The gradual acceptance of the Copernican theory of the universe Part 1

The gradual acceptance of the Copernican theory of the universe.

by Dorothy Stimson.

PREFACE

This study does not belong in the field of astronomy, but in that of the history of thought; for it is an endeavor to trace the changes in people's beliefs and conceptions in regard to the universe as these were wrought by the dissolution of superst.i.tion resulting from the scientific and rationalist movements. The opening chapter is intended to do no more than to review briefly the astronomical theories up to the age of Copernicus, in order to provide a background for the better comprehension of the work of Copernicus and its effects.

Such a study has been rendered possible only by the generous loan of rare books by Professor Herbert D. Foster of Dartmouth College, Professor Edwin E. Slosson of Columbia University, Doctor George A.

Plimpton and Major George Haven Putnam, both of New York, and especially by the kindly generosity of Professor David Eugene Smith of Teachers College who placed his unique collection of rare mathematical books at the writer's disposal and gave her many valuable suggestions as to available material. Professors James T. Shotwell and Harold Jacoby of Columbia University have read parts of this study in ma.n.u.script. The writer gratefully acknowledges her indebtedness not only to these gentlemen, but to the many others, librarians and their a.s.sistants, fellow-students and friends, too numerous to mention individually, whose ready interest and whose suggestions have been of real service, and above all to Professor James Harvey Robinson at whose suggestion and under whose guidance the work was undertaken, and to the Reverend Doctor Henry A. Stimson whose advice and criticism have been an unfailing source of help and encouragement.

PART ONE

AN HISTORICAL SKETCH OF THE HELIOCENTRIC THEORY OF THE UNIVERSE.

CHAPTER I.

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.

[Footnote 1: The earliest observation Ptolemy uses is an Egyptian one of an eclipse occurring March 21, 721 B.C. (c.u.mont: 7). [In these references, the Roman numerals refer to the volume, the Arabic to the page, except as stated otherwise. The full t.i.tle is given in the bibliography at the back under the author's name.]]

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 sh.o.r.es 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.

[Footnote 2: Warren: 40. See "Calendar" in Hastings: _Ency. of Religion and Ethics_.]

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 Laertius 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]

[Footnote 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.]

[Footnote 4: See Plutarch: _Moralia: De placitas Philosophorum_, Lib.

I et II, (V. 264-277, 296-316).]

[Footnote 5: Diogenes Laertius: _De Vitis_, Lib. IX, c. 3 (252).]

[Footnote 6: Plato: _Timaeus_, sec. 39 (III, 459 in Jowett's translation).]

[Footnote 7: Aristotle: _De Mundo_, c. 2 et 6 (III, 628 and 636).]

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?

[Footnote 8: Plutarch: _Op. cit._, Lib. III, c. 2 (V, 303-4).]

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 Laertius,[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.

[Footnote 9: Diogenes Laertius: _De Vitis_, Lib. VIII, c. 1, et 8 (205, 225).]

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.

[Footnote 10: Diogenes: _Op. cit._, Lib. VIII, c. 7 (225).]

[Footnote 11: Cicero: _Academica_, Lib. II, c. 39 (322).]

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 circ.u.mference."

[Footnote 12: Plutarch: _Op. cit._, Lib. II (V. 299-300).]

[Footnote 13: Archimedes: _Arenarius_, c. 1. Delambre: _Astr. Anc._, I, 102.]

[Footnote 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 Laertius and Vitruvius. (Schiaparelli: _Die Vorlaufer des Copernicus im Alterthum_, 75. See also Heath: _Op. cit._)]

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 pa.s.sage 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 antic.i.p.ated.[15]

[Footnote 15: Plutarch: _Op. cit._: Bk. III, c. 2 (V, 317-318).]

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.

[Footnote 16: The Stoic contemporary of Aristarchus, author of the famous Stoic hymn. See Diogenes Laertius: _De Vitis_.]

[Footnote 17: Plutarch: _De Facie in Orbe Lunae_, (V, 410).]

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 circ.u.mference 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

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