For details of the standard edition of Galileo’s works see the Note on the Text and Translation, p. xxx. This edition is referred to in the notes below as Opere, followed by volume and page number.
A SIDEREAL MESSAGE
[Title-page]: the Latin that Galileo uses is nuncius, that can stand for either messenger or message, but Galileo clearly intended the latter. See Edward Rosen, ‘The Title of Galileo’s Sidereus Nuncius’, Isis, 41 (1950), 287-9.
patrician: used here in the sense of member of the nobility.
recently discovered by him: Galileo recognized the priority of the Dutch but he insisted that he had not been informed of the way they made their telescope. See the Introduction, p. xii.
planets: Galileo uses the word planetae to describe the four celestial bodies that we call satellites.
Medicean Stars: Galileo had toyed with the idea of calling the satellites Cosmici, which would have enabled him to dedicate them exclusively to Cosimo II, and to pun on the semantic ambiguity between Cosmo (the name of the Grand Duke Cosimo II in Latin) and ‘cosmic’. But since the Grand Duke had three brothers, he had also considered calling them ‘Medicean’ to honour the whole family. On 13 February 1610 he wrote to the Grand Duke’s Secretary of State, Belisario Vinta, to ask his advice (Opere, 10, p. 283). Vinta answered on 20 February that the second title was more appropriate since cosmici could be interpreted in different ways while ‘Medicean’ was unequivocal (Opere, 10, pp. 284-5). But without waiting for Vinta’s reply, Galileo had already rushed into print with a title-page bearing ‘Cosmica Sidera’. When Vinta’s letter arrived and he realized that he had made the wrong choice, Galileo had slips of paper with the word Medicea pasted over the word Cosmica. The correction has not been found in all copies, however, and this confirms that the substitution was only made when the book was in press.
Fourth Grand Duke of Tuscany: the first Medici to bear the title of Grand Duke was Cosimo I, who reigned from 1570 to 1574. He was succeeded by his eldest son, Francesco I, who had no heir and was followed by his brother Ferdinando I, who died on 3 February 1609, when Cosimo II (12 May 1590-28 February 1621) became the Fourth Grand Duke.
columns and pyramids … as the poet says: Galileo has in mind, ‘The pyramids reared to the stars, at such expense’, a line from the Elegies of Sextus Propertius, a Roman poet who lived in the latter half of the first century BC (Elegies, 3.2, verse 19). The verse recalls a passage from the Odes of his contemporary, Horace, quoted in the next note below.
imperishable monuments of literature: the Latin poet Horace wrote in his Odes, 3.30, verses 1-5: ‘I have finished a monument more lasting than bronze and loftier than the Pyramids’ royal pile, one that cannot be destroyed by wasting rain, furious north wind, or the endless passing of years and the swift flight of time.’
inscribed on the … orbs: in traditional astronomy the stars and the planets were said to be carried round by the crystalline spheres in which they were embedded like diamonds in a ring. As a name can be inscribed on a ring, so poets imagined that the names of gods and heroes could be engraved on the surface of the spheres.
introduce Julius Caesar into their company: Suetonius, the second-century AD historian, writes in his Lives of the Caesars (’The Deified Julius’, ch. 88): ‘at the first of the games that Augustus gave in honour of his apotheosis, a comet (stella crinita) shone for seven successive days … and was believed to be the soul of Caesar, who had been taken to heaven’. Ovid in his Metamorphoses, 15.843-50, had described how Venus caught up the passing soul of Caesar and bore it towards the stars of heaven. When she released it, it rose higher than the Moon and, leaving behind a hairy train, gleamed like a star. Both the Greek cometes and the Latin crinitus mean ‘hairy’.
noblest of the planets: in traditional mythology Jupiter is the king of the heavens (Ovid, Metamorphoses, 15. 858-9). Placed between Mars, a ‘hot-tempered’ and warlike planet, and Saturn, a ‘cold’ and contemplative one, Jupiter represented for astrologers the source of just and temperate behaviour, and had been linked to the fortunes of the Medici family by Cosimo I, the grandfather of Cosimo II.
the Sun itself: this is Galileo’s first public commitment to the view that the centre of the world is not the Earth, as Aristotle and Ptolemy believed, but the Sun.
twelve years: the time it takes for Jupiter to complete one revolution around the Sun is 11 years and 315 days.
the Creator of the stars … himself: Galileo not only repeatedly declared that his celestial discoveries had been inspired, he went as far as claiming that God had personally chosen him to be ‘the first and only one’ to make all those that were rendered possible by the telescope, as he wrote to Belisario Vinta on 30 January 1610 (Opere, 10, p. 280).
in preference to all others: princes elsewhere soon became interested in having their names hoisted into the heavens. King Henry IV of France had married Maria de’ Medici, a cousin of the Grand Duke Cosimo II, and from Paris came, with the promise of a generous reward, the request that Galileo call ‘Henry’ the next celestial body he discovered (letter of 20 April 1610 quoted in Galileo’s letter of 25 June to Vincenzo Giugni, Opere, 10, p. 381). The French astronomer, Jean Tarde, in his haste to ingratiate himself with the king of France, dedicated the sunspots (which he assumed were satellites) to the reigning Bourbon family. Not to be outdone, his competitor, the Jesuit Karl Malapert, dedicated the same sunspots to the reigning house of Austria.
Jupiter: the basic textbook of astrology in use in Galileo’s time was written by the astronomer Claudius Ptolemy who lived in Alexandria in the second century AD. Here is what he says about the influence of Jupiter: ‘He makes those who are subjected to his influence magnanimous, generous, god-fearing, honorable, agreeable, kind, magnificent, liberal, just, high-minded, dignified, mindful of their own business, compassionate, good conversationalists, beneficent, affectionate, and with qualities of leadership’ (translation, slightly emended, by W. G. Waddell and F. E. Robbins in Manetho, Ptolemy, Loeb Classical Library (Cambridge, Mass.: Harvard University Press, 1971), 347).
mid-heaven … eastern angle: the mid-heaven lies at the intersection of the ecliptic and the meridian. The eastern angle is situated at the intersection of the ecliptic and the eastern horizon. When drawing a horoscope it is important to know what celestial body was rising in the east at the moment of birth. Cosimo II was born, according to his birth record in the Archives in Florence, ‘on the first hour of the night of 12 May 1590, and was baptized by Cardinal Alessandro de’ Medici, Archbishop of Florence’, the future Pope Leo XI. It was customary in Galileo’s day to indicate hours beginning with sunset. On 12 May 1590 the Sun set over Florence at 19.13 hours local mean time. Given that the birth occurred at one hour after sunset this means that he was born around 20.13 hours.
to teach your Highness mathematics: in 1605 Galileo was invited to teach Cosimo, who was then 15 years old, on the use of the geometrical and military compass that he had recently perfected. He spent the summer at the Tuscan court that year and he returned again to coach the young prince in 1606 and 1608.
Council of Ten: in Venice the Council of Ten, which was responsible for internal security including the police force and censorship, was elected for a period of one year by the Great Council, which comprised all male patricians who were over 25 years old.
Overseers: the Governing Board of the University of Padua was composed of three Overseers (Riformatori in Italian), who were chosen among the members of the Venetian Great Council and appointed for a period of two years.
Sidereal Message, etc.: the original of the report, dated 26 February 1610, that was sent by the Overseers of the University to the Council of Ten, bore the title ‘An Astronomical Announcement to Astronomers’ (Astronomica Denuntiatio ad Astrologos, in Opere, 19, pp. 227-8). In Latin astrologus was often used in the broad sense of astronomus probably because professional astronomers saw casting horoscopes as part of their job. Galileo substituted Astronomica Denuntiatio, first by ‘Astronomical Message’ (Astronomicus Nuncius), and then by ‘Sidereal Message’ (Sidereus Nuncius).
Lunardo Marcello: the original of the report of the Overseers has Lunardo Mocenigo not Lunardo Marcello (Opere, 19, p. 228).
cosmic stars: this title of the work, as it appears here on the inside, bears the early form Astronomical Message, which was replaced by Sidereal Message on the cover. We also find ‘cosmic stars’ instead of ‘Medicean stars’ for the reason explained above in the note to p. 1.
more than ten times as numerous … familiar: before Galileo the standard number was the one given in Ptolemy’s Almagest written in the second century AD, where we find the position and magnitude of 1,022 stars. In Galileo’s own day the Danish astronomer, Tycho Brahe (1546-1601), had published a list of 777 stars in 1592, which he later increased in some haste in order to offer to his patron, the emperor Rudolph II, a catalogue of 1,000 stars.
sixty terrestrial diameters: Galileo wrote diameters when what is meant are radii, namely semi-diameters. That this is not a mathematical error but a peculiar linguistic usage is clear from the way he consistently uses diameter for radius in a letter dated 7 January 1610 (Opere, 10, p. 273, line 4, and p. 277, line 124). When Galileo intended diameter, he used the expression ‘the whole diameter’, as we find when he speaks of the Moon. In the Dialogue on the Two Chief World Systems, however, he gave the distance of the Moon from the Earth as ‘56 times the semi-diameter of the Earth’ (see p. 287 below).
two diameters away: in August 1609 Galileo had an instrument that magnified nine times (letter to Doge Leonardo Donato, 24 August 1609, Opere, 10, p. 250, lines 10-11). By January 1610 he had one that magnified twenty times, and he claimed that he would soon be able to increase that power to thirty (letter to Antonio de’ Medici, 7 January 1610, Opere, 10, pp. 273, 277).
thirty times … with the naked eye: when the linear or transverse magnification is thirty, an object appears thirty times closer, its surface is 302, namely 900 times greater, and its volume is 303, namely 27,000 times bigger. Galileo gives the increment of magnification not only for the distance but also for the surface and the volume, something that may not be very useful but it allowed him to mention the sensational increases from thirty to 900 to 27,000.
wandering stars: the planets were called wandering stars to distinguish them from the ‘fixed’ stars that rotate every twenty-four hours but do not change position relative to each other.
never stray beyond certain limits: in Ptolemy’s system, the orbits or spheres (called deferents) of Mercury and Venus revolve around the Sun, but the two planets themselves revolve on epicycles that are attached to their deferents in such a way that they always rise or set a little ahead or a little after the Sun. An alternative system was constructed by Heraclides of Pontus (fourth century BC) in which Mercury and Venus travel around the Sun, and it is probably this model that Galileo had in mind. By the end of January 1610 Galileo had convinced himself that the satellites of Jupiter were not carried by epicycles but had ‘their own proper and particular movements’ around Jupiter in the same way as Venus and Mercury, ‘and perhaps the other known planets, go around the Sun’ (letter of 30 January 1610 to Vinta, Opere, 10, p. 280).
About ten months ago: in the manuscript of the Sidereal Message that he had started writing halfway through January 1610, Galileo had written ‘about eight months ago’ (Opere, 3, folio 18). Taken literally this would mean that he heard about the telescope in May 1609, but in an earlier letter dated 29 August 1609, Galileo had told his brother-in-law, Benedetto Landucci, that ‘about two months ago the rumour was spread here that in Flanders a spyglass (occhiale) had been given to Count Maurice’ (Opere, 10, p. 253). This would indicate June or early July as the time when the news reached him.
Jacques Badouère: (also written Badouer, Badovere, or Badoire), the son of a wealthy French Protestant, who studied at the University of Padua between 1598 and 1599 and was a paying guest in Galileo’s house during most of that time.
sixty times bigger: if the telescope enlarged the area more than sixty times, it had a magnification power of about eight times, and it must be the one that Galileo presented to the Doge on 24 August 1609 (Opere, 10, p. 250).
two terrestrial diameters away: two diameters stand here for two semi-diameters, i.e. two earth-radii. See the note to p. 7 above.
the rays are carried … ECF and EDG: Galileo considers the rays as coming from the eye.
only a few minutes of an arc: ‘object FG’ is the field of vision of the tube without the lenses, and ‘object HI’ the field of vision that is observed when the lenses are inserted. The visual angle (CED) is the same in both cases since HI is seen with the telescope under the same angle as was FG with the naked eye. If the procedure with the sheets of different sizes is carried out, the ratio of these two fields of vision will be known. But how can we determine the distance HI? The difficulty is that the tube, as it is drawn, does not give us the focal length of the objective lens or the eyepiece. Galileo realized that varying the size of the aperture of the objective lens produced a change in the field of view but he did not work out the ratio.
we shall provide … instrument: Galileo never got around to it because he could not work out the optical properties of his telescope in spite of urgent requests from friends, notably Sagredo (e.g. letters of Sagredo to Galileo of 2 June, 30 June, and 7 July 1612, Opere, 11, pp. 315, 349-50, 356). Writing from Rimini on 13 September 1616, six years after the publication of the Sidereal Message, Malatesta Porta voiced his disappointment: ‘How long will you keep us on tenterhooks? You promised in your Sidereal Message to let us know how to make a telescope so that we could see all the things that are invisible to the naked eye, and you haven’t done it to the present day’ (Opere, 12, p. 281).
a certain spot… region of the Moon: the large spot meant here is not the circular one discussed below but an irregular area near the top that crosses the boundary between light and darkness at first and last quarter as shown in the figure.
they present themselves… unbroken line: Galileo’s argument is cogent for a telescope that only magnifies twenty times, but with modern instruments the unevenness of the Moon’s rim can easily be observed. Most lunar mountains are less than 6,000 metres (4 Italian miles; see note to p. 19), but the highest ranges happen to be close to the rim. Mt Leibniz on the southern limb rises to 9,000 metres.
aether: aether for the ancients and up to the time of Galileo was the material out of which celestial bodies were made. It was considered perfect and unchangeable in contrast to the four terrestrial elements of earth, water, air, and fire. Hence the belief, mentioned below on p. 23, that the Earth is the refuse of the world.
7,000 Italian miles: the Italian mile, which is also called the Roman mile, is approximately 1.5 km or 0.93 English mile. So 7,000 such miles give 10,500 km for the diameter of the Earth, which is roughly 18% off the correct value of 12,756 km for the diameter at the equator.
the sum of the squares … 1,010,000: Galileo is applying the well-known Pythagorean theorem to the right-angle triangle DCE so that we have (DE)2 = (DC)2 + (CE)2.
even 1 mile high: at 8,850 metres Mt Everest is approximately six times higher than Galileo’s estimate for the highest mountain on the Moon. In his day the heights of mountains on Earth could not be determined accurately, and widely diverging values were produced.
The System of the World: Galileo wanted to call the book On the System of the World as he told Belisario Vinta, the Grand Duke’s Secretary of State, in a letter of 7 May 1610 (Opere, 10, p. 351), but he later changed this to Dialogue on the Tides, to emphasize his physical proof for the motion of the Earth. When the censors objected to this title, he altered it to Dialogue on the Two Chief World Systems.
so childish … answer: this is a harsh indictment of the idea that Venus might be responsible for the Moon’s secondary light. In the Dialogue on the Two Chief World Systems Galileo rejects the suggestion with equally strong language and calls it a ‘vain idea’ (vanità) (Opere, 7, p. 116; see p. 216 in this volume).
permeating … the solid body of the Moon: the theory that the secondary light of the Moon is caused by sunlight rested on the assumption that the lunar globe is partly translucent, and that when it is exposed to the rays of the Sun it soaks up this light, so to speak.
ecliptic: the apparent path that the Sun traces out in the sky during the year. The Moon crosses it about twice per month. If this happens during new moon a solar eclipse occurs; if during full moon a lunar eclipse.
will be considered more fully: in the First Day of the Dialogue on the Two Chief World Systems Galileo discusses the Moon at length (Opere, 7, pp. 85-126; pp. 183-226 in this volume).
round of stars: Galileo’s phrase stellarum corea (literally ‘dance of stars’) is rendered by ‘round of stars’ to convey his conviction that the Earth formed part of the harmonious dance of the stars and the planets that go round and round.
surpasses the Moon in brightness: ‘The Earth’, writes Galileo in the Dialogue on the Two Chief World Systems, ‘repays the debt when the Moon needs it most, reflecting the Sun’s rays to give it a very strong light, which I reckon must exceed the light which the Earth receives from the Moon by the same amount as the Earth’s surface is larger than the Moon’s’ (Opere, 7, p. 92; pp. 189-90 below).
a thousand physical arguments: where we would use a vaguer expression such as ‘a very large number’, Galileo writes ‘six hundred physical arguments’ which I have rendered by ‘a thousand’.
four or five times greater: as Galileo had mentioned earlier, when a telescope (in this case his best) has a linear magnification of thirty, objects appear thirty times closer, their area is increased by 302, and their volume by 303. See the note to p. 7 above. Here he refers to a telescope that made objects appear 100 times bigger but stars merely four or five times greater. This means that the magnification decreased from ten to about two, but his numbers are probably meant as suggestive and should not be taken as rigorous.
the brightness that surrounds it: in the Optics of Ptolemy, which Galileo follows, what is taken into consideration is not how the rays travel but the triangle that has the object as its base and the eye as its summit. Here the object, which is assumed to be real, is not only the body of the star but the brightness that surrounds it.
the Dog Star: Sirius, the brightest star in the constellation Canis Major.
six new orders of magnitude: the magnitude scale dates back to the second century BC, when the Greek astronomer Hipparchus ranked the stars visible to the naked eye into six groups. The brightest stars were characterized as first magnitude. The next-brightest stars were labelled second magnitude, and so on, down to the faintest stars visible, which were classified as sixth magnitude. The human eye is such that a change of one magnitude corresponds to a factor of 2.5 in a pattern of brightness, so that a first-magnitude star is roughly 2.5 brighter than a second-magnitude star, which is roughly 2.5 brighter than a third magnitude star, and so on. Galileo introduces a new sequence of six magnitudes for stars that are invisible to the naked eye. A star of the seventh magnitude is seen with the telescope as if it were a star of the second magnitude observed with the naked eye, and so on. The idea is interesting, but Galileo did not have a telescope that enabled him to carry it out properly.
five hundred: to be interpreted as ‘very many’ and not as the result of a careful counting of the number of stars by Galileo.
Pleiades … hardly ever visible: in Greek mythology the seven daughters of Atlas and Pleione were changed into stars. Six are brighter than the fifth magnitude. The seventh (and two other ones) are brighter than the sixth magnitude but can only be seen by people with especially good eyesight.
Milky Way: Aristotle took the Milky Way to be a sort of high fog in the elemental region, formed, like comets, from hot vapours that rise from the uppermost part of the terrestrial sphere (Meteorology, book 1, chapter 8, 345 a 11-346 b 15). At the end of the sixteenth century Tycho Brahe maintained that the Milky Way was made of the same matter as the stars but more ‘diffused’ in character. Christopher Clavius, who taught at the Roman College during this period, considered it more likely that the Milky Way was a denser part of the aether and could absorb light from the Sun, the view that the telescope was just about to discredit. On the history of the Milky Way, see Stanley L. Jaki, The Milky Way: An Elusive Road to Science (New York: Science History Publications, 1972).
Galaxy: galaxia is the Greek word for the Milky Way, from gala = milk.
nebulous: not used here in the modern sense of interstellar cloud of dust or gas but in the broader sense of ‘cloudlike’ (from the Latin nebula which means cloud) as we find it in Ptolemy’s Almagest, who mentions seven such formations including the star clusters in Orion and Praesepe that Galileo describes.
Aselli: the two large stars in the engraving of the nebula Praesepe are the Aselli or ass-colts, which are now referred to as γ and δ Cancri. The ‘cloudlike’ area between them is what Ptolemy listed as nebulous.
7th of January … at the first hour of night: the observation is recorded as follows in Galileo’s letter of 7 January 1610: ‘Many fixed stars are seen with the spyglass but not without it. This very evening I saw Jupiter accompanied by three fixed stars that are completely invisible because they are so small’ (Opere, 10, p. 277). The ‘first hour of the night’ does not refer to one hour after midnight as it does for us. In Galileo’s day time was recorded ‘from sunset’, and the civil day began and ended with the setting of the Sun. The first hour in Padua on 7 January 1610 began around 16.30 hours our time. On this day Galileo began keeping an Astronomical Logbook of his observations (see Jean Meeus, ‘Galileo’s First Records of Jupiter’s Satellites’, Sky and Telescope, 24 (1962), 137-9).
three little stars: on account of the very narrow visual field of his telescope Galileo was not able to see the fourth satellite until 13 November when it had come closer to the other three.
parallel to the ecliptic: if the three celestial bodies had been stars, the fact that they were lying on a straight line parallel to the ecliptic would have enabled Galileo to measure the movement of Jupiter exactly. ‘Ori.’ and ‘Occ.’ (for ‘oriens’ and ‘occidens’) in this and the following illustrations indicate east and west respectively.
15th of January: on this day Galileo began making his entry in his Astronomical Logbook in Italian as he had done until then, but halfway through he switched to Latin (Opere, 3, pp. 427–8). The realization that the celestial bodies near Jupiter were satellites probably made him think of publishing this extraordinary news in Latin, the language of the scientific community.
the narrow circle along which they travel … effect: the orbits of the satellites are very nearly circular and too small to account for the considerable change in brightness of the satellites at different positions.
an oval motion … appearances: Galileo is thinking of a stretching out of the line, known as the apsis, which connects the point on the orbit of the satellite that is nearest to Jupiter to the point on the other side that is furthest from the planet. He makes no reference to Kepler, who had published his discovery that the orbits of the planets are elliptical in his Astronomia Nova of 1609.
the great lights: this expression for the Sun and the Moon is borrowed from the Bible: ‘And God made the two great lights, the greater light to rule the day, and the lesser light to rule the night’ (Genesis 1: 16).
the Moon does not: the largest angle subtended by the Moon amounts to about 32 seconds of an arc. It seems much larger on the horizon than high in the sky, but this is an optical illusion. A simple experiment will prove this: take a slim pencil of about 5 mm across, hold it at arm’s length between your eye and the Moon. It will be completely covered whether it is near the horizon or high above in the sky.
System: in the First Day of the Dialogue on the Two Chief World Systems (the name under which his System finally appeared in 1632) Galileo points out the reasons why there is no atmosphere on the Moon: ‘if clouds ever formed over any part of [the Moon’s] surface as they do around the Earth, they would block out some of the things which we can see through a telescope, and we would see some change in its visual appearance; but in all my long and diligent observations I have never seen any such change’ (Opere, 7, p. 126; pp. 225–6 below).
sphere of elements: according to Aristotelian cosmology the Earth is surrounded by successive layers of the four elements: earth, water, air, and fire.
Mark Welser: a member of a prominent family of bankers in Augsburg. He had studied in Rome and was a friend of the Jesuits.
Apelles: the writer was the Jesuit Christoph Scheiner; for this pseudonym see the Introduction, n. 17.
for the past eighteen months: this would imply that Galileo first observed the sunspots around October 1610 which is the time Christoph Scheiner also saw them, as he mentions in his first letter to Mark Welser dated 12 November (Opere, 5, p. 25); see the Introduction, p. xvi above. Galileo insisted to his dying day that he was the first to have seen them but both he and Scheiner were probably preceded by the Dutch astronomer Johann Fabricius, who was the first to publish information about them.
parallax: the technical word that is used to indicate the apparent difference in the position of an object in the sky when it is viewed from different positions on Earth.
as the Pythagoreans and Copernicus maintain: Nicolaus Copernicus (1473–1543) was a Polish astronomer who had studied in Italy. His book, On the Revolutions of the Heavenly Spheres, was published in the year he died. In it he defended the belief, which he attributed to Pythagoras (sixth century BC), that the Sun is at rest and the Earth is in motion, against the view of Claudius Ptolemy (flourished at Alexandria c. AD 150) that the Earth was at rest.
bodily conjunctions: these refer to both the ‘transits’ of Venus, when it passes directly across the face of the Sun, and the ‘occultations’, when it passes directly behind the Sun.
eccentrics, deferents, equants, epicycles, etc.: in the Ptolemaic system the planets are assumed to rotate on a small circle, called an epicycle, whose centre is attached to the rim of another circle, called the deferent, which in turn moves around the centre of the entire system.
none will be found in the future: Galileo later changed his mind. See his third letter, pp. 53–4 below.
method discovered by a pupil of mine: this pupil is Benedetto Castelli, a Benedictine monk who studied with Galileo in Padua, and followed him to Florence in 1611. At Galileo’s request he was appointed professor of mathematics at the University of Pisa in 1613. His method consisted in drawing a circle on paper and then fitting the telescopic image of the sunspots on this circle in order to trace the exact placement of the spots.
thus forming … varying shapes: Prince Federico Cesi had written from Rome to Galileo on 14 September 1612 to inform him that a Dominican had supported his position in a debate at the Roman College while the Jesuits had sided with Scheiner in calling them small stars. When the Dominican pointed out that stars were round and not irregular in shape, the Jesuits retorted that clusters of stars might have a variety of shapes (Opere, 12, p. 395).
have their own individual motion: in other words, the ‘wandering stars’ are planets.
Change is not alien to the heavens: Aristotelians considered the heavens immutable. See below, First Day of the Dialogue, p. 158 ff.
I have already written: see Galileo’s first letter, pp. 44-5 above.
Has Saturn devoured its children?: in classical mythology, Saturn devoured his newborn children to forestall a prophecy that he would be overthrown by one of his sons.
plausible conjectures: since the Earth has one satellite (the Moon) and Jupiter had been found to have four, Galileo thought it very likely that Saturn had two. See the Introduction, p. xv above.
SCIENCE AND RELIGION
LETTER TO DON BENEDETTO CASTELLI
Signore: for Benedetto Castelli see the note to p. 47 above, and the Introduction, p. xviii.
Niccolò Arrighetti: a mutual friend of Castelli and Galileo; he called on Galileo in Florence on 20 December 1613, the day before Galileo wrote this letter. Castelli, in a letter of 14 December, had already told Galileo that he had been the guest of the Grand Duke two days earlier, on 12 December.
the whole university: Castelli began teaching mathematics at the University of Pisa in November 1613.
Madame: mother of the Grand Duke Cosimo II, Christina of Lorraine, the widow of Grand Duke Ferdinand I. Her title was Grand Duchess.
Archduchess: Maria Maddalena of Austria, the wife of Cosimo II.
Don Antonio: Antonio de’ Medici, the natural son of the Grand Duke Francesco I and Bianca Cappello.
the passage in Joshua: the reference is to Joshua 10: 12-13, where it is narrated that the Sun stood still in the sky in response to the prayers of Joshua, so that his army was able to complete the rout of their enemies in battle.
experience of our senses … necessary demonstrations: Galileo stresses that his arguments are based on rigorous mathematical reasoning (‘necessary demonstrations’) as well as careful observation and experimentation (‘the experience of our senses)’.
matters of faith: those assertions that a Catholic cannot doubt. Galileo uses the technical Latin phrase ‘de Fide’.
Joshua’s prayers: the reference is again to Joshua 10: 12-13.
two motions: in the geocentric system used prior to Copernicus the Sun has two motions. The first carries it in twelve months across the twelve signs of the zodiac. The second is the daily motion around the Earth that it shares with all the planets and the stars.
Primum Mobile: the tenth and outermost concentric sphere of the universe in Ptolemaic astronomy. It was thought to revolve around the Earth from east to west in twenty-four hours and to cause the other nine spheres to revolve with it.
all the more quickly: Galileo maintains that arresting the Sun’s annual motion would not prolong but shorten the length of the day.
faster than the Sun’s: the time the Moon takes to complete its daily rotation from east to west is greater than that that the Sun requires for its daily rotation. This is why the Moon rises fifty minutes later every day. The reason is that the Earth revolves around its axis in twenty-four hours but the Moon takes about 29.5 days to revolve around the Sun while making one rotation around its own centre. The relation between the two motions is 24 divided by 29.5 which gives about fifty minutes.
turns on its own axis: the important discovery that the Sun rotates around itself was communicated by Galileo in his Letters on the Sunspots published in 1613 (not included in the extracts in this volume).
imparts … planets which revolve around it: Galileo conjectures that the revolutions of the planets around the Sun in the Copernican system are caused by the rotation of the Sun on its axis. This entails a better explanation of the miracle of Joshua because stopping the Sun would freeze all the heavenly motions and not just the daily revolution of the Sun around the Earth, as would be the case in the Ptolemaic system.
LETTER TO THE GRAND DUCHESS CHRISTINA
Augustine writes: Galileo gives as reference, ‘Saint Augustine, On the Literal Meaning of Genesis, book 2, at the end’. The translations of Galileo’s quotations from Augustine are adapted from De Genesi ad Literam: The Literal Meaning of Genesis, translated and annotated by John Hammond Taylor, SJ (New York: Paulist Press, 1982).
my first announcement: Galileo is referring to his Sidereal Message published in 1610.
arguments … this alternative position: the phases of Venus that Galileo discovered with his telescope in December 1610 could not be explained on the Ptolemaic system.
the injury … mathematicians everywhere: Galileo is referring to an attack that was made by a Dominican, Tommaso Caccini, in the Florentine church of Santa Maria Novella on 21 December 1614.
a priest and a canon: although Copernicus was a canon he was never ordained a priest.
Bishop of Fossombrone: the Dutch priest and mathematician, Paul van Middelburg, was appointed to the Italian see of Fossombrone in 1594. In the preface to his On the Revolutions of the Heavenly Spheres Copernicus states that it was Middelburg who got him interested in the problem of the reform of the calendar.
tables … movements of all the planets: this is a reference to the Prutenic Tables published by Erasmus Reinhold in 1551 and based on the Copernican system.
Cardinal … Kulm: the Cardinal of Capua is Nikolaus von Schönberg (1472-1537), a Dominican friar who was made Cardinal in 1535. He wrote to Copernicus in 1536 to urge him to publish his new astronomy as soon as possible, but the work only appeared in 1543. Tiedeman Giese (1480-1550) was the Bishop of Kulm and a friend of Copernicus, whom he encouraged.
Lactantius: Christian apologist of the third-fourth centuries, widely admired for the elegance of his Latin style, for which he was called the ‘Christian Cicero’. He considered it ridiculous that anyone should believe that there are people at the south pole who have their feet opposite to ours.
Tertullian … wrote: Galileo gives as reference, ‘Tertullian, Against Marcion, book 1, chapter 18’.
in the words of St Augustine: Galileo gives as reference, ‘Saint Augustine, On the Literal Meaning of Genesis, book 2, chapter 9’, adding, ‘This can also be found in Peter Lombard, the master of the Sentences’. A text that is close to the one of St Augustine that Galileo quotes can be found in Distinction 14 of book 2 of the Sentences.
a very eminent churchman: Galileo gives the name of Cardinal Baronio in the margin. Cesare Baronio (1538-1607) was a famous Church historian whom Galileo could have met in Padua.
‘In discussing … through experience and reason’: Galileo gives as his reference, ‘Pereira, On Genesis, near the beginning’. Benedetto Pereira was a Jesuit who taught at the Roman College and he had published his book in Venice in 1607.
in Saint Augustine we read: Galileo gives as reference, ‘In his seventh letter, to Marcellinus’.
‘What we know … what we do not know?’: this was a commonplace in Galileo’s day. The source is probably Themistius, a fourth-century AD philosopher, who made this observation when commenting on Aristotle’s On the Soul, book 3, chapter 3, 427b 1-13.
’He has given up … to the end’: Galileo gives as reference, ‘Ecclesiasticus chapter 3 [verse 11]’.
as Aristotle tells us: Aristotle, On the Heavens, book 2, chapter 13 (293a 30-2).
Plutarch … life of Numa: Plutarch, Life of Numa Pompilius, 11.3, in Plutarch, Lives (Dryden’s translation revised by Arthur Hugh Clough) (New York: Random House, reprint of the 1864 edition), 83.
as we learn from Archimedes: Archimedes, The Sand Reckoner, in T. L. Heath (ed.), Works of Archimedes (New York: Dover [no date]), 222.
Seleucus the mathematician: lived in the second century BC.
Nicetas, according to Cicero: Cicero wrote Hicetas (Academica, 2.39) but Galileo misspells the name, repeating the error ‘Nicetas’ that had been made in the dedication of Copernicus’ On the Revolutions of the Heavenly Spheres, which must have been his source.
Seneca … in his book On Comets: Seneca, Natural Questions, 7.2. Galileo quotes the passage in his Observations on the Copernican Theory (p. 97 below).
Scripture … could not exist: Galileo is referring to writers who used Scripture to refute the Copernican theory. These include Martin Horky’s A Very Short Excursion Against the Sidereal Message, Ludovico delle Colombe’s Against the Motion of the Earth (1610 or 1611), and Francesco Sizzi’s Dianoia astronomica, optica, physica (1611).
writer … recently published a book: Galileo has in mind a recent book by Ulisse Albergotti who claimed that the Moon does not shine because it reflects light coming from the Sun but on account of some kind of internal light.
St Jerome: Galileo gives as reference, ‘Letter to Paulinus’ and indicates the number as 103 but modern scholars and editors designate it as number 53.
Archimedes, Ptolemy, Boethius, and Galen: the classical authorities in geometry, astronomy, music, and medicine, respectively.
the following words of St Augustine: Galileo gives as reference, ‘On the Literal Meaning of Genesis, book 1, chapter 21’ but the text is given in the version in which it appears in the book by Pereira that Galileo had already mentioned (see note to p. 70).
the former mathematician … Pisa: Galileo alludes to Antonio Santucci who had been professor of mathematics at the University of Pisa from 1594 until his death in 1613.
other mathematicians: in the margin Galileo gives the name of Clavius, the most famous mathematician of the Roman College, who had recently died in 1612.
the glory and greatness of God … the heavens: Galileo’s phrase recalls specifically Psalm 19: 1, ‘The heavens are telling the glory of God, and the firmament proclaims his handiwork’.
the heavens are stretched out like a skin: Psalm 104: 2; modern translations render as ‘stretched out like a tent’.
But someone may ask … conclusions: Galileo gives as reference, ‘On the Literal Meaning of Genesis, chapter 9’.
Although this problem … Old or the New Testament: the quotation is from On the Literal Meaning of Genesis, book 2, chapter 18.
St Jerome writes: Galileo gives as reference, ‘On Jeremiah, chapter 28’.
and elsewhere: Galileo gives as reference, ‘On Matthew, chapter 13.’
Job chapter 27: the reference should be to Job 26: 7.
In St Thomas’s own words: Thomas Aquinas (1225-74) was considered one of the greatest theological authorities of the Catholic Church. The reference is to Aquinas’ Commentary on the Book of Job, translated by Brian Mullady, now available as E-text, www.opwest.org/Archive/2002/Book_of_Job/tajob.html.
mean motion … prosthaphaeresis of the Sun: when discussing the technical details of his new heliocentric theory Copernicus continued to use the terminology of the geocentric theory. For instance, in On the Revolutions of the Heavenly Spheres, book 3, chapter 14, he published tables on ‘the simple uniform motion of the Sun’ (namely the apparent motion of the Sun against the background of the fixed stars) and the ‘regular motion of the anomaly of the Sun’ (namely the angular distance of the Sun from its apogee, the place where it is furthest from the Earth). Copernicus uses ‘prosthaphaeresis’ for the shift in the apparent position of the Sun that is caused by the Earth’s annual motion.
Didachus of Stunica: Diego de Zuñiga was a Spanish theologian. His Commentaries on Job appeared in Toledo in 1584 and were reprinted in Rome in 1591. On 6 March 1616 the Congregation of the Index decreed that the book, along with Copernicus’ On the Revolutions of the Heavenly Spheres, was to be ‘suspended until corrected’.
Council of Trent … fourth Session: special authority was given to the pronouncements of formally constituted Councils of the Church. The Council of Trent (1545-63) reasserted the traditional teaching of the Catholic Church in response to the challenge of the Protestant Reformation. The Council held its fourth session on 8 April 1546.
My reply … useful in the Church: Galileo gives as reference, ‘On the Literal Meaning of Genesis, book 2, chapter 10’.
Dionysius the Areopagite: mentioned in Acts 17: 34 as being converted by St Paul. The writings ascribed to him and held to be genuine at the time of Galileo are now thought to have been written in the fifth century AD.
Bishop of Avila: Alfonso Tostado, Bishop of Avila in the fifteenth century, wrote a commentary of the book of Joshua.
Paul of Burgos: the name taken by the Spanish Jew Selemch-Ha-Levi (c. 1351-1435) after his conversion to Christianity. He became archbishop of Burgos and was appointed Lord Chancellor by King Henry in 1416.
miracle at the time of Hezekiah … the sundial: the reference is to Isaiah 38: 8, where the shadow on a sundial is said to have miraculously moved back as a sign that Hezekiah’s life would be prolonged.
In matters that are obscure … meaning of Scripture to be ours: Galileo gives as reference, ‘St Augustine, On the Literal Meaning of Genesis, book 1, chapters 18 and 19’. This first quotation comes from chapter 18 but the next six are all from chapter 19, which is reproduced in almost its entirety.
motion of the Primum Mobile: see the note to p. 59 above.
which prompted Dionysius … to say: Galileo gives as reference, ‘in his letter to Polycarp’. On Dionysius see the note to p. 84 above.
St Augustine … is of the same opinion: Galileo gives as reference, ’On the Miracles of Holy Scripture, book 2’. This work was believed to be by Saint Augustine but it was written by an Irish monk in the seventh century.
the Bishop of Avila … at length: Galileo gives as reference, ‘Questions 22 and 24 of chapter 10 of his commentary on Joshua’. On the Bishop of Avila see the note to p. 84 above.
as I believe I have demonstrated … Sunspots: see the note to p. 60 above.
Dionysius … On the Divine Names: on Dionysius see the note to p. 84 above. The Latin text that Galileo is using was translated from the Greek by Joachim Périon and published in Paris in 1598.
Cajetan: Thomas de Vio (1468-1534), author of a commentary on Thomas Aquinas’s Summa Theologica.
Magalhães: Cosme de Magalhães: (1533-1624), the author of a Commentary on Joshua that was published in 1612 and is one of the sources of Galileo’s patristic quotations.
the hymn: the first two of five stanzas of the hymn ‘Caeli Deus sanctissime’ that is sung at Vespers on Wednesdays.
‘Before he had made … hinges of the earth’: the reference is to Proverbs 8: 26, but the meaning of the word translated ‘hinges’ (cardines in the Vulgate) is obscure and modern translations vary.
LETTER FROM ROBERTO BELLARMINE TO PAOLO
ANTONIO FOSCARINI, 12 APRIL 1615
Paolo Antonio Foscarini: In February or March 1615 Foscarini published in Naples a 64-page Letter Concerning the Opinion of the Pythagoreans and Copernicus about the Mobility of the Earth and the Stability of the Sun and the New Pythagorean System of the World, in which he argued that it is not at variance with the Bible. A copy was immediately sent to Galileo by Prince Federico Cesi, his Roman friend and patron. Foscarini himself sent a copy to Cardinal Bellarmine and this elicited the present letter. See the English translation in Richard J. Blackwell, Galileo, Bellarmine and the Bible (Notre Dame, Ind.: University of Notre Dame Press, 1991), 217-51.
all the appearances are saved: see the Introduction, n. 25.
‘The Sun also … where it rises’: Ecclesiastes 1: 5, traditionally attributed to Solomon.
it appears … moving away from the ship: Bellarmine is replying to Foscarini who had quoted a verse from Virgil, ‘When we set out from harbour the shore and town recede’ (Aeneid, 3.72), that had already been used by Copernicus in his On the Revolutions of the Heavenly Spheres, book 1, chapter 8.
OBSERVATIONS ON THE COPERNICAN THEORY
The manuscripts of these essays bear no date but were written in 1615 and 1616.
calculations … of astrologers: the Copernican hypothesis made it easier to work out some of the calculations related to horoscopes, something that Galileo did regularly, like all the astronomers of his day.
Plato’s teacher … and Seleucus the mathematician: to the ‘precursors’ of Copernicus mentioned in the Letter to the Grand Duchess (see p. 71 above) Galileo now adds the name of Ecphantus of Syracuse (between 500 and 300 BC).
Seneca … On Comets: Seneca, Natural Questions, book 7, chapter 2.
On the Magnet: William Gilbert (1544-1603) published his On the Magnet in 1600. The work was closely studied by Galileo, but although Gilbert says that the Earth rotates on its axis in twenty-four hours he does not say that it revolves around the Sun.
Johannes Kepler: Kepler (1571-1630) not only championed Copernican-ism but discovered that the orbit of the Earth around the Sun is not a circle but an ellipse.
past and present emperor: Kepler was the court mathematician of the emperor Rudolph II (1552-1612) and his brother Matthias (1557-1619) who succeeded him.
Ephemerides: in his Ephemerides published in 1609, the German astronomer David Tost (known as Origanus) states that the Earth turns on its axis but he does not come out in favour of the Copernican hypothesis but rather in favour of the one of Tycho Brahe for whom the planets go around the Sun, which, in turn, makes an annual revolution around the Earth.
prince of present-day philosophy: namely Aristotle.
Cardinal of Capua and the Bishop of Kulm: see the Letter to the Grand Duchess, p. 64 above and note.
showing them to be invalid: Galileo is referring to chapters 7 and 8 of book 1 of Copernicus’ On the Motions of the Heavenly Spheres.
properties … declinations of the ecliptic: the stars on the celestial sphere are like cities on a globe where they are located using latitude and longitude. Longitude says how far a city is east or west along the Earth’s equator; latitude says how far a city is north or south of the Earth’s equator. Right ascension (RA) is like longitude. It locates where a star is along the celestial equator. The declination corresponds to latitude, and the ecliptic is the apparent path that the Sun traces in the sky during the year.
“To us who are being carried along … move away”: these two lines are two verses at the end of the Preface to book 2 of On the Revolutions of the Heavenly Spheres, and are almost certainly by Copernicus himself.
Ptolemy … simpler than the second: In book 3, chapter 3 of his Almagest, Ptolemy explains how we can account for the motion of the Sun by using one of two models: the first uses an epicycle revolving on a deferent circle, and the second a circle that is eccentric, i.e. rotates around a point that is not the centre of the system. In chapter 4 Ptolemy goes on to say that he prefers the second model.
The four Medicean planets: see Galileo’s account in the Sidereal Message and the first of the Letters on the Sunspots, pp. 27-32 and 44 above.
the three superior planets: Mars, Jupiter, and Saturn.
second anomaly: the principal motion of the planets is a regular west-to-east motion, and ancient astronomers had good values for the average speed of each planet. But the planets were observed to have two anomalies to their otherwise regular motion. The speed of each planet is not constant, and there is a point of minimum speed (the apogee) and a point of maximum speed (the perigee). This irregularity was called the first anomaly. The planets were also observed to stop their forward (west-to-east) motion, reverse direction, stop again, and finally resume forward motion. This was called the second anomaly.
a preface … unsigned: Johann Kepler had revealed at the beginning of his Astronomia Nova published in 1609 that in his own copy of Copernicus’ book there was a note, written by Jerome Schreiber of Nuremberg, stating that this preface had been inserted by Andreas Osiander, a Protestant theologian who had supervised the printing, for reasons similar to those set forth here by Galileo.
not just sixteen times as he says: Galileo stresses the error of Osiander who compared the size of Venus to the area of a circle when he should have considered the area of a sphere.
let it be recognized as true and correct: Galileo describes here the implications of the discovery of the phases of Venus that he discovered with his telescope.
the Council: the Council of Trent (1545-63); see note to p. 84 above.
because Scripture says they did: Bellarmine had written, ‘It would be just as heretical to deny that Abraham had two sons and that Jacob had twelve, as it would be to deny that Christ was born of a virgin’ (see Letter of Bellarmine to Foscarini, p. 95 above). Here Galileo adds Tubal’s dog (Tobit 11: 9 as mentioned in the Latin Vulgate but not in other editions).
Sarsi: the pen name of Orazio Grassi, a Jesuit professor of the Roman College, who published in 1619 a book entitled The Astronomical and Philosophical Balance to which Galileo replied in The Assayer that appeared in 1623. He stressed that ‘assayer’ (saggiatore in Italian) is a delicate weighing instrument employed in the assay of pure gold, not a crude balance or steelyard like the one Grassi used.
Orlando furioso: a romantic poem by Ludovico Ariosto, first published in 1532 and a highly popular work of fiction in Galileo’s day. Galileo will refer to Ariosto’s poem again in his Dialogue on the Two Chief World Systems; see below, pp. 245 and 341 and notes.
this great book: The metaphor, ‘book of nature’, which is often used in the seventeenth century, might come from the Bible. In his early notebooks, the Juvenilia (Opere, 1, p. 64), Galileo quotes Isaiah 34: 4: ‘The skies will be rolled up like a scroll’ (‘book’ in the Latin Vulgate edition that Galileo was using), and Revelation 6: 14: ‘The sky will vanish like a scroll that is rolled up’ (again ‘book’ in the Latin Vulgate edition).
signor Mario: Grassi had criticized a booklet written by Galileo but published under the name of one of his young friends, the Florentine Mario Guiducci.
And yet I have shown … anyone who cares to look: in the first of the Letters on the Sunspots; see pp. 36-7 above.
Suidas: the Suda (‘Fortress’) is the title of a Greek lexicon-encyclopedia, but before the twentieth century the name, in the form ‘Suidas’, was thought to refer to its compiler, who seems to have lived in the tenth century AD. Included in the lexicon are texts from classical Greek works and commentaries. Though mostly derived from late and corrupt sources, the Suda preserves much information about Greek literature that would otherwise be lost.
sonority or transonority: Galileo stresses that sound is a physical phenomenon caused by the air impinging on the eardrums and that there is no need to postulate an occult qualilty of ‘sonority’ or ‘transonority’.
DIALOGUE ON THE TWO CHIEF WORLD SYSTEMS
Most Serene Grand Duke: Ferdinando II (1610-70), Grand Duke of Tuscany.
To the discerning reader: this letter is the preface that Riccardi required to be added as a condition of granting his imprimatur. For the circumstances of the printing of the Dialogue see the Introduction, pp. xxiv-xxvi.
A salutary edict: Copernicus’ On the Revolutions of the Heavenly Spheres was placed on the Index of proscribed books on 3 March 1616.
the opinion of Pythagoras … Earth: Copernicus believed that Pythagoras (sixth century BC) had taught that the Sun is at rest and that the Earth is in motion.
Peripatetics only in name: ‘Peripatetic’ is a name given to the followers of Aristotle, originally derived from the colonnades (peripatoi in Greek) of the school in Athens where the Aristotelians would walk up and down during their discussions.
cause of the tides: in 1616 Galileo wrote a Discourse on the Tides that became the Fourth Day of the present Dialogue.
Sagredo: Giovan Francesco Sagredo (1571-1620) was a Venetian patrician and a talented amateur of science. He had studied with Galileo at Padua and became his close friend. In the Dialogue, he speaks for the intelligent layman who is already half-converted to the new astronomy.
Salviati: Filippo Salviati (1538-1614) was a noble Florentine who often had Galileo as his guest in his villa near Florence. Galileo wished to perpetuate his memory by making him his spokesman in the Dialogue.
a Peripatetic philosopher: this philosopher could have been Cesare Cremonino (1550-1631) who was Galileo’s colleague at the University of Padua and was famous for his commentaries on Aristotle.
Simplicius: a sixth-century interpreter of Aristotle. It is generally agreed that the Simplicio of the Dialogue is a composite of Galileo’s Peripatetic opponents.
FIRST DAY
Aristotelian and Ptolemaic system … Copernican system: see note to p. 37 above.
splendid proofs … ‘continuity’: see Aristotle, On the Heavens, book 1, chapter 1, section 268a 1-268b 10.
necessary demonstrations: see the note to p. 56 above.
laughing-stock … Senate itself: pestered by his mother about what had been debated at the Senate, Papirius told her that it concerned the question whether it would be better to allow one man two wives, or one woman two men. The result was that a large and noisy delegation of townswomen appeared before the Senate to argue for the latter alternative. The anecdote is told by Macrobius, Saturnalia, 1.6.18-26.
which you know already: this is the first of a number of allusions to the Platonic theory of recollection.
I will follow Aristotle: Aristotelians insisted that qualitative properties disclosed the nature of things whereas Galileo maintained that quantitative relations provided the genuine clues to an understanding of reality. Mathematics, for him, is the grammar of science. See his description of the language of nature in The Assayer, p. 115 above.
simple bodies … principle of motion: the four Aristotelian elements naturally moved either downwards (earth and water) or upwards (air and fire).
integral bodies: the four elements; what Galileo earlier called ‘simple bodies’ (see previous note).
worthy of Plato: Galileo seems to have in mind a passage in Plato’s Timaeus, 38-9, but he has taken great liberties with the text.
the Lincean Academician: Galileo is referring to himself. In 1611, as a recognition for his telescopic discoveries, he had been made a member of the Lincean Academy by its founder, Prince Federico Cesi.
If a body … impact: this and later passages enclosed in brackets were added by Galileo in his own copy of the first edition.
braccia: the unit of length that Galileo uses is the braccio (plural braccia) which is 58.4 cm or about an inch less than 2 feet.
proofs concerning local motion: see the Second Day of the Dialogue, pp. 284 ff., and the selection from the Two New Sciences, pp. 382 ff. below.
maintaining its allotted velocity: from the viewpoint of Newtonian physics, which was developed half-a-century later, the ‘Platonic’ cosmology produces no gain. Rather it implies two major miracles. First, it involves changing instantaneously the direction of the movement of the falling planets, which is as difficult as conferring instantaneously the determined velocity to a body. Indeed, in the natural order of things it is impossible. Secondly, it implies that the force of attraction of the Sun has doubled at the very moment when the circular motion is substituted for a downward one. But neither of these considerations can be said to hold for Galileo, who considers the operations of conferring motion on a body at rest and that of changing its direction as altogether different. In the first case something new has to be produced, but in the other the changes are merely accidental. As to the doubling of the force of attraction, Galileo has no need for it whatsoever since, for him, circular motion is inertial and does not engender centrifugal forces, so that no force of attraction from the Sun is necessary to make the planets describe their particular orbits and stay in them. Furthermore, Galileo does not work on the assumption that the Sun attracts the planets; they move towards the Sun by virtue of an inclination that has its origin in their bodies. For a fuller discussion, see William R. Shea, Galileo’s Intellectual Revolution, 2nd edn. (New York: Science History Publications, 1977), 121-9.
‘the same reasoning … parts’: this axiom is quoted by Aristotle, On the Heavens, book 1, chapter 3, section 270a, 11.
‘there is no arguing … first principles’: see Aristotle, Physics, book 1, chapter 2, section 185a, 3.
even though he proved it … contrary motion: see On the Heavens, book 4, chapters 4-5, section 311a, 15-312b.
‘But the movements of contraries … exempt from contraries’: Galileo has paraphrased a passage in On the Heavens, book 1, chapter 3, section 270a, 14-17.
two whole books: Aristotle’s On Generation and Corruption consists of two ‘books’.
horned arguments known as sorites: the source of the ‘liar’s paradox’ is the apostle Paul’s letter to Titus, where he warns him not to rely on the Cretans for, as one of themselves said, ‘All Cretans are liars’ (Titus 1: 12). This was called a ‘horned argument’ or a ‘forked question’ by medieval logicians. It is not a sorites, whose name derives from the Greek word soros, meaning ‘pile’ or ‘heap’. The classic example of a sorites is the paradox that arises when one considers a heap of sand from which grains are individually removed. Is it still a heap when only one grain remains? If not, when did it change from a heap to a non-heap? Note that it is the Aristotelian, Simplicio, who makes the mistake of confusing ‘a horned argument’ with a sorites.
Cremonino: see the note on ‘A Peripatetic philosopher’, p. 126 above.
a priori … a posteriori: the terms a priori and a posteriori are used to distinguish two types of knowledge or kinds of argument. A priori knowledge or justification is independent of experience (e.g. mathematial proofs); a posteriori knowledge or justification is dependent on experience or experimentation (e.g. the statement ‘some students are bilingual’).
Abyla and Calpe: Calpe is the Rock of Gibraltar, and Abyla is a hill on the African side of the Strait. Abyla and Calpe were called the Pillars of Hercules by the ancients.
Pythagoras sacrificed a hundred oxen: Pythagoras is said by the ancient Greek writers, Porphyry and Plutarch, to have sacrificed an ox, but Cicero already doubted the veracity of the tale (On the Nature of the Gods, 3.88).
two new stars: a very bright star, now known as a supernova, suddenly appeared in 1572 and was studied by the Danish astronomer Tycho Brahe. A second supernova appeared in 1604 and was the subject of well-attended lectures that Galileo delivered at the University of Padua.
Anti-Tycho: the title of a book published in 1621 by the Italian astronomer Scipione Chiaramonti.
parallax: see the note on p. 35 above.
sunspots: see the Letters on the Sunspots, pp. 33-54 above.
the Sun’s eccentric sphere: in the Ptolemaic system the Sun’s centre of revolution is not the centre of the Earth but is slightly off centre, hence the word ‘excentric’.
Demosthenes: a prominent statesman and orator of ancient Athens, 384-322 BC.
Mark Welser: see the note to p. 33 above.
Prytaneum: the town hall of a Greek city-state, normally housing the chief magistrate and the common altar or hearth of the community.
natura nihil frustra facit: an ancient aphorism that was often quoted by the Scholastic philosophers but is not found as such in Aristotle.
if the Moon had an epicycle: Copernicus never abandoned the notion that perfect motion had to be circular and in this he was followed by Galileo. In the case of the Moon, Copernicus uses not only one but two epicycles, the second rotating on the first that is attached, in turn, to a third and larger circle called the deferent (On the Motion of the Heavenly Spheres, book 4, chapter 2).
Antichthons: the Greek word Antichthon means Counter-Earth, a hypothetical body of the solar system that the Pythagoreans are said to have postulated to support their heliocentric cosmology (see Aristotle, On the Heavens, book 2, chapter 13, section 293a, 15-30).
the ray from their eye: on Galileo’s theory of optics see the note to p. 205 below.
distinguished professor in Padua: perhaps Cesare Cremonini. See the note to p. 126 above.
in the Assayer and his Letters on the Sunspots: these passages, which cover the same topic, are not translated in this anthology. They can be found for The Assayer in Opere, 6, pp. 283 ff., and for the Letters see Galileo Galilei and Christoph Scheiner, On Sunspots, trans. Eileen Reeves and Albert Van Helden (Chicago: Chicago University Press, 2010), 284.
‘we should not expect … luminous body’: the text that Simplicio is made to quote may be by an author who has not been identified or it could be a literary device that Galileo uses to show how obscure is the material upon which Simplicio bases his arguments.
darkness is the absence of light: Galileo mocks Simplicio by having him solemnly introduce a trivial and obvious definition of darkness. Aristotle uses the same words but in a less naive context (On the Soul, book 2, chapter 7, section 418b ff., and On Sensation, section 439a 20).
his visual rays: Galileo was both influenced and hampered by the traditional description of how light-rays travel. We are all familiar today with the correct theory, which is that of intromission, meaning that vision is caused by rays of light entering the pupil, whereas the rival theory of extromission, which accounted for vision by rays streaming from our eyes, was more commonly accepted in Galileo’s day. Whether the rays originate from the object or from the eye, the geometrical description of the situation is the same because the direction of the rays does not alter the way they are traced. We still speak of ‘eye contact’, of hard stares, and of gazing as ‘looking outward’. In the Sidereal Message Galileo considers the rays as being carried from the eye to the object when lenses are placed between the eye and what is being observed (see above, p. 9), and in a letter to the Jesuit Christopher Grienberger, he writes, ‘our visual rays leave our eye as from the vertex [of a triangle] and stretch out spherically until they reach the perimeter of the Moon’ (letter of 1 September 1611, Opere, ii, p. 118). In a comment on comets written in 1619 Galileo still speaks of ‘visual rays proceeding from the eye’ (Note on Orazio Grassi’s De tribus cometis anni MDCXVIII, Opere, 6, p. 107). As late as 1632 we find in the Third Day of the Dialogue on the Two Chief World Systems that the pupil is ‘that hole from which the visual rays come out’ (Opere, 7, p. 391, not in the present selection).
pillar of cloud… bright by night: the reference is to Exodus 13: 21-2.
forty times more: Galileo is comparing the surfaces of the Earth and the Moon when he should have compared their volumes, which are as 14 to 1.
book of conclusions: Galileo refers to a booklet, A Mathematical Discourse on Controversies over Astronomical Novelties published in 1614. It was written by Johann Georg Locher at the instigation of his teacher, the Jesuit Christoph Scheiner.
Cleomedes, Vitellio, Macrobius: Cleomedes is a first-century Greek writer known only through his book On the Circular Motions of the Celestial Bodies, which is a compendium of Greek sources (see Alan C. Bowen and Robert B. Todd, Cleomedes’ Lectures on Astronomy: A Translation of The Heavens, with an Introduction and Commentary (Berkeley and Los Angeles: University of California Press, 2004). Vitellio (or Witelo) was a Polish friar who lived in Italy in the thirteenth century and wrote an important work on perspective. Macrobius was a Roman grammarian and Neoplatonist philosopher who lived at the end of the fourth and the beginning of the fifth century AD. His Commentary on Cicero’s Dream of Scipio contains the idea mentioned here.
some other modern author: this author could be the Jesuit François de Aguilon, who published a book on optics in 1613.
a man … secret device: this is perhaps the Bohemian Martin Horky, an opponent of Galileo’s discoveries. In a letter to Kepler on 24 May 1610, Horky bragged that he had a better telescope than Galileo and that he intended to make an instrument that would enable people to communicate over a distance of 15 miles (Opere, 10, p. 359).
ancient spots: the dark areas that can be seen on the Moon without the aid of the telescope. See the Sidereal Message, p. 11 above.
Michelangelo: Michelangelo Buonarroti (1475-1564), whose reputation as a supremely gifted artist was already established in his lifetime, thanks especially to the status given to him in Vasari’s Lives of the Artists.
Archytas: a Pythagorean philosopher (428-350 BC) and a contemporary of Plato. He was born in Taranto in southern Italy, and is said to have experimented with toy flying-machines, including a wooden dove that flew by ‘the secret blowing of air enclosed inside’, perhaps a primitive compressed-air mechanism.
hoops: these ruzzole, as they are called in Italian, are wooden discs about 15 cm in diameter and 2 cm thick. There is a groove in the rim around which a cord is wound and then pulled to set the disc in motion.
Socrates’ demon: Socrates called the source of his inspiration his ‘demon’. Sagredo pokes fun at Simplicio and offers to become his source of inspiration by using the Socratic method of questioning.
the one explaining … square ones: Galileo is referring to the Mechanical Questions, chapter 8, section 851b, 15-852a, 14. The work was considered to be by Aristotle but is now believed to have been written later.
our narrative poem: Galileo is alluding to the long-standing debate on the relative merits of Tasso’s Gerusalemme liberata and Ariosto’s Orlando furioso, to which Galileo contributed forcefully in favour of Ariosto’s freewheeling, episodic poem in preference to Tasso’s attempt (not entirely successful) at writing a monothematic epic. Sagredo continues the allusion on p. 247 when he says, ‘I am content to excuse you from telling this story now.’
a problem … yet been able to solve: the unsolved problem is the law governing the distance covered by freely falling bodies. Galileo provides the solution below; see pp. 284 ff.
the Academician … on motion: the Academician is Galileo himself (see note to p. 139), and the treatise is On Naturally Accelerated Motion that was eventually published in 1638 at the end of the Third Day of Galileo’s Discourses on Two New Sciences. See the extract on pp. 382 ff. in this volume.
spirals: On the Spirals is one of the works of Archimedes (287-212 BC), the ancient mathematician that Galileo most admired.
as we have already discussed and established at length: in the First Day; see pp. 139-48 above.
must terminate … Earth: the erroneous belief that falling bodies must reach the centre of the Earth made it impossible to work out the correct path.
this fancy of mine: Galileo later reached the correct solution that the path of projectiles is a parabola, and he tried to pass off as a jest the explanation given here that the mixture of the straight motion of the falling body and the uniform diurnal motion of the Earth would give rise to a semicircle that ended at the centre of the Earth (letter to Pierre Carcavy, 5 June 1637, Opere, 17, p. 89).
which you allowed for it at the outset: see p. 138 above.
with his great genius: Galileo’s phrase here, ‘per altezza d’ingegno’, is quoted from Dante’s well-known praise of his late friend Guido Cavalcanti (Inferno, 10.59).
Alexandretta: port at the north-east extremity of the Mediterranean (modern Iskenderun), through which Sagredo travelled en route to the Syrian city of Aleppo.
handbook of assertions: the ‘handbook’ by the Jesuit Clemente Clementi is entitled An Encyclopedia Explained and Defended with One Hundred Philosophical Assertions (Rome, 1624).
in Copernicus’ book: Galileo is referring to On the Revolutions of the Heavenly Spheres, book 1, chapter 12 where the tables are printed at the end. Whereas the ancients used chords we now use sines (a chord is equal to double the sine of half the angle).
all humans naturally desire knowledge: this is the first sentence of Aristotle’s Metaphysics.
including Ptolemy: Galileo’s source is Copernicus’ On the Revolutions of the Heavenly Spheres, book 1, chapter 7, where Copernicus paraphrases, rather loosely, Ptolemy’s Almagest, book 1, chapter 7.
our knowledge … remembering: Galileo returns to the Platonic theme of recollection; see p. 130 above.
part of the tangent… point of contact: a secant line of a circle is a line that intersects two points on the curve. If the secant is defined by two points, P and Q, with P fixed and Q variable, as Q approaches P along the curve, the secant becomes closer and closer to being the tangent at P, namely it ‘just touches’ the curve at that point.
the modern author just cited: Galileo is referring to the Jesuit Christoph Scheiner.
canna: a unit of length whose value varied in different regions of Italy, but was usually approximately 2 metres.
56 times the semi-diameter of the Earth: Galileo has modified the terminology that he used in the Sidereal Message, when he gave the distance of the Moon from the Earth as ‘almost sixty terrestrial diameters’; see the note on p. 7 above.
Quandoque bonus: Simplicio quotes the first two words of the Roman poet Horace’s famous phrase, ‘quandoque bonus dormitat Homerus’ (‘sometimes good Homer nods’) in his Ars Poetica, line 359.
either assisting or informing: the assisting spirits were angels who guided the planets in their course; the informing spirits were the internal moving principles of animate beings.
THIRD DAY
is finite … or is infinite and boundless: Copernicus states that the size of the Earth compared to the size of the heavens is ‘like a point compared to a solid body or a finite magnitude compared to an infinite one’, but he does not consider whether the universe itself is finite or infinite (On the Revolution of the Heavenly Spheres, book 1, chapter 6).
finite, bounded, and spherical: see Aristotle, On the Heavens, book 1, chapters 5-8, section 271b-277b, 27.
would refuse even to look … accept them: the field of view of Galileo’s telescope was so narrow that only one-quarter of the Moon could be seen at a time, and people found this frustrating because they expected to see it whole. His friend, the philosopher Cesare Cremonini, was candid about his failure: ‘Looking through those lenses’, he told a friend, ‘just makes me dizzy’ (as reported by Paolo Gualdo in his letter to Galileo, 20 July 1611, Opere, 11, p. 165). Another professor, Giulio Libri, who had been Galileo’s colleague in Padua before moving to Pisa, had the same trouble. When he died at the end of 1610 Galileo joked that although he had failed to see the new stars while on Earth, he might see them on his way to heaven (letter of Galileo to Paolo Gualdo in Padua, 17 December 1610, Opere, 10, p. 484). Galileo’s bugbears were the pedants who swore by their books instead of looking through the telescope. ‘This kind of person’, he wrote to Kepler, ‘thinks philosophy [used here in the sense of natural philosophy or natural science] is a book like the Aeneid or the Odyssey, and that truth is to be discovered, not in the world or in nature, but by comparing texts (I use their own words)’ (letter to Kepler, 19 August 1610, Opere, 10, p. 422).
on another occasion: Salviati is referring to a passage in the Second Day (p. 295 above) where he criticized a student of the Jesuit Christoph Scheiner for failing to grasp that the year would last one natural day if the Earth did not revolve on its axis.
FOURTH DAY
our own Tyrrhenian sea: Salviati is referring to the coast of his (and Galileo’s) native Tuscany.
three intervals… tides: at the beginning of the seventeenth century it was generally recognized that the tides went through four different cycles: the daily cycle with high and low tide recurring at intervals of 12 hours; the monthly cycle whereby the tides lag behind 50 minutes each day until they have gone round the clock and are back to their original position; the half-monthly cycle with high tides at new and full moon and low tides at quadrature and, finally, the half-yearly cycle with greater tides at the equinoxes than at the solstices. Galileo enumerates three periods: the diurnal, whose intervals ‘in the Mediterranean ... are of roughly six hours each’, the monthly, which ‘appears to derive from the motion of the Moon’, and the annual, which ‘appears to derive from the Sun’. But he fails to state the differences in the tides when the Moon is new, full, or at quadrature, and although he mentions that the tides at the solstices vary in size from those at the equinoxes, it is only some forty pages later (see pp. 351-2 below) that he states, erroneously, that they are greater at the solstices.
Scylla and Charybdis: in classical mythology, two monsters on either side of the Strait of Messina who embodied the danger to sailors of passing through the strait.
a prelate: Marcantonio de Dominis, a former Jesuit who was made bishop of Split in Croatia, left the Roman Church to become an Anglican, recanted, and returned to Rome, where he died in prison in 1624, the year of the publication of his book on the tides.
the Moon with its temperate heat … rarefied: Girolamo Borro, who lectured at Pisa when Galileo was a student there, invokes the ‘temperate heat’ of the Moon that acts as an attractive force on the analogy of fire causing water to rise as it nears the boiling-point. Bernardino Telesio had suggested a rather more vague relationship between the Sun, the Moon, and the tides. He assumed that the sea rises and tends to boil over when it is heated by the Sun, and that it sets itself in motion to avoid evaporation, thus producing the flow and ebb of the tides (Girolamo Borro’s On the Tides in the Sea and the Inundation of the Nile appeared in 1577 and was reprinted as least twice, the third time in 1583; Bernardino Telesio’s views are to be found in his On the Nature of Things, book 1, chapter 12, a work that was published in 1565 and reprinted several times).
the water only rises… where we are: to account for the tides, Marcantonio de Dominis postulated that an attractive force acted from the Moon on the ocean. A common objection to de Dominis’ explanation was that high tide does not occur once a day when the Moon is directly above the sea but twice, the second time when the Moon is below the horizon. His theory, like Galileo’s own hypothesis, entailed a 24-hour cycle and was rejected for failing to agree with experience. Galileo, of course, could not level this criticism at de Dominis, and he attacked him for failing to realize that water rises and falls only at the extremities and not at the centre of the Mediterranean. De Dominis can hardly be blamed for failing to detect this phenomenon: it only exists as a consequence of Galileo’s own theory.
like the breath … whale: this animistic interpretation of the tides on the analogy with respiration is set forth in Antonio Ferrari (known as Galateo), On the Location of the Elements (Basel, 1558).
Ancona, Ragusa, or Corfu: Ancona is on the western shore of the Adriatic; Ragusa (modern Dubrovnik) and Corfu are on its eastern shore.
This will be easier to understand … just now: of the many ways that water can be made to flow, Galileo considered particularly suggestive the to-and-fro motion of water at the bottom of a boat that is alternately speeded up and slowed down. He likened the piling of the water now at one end and now at the other to the action of the tide. The analogy is not entirely satisfactory, however, since the acceleration or retardation is shared uniformly by the whole boat whereas, for the flux and reflux of the tides, it is not uniform throughout the sea basins in which they occur. Galileo parries this criticism by introducing a more sophisticated model familiar to contemporary mathematicians and astronomers. He asks his readers to imagine that the ecliptic and the equator coincide. A point on the surface of the Earth can be considered to move on an epicycle attached to a deferent representing the Earth’s orbit, as in the figure. The epicycle revolves once daily. For half the day the speed of the point is greater than that of the epicycle’s centre (the centre of the Earth); for the other half the speed is less. Maximum and minimum velocities occur when a given point is collinear with the centre of both epicycle and deferent. This means that the greatest speed is at midnight and the lesser at noon, and thus entails a twelve-hour period for the tides, not a six-hour period as is actually the case since there are two high and two low tides every day.
a mechanical model: in the Dialogue on the Tides written in 1616 Galileo had written, ‘I have a mechanical model that I will disclose at the appropriate time in which the effects of this marvellous composition of movements can be observed in detail’ (Opere, 5, p. 386). Here the words ‘that I will disclose at the appropriate time’ have disappeared. This would seem to indicate that he had not been able, in the interval of sixteen years, to translate his idea into practice.
I come, secondly … maximum slowness: see the note to p. 323 above.
Aristotle … threw himself into the sea and drowned: the legend that Aristotle would have drowned himself in despair because he could not understand the cause of the tides goes back to the early Church Fathers and is found in Justin Martyr, a second-century Christian apologist, and Gregory of Nanzianus, a fourth-century archbishop of Constantinople. See I. During, Aristotle and the Ancient Biographical Tradition (Gothenburg, 1957).
the strait between Scylla and Charybdis: the strait of Messina; see the note to p. 312 above.
Atlantic: Galileo writes ‘Ethiopian’ (Etiopico) for the southern part of the Atlantic Ocean. The ambiguity surrounding the word ‘Ethiopian’ goes back to antiquity.
‘Even as the Aegean Sea’, etc.: Galileo is quoting Torquato Tasso, Gerusalemme liberata, 12.63. In Max Wickert’s translation (The Liberation of Jerusalem, Oxford World’s Classics (Oxford: Oxford University Press, 2009)): ‘Even as the Aegean Sea, when Aquilo | and Notus cease to blow and churn and pound, | does not fall still, but in the heave and throe | of waves retains the motion and the sound …’. This flattering reference to Tasso as ‘the divine poet’ contrasts with Galileo’s earlier dismissive attitude when he compared him unfavourably to Ariosto; see the note to p. 245 above.
as we have said on another occasion: see pp. 232-4 above.
stronger than those coming from the west: Galileo’s claim to recorded evidence for the Mediterranean is puzzling for the prevailing wind east of Italy is a west wind in all seasons, and not an east wind as Sagredo vouches for.
the wretched Orlando: in Ariosto’s Orlando furioso, Orlando tries to deny the unmistakeable evidence that Angelica, the object of his love, has married his rival Medoro. He is driven mad by jealousy when he can no longer deny the truth; hence Sagredo’s reply. On Ariosto’s poem see the note to p. 245 above.
told of Aristotle: see p. 326 above.
Mars … and even the Moon: Galileo is aware of the fact that his theory of the tides does not sit easily on the known astronomical motion of the Sun, and he is anxious to remind his reader that the motions of the planets, for instance Mars and the Moon, are not perfectly understood. Kepler had found that the path of Mars is elliptical but Galileo would have nothing of this.
a marked difference … divided by the equinoctial points: the average apparent speed of the Sun around the Earth is about one degree per day (1/365.25 of the circle), but it speeds up and slows down. It takes 187 days to move from the vernal to the autumn equinox (21 March-21 September) and 178 days from the autumn back to the vernal equinox (21 September-21 March).
The additions are equal… are the smallest: Galileo wishes to argue that the inclination of the Earth’s axis with respect to its orbit around the Sun entails a modification of his original model. The annual and the diurnal motions are in the same line only at the solstices when their combination produces the greatest acceleration and the greatest retardation. At the equinoxes the two motions are inclined at their maximum angle, and the effect of their combination is consequently least. This is what Galileo’s theory entails, but the reverse holds true: the equinoctial tides are the most extreme because they receive the maximum effect of the sun’s gravitational pull, something Galileo did not consider.
solstitial colure: the meridian of the celestial sphere that passes through the two poles and the two solstices.
An ancient mathematician: this is Seleucus, a Hellenized Babylonian astronomer who flourished in the second century BC.
similar childish ideas: in the Introduction to his Astronomía Nova, published in 1609, the German astronomer Johann Kepler had conjectured that the Moon causes the tides.
The fourth argument … says are imperceptible: Galileo hoped that better telescopes would reveal that the motion of the Earth around the Sun had as a consequence a shift in the observed positions of the fixed stars at an interval of six months. This apparent displacement or difference in the apparent position of an object viewed along two different lines of sight is called parallax (see note to p. 35 above). The stars are actually too far for such a displacement to be noted.
signor Cesare … Lincean Academy: in 1631, a year before the publication of the Dialogue, Galileo received an essay by Cesare Marsili (1552-1633) in which he declared that he had detected a shift in the meridian that had been traced on the floor of the church of St Petronio in Bologna, where it can still be seen. Marsili’s observations were not conclusive of the motion of the Earth, but Galileo had great hopes that they would be.
a most learned and eminent person … submit: this person is none less than the Pope, Urban VIII, and it was unfortunate that the argument should have been made by Simplicio, who cut such a pitiful figure in the Dialogue. Worse still, it is immediately ridiculed by Salviati, who had acted as Galileo’s spokesman throughout the entire discussion.
THE TRIAL
eventually printed in Florence: the Dialogue was published in Florence on 21 February 1632 but an outbreak of the plague rendered communications difficult and copies of the book did not reach Rome before April. When questions were raised about the way the book had been authorized as well as about its content, the Pope suspended further distribution and appointed a special Commission of Enquiry. The members were Niccolò Riccardi, the Master of the Sacred Palace, an office which included the responsibility of licensing books to be printed; Agostino Oreggi, who was the papal theologian; and, in all likelihood, a Jesuit by the name of Melchior Inchofer, who had had one of his own books placed on the Index.
Galileo’s First Deposition: Galileo was summoned to Rome in September 1632 but he pleaded ill-health and managed to postpone his trip for another five months. He arrived in Rome on 13 February 1633, and while his case was being studied by the Vatican officials he stayed with Francesco Niccolini, the Tuscan Ambassador and an old friend. On 12 April he was driven to the headquarters of the Holy Office, where he was not placed in a cell but provided with a three-room suite. He was kept in the Vatican until 30 April, when he was allowed to return to the Florentine Embassy.
the Revd Brother … Procurator Fiscal of the Holy Office: Galileo’s trial was not conducted before the Cardinals of the Holy Office but before two officials: Vincenzo Maculano, a Dominican scholar and engineer who had recently been appointed Commissioner-General, and Carlo Sinceri, who had joined the Holy Office as early as 1606. The ‘court’ met only four times: on 12 April, 30 April, 10 May, and 21 June 1633. No one else was present.
he was questioned as follows: the introductory and concluding text of this document, and the questions put to Galileo, are in Latin; Galileo’s replies are given in Italian.
several Cardinals … d’Ascoli: Cardinals [Robert] Bellarmine and [Giovanni Battista] Bonsi are mentioned by their surname, the others are referred to by the names of the church of which they were the titular: ‘Aracoeli’ stands for Agostino Galamani, ‘Sant’Eusebio’ for Ferdinando Taverna, and ‘d’Ascoli’ for Felice Centini.
the Cardinal’s reply to a letter: see Bellarmine’s letter to Foscarini in this volume, pp. 94-6.
Document B: see p. 370 below.
the injunction he was given: acting on the orders of Pope Paul V, Cardinal Bellarmine met Galileo on 26 February 1616 and enjoined him to cease teaching that the Earth moved. See next note.
that he could not in any way … the said theory: an unsigned memorandum reads: ‘In the residence of his Eminence Cardinal Bellarmine, the above-mentioned Galileo was summoned and was admonished by his Eminence, in the presence of the Revd Father Michelangelo Seghizzi, of the Dominican Order, the Commissioner-General of the Holy Office, that the above opinion was an error and that he should abandon it. And immediately thereafter, in my presence and that of witnesses, the Cardinal still being present, the said Commissioner enjoined and commanded the said Galileo, in the name of his Holiness the Pope and of the whole Congregation of the Holy Office, that he should relinquish altogether the above opinion, that the Sun is the centre of the world and at rest and that the Earth moves; and that he should not henceforth hold, teach, or defend it in any way, verbally or in writing. Otherwise, proceedings would be taken against him by the Holy Office. The said Galileo acquiesced in this ruling and promised to obey it.’
Galileo … having requested a hearing: Galileo had a private meeting outside the courtroom with Maculano on 27 April, when he agreed to a plea-bargain of sorts. Galileo agreed to admit that he had erred in arguing too strongly for the Copernican position, and Maculano promised to recommend leniency. Hence Galileo’s request for a second hearing.
I am more desirous of glory than is seemly: Galileo quotes (in Latin) Cicero, Letters to his Friends, 9.14.
I, Galileo … whole Christian Commonwealth: Galileo appeared before the Holy Office in their office in the convent adjoining the church of Santa Maria sopra Minerva on 22 June 1633. Of the ten Cardinals who were members, seven were in attendance. This was the average number at most meetings. The text that Galileo read was not his own but had been prepared by officials of the Holy Office.
TWO NEW SCIENCES
Salviati, Sagredo, and Simplicio: the three interlocutors who appear in the Two New Sciences that was published in 1638 bear the same names as those in the Dialogue of 1632. See the notes to pp. 125-6 above. Salviati remains a spokesman for Galileo but Sagredo occasionally takes positions that Galileo had once considered and then rejected. Simplicio is no longer the stubborn Aristotelian philosopher but an earnest enquirer.
Arsenal: the name of the Venetian shipyard.
exactly that amount of force … state of rest: what Sagredo presents here is the view that Galileo held when he first examined the question of natural acceleration in his early work by seeking its cause in terms of an ‘impressed force’. He came to reject this approach as fruitless.
our Author’s purpose: during the Third Day, Salviati has been reading out loud a Latin treatise on motion composed by the author (Galileo) when he was a professor at the University of Padua.
impact … just one braccio: it is true that impact is proportional to the height of fall, but this does not apply to the speed acquired as Sagredo suggests, making an assumption that Galileo had accepted in 1604 and abandoned later.
vires acquirat eundo: Virgil, Aeneid, 4.175, where the reference is to rumour.
the Academician: Galileo; see the note to p. 139 above.
the reading: Salviati had resumed reading Galileo’s Latin treatise on motion.
from unity, 1, 3, 5, etc.: the ‘odd number’ rule is equivalent to the ‘squared times’ law: when the distance increases over three successive equal periods of time, the total distance covered in the first interval of time is 1 or 12; in the second interval of time, 1 + 3 = 4 or 22, and in the third interval of time, 1 + 3 + 5 = 9 or 32.