Chapter III The Later Development and Scientific Defense of the Copernican System
Copernicus accomplished much, but even his genius could not far outrun the times in which he lived. When one realizes that not only all the astronomers before him, but he and his immediate successor, Tycho Brahe, made all their observations and calculations unaided by even the simplest telescope, by logarithms or by pendulum clocks for accurate measurement of time,140 one marvels not at their errors, but at the greatness of their genius in rising above such difficulties. This lack of material aids makes the work of Tycho Brahe,141 accounted one of the greatest observers that has ever lived,142 as notable in its way perhaps as that of Copernicus.
His life143 was a somewhat romantic one. Born of noble family on December 14th, 1546, at Knudstrup in Denmark, Tyge Brahe, the second of ten children,144 was early practically adopted by his father’s brother. His family wished him to become a statesman and sent him in 1559 to the university at Copenhagen to prepare for that career. A partial eclipse of the sun on August 21st, 1560 as foretold by the astronomers thrilled the lad and determined him to study a science that could foretell the future and so affect men’s lives.145 When he was sent to Leipsic with a tutor in 1562 to study law, he devoted his time and money to the study of mathematics and astronomy. Two years later when eighteen years of age, he resolved to perform anew the task of Hipparchos and Ptolemy and make a catalogue of the stars more accurate than theirs. His family hotly opposed these plans; and for six years he wandered through the German states, now at Wittenberg, now at Rostock (where he fought the duel in which he lost part of his nose and had to have it replaced by one of gold and silver)146 or at Augsburg—everywhere working on his chosen subjects. But upon his return to Denmark (1570) he spent two years on chemistry and medicine, till the startling appearance of the New Star in the constellation of Cassiopæa (November, 1572) recalled him to what became his life work.147
Through the interest and favor of King Frederick II, he was given the island of Hveen near Elsinore, with money to build an observatory and the pledge of an annual income from the state treasury for his support.148 There at Uraniborg from 1576 to 1597 he and his pupils made the great catalogue of the stars, and studied comets and the moon. When he was forced to leave Hveen by the hostility and the economical tendencies of the young king,149 after two years of wandering he accepted the invitation of the Emperor Rudolphus and established himself at Prague in Bohemia. Among his assistants at Prague was young Johann Kepler who till Tycho’s death (on October 24, 1601) was his chief helper for twenty months, and who afterwards completed his observations, publishing the results in the Rudolphine Tables of 1627.
This “Phoenix among Astronomers”—as Kepler calls him,150—was the father of modern practical astronomy.151 He also propounded a third system of the universe, a compromise between the Ptolemaic and the Copernican. In this the Tychonic system,152 the earth is motionless and is the center of the orbits of the sun, the moon, and the sphere of the fixed stars, while the sun is the center of the orbits of the five planets.153 Mercury and Venus move in orbits with radii shorter than the sun’s radius, and the other three planets include the earth within their circuits. This system was in harmony with the Bible and accounted as satisfactorily by geometry as either of the other two systems for the observed phenomena.154 To Tycho Brahe, the Ptolemaic system was too complex,155 and the Copernican absurd, the latter because to account for the absence of stellar parallax it left vacant and purposeless a vast space between Saturn and the sphere of the fixed stars,156 and because Tycho’s observations did not show any trace of the stellar parallax that must exist if the earth moves.157
Though Tycho thus rejected the Copernican theory, his own proved to be the stepping stone toward the one he rejected,158 for by it and by his study of comets he completely destroyed the ideas of solid crystalline spheres to the discredit of the scholastics; and his promulgation of a third theory of the universe helped to diminish men’s confidence in authority and to stimulate independent thinking.
Copernicus worked out his system by mathematics with but slight aid from his own observations. It was a theory not yet proven true. Tycho Brahe, though denying its validity, contributed in his mass of painstaking, accurate observations the raw material of facts to be worked up by Kepler into the great laws of the planets attesting the fundamental truth of the Copernican hypothesis.
Johann Kepler159 earned for himself the proud title of “lawmaker for the universe” in defiance of his handicaps of ill-health, family troubles, and straitened finances.160 Born in Weil, Wurtemberg, (December 27, 1571) of noble but indigent parents, he was a sickly child unable for years to attend school regularly. He finally left the monastery school in Mulifontane in 1586 and entered the university at Tübingen to stay for four and a half years. There he studied philosophy, mathematics, and theology (he was a Lutheran) receiving the degree of Master of Arts in 1591. While at the university he studied under Mæstlin, professor of mathematics and astronomy, and a believer in the Copernican theory. Because of Mæstlin’s teaching Kepler developed into a confirmed and enthusiastic adherent to the new doctrine.
In 1594 he reluctantly abandoned his favorite study, philosophy, and accepted a professorship in mathematics at Grætz in Styria. Two years later he published his first work: Prodromus Dissertationum continens mysterium cosmographicum etc. (1596) in which he sought to prove that the Creator in arranging the universe had thought of the five regular bodies which can be inscribed in a sphere according to which He had regulated the order, the number and the proportions of the heavens and their movements.161 The book is important not only because of its novelty, but because it gave the Copernican doctrine public explanation and defense.162 Kepler himself valued it enough to reprint it with his Harmonia Mundi twenty-five years later. And it won for him appreciative letters from various scientists, notably from Tycho Brahe and Galileo.163
As Kepler, a Lutheran, was having difficulties in Grætz, a Catholic city, he finally accepted Tycho’s urgent invitation to come to Prague.164 He came early in 1600, and after some adjustments had been made between the two,165 he and his family settled with Tycho that autumn to remain till the latter’s death the following November. Kepler himself then held the office of imperial mathematician by appointment for many years thereafter.166
With the researches of Tycho’s lifetime placed at his disposal, Kepler worked out two of his three great planetary laws from Tycho’s observations of the planet Mars. Yet, as M. Bertrand remarks,167 it was well for Kepler that his material was not too accurate or its variations (due to the then unmeasured force of attraction) might have hindered him from proving his laws; and luckily for him the earth’s orbit is so nearly circular that in calculating the orbit of Mars to prove its elliptical form, he could base his work on the earth’s orbit as a circle without vitiating his results for Mars.168 That a planet’s orbit is an ellipse and not the perfect circle was of course a triumph for the new science over the scholastics and Aristotelians. But they had yet to learn what held the planets in their courses.
From Kepler’s student days under Mæstlin when as the subject of his disputation he upheld the Copernican theory, to his death in 1630, he was a staunch supporter of the new teaching.169 In his Epitome Astronomiæ Copernicanæ (1616) he answered objections to it at length.170 He took infinite pains to convert his friends to the new system. It was in vain that Tycho on his deathbed had urged Kepler to carry on their work not on the Copernican but on the Tychonic scheme.171
Kepler had reasoned out according to physics the laws by which the planets moved.172 In Italy at this same time Galileo with his optic tube (invented 1609) was demonstrating that Venus had phases even as Copernicus had declared, that Jupiter had satellites, and that the moon was scarred and roughened—ocular proof that the old system with its heavenly perfection in number (7 planets) and in appearance must be cast aside. Within a year after Galileo’s death Newton was born173 (January 4, 1643). His demonstration of the universal application of the law of gravitation (1687) was perhaps the climax in the development of the Copernican system. Complete and final proof was adding in the succeeding years by Roemer’s (1644-1710) discovery of the velocity of light, by Bradley’s (1693-1762) study of its aberration,174 by Bessel’s discovery of stellar parallax in 1838,175 and by Foucault’s experimental demonstration of the earth’s axial motion with a pendulum in 1851.176