Galileo di Vincenzo Bonaulti de Galilei ([ɡaliˈlɛːo ɡaliˈlɛi]; 15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath, from Pisa. Galileo has been called the "father of observational astronomy", the "father of modern physics", the "father of the scientific method", and the "father of modern science". Galileo studied speed and velocity, gravity and free fall, the principle of relativity, inertia, projectile motion and also worked in applied science and technology, describing the properties of pendulums and "hydrostatic balances", inventing the thermoscope and various military compasses, and using the telescope for scientific observations of celestial objects. His contributions to observational astronomy include the telescopic confirmation of the phases of Venus, the observation of the four largest satellites of Jupiter, the observation of Saturn's rings, and the analysis of sunspots. Galileo's championing of heliocentrism and Copernicanism was controversial during his lifetime, when most subscribed to geocentric models such as the Tychonic system. He met with opposition from astronomers, who doubted heliocentrism because of the absence of an observed stellar parallax. The matter was investigated by the Roman Inquisition in 1615, which concluded that heliocentrism was "foolish and absurd in philosophy, and formally heretical since it explicitly contradicts in many places the sense of Holy Scripture". Galileo later defended his views in Dialogue Concerning the Two Chief World Systems (1632), which appeared to attack Pope Urban VIII and thus alienated him and the Jesuits, who had both supported Galileo up until this point. He was tried by the Inquisition, found "vehemently suspect of heresy", and forced to recant. He spent the rest of his life under house arrest. While under house arrest, he wrote Two New Sciences, in which he summarized work he had done some forty years earlier on the two sciences now called kinematics and strength of materials GALILEO GALILEI Dialogue Concerning the Two Chief World Systems—Ptolemaic & Copernican translated by Stillman Drake, fore­ word by Albert Einstein SECOND EDITION UNIVERSITY OF CALIFORNIA PRESS BERKELEY AND LOS ANGELES 1967 Take note, theologians, that in your desire to make matters of faith out of propositions relat­ ing to the fixity of sun and earth you run the risk of eventually having to condemn as heretics those who would declare the earth to stand still and the sun to change position — eventually, I say, at such a time as it might be physically or F irst P rinting, 1953 F irst P aper-bound E dition (R evised), 1962 logically proved that the earth moves and the Second R evised E dition, 1967 sun stands still. Library of Congress Catalog Card N umber 53-11238 -Note added by Galileo in the preliminary leaves of his own copy of the Dialogue. UNIVERSITY o f CALIFORNIA PRESS, BERKELEY AND LOS ANGELES, CALIFORNIA CAMBRIDGE UNIVERSITY PRESS, LONDON, ENGLAND C o p y r ig h t , 1953, 1962, a n d 1967, b y t h e R e g e n t s o p t h e U n iv e r s it y o p C a l ip o r n u PRINTED IN THE UNITED STATES OP AMERICA DESIGNED BY JOHN B. GOETZ VORWORT FOREWORD GJ ALiLEOS Dialog iiber die beiden hauptsdchlichen Welt- ALiLEO^s Dialogue Concerning the Two Chief World systeme ist eine Fundgrube fur jeden, der sich fur die Geistes- G Systems is a mine of information for anyone interested in the geschichte des Westens und fiir deren Riickwirkung auf die cultural history of the Western world and its influence upon okonomische und politische Entwicklung interessiert. economic and political development. Da offenbart sich ein Mann, der den leidenschaftlichen Willen, A man is here revealed who possesses the passionate will, the die Intelligenz und den Mut hat, sich als Vertreter des ver- intelligence, and the courage to stand up as the representative niinftigen Denkens der Schar derjenigen entgegenzustellen, die of rational thinking against the host of those who, relying on the auf die Unwissenheit des Volkes und die Indolenz der Lehren- ignorance of the people and the indolence of teachers in priest’s den in Priester- und Professoren-Gewande sich stiitzend, ihre and scholar’s garb, maintain and defend their positions of au­ Machtpositionen einnehmen und verteidigen. Seine ungewohn- thority. His unusual literary gift enables him to address the liche schriftstellerische Begabung erlaubt es ihm, zu den Gebilde- educated men of his age in such clear and impressive language ten seiner Zeit so klar und eindrucksvoll zu sprechen, dass er as to overcome the anthropocentric and mythical thinking of his das anthropozentrische und mythische Denken der Zeitgenossen contemporaries and to lead them back to an objective and causal iiberwand und sie zu einer objektiven, kausalen Einstellung zum attitude toward the cosmos, an attitude which had become lost Kosmos zuriickfuhrte, die mit der Bliite der griechischen Kultur to humanity with the decline of Greek culture. der Menschheit verloren gegangen war. In speaking this way I notice that I, too, am falling in with Wenn ich dies so ausspreche, sehe ich zugleich, dass ich der the general weakness of those who, intoxicated with devotion, weitverbreiteten Schwache aller derer zum Opfer falle, die trun- exaggerate the stature of their heroes. It may well be that during ken von einer ubermassigen Verliebtheit die Statur ihrer Heroen the seventeenth century the paralysis of mind brought about by iibertrieben darstellen. Es mag sein, dass die Lahmung der Geis- the rigid authoritarian tradition of the Dark Ages had already ter durch starre autoritare Tradition des dunklen Zeitalters im so far abated that the fetters of an obsolete intellectual tradition siebzehnten Jahrhundert bereits so weit gemildert war, dass die could not have held much longer — with or without Galileo. Fesseln einer iiberlebten intellektuellen Tradition nicht mehr Yet these doubts concern only a particular case of the general fiir die Dauer standhalten konnten — mit oder ohne Galileo. problem concerning the extent to which the course of history Nun, dieser Zweifel betrifft ja nur einen Sonderfall der Frage, can be decisively influenced by single individuals whose qualities inwieweit der Verlauf der menschlichen Geschichte durch ein- impress us as accidental and unique. As is understandable, our V or- viii zelne Individuen und deren als zufallig und einmalig empfundene age takes a more sceptical view of the role of the individual than ix Fore­ Qualitaten entscheidend beeinflusst werden kann. Unsere Zeit did the eighteenth and the first half of the nineteenth century. wort word steht solchen Auffassungen skeptischer gegeniiber als das acht- For the extensive specialization of the professions and of knowl­ zehnte Jahrhundert und die erste Halfte des neunzehnten Jahr- edge lets the individual appear “replaceable,” as it were, like a hunderts — begreiflicherweise. Denn die weitgehende Spezi- part of a mass-produced machine. alisierung der Berufe und des Wissens lasst den Einzelnen Fortunately, our appreciation of the Dialogue as a historical gewissermassen als „auswechselbar“ erscheinen wie den Einzel- document does not depend upon our attitude toward such pre­ teil einer durch Massenfabrikation hergestellten Maschine. carious questions. To begin with, the Dialogue gives an ex­ Der Wert des Dialogs als Dokument ist gliicklicherweise tremely lively and persuasive exposition of the then prevailing von der Stellung zu solch prekaren Fragen unabhangig. Vor views on the structure of the cosmos in the large. The naive pic­ allem gibt der Dialog eine uberaus lebendige und iiberzeugende ture of the earth as a flat disc, combined with obscure ideas about Darstellung der herrschenden Ansichten uber den Bau des Kos- star-filled space and the motions of the celestial bodies, prevalent mos im Grossen, Die im friiheren Mittelalter herrschende kind- in the early Middle Ages, represented a deterioration of the much liche Auffassung der Erde als einer fiachen Scheibe, verkniipft earlier conceptions of the Greeks, and in particular of Aristotle’s mit ganz unklaren Ideen iiber den von den Sternen erfullten ideas and of Ptolemy’s consistent spatial concept of the celestial Raum und die Bewegung der Gestirne, waren langst durch das bodies and their motions. The conception of the world still pre­ Weltbild der Griechen, speziell durch Ideen des Aristoteles und vailing at Galileo’s time may be described as follows: durch die ptolemaische konsequente raumliche Auffassung der There is space, and within it there is a preferred point, the Gestirne und deren Bewegung verbessert. Das Weltbild, welches center of the universe. Matter — at least its denser portion — zur Zeit Galileos noch vorherrschte, war etwa folgendes: tends to approach this point as closely as possible. Consequently, Es gibt einen Raum, der einen bevorzugten Punkt, den Welt- matter has assumed approximately spherical shape (earth). mittelpunkt besitzt. Die Materie — wenigstens der dichtere Teil Owing to this formation of the earth the center of the terrestrial derselben — sucht sich diesem Punkt moglichst zu nahern. Sie sphere practically coincides with that of the universe. Sun, moon, hat demzufolge ungefahr Kugelgestalt angenommen (Erde). and stars are prevented from falling toward the center of the Vermdge dieser Entstehung der Erde f allt der Mittelpunkt dieser universe by being fastened onto rigid (transparent) spherical Erdkugel praktisch mit den Weltmittelpunkt zusammen. Sonne, shells whose centers are identical with that of the universe (or Mond und Sterne sind, damit sie nicht nach dem Weltmittel­ space). These spherical shells revolve around the immovable punkt fallen, auf (durchsichtigen) starren Kugelschalen befes- globe (or center of the universe) with slightly differing angular tigt, deren Mittelpunkt mit den Weltmittelpunkt (oder Raum- velocities. The lunar shell has the smallest radius; it encloses mittelpunkt) zusammenfallt. Diese Kugelschalen drehen sich everything “terrestrial.” The outer shells with their heavenly um den ruhenden Erdball (bezw. um den Weltmittelpunkt) mit bodies represent the “celestial sphere” whose objects are en­ etwas verschiedenen Winkelgeschwindigkeiten.