The Essential Galileo

GALILEO GALILEI

The Essential Galileo

GALILEO GALILEI

The Essential Galileo

Edited and Translated by
Maurice A. Finocchiaro

Hackett Publishing Company, Inc.
Indianapolis/Cambridge

Copyright © 2008 by Hackett Publishing Company, Inc.

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   Library of Congress Cataloging-in-Publication Data

Galilei, Galileo, 1564–1642.

[Selections. English. 2008]

The essential Galileo / Galileo Galilei ; edited and translated by

Maurice A. Finocchiaro.

       p.   cm.

Includes bibliographical references and index.

ISBN 978-0-87220-937-4 (pbk.) — ISBN 978-0-87220-938-1 (cloth)

1. Science—Early works to 1800. 2. Astronomy—Early works to 1800.

3. Science—History. 4. Galilei, Galileo, 1564–1642. 5. Scientists—

Italy. I. Finocchiaro, Maurice A., 1942– II. Title.

Q155.G27 2008

500—dc22                                                                           2008018659

ePub ISBN: 978-1-60384-258-7

Contents

Preface and Acknowledgments

Introduction: Galileo's Legacy, Life, and Works

Chronology of Galileo's Career and Aftermath

Glossary of Terms and Names

Annotated Bibliography and Cited Works

Chapter 1:
The Sidereal Messenger
(1610)

Chapter 2: From
Discourse on Bodies in Water
(1612)

§2.1 Shape vs. Density in Floating and Sinking

Chapter 3: From
History and Demonstrations Concerning Sunspots
(1613)

§3.1 Solar Rotation and Indifferent Motion

§3.2 Heavenly Changes and Aristotelian Empiricism

§3.3 Knowing Properties vs. Knowing Essences

Chapter 4: Letters on Copernicanism and Scripture (1613–15)

§4.1 Letter to Castelli (1613)

§4.2
Letter to the Grand Duchess Christina
(1615)

Chapter 5: Reply to Cardinal Bellarmine (1615)

§5.1 Cardinal Bellarmine's Letter to Foscarini

§5.2 Galileo's Considerations on the Copernican Opinion, Part I

§5.3 Galileo's Considerations on the Copernican Opinion, Part II

§5.4 Galileo's Considerations on the Copernican Opinion, Part III

Chapter 6: From the Earlier Trial-Documents (1615–16)

§6.1 Lorini's Complaint (7 February 1615)

§6.2 Caccini's Deposition (20 March 1615)

§6.3 Special Injunction (26 February 1616)

§6.4 Decree of the Index (5 March 1616)

§6.5 Cardinal Bellarmine's Certificate (26 May 1616)

Chapter 7: From
The Assayer
(1623)

§7.1 Comets, Tycho, and the Book of Nature in Mathematical Language

§7.2 Heat, Atoms, and Primary vs. Secondary Qualities

Chapter 8: From
Dialogue on the Two Chief World Systems
(1632)

§8.1 Preface: To the Discerning Reader

§8.2 Day II: Independent-mindedness and Aristotle's Authority

§8.3 Day II: Diurnal Rotation, Simplicity, and Probability

§8.4 Day II: The Case against Terrestrial Rotation, and the Value of Critical Reasoning

§8.5 Day II: Vertical Fall, Conservation of Motion, and the Role of Experiments

§8.6 Day III: Heliocentrism and the Role of the Telescope

§8.7 Day IV: The Cause of the Tides and the Inescapability of Error

§8.8 Day IV: Ending

Chapter 9: From the Later Trial-Documents (1632–33)

§9.1 Special Commission's Report on the
Dialogue
(September 1632)

§9.2 Galileo's First Deposition (12 April 1633)

§9.3 Galileo's Second Deposition (30 April 1633)

§9.4 Galileo's Third Deposition (10 May 1633)

§9.5 Galileo's Defense (10 May 1633)

§9.6 Galileo's Fourth Deposition (21 June 1633)

§9.7 Inquisition's Sentence (22 June 1633)

§9.8 Galileo's Abjuration (22 June 1633)

Chapter 10: From
Two New Sciences
(1638)

§10.1 Day I: The Problem of Scaling

§10.2 Day I: Critique of Aristotle's Law of Fall

§10.3 Day I: The Pendulum

§10.4 Day II: The Mathematics of Strength, Size, and Weight

§10.5 Day III: A New Science of Motion

§10.6 Day III: Definition of Uniform Acceleration

§10.7 Day III: Laws of Falling Bodies

§10.8 Day IV: The Parabolic Path of Projectiles

Preface and Acknowledgments

This is a collection of Galileo's most important writings, covering his entire career. Here the relevant concept of importance centers on their historical impact, and the history in question includes not only Galileo's life and the 17th century, but also the historical aftermath up to our own day. Moreover, the relevant historical impact is interdisciplinary in the sense that it affects the history of science (especially physics and astronomy), the philosophy of science (especially epistemology and scientific methodology), and general culture (especially the relationship between science and the Catholic Church, or more broadly science and religion).

In making the selections by applying such a criterion of importance, I consulted a number of scholars who provided valuable suggestions that reflected this and additional noteworthy criteria. Their names will be acknowledged below, and I hope they will easily see that I adopted many of their suggestions. I could not adopt literally all of their good suggestions, simply for lack of space. In fact, an important guiding principle has been that the resulting volume should be relatively small and inexpensive, in accordance with a time-tested formula provided by the publisher.

The translations are based on the text found in the National Edition of Galileo's collected works (Galilei 1890–1909). To facilitate references, the page numbers of that edition are reproduced here by placing the corresponding numerals in square brackets in the text. Similarly, I have added section numbers preceded by the section sign (§), in order to keep track of the various selections, to provide a more convenient means of cross-referencing, and to give to the text some structure that may serve as a guide for discussion. Additionally, section titles have been added, except within the two works that are included in their entirety (
The Sidereal Messenger
and the
Letter to the Grand Duchess Christina
), in which only section numbers are provided. Such section numbers and titles are bracketed when referring to passages from longer Galilean works, but they are not when referring to letters, trial documents, and self-contained essays.

For some of the translations I have revised works that are in the public domain. Others are taken from my own previously published translations. And a few have been newly made for this volume.

In particular, for
The Sidereal Messenger
(
Chapter 1
), I have revised the translation published by Edward Stafford Carlos in 1880. For the selection from
Discourse on Bodies in Water
(
Chapter 2
), I have revised the translation first published by Thomas Salusbury in 1665, and reprinted without revision by Stillman Drake (1960). For the selections from
Two New Sciences
(
Chapter 10
), I have revised the translation first published by Henry Crew and Alfonso De Salvio in 1914. With rare exceptions indicated in the notes, my revisions are usually made without comment. In this I was guided by the desire to improve accuracy and readability. For these Galilean works, it would have been ideal to reprint (with or without revisions) the excellent translations published, respectively, by Albert Van Helden (1989) and by Drake (1981) and (1974). However, copyright considerations made this ideal unfeasible. On the other hand, a beneficial byproduct of this practical necessity has been that the translations in this volume have greater linguistic and stylistic uniformity than they would otherwise have.

For the selections from
Dialogue on the Two Chief World Systems
,
Ptolemaic and Copernican
(
Chapter 8
), I have reprinted parts of the translation found in my
Galileo on the World Systems
(1997). Similarly, I have reprinted parts of my
Galileo Affair
(1989) for the following translations: the “Letters on Copernicanism and Scripture” (
Chapter 4
), the “Reply to Cardinal Bellarmine” (
Chapter 5
), the selections “From the Earlier Trial-Documents” (
Chapter 6
), and the selections “From the Later Trial-Documents” (
Chapter 9
). Such reprintings are almost completely verbatim, but they do contain a few corrections, which have been indicated in the notes.

The new translations are the selections from the
History and Demonstrations Concerning Sunspots
(
Chapter 3
) and from
The Assayer
(
Chapter 7
).

Needless to say, in all these cases, I have consulted and benefited from the translations already available in multiple languages, especially the following: for
The Sidereal Messenger
, the translations by Van Helden (1989), Lanzillotta (in Galilei 1953), Drake (1983), Pantin (1992), and Maria Timpanaro Cardini (in Galilei 1993); for the
Discourse on Bodies in Water
, the translation by Drake (1981); for the
History and Demonstrations Concerning Sunspots
, the translations by Drake (1957) and Reeves and Van Helden (forthcoming); for
Chapters 4
,
5
,
6
,
8
, and
9
, which come from my previously published books, the translations acknowledged in the prefaces to those works; for
The Assayer
, the translations by Arthur Danto (in Galilei 1954) and Drake and O'Malley (1960); and for the
Two New Sciences
, the translations by Drake (1974) and Adriano Carugo and Ludovico Geymonat (in Galilei 1958).

The notes, with very few exceptions, have been compiled especially for this volume, even when I was revising or reprinting previous translations. The reason is that some of those sources have too few annotations and some too many, and that in any case the notes had to be adopted for the present purpose. Thus, for example, since almost all terms and names requiring explanation occur in more than one selection, they are not explained in the notes but in the Glossary. A term or name is deemed as not requiring explanation when it is sufficiently explained or identified in the context of its occurrence (e.g., Lorini's name), or when it is commonly known or easily found in a small desk-dictionary (e.g., Archimedes, Aristotle, Copernicus, Euclid, Plato, Ptolemy, etc.). The few terms and names that occur only once (and that require explanation) are explained in notes at those places.

Finally, I would like to express thanks and acknowledgments to a number of people and institutions that helped in the creation of this book. Many scholars provided suggestions and encouragement: Mario Biagioli, Michele Camerota, Albert DiCanzio, Matthias Dorn, Paula Findlen, Owen Gingerich, Franco Giudice, André Goddu, W. Roy Laird, Ernan McMullin, David Miller, Ron Naylor, Margaret Osler, Paolo Palmieri, Michael Segre, Michael Shank, Robert Westman, and K. Brad Wray. The University of California Press granted me permission to reprint parts of my
Galileo Affair
and
Galileo on the World Systems
. The University of Nevada, Las Vegas, its Department of Philosophy, and my departmental colleagues have continued to provide institutional and moral support. And I thank Brian Rak, Editor at Hackett Publishing Company, for his initial and constant encouragement and for his continued patience.

Introduction

Galileo's Legacy, Life, and Works

Galileo's Legacy

[§0.1] Galileo Galilei was one of the founders of modern science. That is, science as we know it today emerged in the 16th and 17th centuries thanks to the discoveries, inventions, ideas, and activities of a group of people like Galileo that also included Nicolaus Copernicus, Johannes Kepler, René Descartes, Christiaan Huygens, and Isaac Newton. Frequently Galileo is singled out as the most pivotal of these founders and called the Father of Modern Science. Although many people have repeated or elaborated such a characterization, it is important that it originates in the judgment of practicing scientists themselves, such as Albert Einstein and Stephen Hawking.
¹
Thus, scientists and other educated persons ought to know something about Galileo's scientific achievements. One of the aims of this book is to make available in a single volume those Galilean writings that contain his most important contributions to physics and astronomy, for example: the law of inertia, and the laws of falling bodies, of the pendulum, and of projectile motion; the telescope; the mountains on the moon, the satellites of Jupiter, the phases of Venus, and sunspots; and the confirmation of the Copernican theory of the earth's motion.

Galileo is also a cultural icon and symbol because he was tried and condemned as a suspected heretic by the Catholic Church through its institution of the Inquisition. This tragedy, which some have labeled the greatest scandal in Christendom, continues to have repercussions after four centuries. For example, in the period 1979–92, Pope John Paul II undertook a highly-publicized rehabilitation of Galileo, which however turned out to be partial and to add more fuel to the controversy known as the Galileo affair. The point is that the trial of Galileo continues to fascinate scientists, churchmen, scholars, and laypersons alike, and everybody seems to find in it something to learn regarding the relationship between science and religion, between individual freedom and institutional authority, between scientific research and political power or social responsibility, and so on. Thus, once again, all educated persons ought to have some accurate and reliable information about the trial and condemnation of Galileo. And a second purpose of this book is to make easily available the most important of the relevant documents, which happen to have survived through an almost miraculous set of circumstances, that is, documents such as the charges and complaints against Galileo, the various depositions recorded during the proceedings, the Inquisition's official sentence that announced the verdict and condemnation, and the abjuration which he was required to recite.

Thirdly, the historical circumstances of Galileo's time and his own personal inclinations made Galileo into a kind of philosopher. Of course, he was not a systematic metaphysician who speculated about the eternal problems of being and nothingness. Instead he was a concrete-oriented and practical-oriented critical thinker like Socrates, with the difference that whereas Socrates dealt with moral or ethical questions of good and evil and the meaning of life, Galileo dealt with epistemological and methodological questions about the nature of truth and knowledge and the truth and knowledge of nature.
²
His contributions to scientific knowledge were so radical that he constantly had to discuss with his opponents (scientific as well as ecclesiastic) not only what the facts were and what their best theoretical interpretation was, but also what the proper rules for establishing the facts and for interpreting them were. With scientific opponents he had to discuss questions like these: whether artificial instruments like the telescope have a legitimate role in learning new truths about reality; whether authorities such as Aristotle should be relied upon to the exclusion of one's own independence of mind; whether mathematics has an important, and perhaps essential, role to play in the study of natural phenomena. With ecclesiastic opponents, Galileo had to discuss whether Scripture should be treated as a source of scientific information about physical reality; whether scientific theories that contradict the literal meaning of Scripture should be treated as mere hypotheses; whether hypotheses are potentially true descriptions of reality or merely convenient instruments of calculation and prediction; and so on. Thus, a third aim of this book is to collect the most important of these methodological and epistemological discussions, either from essays that contain relatively sustained arguments, or from passages that discuss primarily scientific issues but also offer the occasion for important philosophical clarifications.

Thus, Galileo's legacy clearly has a three-fold character, relating to science, philosophy, and culture.
³
However, this distinction ought not to be regarded as a separation. That is, this three-fold distinction reflects the various points of view which 21st-century readers can adopt toward Galileo and his writings and which can guide our assimilation of his legacy. The distinction does not reflect Galileo's own point of view and so is not something that guided his own thinking and activities. If we examine the latter, we find that the three aspects of his legacy were interwoven in various ways. The following sketch of Galileo's life and works gives us a glimpse at such interweaving, as well as a historical background to the selected writings collected here.

Galileo's Life and Works

[§0.2] Galileo was born in Pisa in 1564. His father Vincenzio was a musical practitioner and theorist who made a significant contribution to the theory of music, stressing the need to test the empirical accuracy of rules of harmony; he thus influenced Galileo's own empirical approach. In 1581 Galileo enrolled at the University of Pisa to study medicine but soon switched to mathematics, which he also studied privately outside the university. In 1585 he left the university without a degree and began several years of private teaching and independent research. In 1589 he was appointed professor of mathematics at the University of Pisa, and then from 1592 to 1610 at the University of Padua.

During this period, his research dealt primarily with the nature of motion in general and falling bodies in particular. His orientation was critical of Aristotelian physics and was fundamentally Archimedean; that is, he followed Archimedes' mathematical approach, accepted his physical principles of statics, and tried to build upon them for the analysis of how bodies move. In his study of falling bodies, Galileo became an ingenious, skillful, and indefatigable experimenter who pioneered the method of experimentation as a procedure involving the combination of empirical observation with both quantitative mathematization and conceptual theorizing. By this procedure he formulated, justified, and to some extent systematized such mechanical principles as the following: an approximation to the law of inertia; the composition of motion into component elements; the laws that in free fall the distance fallen increases as the square of the time elapsed and that the velocity acquired is directly proportional to the time; and the parabolic path of projectiles. However, he did not publish any of these individual results during that earlier period of his career; and indeed he did not publish a systematic account of them until 30 years later, in the
Two New Sciences
(Leiden, 1638).

[§0.3] A main reason for this delay was that beginning in 1609 Galileo became actively involved in astronomy. To be sure, he had been previously acquainted with the new theory of a moving earth published by Nicolaus Copernicus in 1543. He had been appreciative of the fact that Copernicus had advanced a novel argument supporting that ancient idea, namely, a detailed mathematical demonstration that the known facts about the motion of the heavenly bodies could be explained more systematically and coherently (not just more simply) if we attribute to the earth a daily axial rotation and an annual heliocentric revolution. Galileo had also acquired the general impression that this geokinetic theory was more consistent with the new physics he was researching than was the geostatic theory. In particular, he had also been attracted to Copernicanism because he thought that the earth's motion could best explain why the tides occur. But he had not articulated, let alone published, this general impression and this particular feeling.

On the other hand, Galileo had been acutely aware of the considerable evidence against Copernicanism. The earth's motion seemed epistemologically absurd because it contradicted direct sense experience. It seemed astronomically false because it had consequences that could not be observed, such as the similarity between terrestrial and heavenly bodies, Venus' phases, and annual stellar parallax. It seemed mechanically impossible because the available laws of motion implied that bodies on a rotating earth would, for example, follow a slanted rather than vertical path in free fall, and would be thrown off by centrifugal force. And it seemed theologically heretical because it contradicted the literal meaning and the traditional interpretation of some passages in the Bible. Until 1609 Galileo apparently judged that the anti-Copernican arguments far outweighed the pro-Copernican ones. Thus we find him teaching geostatic astronomy in his courses and reacting in a lukewarm and evasive manner when an enthusiastic Copernican like Johannes Kepler tried to engage him.

[§0.4] However, the telescopic discoveries that began in 1609 led Galileo to a major reassessment of Copernicanism, and so for the next seven years he was seriously and explicitly involved in astronomical research and discussions. In 1609 he perfected the telescope to such an extent as to make it an astronomically useful instrument that could not be duplicated by others for some time. By its means he made several startling discoveries, which he immediately published in
The Sidereal Messenger
(Venice, 1610): that the moon's surface is full of mountains and valleys; that innumerable other stars exist besides those visible with the naked eye; that the Milky Way and the nebulas are dense collections of large numbers of individual stars; and that the planet Jupiter has four moons revolving around it at different distances and with different periods. As a result, Galileo became a celebrity, resigned his professorship at Padua, was appointed Philosopher and Chief Mathematician to the grand duke of Tuscany, and moved to Florence the same year. Soon thereafter, he also discovered sunspots and the phases of Venus.

Although most of these discoveries were also made independently by other observers, no one understood their significance as well as Galileo. Their importance was threefold. Methodologically, the telescope implied a revolution in astronomy insofar at it was a new instrument that enabled the gathering of a new kind of data transcending the previous reliance on naked-eye observation. Substantively, those particular discoveries significantly strengthened the case in favor of the physical truth of Copernicanism by refuting almost all empirical astronomical objections and providing some new supporting observational evidence. Finally, this enhancement of the evidentiary solidity of Copernicanism was not equivalent to a settling of the issue or a conclusive establishment of its truth, for several reasons: there was still some astronomical counterevidence (e.g., the lack of annual stellar parallax); the criticism of the mechanical objections and the physics of a moving earth had not yet been articulated (although, as stated above, Galileo had been working on both projects); and the theological objections had not yet been dealt with. Thus, Galileo began to conceive of a work on the system of the world in which all these aspects of the question would be discussed. This synthesis of Galileo's astronomy, physics, and methodology was not to be published for another twenty years, until his
Dialogue on the Two Chief
World Systems, Ptolemaic and Copernican
(Florence, 1632).

This particular delay happened because Galileo got involved in several controversies over floating bodies, sunspots, the astronomical authority of Scripture, and comets. These discussions turned out to be fateful developments that had a drastic and permanent effect on the evolution of his life and career.

[§0.5] In July 1611, Galileo became involved in a controversy with some Tuscan Aristotelian philosophers over the behavior of solid bodies in water.
⁴
The occasion was provided by a casual remark Galileo made to the effect that ice is rarified water, since it floats in water, and hence it is lighter (in specific weight) than water. This was in accordance with the hydrostatic principles of Archimedes. But it contradicted the Aristotelian claim that ice is condensed water, and that it floats because its shape prevents it from overcoming the resistance of the water. The discussion soon turned to the cause of floating, sinking, and motion in water, and the relative role of shape and density. At one point, the Aristotelians introduced the allegedly crucial experiment that ebony wood sinks when shaped into a ball, but floats when shaped into a large thin flat plate; they regarded this experiment as a conclusive demonstration that shape, not specific weight, determines whether a body floats or sinks.

On more than one occasion, this discussion acquired the character of a formal debate. One of these debates took place at the house of Filippo Salviati, Galileo's Florentine friend whom he later immortalized as one the speakers in the
Dialogue
and
Two New Sciences
. Another debate occurred at the court of Grand Duke Cosimo II, in the presence of cardinals Ferdinando Gonzaga and Maffeo Barberini (1568–1644); the latter, who would become Pope Urban VIII in 1623, sided with Galileo. This sort of debate soon convinced Galileo that the philosophical discussion was degenerating into a competitive sport,
⁵
and so he decided to write down his thoughts. The result was the
Discourse on Bodies in Water
, which was published in the spring of 1612. However, rather than ending the controversy, this publication merely moved it into the print medium. In fact, within about a year four books against Galileo's
Bodies in Water
were published by various Aristotelians, including one by Lodovico delle Colombe, who was also criticizing Galileo's ideas on the motion of the earth. Finally, a lengthy reply to these critics was written jointly by Galileo and his disciple Benedetto Castelli, and published only under Castelli's name in the spring of 1615.