of the Middle Ages when men began anew to withstand authority in behalf of observation and were not afraid to follow whither their reason led them.

But not all Greek philosophers, it seems,[3] either knew or accepted the Babylonian cosmology.[4] According to Plutarch, though Thales (640?-546? B. C.) and later the Stoics believed the earth to be spherical in form, Anaximander (610-546? B. C.) thought it to be like a "smooth stony pillar," Anaximenes (6th cent.) like a "table." Beginning with the followers of Thales or perhaps Parmenides (?-500 B. C.), as Diogenes Laërtius claims,[5] a long line of Greek thinkers including Plato (428?-347? B. C.) and Aristotle (384-322 B. C.) placed the earth in the center of the universe. Whether Plato held that the earth "encircled" or "clung" around the axis is a disputed point;[6] but Aristotle claimed it was the fixed and immovable center around which swung the spherical universe with its heaven of fixed stars and its seven concentric circles of the planets kept in their places by their transparent crystalline spheres.[7]

The stars were an even greater problem. Anaximenes thought they were "fastened like nails" in a crystalline firmament, and others thought them to be "fiery plates of gold resembling pictures."[8] But if the heavens were solid, how could the brief presence of a comet be explained?

Among the philosophers were some noted as mathematicians whose leader was Pythagoras (c. 550 B. C.). He and at least one of the members of his school, Eudoxus (409?-356? B. C), had visited Egypt, according to Diogenes Laërtius,[9] and had in all probability been much interested in and influenced by the astronomical observations made by the Egyptian priests. On the same authority, Pythagoras was the first to declare the earth was round and to discuss the antipodes. He too emphasized the beauty and perfection of the circle and of the sphere in geometry, forms which became fixed for 2000 years as the fittest representations of the perfection of the heavenly bodies.

There was some discussion in Diogenes' time as to the author of the theory of the earth's motion of axial rotation. Diogenes[10] gives the honor to Philolaus (5th cent. B. C.) one of the Pythagoreans, though he adds that others attribute it to Icetas of Syracuse (6th or 5th cent. B. C). Cicero, however, states[11] the position of Hicetas of Syracuse as a belief in the absolute fixedness of all the heavenly bodies except the earth, which alone moves in the whole universe, and that its rapid revolutions upon its own axis cause the heavens apparently to move and the earth to stand still.

Other thinkers of Syracuse may also have felt the Egyptian influence; for one of the greatest of them, Archimedes (c. 287-212 B. C), stated the theory of the earth's revolution around the sun as enunciated by Aristarchus of Samos. (Perhaps this is the "hearth-fire of the universe" around which Philolaus imagined the earth to whirl.[12]) In Arenarius, a curious study on the possibility of expressing infinite sums by numerical denominations as in counting the sands of the universe, Archimedes writes:[13] "For you have known that the universe is called a sphere by several astrologers, its center the center of the earth, and its radius equal to a line drawn from the center of the sun to the center of the earth. This was written for the unlearned, as you have known from the astrologers … [Aristarchus of Samos][14] concludes that the world is many times greater than the estimate we have just given. He supposes that the fixed stars and the sun remain motionless, but that the earth following a circular course, revolves around the sun as a center, and that the sphere of the fixed stars having the same sun as a center, is so vast that the circle which he supposes the earth to follow in revolving holds the same ratio to the distance of the fixed stars as the center of a sphere holds to its circumference."

These ancient philosophers realized in some degree the immensity of the universe in which the earth was but a point. They held that the earth was an unsupported sphere the size of which Eratosthenes (c. 276-194 B. C.) had calculated approximately. They knew the sun was far larger than the earth, and Cicero with other thinkers recognized the insignificance of earthly affairs in the face of such cosmic immensity. They knew too about the seven planets, had studied their orbits, and worked out astronomical ways of measuring the passage of time with a fair amount of accuracy. Hipparchus and other thinkers had discovered the fact of the precession of the equinoxes, though there was no adequate theory to account for it until Copernicus formulated his "motion of declination." The Pythagoreans accepted the idea of the earth's turning upon its axis, and some even held the idea of its revolution around the motionless sun. Others suggested that comets had orbits which they uniformly followed and therefore their reappearance could be anticipated.[15]

Why then was the heliocentric theory not definitely accepted?

In the first place, such a theory was contrary to the supposed facts of daily existence. A man did not have to be trained in the schools to observe that the earth seemed stable under his feet and that each morning the sun swept from the east to set at night in the west. Sometimes it rose more to the north or to the south than at other times. How could that be explained if the sun were stationary?

Study of the stars was valuable for navigators and for surveyors, perhaps, but such disturbing theories should not be propounded by philosophers. Cleanthes,[16] according to Plutarch,[17] "advised that the Greeks ought to have prosecuted Aristarchus the Samian for blasphemy against religion, as shaking the very foundations of the world, because this man endeavoring to save appearances, supposed that the heavens remained immovable and that the earth moved through an oblique circle, at the same time turning about its own axis." Few would care to face their fellows as blasphemers and impious thinkers on behalf of an unsupported theory. Eighteen hundred years later Galileo would not do so, even though in his day the theory was by no means unsupported by observation.

Furthermore, one of the weaknesses of the Greek civilization militated strongly against the acceptance of this hypothesis so contrary to the evidence of the senses. Experimentation and the development of applied science was practically an impossibility where the existence of slaves made manual labor degrading and shameful. Men might reason indefinitely; but few, if any, were willing to try to improve the instruments of observation or to test their observations by experiments.

At the same time another astronomical theory was developing which was an adequate explanation for the phenomena observed up to that time.[18] This theory of epicycles and eccentrics worked out by Apollonius of Perga (c. 225 B. C.) and by Hipparchus (c. 160 B. C.) and crystallized for posterity in Ptolemy's great treatise on astronomy, the Almagest, (c. 140 A. D.) became the fundamental principle of the science until within the last three hundred years. The theory of the eccentric was based on the idea that heavenly bodies following circular orbits revolved around a center that did not coincide with that of the observer on the earth. That would explain why the sun appeared sometimes nearer the earth and sometimes farther away. The epicycle represented the heavenly body as moving along the circumference of one circle (called the epicycle) the center of which moves on another circle (the deferent). With better observations additional epicycles and eccentric were used to represent the newly observed phenomena till in the later Middle Ages the universe became a

With Centric and Eccentric scribbled o'er,
Cycle and Epicycle, Orb in Orb"—[19]

Yet the heliocentric theory was not forgotten. Vitruvius, a famous Roman architect of the Augustan Age, discussing the system of the universe, declared that Mercury and Venus, the planets nearest the sun, moved around it as their center, though the earth was the center of the universe.[20] This same notion recurs in Martianus Capella's book[21] in the fifth century A. D. and again, somewhat modified, in the 16th century in Tycho Brahe's conception of the universe.

Ptolemy devotes a column or two of his Almagest[22] (to use the familiar Arabic name for his Syntaxis Mathematica) to the refutation of the heliocentric theory, thereby preserving it for later ages to ponder on and for a Copernicus to develop. He admits at the outset that such a theory is only tenable for the stars and their phenomena, and he gives at least three reasons why it is ridiculous. If the earth were not at the center, the observed facts of the seasons and of day and night would be disturbed and even upset. If the earth moves, its vastly greater mass would gain in speed upon other bodies, and soon animals and other lighter bodies would be left behind unsupported in the air a notion "ridiculous to the last degree," as he comments, "even to imagine it." Lastly, if it moves, it would have such tremendous velocity that stones or arrows shot straight up in the air must fall to the ground east of their starting point,—a "laughable supposition" indeed to Ptolemy.

This book became the great text of the Middle Ages; its author's name was given to the geocentric theory it maintained. Astronomy for a thousand years was valuable only to determine the time of Easter and other festivals of the Church, and to serve as a basis for astrology for the mystery-loving people of Europe.

To the Arabians in Syria and in Spain belongs the credit of preserving for Europe during this long period the astronomical works of the Greeks, to which they added their own valuable observations of the heavens—valuable because made with greater skill and better instruments,[23] and because with these observations later scientists could illustrate the permanence or the variability of important elements. They also discovered the so-called "trepidation" or apparent shifting of the fixed stars to explain which they added another sphere to Ptolemy's eight. Early in the sixth century Uranus translated Aristotle's works into Syrian, and this later was translated into Arabic.[24] Albategnius[25] (c. 850-829 A. D.), the Arabian prince who was the greatest of all their astronomers, made his observations from Aracte and Damascus, checking up and in some cases amending Ptolemy's results.[26]

Then the center of astronomical development shifted from Syria to Spain and mainly through this channel passed on into Western Europe. The scientific fame of Alphonse X of Castile (1252-1284 A. D.) called the Wise, rests chiefly upon his encouragement of astronomy. With his support the Alfonsine Tables were calculated. He is said[27] to have summoned fifty learned men from Toledo, Cordova and Paris to translate into Spanish the works of Ptolemy and other philosophers. Under his patronage the University of Salamanca developed rapidly to become within two hundred years one of the four great universities of Europe[28]—a center for students from all over Europe and the headquarters for new thought, where Columbus was sheltered,[29] and later the Copernican system was accepted and publicly taught at a time when Galileo's views were suppressed.[30]

Popular interest in astronomy was evidently aroused, for Sacrobosco (to give John Holywood[31] his better known Latin name) a Scotch professor at the Sorbonne in Paris in the 13th century, published a small treatise De Sphæri Mundo that was immensely popular for centuries,[32] though is was practically only an abstract of the Almagest. Whewell[33] tells of a French poem of the time of Edward I entitled Ymage du Monde, which gave the Ptolemaic view and was illustrated in the manuscript in the University of Cambridge with a picture of the spherical earth with men upright on it at every point, dropping balls down perforations in the earth to illustrate the tendency of all things toward the center. Of the same period (13th century) is an Arabian compilation in which there is a reference to another work, the book of Hammarmunah the Old, stating that "the earth turns upon itself in the form of a circle, and that some are on top, the others below … and there are countries in which it is constantly day or in which at least the night continues only some instants."[34] Apparently, however, such advanced views were of no influence, and the Ptolemaic theory remained unshaken down to the close of the 15th century.

Aside from the adequacy of this explanation of the universe for the times, the attitude of the Church Fathers on the matter was to a large degree responsible for this acquiescence. Early in the first century A. D., Philo Judæus[35] emphasized the minor importance of visible objects compared with intellectual matters, a foundation stone in the Church's theory of an homocentric universe. Clement of Alexandria (c. 150 A. D.) calls the heavens solid since what is solid is capable of being perceived by the senses.[36] Origen (c. 185-c. 254.) has recourse to the Holy Scriptures to support his notion that the sun, moon, and stars are living beings obeying God's commands.[37] Then Lactantius thunders against those who discuss the universe as comparable to people discussing "the character of a city they have never seen, and whose name only they know." "Such matters cannot be found out by inquiry."[38] The existence of the antipodes and the rotundity of the earth are "marvelous fictions," and philosophers are "defending one absurd opinion by another"[39] when in explanation why bodies would not fall off a spherical earth, they claim these are borne to the center.

How clearly even this brief review illustrates what Henry Osborn Taylor calls[40] the fundamental principles of patristic faith: that the will of God is the one cause of all things (voluntate Dei immobilis manet et stat in sæculum terra.[41] Ambrose: Hexæmeron.) and that this will is unsearchable. He further points out that Augustine's and Ambrose's sole interest in natural fact is as "confirmatory evidence of Scriptural truth." The great Augustine therefore denies the existence of antipodes since they could not be peopled by Adam's children.[42] He indifferently remarks elsewhere:[43] "What concern is it to me whether the heavens as a sphere enclose the earth in the middle of the world or overhang it on either side?" Augustine does, however, dispute the claims of astrologers accurately to foretell the future by the stars, since the fates of twins or those born at the same moment are so diverse.[44]

Philastrius (d. before 397 A. D.) dealing with various heresies, denounces those who do not believe the stars are fixed in the heavens as "participants in the vanity of pagans and the foolish opinions of philosophers," and refers to the widespread idea of the part the angels play in guiding and impelling the heavenly bodies in their courses.[45]

It would take a brave man to face such attitudes of scornful indifference on the one hand and denunciation on the other, in support of a theory the Church considered heretical.

Meanwhile the Church was developing the homocentric notion which would, of course, presuppose the central position in the universe for man's abiding place. In the pseudo-Dionysius[46] is an elaborately worked out hierarchy of the beings in the universe that became the accepted plan of later centuries, best known to modern times through Dante's blending of it with the Ptolemaic theory in the Divine Comedy.[47] Isidore of Seville taught that the universe was created to serve man's purposes,[48] and Peter Lombard (12th cent.) sums up the situation in the definite statement that man was placed at the center of the universe to be served by that universe and in turn himself to serve God.[49] Supported by the mighty Thomas Aquinas[50] this became a fundamental Church doctrine.

An adequate explanation of the universe existed. Aristotle, Augustine, and the other great authorities of the Middle Ages, all upheld the conception of a central earth encircled by the seven planetary spheres and by the all embracing starry firmament. In view of the phrases used in the Bible about the heavens, and in view of the formation of fundamental theological doctrines based on this supposition by the Church Fathers, is it surprising that any other than a geocentric theory seemed untenable, to be dismissed with a smile when not denounced as heretical? Small wonder is it, in the absence of the present day mechanical devices for the exact measurement of time and space as aids to observation, that the Ptolemaic, or geocentric, theory of the universe endured through centuries as it did, upheld by the authority both of the Church and, in essence at least, by the great philosophers whose works constituted the teachings of the schools.

  1. The earliest observation Ptolemy uses is an Egyptian one of an eclipse occurring March 21, 721 B. C. (Cumont: 7). [In these references, the Roman numerals refer to the volume, the Arabic to the page, except as stated otherwise. The full title is given in the bibliography at the back under the author's name.]
  2. Warren: 40. See "Calendar" in Hastings: Ency. of Religion and Ethics.
  3. For a summary of recent researches, see the preface of Heath: Aristarchus of Samos. For further details, see Heath: Op. cit., and the writings of Kugler and Schiaparelli.
  4. See Plutarch: Moralia: De placitas Philosophorum, Lib. I et II, (V, 264-277, 296-316).
  5. Diogenes Laertius: De Vitis, Lib. IX, c. 3 (252).
  6. Plato: Timæus, sec. 39 (III, 459 in Jowett's translation).
  7. Aristotle: De Mundo, c. 2 et 6, (III, 628 and 636).
  8. Plutarch: Op. cit., Lib. III, c. 2 (V, 303-4).
  9. Diogenes Laërtius: De Vitis, Lib. VIII, c. 1, et 8 (205, 225).
  10. Diogenes: Op. cit., Lib. VIII, c. 7, (225).
  11. Cicero: Academica, Lib. II, c. 39 (322).
  12. Plutarch: Op. cit., Lib. II (V. 299-300).
  13. Archimedes: Arenarius, c. 1. Delambre: Astr. Anc., I, 102.
  14. This is the only account of his system. Even the age in which he flourished is so little known that there have been many disputes whether he was the original inventor of this system or followed some other. He was probably a contemporary of Cleanthes the Stoic in the 3rd century B. C. He is mentioned also by Ptolemy, Diogenes Laërtius and Vitruvius. (Schiaparelli: Die Vorlaufer des Copernicus im Alterthum, 75. See also Heath: Op. cit.)
  15. Plutarch: Op. cit.; Bk. III, c. 2 (V, 317-318).
  16. The Stoic contemporary of Aristarchus, author of the famous Stoic hymn. See Diogenes Laërtius: De Vitis.
  17. Plutarch: De Facie in Orbe Lunæ, (V, 410).
  18. Young: 109.
  19. Milton: Paradise Lost, Bk. VIII, 11. 82-85.
  20. Vitruvius: De Architectura, Lib. IX, c. 4 (220).
  21. Martianus Capella: De Nuptiis, Lib. VIII, (668).
  22. Ptolemy: Almagest, Lib. I, c. 7, (1, 21-25). Translated in Appendix B.
  23. Whewell: I, 239.
  24. Whewell: I, 294.
  25. Berry: 79.
  26. His book De Motu Stellarum, translated into Latin by Plato Tiburtinus (fl.1116) was published at Nuremberg (1557) by Melancthon with annotations by Regiomontanus. Ency. Brit. llth. Edit.
  27. Vaughan: I, 281.
  28. Graux: 318
  29. Graux: 319.
  30. Rashdall: II, pt. I, 77.
  31. Dict. of Nat. Biog.
  32. MSS. of it are extremely numerous. It was the second astronomical book to be printed, the first edition appearing at Ferrara in 1472. 65 editions appeared before 1647. It was translated into Italian, French, German, and Spanish, and had many commentators. Dict. of Nat. Biog.
  33. Whewell: I, 277.
  34. Blavatski: II, 29, note.
  35. Philo Judæus: Quis Rerum Divinarum Hæres. (IV, 7).
  36. Clement of Alexandria: Stromatum, Lib. V, c. 14, (III, 67).
  37. Origen: De Principiis, Lib. I, c. 7, (XI, 171).
  38. Lactantius: Divinarum Institutionum, Lib. III, c. 3 (VI, 355).
  39. Ibid: Lib. III, c. 24, (VI, 425-428).
  40. Taylor: Mediæval Mind, I, 74.
  41. By the will of God the earth remains motionless and stands throughout the age.
  42. Augustine: De Civitate Dei, Lib. XVI, c. 9, (41, p. 437).
  43. Augustine: De Genesi, II, c. 9, (v. 34, p. 270). (White's translation).
  44. Augustine: Civitate Dei, Lib. V, c. 5, (v. 41, p. 145).
  45. Philastrius: De Hæresibus, c. 133, (v. 12, p. 1264).
  46. Pseudo-Dionysius: De Cælesti Ierarchia, (v. 122, p. 10354).
  47. Milman: VIII, p. 228-9. See the Paradiso.
  48. Isidore of Seville: De Ordine Creaturarum, c. 5, sec. 3, (v. 83, p. 923).
  49. Lombard: Sententia, Bk. II, Dist. I, sec. 8. (v. 192, p. 655).
  50. Aquinas: Summa Theologica, pt I, qu. 70, art. 2. (Op. Om. Caietani, V, 179).