1 Primary Source 8.4 GALILEO GALILEI, VARIOUS WRITINGS1 Galileo Galilei (1564–1642) was an Italian scientist who, having improved the telescope, perceived the mountains of the Moon, sunspots, the stars of the Milky Way, and four moons of Jupiter (the first planetary satellite discovered since prehistoric times) and confirmed the phases of Venus—much of which undermined the Aristotelian conception of an incorruptible and perfect celestial realm. Galileo’s discoveries inspired him to embrace the Copernican heliocentric system. The Roman Inquisition investigated his assertions and writings in 1616 and concluded that the Copernican theory could be propounded as a hypothesis but not as established fact. In 1632, after his friend and staunch supporter, Cardinal Maffeo Barberini, became Pope Urban VIII, he publicly, though in a rather veiled way, advocated heliocentrism in Dialogue Concerning the Two Chief World Systems, which seemed to ridicule the pope. The Inquisition found him “suspect of heresy,” demanded his repudiation of the heliocentric theory, and placed him under house arrest in his Tuscan villa for the rest of his life. He then went on to conduct experiments in physics and to publish important works on kinematics. For the text online, click here. TO KEPLER (1597)2 I count myself happy, in the search after truth, to have so great an ally as yourself, and one who is so great a friend of the truth itself. It is really pitiful that there are so few who seek truth, and who do not pursue a perverse method of philosophizing. But this is not the place to mourn over the miseries of our times, but to congratulate you on your splendid discoveries in conformation of truth. I shall read your book to the end, sure of finding much that is excellent in it. I shall do so with the more pleasure, because I have been for many years an adherent of the Copernican system,3 and it explains to me the causes of many of the appearances of nature which are quite unintelligible on the commonly accepted hypothesis.4 I have collected many arguments for the purpose of refuting the latter; but I do not venture to bring them to the light of publicity, for fear of sharing the fate of our master, Copernicus, who, although he has earned immortal fame with some, yet with very many (so great is the number of fools) has become an object of ridicule and scorn.5 I should certainly venture to publish my speculations if there were more people like you. But this not being the case, I refrain from such an undertaking. 1 Oliver J. Thatcher, (Ed.), The Library of Original Sources, 10 vols. (Milwaukee, WI: University Research Extension Co., 1907), 5:292-296, 306-7. 2 Johannes Kepler (1571–1630) was a German astronomer who formulated the laws of planetary motion. 3 A heliocentric model of the universe formulated by Nicolaus Copernicus (1473–1543). 4 The Ptolemaic System, whereby the Sun and other planets revolve around the Earth. 5 Copernicus avoided publishing his theory until the year of his death in large part to avoid ridicule, not for fear of the Inquisition. 2 TO BENEDETTO LANDUCCI (1609) You must know that about two months ago a report was spread here that in Flanders a spy-glass had been presented to Prince Maurice,6 so ingeniously constructed that it made the most distant objects appear quite near, so that a man could be seen quite plainly at a distance of two miglia.7 This result seemed to me so extraordinary that it set me thinking; and as it appeared to me that it depended upon the theory of perspective, I reflected on the manner of constructing it, in which I was at length so entirely successful that I made a spy-glass which far surpasses the report of the Flanders one. As the news had reached Venice that I had made such an instrument, six days ago I was summoned before their highnesses the signoria,8 and exhibited it to them, to the astonishment of the whole senate. Many noblemen and senators, although of a great age, mounted the steps of the highest church towers at Venice [St Mark’s], in order to see sails and shipping that were so far off that it was two hours before they were seen steering full sail into the harbor without my spy-glass, for the effect of my instrument is such that it makes an object fifty miglia off appear as large and near as if it were only five. TO KEPLER (1610) You are the first and almost the only person who, even after but a cursory investigation, has, such is your openness of mind and lofty genius, given entire credit to my statements. .9 We will not trouble ourselves about the abuses of the multitude, for against Jupiter even giants, to say nothing of pigmies, fight in vain. Let Jupiter stand in the heavens, and let the sycophants bark at him as they will. In Pisa, Florence, Bologna, Venice, and Padua many have seen the planets; but all are silent on the subject and undecided, for the greater number recognize neither Jupiter nor Mars and scarcely the moon as planets. At Venice one man spoke against me, boasting that he knew for certain that my satellites of Jupiter, which he had several times observed, were not planets because they were always to be seen with Jupiter, and either all or some of them now followed and now preceded him. What is to be done? Shall we decide with Democritus10 or Heraclitus?11 I think, my Kepler, we will laugh at the extraordinary stupidity of the multitude. What do you say to the leading philosophers of the faculty here, to whom I have offered a thousand times of my own accord to show my studies, but who with the lazy obstinacy of a serpent who has eaten his fill have never consented to look at planets, nor moon, nor telescope? Verily, just as serpents close their ears, so do these men close their eyes to the light of the truth. These are great matters; yet they do not occasion me any surprise. People of this sort think that philosophy is a kind of book like the Æneid or the Odyssey,12 and that the truth is to be sought, not in the universe, nor in nature, but (I use their own words) by comparing texts! 6 The Commander in Chief of the Dutch armed forces, Maurice of Nassau, Prince of Orange (1567–1625). 7 Miles. 8 The governing authorities. 9 These and other ellipses in original. 10 Democritus (460–370 B.C) was an ancient Greek philosopher who formulated an atomic theory. 11 Heraclitus (535–475 B.C.) was a pre-Socratic Greek philosopher known for his insistence on ever-present change in the universe. 12 Epic poems by Virgil and Homer, respectively. 3 How you would laugh if you heard the things the first philosopher of the faculty at Pisa brought against me in the presence of the Grand Duke, for he tried, now with logical arguments, now with magical adjurations, to tear down and to argue the new planets out of heaven. DIALOGUE CONCERNING THE TWO CHIEF WORLD SYSTEMS (1632) There has but lately been proclaimed at Rome a wholesome edict, which prohibited the pernicious doctrines of the present day and imposed a timely silence upon the Pythagorean view that the earth moves. There are voices that rashly declare that the decree owes its promulgation not to an intelligent demonstration, but to party feeling unsupported by sufficient knowledge. There are loud demands that councilors entirely unfamiliar with the bases of astronomical science should not by sudden prohibition prevent the advance of inquiring minds. My zeal forbids me to maintain silence in the face of such trivial complaints. Well content with that wise decision, I have decided to make my appearance at the forum of the world as a witness of candid truth. I myself was present then at Rome; I not only had the highest ecclesiastical dignitaries of that court for auditors but also received their applause. So the publication of that decree did not follow without first obtaining the benefit of my knowledge of the question. Therefore, it is my purpose in this present laborious work to demonstrate to foreign nations that as much is known in Italy and especially at Rome concerning this matter as has been acquired by the inquiries of other peoples. By comparing all separate investigations of the Copernican theory I will show that the Roman censor was already familiar with all of them, that this region is not only the home of doctrines that lead to salvation, but that ingenious discoveries to delight the mind also proceed from it. To this end I have taken in the course of the discussions the side of Copernicus, during which I have proceeded from his system as a basis in purely mathematical manner as from an hypothesis, and have sought with the aid of every possible artifice to demonstrate that this system was superior to the theory of the immobility of the earth, even in the light of the opposing arguments brought forward by Peripatetics.13 Three main principles will be discussed. First I will endeavor to prove that all investigations confined to the earth are insufficient means of proving its motion, that such rather are consistent indifferently either with the motion or the rest of the earth; by this means, I hope, many considerations unknown to the ancients will come into discussion. Secondly, the heavenly bodies will be called into evidence, which works out so favorably for the view of Copernicus as to make it appear that this should triumph completely; to this will be added new inquiries, which are to be treated as auxiliaries to astronomy, but not as actually valid natural laws.