Galileo: The Starry Messenger, Letter to the Grand Duchess Christina, and Two New Sciences (First Day)

Summary

This volume gathers three works from the three stages of Galileo's career: the discoverer, the defender, and the old master of mechanics. The Starry Messenger (Sidereus Nuncius), printed at Venice in March 1610 and here read in Edward Stafford Carlos's 1880 English version, reports what Galileo saw through a telescope he had built and improved after hearing of a Dutch spyglass. He describes the Moon as mountainous and cratered, measuring the height of its peaks from the shadows they cast at the terminator, and explains the faint glow on its dark part as sunlight reflected from the Earth. He counts many more fixed stars than the eye can see in Orion's belt and the Pleiades, resolves the Milky Way and several nebulae into crowds of stars, and records night by night, from 7 January 1610, four small bodies circling Jupiter, which he names the Medicean Stars in honour of Cosimo II de' Medici. The Letter to the Grand Duchess Christina, written in 1615 and given here complete in Thomas Salusbury's 1661 translation with its original spelling, answers critics who used Scripture against the motion of the Earth. Galileo argues that Scripture cannot err but its interpreters can; that the Bible speaks of nature in terms suited to ordinary people; that God has given human beings sense and reason to learn what can be learned by them; and that, where a natural conclusion is demonstrated, the true sense of Scripture will agree with it. He draws repeatedly on Augustine and quotes the saying of a churchman, traditionally identified with Cardinal Baronius, that the Holy Spirit teaches how to go to heaven, not how the heavens go. The selection closes with the First Day of the Two New Sciences (Leiden, 1638), in Henry Crew and Alfonso de Salvio's 1914 translation, from an OCR text with the diagrams omitted. Three friends, Salviati, Sagredo and Simplicio, meet at the Venetian Arsenal and range over why large structures are weaker in proportion than small ones, the cohesion of solids and the resistance of the vacuum, the puzzles of infinity and indivisibles, a proposed test of the speed of light with lanterns, the fall of heavy and light bodies through air and water, the pendulum, and the ratios of musical consonance. Galileo's alter ego Salviati argues that in a medium without resistance all bodies would fall with the same speed. Read together, the three pieces show observation, argument about the relation of Scripture to nature, and mathematical physics in one mind.

Plot or Argument

• The Starry Messenger: the telescope and the Moon

  Galileo explains how he came to make a telescope magnifying about thirty times in diameter and how to test one. He then describes the Moon as rough and uneven, like the Earth, with mountains whose shadows shift as the terminator moves; he estimates their height and accounts for the secondary light of the dark Moon as earthshine.

• The Starry Messenger: fixed stars, Milky Way and nebulae

  The telescope shows the fixed stars as points without the enlargement given to planets, and reveals many more of them. Galileo maps additional stars in Orion's belt and sword and in the Pleiades, and reports that the Milky Way and the nebulae of Orion and Praesepe are clusters of small stars.

• The Starry Messenger: the Medicean Stars

  In the longest section Galileo records his nightly observations of Jupiter from 7 January to early March 1610, showing four companions that change position from side to side. He concludes that they revolve around Jupiter and notes that this removes an objection to Copernicus: if Jupiter can carry moons as it travels, so can the Earth.

• Letter to Christina: the occasion

  Galileo tells the Grand Duchess that his discoveries have stirred up professors of the received philosophy, who now try to turn Scripture and the pulpit against him. He protests his submission to the Church and says his aim is to offer whatever may help it decide the Copernican question wisely.

• Letter to Christina: Scripture and natural knowledge

  Scripture cannot lie when its true meaning is understood, but that meaning often differs from the bare sound of the words, which are fitted to the capacity of common people. God who gave human beings sense and reason does not intend them to set these aside in natural questions that can be settled by experience and demonstration, especially in astronomy, of which Scripture says little.

• Letter to Christina: the Fathers and the limits of interpretation

  Galileo gathers passages from Augustine counselling caution in obscure natural questions and warning Christians not to expose the faith to ridicule. He argues that the agreement of the Fathers binds only in matters of faith and morals, that condemning Copernicus without examination would be imprudent, and that Joshua's command to the Sun can be read in harmony with a Copernican cosmos.

• Two New Sciences, First Day: scale and the strength of materials

  At the Arsenal of Venice, Salviati explains why a large machine built in the same proportions as a small one is weaker, telling the story of a marble column that broke over a third support meant to protect it. He then asks what holds solids together, distinguishing fibres from the resistance of the vacuum, and notes that a suction pump cannot raise water more than about eighteen cubits.

• Two New Sciences, First Day: the infinite and the indivisible

  Through the paradox of Aristotle's wheel and the comparison of all numbers with their squares, Salviati argues that terms like greater, equal and less do not apply to infinite quantities. He speculates about indivisible parts in matter, discusses the melting of metals by fire, and proposes a lantern experiment to test whether light travels instantaneously.

• Two New Sciences, First Day: falling bodies, the pendulum and music

  Salviati answers Aristotle's claim that heavier bodies fall faster in proportion to their weight, using a thought experiment of two tied stones, and argues that differences in fall come from the resistance of the medium. The day closes with the equal times of a pendulum's swings, resonance, and the explanation of consonance by the frequencies of vibrating strings.

Characters

• Galileo Galilei, author and observer

  Mathematician of Padua and then Florence who reports his telescopic discoveries and writes the Letter in his own voice.

• Christina of Lorraine, addressee

  Grand Duchess of Tuscany, mother of Cosimo II, who had raised scriptural objections to the Earth's motion at a court breakfast in 1613.

• Cosimo II de' Medici, patron

  Grand Duke of Tuscany, to whom The Starry Messenger is dedicated and after whose family the moons of Jupiter are named.

• Salviati, speaker

  Florentine nobleman in the Two New Sciences who speaks for Galileo's views and leads the discussion.

• Sagredo, speaker

  Venetian gentleman of quick intelligence who asks probing questions and often reports his own tests.

• Simplicio, speaker

  Defender of Aristotle who raises the traditional objections, often in good faith.

• Augustine of Hippo, authority cited

  Church Father whose counsel on caution in natural questions Galileo quotes throughout the Letter.

• Nicolaus Copernicus, authority discussed

  Astronomer whose sun-centred system the Letter asks the Church not to condemn without examination.

Lessons

• Look, record, and let others look

  The Starry Messenger is built on dated, repeated observations, with drawings and instructions so that others can check them. Galileo's claims about Jupiter's moons rest on weeks of watching their positions change. The work shows how a discovery becomes public knowledge.

  • Why does Galileo give the date and hour of so many observations of Jupiter?
  • What does he tell readers about testing a telescope before trusting it?
  • What would have made a reader in 1610 believe or doubt his report?

• Two books from one Author

  In the Letter Galileo insists that Scripture and nature both come from God and cannot finally contradict each other. Conflicts arise from misreading one or the other. He asks interpreters to distinguish what Scripture teaches for salvation from how it speaks of nature in ordinary language.

  • How does Galileo use Augustine to support caution in interpreting Scripture on natural questions?
  • What does he mean when he says Scripture was accommodated to the capacity of the common people?
  • Which questions, in his view, belong to theologians and which to astronomers?

• Argument as well as experiment

  In the First Day Salviati refutes Aristotle on falling bodies first by reasoning: if a heavy stone is tied to a light one, the light one should both slow and speed the pair. Only then does he turn to experience. Galileo shows that a clear thought experiment can expose a contradiction in a long-held view.

  • Explain the tied-stones argument in your own words.
  • Why does Salviati say the remaining difference of two finger-breadths does not save Aristotle's claim?
  • When is a thought experiment enough, and when must one actually drop the balls?

• Wonder at the large and the small

  The First Day moves from cathedral-sized columns to the infinitely small, from the scaling of giants to the paradoxes of number. Galileo's characters treat these puzzles with delight and patience. The dialogue form lets doubt and objection play their part in learning.

  • Why can't a giant be built like a man only larger, according to Salviati?
  • What is surprising about comparing all numbers with all square numbers?
  • What does Simplicio contribute to the conversation, even when he is mistaken?

Context

Galileo worked in an Italy where natural philosophy in the universities followed Aristotle and where astronomy commonly used Ptolemy's geocentric models, while Copernicus's De revolutionibus (1543) offered a sun-centred alternative and Tycho Brahe a compromise system. After the Council of Trent the Catholic Church had reserved to itself the authoritative interpretation of Scripture. The telescope, known in the Netherlands in 1608, gave Galileo new evidence, and his discoveries brought him the patronage of the Medici court in Florence.

Composition

The Starry Messenger was written quickly in Latin and published at Venice in March 1610. The Letter to the Grand Duchess Christina, an expansion of a 1613 letter to his former student Benedetto Castelli, was written in 1615 and circulated in manuscript; it was first printed in 1636 at Strasbourg, in Italian with a Latin translation. Cardinal Robert Bellarmine, in an April 1615 letter to Paolo Antonio Foscarini, held that Copernicanism might be used as a mathematical hypothesis, that a real demonstration of the Earth's motion would require Scripture to be reinterpreted with great care, but that no such demonstration had been given. In 1616 the Congregation of the Index suspended Copernicus's book until corrected, and Bellarmine instructed Galileo not to hold or defend the doctrine. After his Dialogue of 1632 Galileo was tried in 1633, abjured, and was confined to his villa at Arcetri, where he finished the Two New Sciences, printed by the Elzevirs at Leiden in 1638.

Reception

The Starry Messenger made Galileo famous across Europe within months, and Kepler answered it in his Dissertatio cum Nuncio Sidereo (1610). Historians differ on how to weigh the theological, philosophical, personal and political causes of the conflict of 1616 and 1633; some stress Galileo's lack of a conclusive proof of the Earth's motion at the time, others the Church's caution after the Reformation, others the tensions of his own manner and the pope's displeasure over the Dialogue. Salusbury's 1661 English translations are said to have survived in few copies, a scarcity often linked to the Great Fire of London. The Two New Sciences laid foundations for the mechanics of materials and of motion taken up by Huygens and Newton. In 1992, after a commission's study, Pope John Paul II spoke publicly about the case, acknowledging errors by the theologians of Galileo's day.

Comparisons

• copernicus-on-the-revolutions

  The Letter defends the Copernican system that Copernicus set out in 1543, and the moons of Jupiter answer one objection to a moving Earth.

• ptolemy-almagest

  The geocentric system Galileo's discoveries challenged; the phases of Venus and the moons of Jupiter did not fit Ptolemy's arrangement of the planets.

• kepler-new-astronomy-and-harmony-of-the-world

  Kepler, Galileo's contemporary and correspondent, welcomed The Starry Messenger and gave Copernicanism elliptical orbits that Galileo never adopted.

• aristotle-posterior-analytics-and-physics

  Simplicio defends Aristotle's account of falling bodies and the impossibility of a vacuum from the Physics; the First Day answers both.

• principia

  Newton built on Galileo's law of fall and treatment of motion, uniting terrestrial mechanics with the heavens Galileo had observed.

• kuhn-the-structure-of-scientific-revolutions

  Kuhn treats the Copernican change and Galileo's pendulum as classic cases of a shift in how scientists see their problems.

Quotes

For Students

A reading companion for classical Christian high school students. See the student guide.

Reading Guide

Watch for

• The dated log of Jupiter's companions in The Starry Messenger, and the night Galileo realizes they are moving with Jupiter rather than being left behind.
• How Galileo measures the height of lunar mountains from the length of their shadows near the boundary of light and dark.
• In the Letter, the turn from his critics' premise (Scripture cannot err) to his own point (its true meaning is often hard to find).
• The many quotations from Augustine in the Letter, and what each is used to prove.
• In the First Day, Salviati's tied-stones argument against Aristotle and Sagredo's report of dropping a cannon ball and a musket ball.

Key terms and names

Medicean Stars

Galileo's name for the four moons of Jupiter, honouring Cosimo II de' Medici and his brothers; today they are called the Galilean satellites.

Terminator

The line dividing the lit and dark parts of the Moon; the points of light just beyond it convinced Galileo that he was seeing sunlit mountain peaks.

Accommodation

The principle, used in the Letter, that Scripture speaks of nature in language fitted to the understanding of ordinary people rather than in technical terms.

De Fide

A matter of faith that Catholics are bound to believe; Galileo argues that the arrangement of the heavens is not such a matter.

Necessary demonstration

A proof that compels assent, as in geometry; the Letter contrasts it with probable reasons and bare narration.

Simplicio

The Aristotelian speaker in the Two New Sciences, named after the ancient commentator Simplicius, who voices the traditional objections.

Resistance of the vacuum

Salviati's name in the First Day for the force that holds smooth surfaces together and limits a suction pump to about eighteen cubits.

Seminar Questions

1. Comprehension What four discoveries does Galileo report in The Starry Messenger, and which does he treat as most important?
2. Comprehension In the Letter, why does Galileo say Scripture often speaks of God as having hands, feet and anger, and what does this show about how it speaks of the heavens?
3. Comprehension In the First Day, how does Salviati show that a heavier stone cannot fall faster simply because it is heavier?
4. Interpretation Galileo quotes the saying that the Holy Spirit teaches how to go to heaven, not how the heavens go. How far does this principle settle the question, and what questions does it leave open?
5. Interpretation Bellarmine held that Scripture should be reinterpreted only if the Earth's motion were truly demonstrated. Does the Letter offer such a demonstration, or does it argue for something else?
6. Interpretation Why might Galileo have chosen a dialogue among three friends for the Two New Sciences rather than a treatise in his own voice?
7. Big Question If two truths can never contradict each other, what should a believer do when a scientific claim and a reading of Scripture seem to clash?

Faith Connections

• Joshua 10:12-14 (Scripture)

  The Sun standing still over Gibeon was the passage most often cited against the Earth's motion. Galileo argues near the end of the Letter that it can be read in harmony with the Copernican system, while his critics read it plainly.

• Psalm 19:1-6 (Scripture)

  The heavens declare the glory of God, and the Sun goes forth like a bridegroom. The psalm supports Galileo's theme that God is read in the book of the heavens, and its imagery was also cited for the Sun's motion.

• Augustine, The Literal Meaning of Genesis I.19 (Church Fathers)

  Augustine warns that Christians who speak foolishly about the heavens and the earth bring the faith into contempt among those who know these things by reason and experience. Galileo builds much of the Letter on this caution.

• Robert Bellarmine, Letter to Paolo Antonio Foscarini (12 April 1615) (Great Conversation)

  Bellarmine agreed that a true demonstration would require careful reinterpretation of Scripture but judged that none had been given, and asked that Copernicanism be treated as a hypothesis. Reading it beside the Letter shows how much the two men shared and where they parted.

Logic and Rhetoric

Central argument: Scripture and nature both come from God, so a true reading of one cannot contradict a true finding in the other. Scripture speaks of nature in terms fitted to common understanding and was given chiefly to teach salvation. God gave human beings sense and reason to learn natural truths that experience and demonstration can reach. Therefore, in natural questions such as the arrangement of the heavens, theologians should not condemn conclusions on the basis of the literal sound of a text, and where a conclusion is demonstrated, Scripture must be interpreted to agree with it.

Rhetorical device: concession (concessio). In the Letter Galileo first grants his opponents' principle that the Sacred Scripture can never lie when its true meaning is understood (quotes[2]), and then builds his whole case on the qualifying clause about its true meaning.

Debate: Resolved: That in 1615 the Church's call for a conclusive demonstration before reinterpreting Scripture was a reasonable standard.

Memory Work

That the intention of the Holy Ghost, is to teach us how we shall go to Heaven, and not how Heaven goeth.

for two truths can never contradict each other.

Writing Prompts

Essay: Galileo says that God who gave us sense and reason does not intend us to set them aside in natural questions. Explain how this claim, together with the principle of accommodation, shapes his reading of Scripture in the Letter to the Grand Duchess Christina, and evaluate the strongest objection a theologian of 1615 such as Bellarmine could raise.

Comparison with On the Revolutions of the Heavenly Spheres: Copernicus dedicated his book to Pope Paul III and warned that those ignorant of mathematics might twist Scripture against it; Galileo quotes that preface in the Letter. Compare how each author presents the relation between astronomy and Scripture, and argue which strategy was more prudent.

Medical Lens

Galileo began as a medical student at Pisa in 1581 before turning to mathematics, and his father wished him to become a physician. The works here are not medical, but the First Day measures short intervals by pulse-beats, a reminder that the pulse was the ordinary clock of the period; tradition (not the text) links Galileo's early pendulum observations to the pulsilogium that his Paduan colleague Santorio Santorio used to time the pulse. The closing discussion of consonance explains hearing as the regular striking of air waves on the tympanum, an early physical account of the ear.

• Two New Sciences, First Day, on fall through water and air

  Salviati times the descent of bodies through air and water in pulse-beats, using the pulse as a unit of time.

  Physicians Doctors
• Two New Sciences, First Day, closing discussion of consonance

  Musical intervals are explained by the number of air pulses striking the eardrum in a given time.

Creative Prompts

• Dialogue

  Write a conversation in 1615 between Galileo and Cardinal Bellarmine about what would count as a true demonstration of the Earth's motion, letting each make his strongest case.

• Classroom

  Have students keep a two-week observing log of the Moon or Jupiter with binoculars, sketching positions with date and hour as Galileo did, and compare their drawings with his.

• Essay

  Explain how Galileo uses Augustine in the Letter to the Grand Duchess Christina, and assess whether his reading of Augustine's caution is faithful to the passages he quotes.

• Classroom

  Drop two balls of the same size but different weights from the same height, then a ball and a sheet of paper, and use the results to reconstruct Salviati's argument about the resistance of the medium.

Further Reading

• Dialogue Concerning the Two Chief World Systems, Galileo Galilei, trans. Stillman Drake

• The Galileo Affair: A Documentary History, Maurice A. Finocchiaro (ed.)

  Translations of the Letter to Castelli, Bellarmine's letter to Foscarini, the 1616 and 1633 documents.

• Galileo at Work: His Scientific Biography, Stillman Drake

• Galileo's Daughter, Dava Sobel

• The Literal Meaning of Genesis, Augustine of Hippo

  The source of several passages Galileo quotes in the Letter.