Five-minute digest
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.
Top 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.
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.
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.
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.
Verified Quotes
“the Moon certainly does not possess a smooth and polished surface, but one rough and uneven, and, just like the face of the Earth itself, is everywhere full of vast protuberances, deep chasms, and sinuosities.”
“the Galaxy is nothing else but a mass of innumerable stars planted together in clusters.”
“That it is both piously spoken, and prudently affirmed, That the Sacred Scripture can never lye, when ever its true meaning is understood”
“That the intention of the Holy Ghost, is to teach us how we shall go to Heaven, and not how Heaven goeth.”
“But that that self same God who hath indued us with Senses, Discourse, and Understanding hath intended, laying aside the use of these, to give the knowledg of those things by other means, which we may attain by these”
“for two truths can never contradict each other.”
“Aristotle says that "an iron ball of one hundred pounds falling from a height of one hundred cubits reaches the ground before a one-pound ball has fallen a single cubit." I say that they arrive at the same time.”
“Having observed this I came to the conclusion that in a medium totally devoid of resistance all bodies would fall with the same speed.”
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.
- 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.