Tycho Brahe: a picture of scientific life and work in the sixteenth century/Chapter 1
THE REVIVAL OF ASTRONOMY IN EUROPE.
The early part of the sixteenth century must always rank among the most remarkable periods in the history of civilisation. The invention of printing had made literature the property of many to whom it had hitherto been in- accessible, and the downfall of the Byzantine Empire had scattered over Europe a number of fugitive Greeks, who carried with them many treasures of classical literature hitherto unknown in the Western world, while Raphael, Michael Angelo, and other contemporaries of Leo X. revived the glory of the ancients in the realm of art. The narrow limits of the old world had vanished, and the Portuguese and Spanish navigators had led the way to boundless fields for human enterprise, while the Reformation revolutionised the spirit of mankind and put an end to the age of ignorance and superstition.
During this active period there were also signs of renewed vigour among the devotees of science, and the time was particularly favourable to a revival of astronomical studies. Students of astronomy were now enabled to study the Greek authors in the original language, instead of having to be content with Latin reproductions of Arabian translations from the Greek, which, through the Italian universities, had been introduced into Europe during the Middle Ages. Another impulse was given by the voyages of discovery, as navigators were obliged to trust entirely to the stars and the compass, and therefore required as perfect a theory as possible of the motions of the heavenly bodies. We see accordingly at the end of the fifteenth century and the beginning of the sixteenth considerable stir in the camp of science, but as yet only in Germany—a circumstance not difficult to explain. Though divided into a great number of semi-independent states, Germany bore still the proud name of the Holy Roman Empire, and on account of the claims represented by this name the Germans had for a long time been in constant intercourse with Italy, the land with the great past, and still, notwithstanding its political misery, the leader of civilisation. It was an intercourse of a peaceful and commercial as well as of a warlike character; but in both ways was this of benefit to the Germans, producing among them much knowledge of foreign affairs, and giving them greater facilities for taking up the scientific work of the ancients than were found in other parts of Europe.
The first astronomer of note was Georg Purbach (1423–1461), who studied at the University of Vienna, and afterwards for some time in Italy. His principal work on astronomy (Theoricæ Novæ Planetarum) attempted to develop the old hypothesis of material celestial spheres, and was but a mixture of Aristotelean cosmology and Ptolemean geometry; but he was the first European to make use of trigonometry, the principal legacy which astronomers owe to the Arabs. Purbach endeavoured to get beyond the rudiments of spherical astronomy, which hitherto had formed the only subject for astronomical lectures, and had been taught through the medium of a treatise written in the thirteenth century by John Holywood (Johannes de Sacrobosco) for use in the University of Paris. While lecturing at Vienna, Purbach's attention was drawn to a young disciple of great promise, Johann Müller, from Königsberg, a small village in Franconia, where he had been born in 1436. He is generally known by the name of Regiomontanus, though he does not seem to have used this name himself, but always that of Johannes de Monteregio. He entered heart and soul into his teacher's studies of the great work of Ptolemy, which embodied all the results of Greek astronomy, and the talented pupil soon became an invaluable co-operator to Purbach. They did not confine themselves to theoretical studies, but, with such crude instruments as they could construct, they convinced themselves of the fact that the places of the planets computed from the astronomical tables of King Alphonso X. of Castile differed very considerably from the actual positions of the planets in the sky. In the midst of these occupations the two astronomers had the good luck to become acquainted with a man who was well qualified to help them to carry out their greatest wishes. This man was Cardinal Bessarion, a Greek by birth, who, as Bishop of Nicæa, had accompanied the Byzantine Emperor on his journey to the Council of Ferrara in 1438, where he tried to bring about a reconciliation between the Greek and Roman Churches. Bessarion remained in Italy and joined the Roman Church, but he never forgot his old country, and contributed very much to make the classical Greek literature known in the West. The translation of the original Almagest (as Ptolemy's work was generally called, from a corruption of the Arabic Al megist, in its turn derived from μέγιστη σύνταξις) was a subject in which he was particularly interested, and during his stay at Vienna as Papal Nuncio he succeeded in communicating to Purbach his own anxiety to make Ptolemy better known in the scientific world. Purbach was on the point of starting for Italy for the purpose of collecting Greek manuscripts, when he died suddenly in 1461, but Regiomontanus succeeded to his place in the Cardinal's friendship, and set out for Italy with Bessarion in the following year.
Regiomontanus stayed about seven years in Italy, visiting the principal cities, and losing no chance of studying the Greek language and collecting Greek manuscripts. At Venice he wrote a treatise on trigonometry, which branch of mathematics he also, during the remainder of his life, continued to develop, so that he constructed a table of tangents (tabula fecunda), and probably only was prevented by his early death from completing his treatise by introducing the use of tangents therein. After his return to Germany, he settled, in 1471, at Nürnberg. This city was one of the chief centres of German industry and literary life, and no other German city had such regular commercial communication with Italy, from whence the produce of the East was brought into the market, and nowhere did the higher classes of citizens use their wealth so willingly in support of art and science. The new art of printing had recently been introduced at Nürnberg, where a regular printing-press was now working—a circumstance of particular importance to the collector of Greek writings. A wealthy citizen, Bernhard Walther (born 1430, died 1504), became at once the friend and disciple of Regiomontanus, and arranged an observatory for their joint use. Instruments, as fine as the skilful artisans of Nürnberg could make them, adorned the earliest of European observatories, and the two friends made good use of them (they observed already the comet of 1472), and originated several new methods of observing. But Regiomontanus did not forget the printing operations, and published not only Purbach's Theoricæ Novæ and trigonometrical tables, but also his own celebrated Ephemerides, the first of their kind, which, some years afterwards, were made known to the navigators through the German geographer Martin Behaim, and guided Diaz, Columbus, Vasco de Gama, and many others safely across the ocean. Nothing spread the fame of the astronomer like these Ephemerides, and the Pope was thus induced to invite Regiomontanus to Rome to reform the confused calendar. The invitation was obeyed in 1475, but Regiomontanus died in July 1476 very suddenly at Rome. He only reached the age of forty, and no doubt much might have been expected from him if death had not so early stopped his career; but he had rendered great service to science, not only by his endeavours to save the Greek authors from oblivion, but by his Ephemerides, his development of trigonometry, and his observations. Walther survived him twenty-eight years, and continued his observations, which were published in 1544.
By Purbach and Regiomontanus the astronomy of the Alexandrian school had been introduced at the German Universities, and the increased demands which navigators made on astronomers continued to help forward the study of astronomy in Germany, which country, by having a sovereign in common with Spain, for a while had much intercourse with the latter country. Of the astronomers who worked during the first half of the sixteenth century we shall here mention Peter Apianus or Bienewitz, who taught at the University of Ingolstadt. Besides other works, he published in 1540 a large book, Astronomicum Cæsareum, dedicated to Charles the Fifth. In this beautiful volume the author represented, by means of movable circles of cardboard of various colours, the epicyclical motions of the planets according to the Ptolemean system, and expected to be able in this way to find their positions without computation. The book was received with much applause, and is really in some ways to be admired, though one cannot help agreeing with Kepler in regretting the "miserable industry" of Apianus, which after all only produced a very rough approximation to the real motions of the stars, but which is eminently characteristic of the low state of science at that time. Apianus deserves more thanks for having paid much attention to comets, and for having discovered the important fact that the tails of these bodies are turned away from the sun. This was also pointed out about the same time by Fracastoro of Verona in a work published in 1538, containing an elaborate attempt to revive the theory of concentric spheres of Eudoxus, which had been pushed into the background by the Ptolemean system of the world.
Only three years after Apian's volume appeared the great work of Nicolaus Copernicus, De Revolutionibus (1543), which was destined to become the corner-stone of modern astronomy. We shall in the following so often have occasion to refer to the labours of this great man, that a few words will suffice in this place. Copernicus, who not only discovered the greatest truth in astronomy, but who even by his opponents was admitted to be an astronomer worthy of being classed with Hipparchus and Ptolemy, was born in 1473 at Thorn, on the Vistula, a town which belonged to the Hansa League, and a few years before had come under the suzerainty of Poland. He studied first at the University of Krakau, where astronomy was specially cultivated, and at the age of twenty-four he proceeded to Bologna, where he enjoyed the teaching of Domenico Maria Novara. Thus Copernicus not only became acquainted with Ptolemy's work, but also acquired some familiarity with the astrolabe or astronomical circle, one of the few crude instruments then in use. From about the end of 1505 till his death in 1543, Copernicus lived in the diocese of Ermland, in Prussia, most of the time in the town of Frauenburg, where he held a canonry at the cathedral. It is much to be regretted that we are utterly unacquainted with the manner in which Copernicus came to design the new system of astronomy which has made his name immortal. But he had probably early perceived that, however valuable the labours of Regiomontanus had been, they had not improved the theory of celestial motion, so that the most important problem, that of computing beforehand the positions of the planets and accounting for their apparently intricate movements, was practically untouched since the days of Ptolemy. That great mathematician had completed and extended the planetary system of Hipparchus, and had in a wonderfully ingenious manner represented the complicated phenomena. But more than 1400 years had elapsed since his time, and the system, however perfect from a mathematical point of view, had long been felt to be too complicated, and not agreeing closely enough with the observed movements of the planets. This circumstance led Copernicus to attempt the construction of a new system, founded on the idea that the sun, and not the earth, is the ruler of the planets. But though Copernicus on the basis of this idea developed a theory of the planetary movements as complete as that of Ptolemy, he was unable to do more than to demonstrate the possibility of explaining the phenomena by starting from the heliocentric idea. Having no materials from which to deduce the true laws of the motion of the planets in elliptic orbits, he was obliged to make use of the excentric circles and epicycles of the ancients, by which he greatly marred the beauty and simplicity of his system. He did not possess accurate instruments, and took but few observations with those he had. The idea does not seem to have struck him that it was indispensable to follow the planets through a number of years with carefully constructed instruments, and that only in that way could the true theory of planetary motion be found.
There was much to be done yet ere the reform of astronomy could be accomplished. The pressing want of new tables to take the place of the antiquated Alphonsine tables was supplied a few years after the death of Copernicus by Erasmus Reinhold, but though the positions of the planets could be computed from them with greater accuracy than from the old tables, the "Prutenic tables" (published in 1551) did not by this superiority offer any proof of the actual truth of the Copernican principle.
A century had now elapsed since the study of astronomy had commenced to revive in Italy and Germany, but as yet the work accomplished had chiefly been of a tentative and preparatory kind, Copernicus alone having attempted to make science advance along a new path. Still, much useful work had been done. The labours of the ancients had now become accessible in the originals; the Arabs and Regiomontanus had developed trigonometry, and thereby greatly facilitated astronomical computations; Copernicus had shaken the implicit conviction of the necessity of clinging to the complicated Ptolemean system, and had offered the world an alternative and simpler system, while new tables had been computed to take the place of the Alphonsine tables. But otherwise the astronomy of the ancients reigned undisturbed. No advance had been made in the knowledge of the positions of the fixed stars, those stations in the sky by means of which the motions of the planets had to be followed; the value of almost every astronomical quantity had to be borrowed from Ptolemy, if we except a few which had been redetermined by the Arabs. No advance had been made in the knowledge of the moon's motion, so important for navigation, nor in the knowledge of the nature of the planetary orbits, the uniform circular motion being still thought not only the most perfect, but also the only possible one for the planets to pursue. Whether people believed the planets to move round the earth or round the sun, the complicated machinery of the ancients had to be employed in computing their motions, and crude as the instruments in use were, they were more than sufficient to show that the best planetary tables could not foretell the positions of the planets with anything like the desirable accuracy.
No astronomer had yet made up his mind to take nothing for granted on the authority of the ancients, but to determine everything himself. Nobody had perceived that the answers to the many questions which were perplexing astronomers could only be given by the heavens, but that the answers would be forthcoming only if the heavens were properly interrogated by means of improved instruments, capable of determining every astronomical quantity anew by systematic observations. The necessity of doing this was at an early age perceived by Tycho Brahe, whose life and work we shall endeavour to sketch in the following pages. By his labours he supplied a sure foundation for modern astronomy, and gave his great successor, Kepler, the means of completing the work commenced by Copernicus.
- The Tabulæ Alphonsinæ had been computed in the middle of the thirteenth century by a number of Arabian and Jewish astronomers under the personal direction of King Alphonso el Sabio. They were founded on the theory of Ptolemy and the observations of the Arabs, and were first printed at Venice in 1483.
- The treatise De Triangulis Omnimodis, libri v., was first published at Nürnberg in 1533, while Regiomontanus himself printed the Tabulæ Directionum in 1475, containing both a table of sines for every minute, and the above-mentioned table of tangents for every degree, extended to every minute by Reinhold in a new edition in 1554.
- The Greek text of Ptolemy's work from the MS. brought home by Regiomontanus was published at Bâle in 1538.
- We shall return to this subject in Chapter VII.