Galileo’s Daughter
A drama of science, faith and love
Dava Sobel

To the fathers,

Galileo Galilei

&

Samuel Hillel Sobel, MD,

in loving memory

Table of Contents

Cover Page

Title Page

PART ONE To Florence

[I] She who was so precious to you

[II] This grand book the universe

[III] Bright stars speak of your virtues

[IV] To have the truth seen and recognised

[V] In the very face of the Sun

[VI] Observant executrix of God’s commands

[VII] The malice of my persecutors

[VIII] Conjecture here among shadows

PART TWO On Bellosguardo

[IX] How our father is favoured

[X] To busy my self in your service

[XI] What we require above all else

[XII] Because of our zeal

[XIII] Through my memory of their eloquence

[XIV] A small and trifling body

[XV] On the right path by the grace of God

[XVI] The tempest of our many torments

PART THREE In Rome

[XVII] While seeking to immortalise your fame

[XVIII] Since the Lord chastises us with these whips

[XIX] The hope of having you always near

[XX] That I should be begged to publish such a work

PART FOUR Care of the Tuscan Embassy, Villa Medici, Rome

[XXI] How anxiously I live, awaiting word from you

[XXII] In the comfort of the Holy Office of the Inquisition

[XXIII] Vainglorious ambition, pure ignorance and inadvertence

[XXIV] Faith rested in the miraculous Madonna of Imprueta

[XXV] Judgment passed on your book and your person

PART FIVE At Siena

[XXVI] Not knowing how to refuse him the keys

[XXVII] Terrible destruction on the feast of San Lorenzo

[XXVIII] Recitation of the penitential psalms

[XXIX] The book of life, or, A prophet accepted in his own land

PART SIX From Arcetri

[XXX] My soul and its longing

[XXXI] Until I have this from your lips

[XXXII] As I struggle to understand

[XXXIII] The memory of the sweetnesses

IN GALILEO’S TIME

FLORENTINE WEIGHTS, MEASURES, CURRENCY

BIBLIOGRAPHY

NOTES

APPRECIATION

INDEX

About the Author

Praise

Copyright

About the Publisher

PART ONE To Florence

[I] She who was so precious to you

MOST ILLUSTRIOUS LORD FATHER

WE ARE TERRIBLY SADDENED by the death of your cherished sister, our dear aunt; but our sorrow at losing her is as nothing compared to our concern for your sake, because your suffering will be all the greater, Sire, as truly you have no one else left in your world, now that she, who could not have been more precious to you, has departed, and therefore we can only imagine how you sustain the severity of such a sudden and completely unexpected blow. And while I tell you that we share deeply in your grief, you would do well to draw even greater comfort from contemplating the general state of human misery, since we are all of us here on Earth like strangers and wayfarers, who soon will be bound for our true homeland in Heaven, where there is perfect happiness, and where we must hope that your sister’s blessed soul has already gone. Thus, for the love of God, we pray you, Sire, to be consoled and to put yourself in His hands, for, as you know so well, that is what He wants of you; to do otherwise would be to injure yourself and hurt us, too, because we lament grievously when we hear that you are burdened and troubled, as we have no other source of goodness in this world but you.

I will say no more, except that with all our hearts we fervently pray the Lord to comfort you and be with you always, and we greet you dearly with our ardent love.

FROM SAN MATTEO, THE 10TH DAY OF MAY 1623.

Most affectionate daughter,

S. Maria Celeste

The day after his sister Virginia’s funeral, the already world-renowned scientist Galileo Galilei received this, the first of 124 surviving letters from the once-voluminous correspondence he carried on with his elder daughter. She alone of Galileo’s three children mirrored his own brilliance, industry and sensibility, and by virtue of these qualities became his confidante.

Galileo’s daughter, born of his long illicit liaison with the beautiful Marina Gamba of Venice, entered the world in the summer heat of a new century, on 13 August 1600 – the same year the Dominican friar Giordano Bruno was burned at the stake in Rome for insisting, among his many heresies and blasphemies, that the Earth travelled around the Sun, instead of remaining motionless at the centre of the universe. In a world that did not yet know its place, Galileo would engage this same cosmic conflict with the Church, treading a dangerous path between the Heaven he revered as a good Catholic and the heavens he revealed through his telescope.

Galileo christened his daughter Virginia, in honour of his ‘cherished sister’. But because he never married Virginia’s mother, he deemed the girl herself unmarriageable. Soon after her thirteenth birthday, he placed her at the Convent of San Matteo in Arcetri, where she lived out her life in poverty and seclusion.

Virginia adopted the name Maria Celeste when she became a nun, in a gesture that acknowledged her father’s fascination with the stars. Even after she professed a life of prayer and penance, she remained devoted to Galileo as though to a patron saint. The doting concern evident in her condolence letter was only to intensify over the ensuing decade as her father grew old, fell more frequently ill, pursued his singular research nevertheless, and published a book that brought him to trial by the Holy Office of the Inquisition.

The ‘we’ of Suor Maria Celeste’s letter speaks for herself and her sister, Livia – Galileo’s strange, silent second daughter, who also took the veil and vows at San Matteo to become Suor Arcangela. Meanwhile their brother, Vincenzio, the youngest child of Galileo and Marina’s union, had been legitimised in a fiat by the grand duke of Tuscany and gone off to study law at the University of Pisa.

Thus Suor Maria Celeste consoled Galileo for being left alone in his world, with daughters cloistered in the separate world of nuns, his son not yet a man, his former mistress dead, his family of origin all deceased or dispersed.

Galileo, now fifty-nine, also stood boldly alone in his world-view, as Suor Maria Celeste knew from reading the books he wrote and the letters he shared with her from colleagues and critics all over Italy, as well as from across the continent beyond the Alps. Although her father had started his career as a professor of mathematics, teaching first at Pisa and then at Padua, every philosopher in Europe tied Galileo’s name to the most startling series of astronomical discoveries ever claimed by a single individual.

In 1609, when Suor Maria Celeste was still a child in Padua, Galileo had set a telescope in the garden behind his house and turned it skywards. Never-before-seen stars leaped out of the darkness to enhance familiar constellations; the nebulous Milky Way resolved into a swath of densely packed stars; mountains and valleys pockmarked the storied perfection of the Moon; and a retinue of four attendant bodies travelled regularly around Jupiter like a planetary system in miniature.

‘I render infinite thanks to God’, Galileo intoned after those nights of wonder, ‘for being so kind as to make me alone the first observer of marvels kept hidden in obscurity for all previous centuries.’

The new-found worlds transformed Galileo’s life. He won appointment as chief mathematician and philosopher to the grand duke in 1610, and moved to Florence to assume his position at the court of Cosimo de’ Medici. He took along with him his two daughters, then ten and nine years old, but he left Vincenzio, who was only four when greatness descended on the family, to live a while longer in Padua with Marina.

Galileo found himself lionised as another Columbus for his conquests. Even as he attained the height of his glory, however, he attracted enmity and suspicion. For instead of opening a distant land dominated by heathens, Galileo trespassed on holy ground. Hardly had his first spate of findings stunned the populace of Europe before a new wave followed: he saw dark spots creeping continuously across the face of the Sun, and ‘the mother of loves’, as he called the planet Venus, cycling through phases from full to crescent, just as the Moon did.

All his observations lent credence to the unpopular Sun-centred universe of Nicolaus Copernicus, which had been introduced over half a century previously but foundered on lack of evidence. Galileo’s efforts provided the beginning of a proof. And his flamboyant style of promulgating his ideas – sometimes in bawdy humorous writings, sometimes loudly at dinner parties and staged debates – transported the new astronomy from the Latin Quarters of the universities into the public arena. In 1616, a pope and a cardinal inquisitor reprimanded Galileo, warning him to curtail his forays into the supernal realms. The motions of the heavenly bodies, they said, having been touched upon in the Psalms, the Book of Joshua, and elsewhere in the Bible, were matters best left to the Holy Fathers of the Church.

Galileo obeyed their orders, silencing himself on the subject. For seven cautious years he turned his efforts to less perilous pursuits, such as harnessing his Jovian satellites in the service of navigation, to help sailors discover their longitude at sea. He studied poetry and wrote literary criticism. Modifying his telescope, he developed a compound microscope. ‘I have observed many tiny animals with great admiration,’ he reported, ‘among which the flea is quite horrible, the gnat and the moth very beautiful; and with great satisfaction I have seen how flies and other little animals can walk attached to mirrors, upside down.’

Shortly after his sister’s death in May of 1623, however, Galileo found reason to return to the Sun-centred universe like a moth to a flame. That summer a new pope ascended the throne of Saint Peter in Rome. The Supreme Pontiff Urban VIII brought to the Holy See an intellectualism and an interest in scientific investigation not shared by his immediate predecessors. Galileo knew the man personally – he had demonstrated his telescope to him and the two had taken the same side one night in a debate about floating bodies after a banquet at the Florentine court. Urban, for his part, had admired Galileo so long and well that he had even written a poem for him, mentioning the sights revealed by ‘Galileo’s glass’.

The presence of the poet pope encouraged Galileo to proceed with a long-planned popular dissertation on the two rival theories of cosmology: the Sun-centred and the Earth-centred, or, in his words, the ‘two chief systems of the world’.

It might have been difficult for Suor Maria Celeste to condone this course – to reconcile her role as a bride of Christ with her father’s position as potentially the greatest enemy of the Catholic Church since Martin Luther. But instead she approved of his endeavours because she knew the depth of his faith. She accepted Galileo’s conviction that God had dictated the Holy Scriptures to guide men’s spirits but proffered the unravelling of the universe as a challenge to their intelligence. Understanding her father’s prodigious capacity in this pursuit, she prayed for his health, for his longevity, for the fulfilment of his ‘every just desire’. As the convent’s apothecary, she concocted elixirs and pills to strengthen him for his studies and protect him from epidemic diseases. Her letters, animated by her belief in Galileo’s innocence of any heretical depravity, carried him through the ordeal of his ultimate confrontation with Urban and the Inquisition in 1633.

No detectable strife ever disturbed the affectionate relationship between Galileo and his daughter. Theirs is not a tale of abuse or rejection or intentional stifling of abilities. Rather, it is a love story, a tragedy and a mystery.

Most of Suor Maria Celeste’s letters travelled in the pocket of a messenger, or in a basket laden with laundry, sweetmeats or herbal medicines, across the short distance from the Convent of San Matteo, on a hillside just south of Florence, to Galileo in the city or at his suburban home. Following the angry papal summons to Rome in 1632, however, the letters rode on horseback some two hundred miles and were frequently delayed by quarantines imposed as the Black Plague spread death and dread across Italy. Gaps of months’ duration disrupt the continuity of the reportage in places, but every page is redolent of daily life, down to the pain of toothache and the smell of vinegar.

Galileo held on to his daughter’s missives indiscriminately, collecting her requests for fruits or sewing supplies alongside her outbursts on ecclesiastical politics. Similarly, Suor Maria Celeste saved all of Galileo’s letters, as rereading them, she often reminded him, gave her great pleasure. By the time she received the last rites, the letters she had gathered over her lifetime in the convent constituted the bulk of her earthly possessions. But then the mother abbess, who would have discovered Galileo’s letters while emptying Suor Maria Celeste’s cell, apparently buried or burned them out of fear. After the celebrated trial at Rome, a convent dared not harbour the writings of a ‘vehemently suspected’ heretic. In this fashion, the correspondence between father and daughter was long ago reduced to a monologue.

Standing in now for all the thoughts he once expressed to her are only those he chanced to offer others about her. ‘A woman of exquisite mind,’ Galileo described her to a colleague in another country, ‘singular goodness, and most tenderly attached to me.’

On first learning of Suor Maria Celeste’s letters, people generally assume that Galileo’s replies must lie concealed somewhere in the recesses of the Vatican Library, and that if only an enterprising outsider could gain access, the missing half of the dialogue would be found. But, alas, the archives have been combed, several times, by religious authorities and authorised researchers all desperate to hear the paternal tone of Galileo’s voice. These seekers have come to accept the account of the mother abbess’s destruction of the documents as the most reasonable explanation for their disappearance. The historical importance of any paper signed by Galileo, not to mention the prices such articles have commanded for the past two centuries, leaves few conceivable places where whole packets of his letters could hide.

Although numerous commentaries, plays, poems, early lectures and manuscripts of Galileo’s have also disappeared (known only by specific mentions in more than two thousand preserved letters from his contemporary correspondents), his enormous legacy includes his five most important books, two of his original handmade telescopes, various portraits and busts he sat for during his lifetime, even parts of his body preserved after death. (The middle finger of his right hand can be seen, encased in a gilded glass egg atop an inscribed marble pedestal at the Museum of the History of Science in Florence.)

Of Suor Maria Celeste, however, only her letters remain. Bound into a single volume with cardboard and leather covers, the frayed, deckle-edged pages now reside among the rare manuscripts at Florence’s National Central Library. The handwriting throughout is still legible, though the once-black ink has turned brown. Some letters bear annotations in Galileo’s own hand, for he occasionally jotted notes in the margins about the things she said and at other times made seemingly unrelated calculations or geometric diagrams in the blank spaces around his address on the verso. Several of the sheets are marred by tiny holes, torn, darkened by acid or mildew, smeared with spilled oil. Of those that are water-blurred, some obviously ventured through the rain, while others look more likely tear-stained, either during the writing or the reading of them. After nearly four hundred years, the red sealing wax still sticks to the folded corners of the paper.

These letters, which have never been published in translation, recast Galileo’s story. They recolour the personality and conflict of a mythic figure, whose seventeenth-century clash with Catholic doctrine continues to define the schism between science and religion. For although science has soared beyond his quaint instruments, it is still caught in his struggle, still burdened by an impression of Galileo as a renegade who scoffed at the Bible and drew fire from a Church blind to reason.

This pervasive, divisive power of the name Galileo is what Pope John Paul II tried to tame in 1992 by reinvoking his torment so long after the fact. ‘A tragic mutual incomprehension’, His Holiness observed of the 350-year Galileo affair, ‘has been interpreted as the reflection of a fundamental opposition between science and faith.’

Yet the Galileo of Suor Maria Celeste’s letters recognised no such division during his lifetime. He remained a good Catholic who believed in the power of prayer and endeavoured always to conform his duty as a scientist with the destiny of his soul. ‘Whatever the course of our lives,’ Galileo wrote, ‘we should receive them as the highest gift from the hand of God, in which equally reposed the power to do nothing whatever for us. Indeed, we should accept misfortune not only in thanks, but in infinite gratitude to Providence, which by such means detaches us from an excessive love for Earthly things and elevates our minds to the celestial and divine.’

[II] This grand book the universe

THE RECENTLY DECEASED RELATIVE Suor Maria Celeste mourned in her first extant letter was Virginia Galilei Landucci, the aunt she’d been named after. At the Convent of San Matteo, she shared her grief with her natural sister, Suor Arcangela (originally the namesake of Galileo’s other sister, Livia), and also with her cousin Suor Chiara – the departed Virginia’s own daughter Virginia.

A repetition of recollected identities echoed through the Galilei family like the sound of chanting, with its most melodic expression in the poetic rhythm of the great scientist’s full name. By accepted practice among established Tuscan families in the mid-sixteenth

century, when Galileo was born, the eldest son might well receive a Christian name derived from his parents’ surname. Accordingly, Vincenzio Galilei and his new wife, Giulia Ammannati Galilei, attracted no special attention when they gave the name Galileo to their first child, born at Pisa on the 15th day of February in the year of Our Lord 1564. (The year was actually recorded as 1563 in the chronicles of that period, however, when New Year’s Day fell on 25 March – the feast of the Annunciation.)

The family name Galilei, ironically, had itself been created from the first name of one of its foremost favourite sons. This was the renowned doctor Galileo Buonaiuti, who taught and practised medicine during the early 1400s in Florence, where he also served the government loyally. His descendants redubbed themselves the Galilei family in his honour and wrote ‘Galileo Galilei’ on his tombstone, but retained the coat of arms that had belonged to the ancestral Buonaiutis since the thirteenth century – a red step-ladder on a gold shield, forming a pictograph of the word buonaiuti, which literally means ‘good help’. The meaning of the name Galileo, or Galilei, harks back to the land of Galilee, although, as Galileo explained on this score, he was not at all a Jew.

Galileo Galilei took a few tentative steps along his famous forebear’s path, studying medicine for two years at the University of Pisa, before he gave himself over to the pursuit of mathematics and physics, his true passion. ‘Philosophy is written in this grand book the universe, which stands continually open to our gaze,’ Galileo believed. ‘But the book cannot be understood unless one first learns to comprehend the language and to read the alphabet in which it is composed. It is written in the language of mathematics, and its characters are triangles, circles, and other geometric figures, without which it is humanly impossible to understand a single word of it; without these, one wanders about in a dark labyrinth.’

Galileo’s father had opposed the idea of his becoming a mathematician and tried, arguing from long personal experience with mathematics and patrician poverty, to dissuade his son from choosing such a poorly paid career.

Vincenzio made a minimal living giving music lessons in the rented Pisan house where Galileo was born and partly raised. He also dabbled in the business dealings of his wife’s family, the Ammannati cloth merchants, to supplement his small teaching income, but he was at heart a composer and musical theorist in the days when musical theory was considered a special branch of mathematics. Vincenzio taught Galileo to sing and to play the organ and other instruments, including the recently remodelled lute, which became their favourite. In the course of this instruction he introduced the boy to the Pythagorean rule of musical ratios, which required strict obedience in tuning and composition to numerical properties of notes in a scale. But Vincenzio subjected these prevailing rules to his own studies on the physics of sound. Music, after all, arose from vibrations in the air, not abstract concepts regarding whole numbers. Using this philosophy, Vincenzio established an ideal tuning formula for the lute by fractionally shortening the intervals between successive frets.

After Vincenzio moved to Florence with his wife in 1572, temporarily leaving Galileo behind in the care of relatives, he joined other virtuoso performers, scholars and poets bent on reviving classic Greek tragedy with music.* Vincenzio later wrote a book defending the new trend in tuning that favoured the sweetness of the instrument’s sound over the ancient adherence to strict numerical relationships between notes. This book openly challenged Vincenzio’s own former music teacher, who prevented its publication in Venice in 1578. Vincenzio persevered, however, until he saw the work printed in Florence three years later. None of these lessons in determination or challenge to authority was lost on the young Galileo.

‘It appears to me’, Vincenzio stated in his Dialogue of Ancient and Modern Music, ‘that they who in proof of any assertion rely simply on the weight of authority, without adducing any argument in support of it, act very absurdly. I, on the contrary, wish to be allowed freely to question and freely to answer you without any sort of adulation, as well becomes those who are in search of truth.’

When Galileo was ten, he journeyed across Tuscany to join his parents and his infant sister, Virginia, in Florence. He attended grammar school near his new home until his thirteenth year, then moved into the Benedictine monastery at Vallombrosa to take instruction in Greek, Latin and logic. Once there, he joined the order as a novice, hoping to become a monk himself, but his father wouldn’t let him. Vincenzio withdrew Galileo and took him home, blaming an inflammation in the youth’s eyes that required medical attention. Money more likely decided the issue, for Vincenzio could ill afford the down payment and regular upkeep required to support his son in a religious vocation that generated no income. A girl was different. Vincenzio would have to pay dowries for his daughters, either to the Church or to a husband, and he could expect no return on either investment. Thus Vincenzio needed Galileo to grow up gainfully employed, preferably as a doctor, so he could help support his younger sisters, now four in number, and two brothers.

Vincenzio planned to send Galileo back to Pisa, to the College of the Sapienza, as one of forty Tuscan boys awarded free tuition and board, but couldn’t obtain the necessary scholarship. A good friend of Vincenzio’s in Pisa offered to take Galileo into his own home, to reduce the cost of the boy’s education. Vincenzio, however, hearing that this friend was romancing one of Galileo’s Ammannati cousins, held off for three years until the love affair ended in marriage and made the house a respectable residence for his son.

In September of 1581, Galileo matriculated at the University of Pisa, where medicine and mathematics both fitted into the Faculty of Arts. Although he applied himself to the medical curriculum to please his father, he much preferred mathematics from the moment he encountered the geometry of Euclid in 1583. After four years of formal study, Galileo left Pisa in 1585, at the age of twenty-one, without completing the course requirements for a degree.

Galileo returned to his father’s house in Florence. There he began behaving like a professional mathematician – writing proofs and papers in geometry, going out to give occasional public lectures, including two to the Florentine Academy on the conic configuration of Dante’s Inferno, and tutoring private students. Between 1588 and 1589, when Vincenzio filled a room with weighted strings of varying lengths, diameters and tensions to test certain harmonic ideas, Galileo joined him as his assistant. It seems safe to say that Galileo, who gets credit for being the father of experimental physics, may have learned the rudiments and value of experimentation from his own father’s efforts.

Having impressed several established mathematicians with his talent, Galileo procured a teaching post at the University of Pisa in 1589 and returned once more to the city of his birth at the mouth of the River Arno. The flooding of the river in fact delayed Galileo’s arrival on campus, so that he missed his first six lectures and found himself fined for these absences. By the end of the year, the university authorities were docking his pay for a different sort of infraction: his refusal to wear the regulation academic regalia at all times.

Galileo deemed official doctoral dress a pretentious nuisance, and he derided the toga in a three-hundred-line verse spoof that enjoyed wide readership in that college town. Any kind of clothing got in the way of men’s and women’s frank appraisals of each other’s attributes, he argued in ribald rhyme, while professional uniforms hid the true merits of character under a cloak of social standing. Worse, the dignity of the professor’s gown barred him from the brothel, denying him the evil pleasures of whoring while resigning him to the equally sinful solace of his own hands. The gown even impeded walking, to say nothing of working.

A long black robe would surely have hindered Galileo’s progress up the Leaning Tower’s eight-storey spiral staircase, laden, as legend has it, with cannonballs to demonstrate a scientific principle. In that infamous episode, the weight of iron on the twenty-five-year-old professor’s shoulders was as nothing compared to the burden of Aristotelian thought on his students’ perceptions of reality. Not only Galileo’s classes at Pisa, but university communities all over Europe, honoured the dictum of Aristotelian physics that objects of different weights fall at different speeds. A cannonball of ten pounds, for example, would be expected to fall ten times faster than a musket ball of only one pound, so that if both were released together from some summit, the cannonball would land before the musket ball had got more than one-tenth of the way to the ground. This made perfect sense to most philosophical minds, though the thought struck Galileo as preposterous. ‘Try, if you can,’ Galileo exhorted one of his many opponents, ‘to picture in your mind the large ball striking the ground while the small one is less than a yard from the top of the tower.’

‘Imagine them joining together while falling,’ he appealed to another debater. ‘Why should they double their speed as Aristotle claimed?’ If the incongruity of these mid-air scenarios didn’t deflate Aristotle’s ideas, it was a simple enough matter to test his assertions with real props in a public setting.

Galileo never recorded the date or details of the actual demonstration himself but recounted the story in his old age to a young disciple, who included it in a posthumous biographical sketch. However dramatically Galileo may have executed the event, he did not succeed in swaying popular opinion down at the base of the Leaning Tower. The larger ball, being less susceptible to the effects of what Galileo recognised as air resistance, fell faster, to the great relief of the Pisan philosophy department. The fact that it fell only fractionally faster gave Galileo scant advantage.

‘Aristotle says that a hundred-pound ball falling from a height of a hundred braccia [arm lengths] hits the ground before a one-pound ball has fallen one braccio. I say they arrive at the same time,’ Galileo resummarised the dispute in its aftermath. ‘You find, on making the test, that the larger ball beats the smaller one by two inches. Now, behind those two inches you want to hide Aristotle’s ninety-nine braccia and, speaking only of my tiny error, remain silent about his enormous mistake.’

Indeed this was the case. Many philosophers of the sixteenth century, unaccustomed to experimental proof, much preferred the wisdom of Aristotle to the antics of Galileo, which made him an unpopular figure at Pisa.

When Vincenzio died in 1591 at the age of seventy, Galileo assumed financial responsibility for the whole family on a maths professor’s meagre salary of sixty scudi annually. (Professors in the more venerated field of philosophy made six to eight times as much, while a father confessor could earn close to two hundred scudi per year, a well-trained physician about three hundred, and the commanders of the Tuscan armed forces between one thousand and two thousand five hundred.) Galileo paid out dowry instalments to his newly married sister Virginia’s fractious husband, Benedetto Landucci, supported his mother and sixteen-year-old brother, Michelangelo, and maintained his sister Livia at the Convent of San Giuliano until he could arrange for her to be wed. By this time, his three other siblings had all died of childhood diseases.

Galileo lent his help ungrudgingly, even enthusiastically. ‘The present I am going to make Virginia consists of a set of silken bed-hangings,’ he had written home from Pisa just before her wedding. ‘I bought the silk at Lucca, and had it woven, so that, though the fabric is of a wide width, it will cost me only about three carlini [about one-hundredth of a scudo] the yard. It is a striped material, and I think you will be much pleased with it. I have ordered silk fringes to match, and could very easily get the bedstead made, too. But do not say a word to anyone, that it may come to her quite unexpectedly. I will bring it when I come home for the Carnival holidays, and, as I said before, if you like I will bring her worked velvet and damask, stuff enough to make four or five handsome dresses.’

In 1592, the year after he buried his father in the Florentine church called Santa Croce, Galileo left Pisa for the chair of mathematics at the University of Padua. If he had to forsake his native Tuscany for the Serene Republic of Venice, at least he enjoyed a more distinguished position there and increased his income to 180 Venetian florins per year.

From the perspective of old age, Galileo would describe his time in Padua as the happiest period of his life. He made important friends with some of the republic’s great cultural and intellectual leaders, who invited him to their homes as well as to consult on shipbuilding at the Venetian Arsenale. The Venetian senate granted him a patent on an irrigation device he invented. Galileo’s influential supporters and quick-spreading reputation as an electrifying lecturer earned him rises that pushed his university salary to 300 and then to 480 florins annually. At Padua he also pursued the seminal studies of the properties of motion that he had begun in Pisa, for wise men regarded motion as the basis of all natural philosophy.

Fatefully during his Paduan idyll, while visiting friends outside the city, Galileo and two gentleman companions escaped the midday heat one afternoon by taking a siesta in an underground room. Natural air-conditioning cooled this chamber by means of a conduit that delivered wind from a waterfall inside a nearby mountain cave. Such ingenious systems ventilated numerous sixteenth-century villas in the Italian countryside but may have admitted some noxious vapours along with the welcome zephyrs, as apparently occurred in Galileo’s case. When the men awoke from their two-hour nap, they complained of various symptoms including cramps and chills, intense headache, hearing loss and muscle lethargy. Within days, the strange malaise proved fatal for one of its victims; the second man lived longer but also died of the same exposure. Galileo alone recovered. For the rest of his life, however, bouts of pain, later described by his son as arthritic or rheumatic seizures, would strike him down and confine him to his bed for weeks on end.

Under happier circumstances – although no one knows precisely when or how – Galileo in Padua met Marina Gamba, the woman who shared his private hours for twelve years and bore him three children.

Marina did not share his house, however. Galileo dwelled on Padua’s Borgo dei Vignali (renamed, in recent times, Via Galileo Galilei). Like most professors, he rented out rooms to private students, many of them young noblemen from abroad, who paid to board under his roof for the duration of their private lessons with him. Marina lived in Venice, where Galileo travelled by ferry at the weekends to enjoy himself. When she became pregnant, he moved her to Padua, to a small house on the Ponte Corvo, only a five-minute walk away from his own (if one could have counted minutes in those days). Even after the ties between Marina and Galileo were strengthened by the growth of their family, their separate living arrangement remained the same.

Suor Maria Celeste Galilei, neé ‘Virginia, daughter of Marina from Venice’, was ‘born of fornication’, that is to say, out of wedlock, according to the parish registry of San Lorenzo in the city of Padua, on 13 August 1600, and baptised on the 21st. Marina was twenty-two on this occasion, and Galileo (though no mention divulges his identity), thirty-six. Such age discrepancies occurred commonly among couples at that time. Galileo’s own father had reached forty-two years before taking the twenty-four-year-old Giulia as his bride.

The following year, 1601, again in August, a registry entry on the 27th marked the baptism of ‘Livia Antonia, daughter of Marina Gamba and of—’ followed by a blank space.

After five more years, on 22 August 1606, a third child was baptised, ‘Vincenzio Andrea, son of Madonna Marina, daughter of Andrea Gamba, and an unknown father’. Technically an ‘unknown father’ for not being married to the mother, Galileo nevertheless asserted his paternity by giving the baby both grandfathers’ names.

Galileo recognised his illegitimate children as the heirs of his lineage, and their mother as his mate, although he ever avoided marrying Marina. Scholars by tradition tended to remain single, and the notations in the parish registry hint at circumstances that would have strengthened Galileo’s resolve. After all, she was ‘Marina from Venice’ – not from Pisa or Florence, or Prato or Pistoia, or any other town within the bounds of Tuscany, where Galileo determined to return some day. And her heritage, ‘daughter of Andrea Gamba’, did not put her on a par with the poor but patrician Galilei family, whose ancestors had signed their names in the record books of a great city government.

[III] Bright stars speak of your virtues

AS HIS PADUAN CAREER increased its brilliance in the early years of the seventeenth century, Galileo continued struggling to meet all his expensive family responsibilities. In 1600 his younger brother, the musical Michelangelo, was invited to play at the court of a Polish prince, and despite the maturity of his twenty-five years, he tapped Galileo for the clothing and money he needed to make the trip. Also in 1600, the same year Galileo saw the birth of his daughter Virginia, he found a husband for his sister Livia. Upon her marriage to Taddeo Galletti in 1601, Galileo negotiated the dowry, paid for the ceremony and the wedding feast, and also bought Livia’s dress, which was made of black Naples velvet with light blue damask that cost more than one hundred scudi. Then, in 1608, Michelangelo got married, moved to Germany, and reneged on his promised share of the sisters’ dowry contracts, precipitating a legal action by brother-in-law Benedetto Landucci, who complained of being cheated out of his expected sum.

Fortunately, Galileo’s endeavours led him to a new source of supplemental income. In the course of teaching military architecture and fortification to private students, he had invented his first commercial scientific instrument in 1597, called the geometric and military compass. It looked like a pair of metal rulers joined by a pivot, covered all over by numbers and scales, with screws and an attachable arch to hold the compass arms open at almost any angle. By 1599, after various modifications, the device functioned as an early pocket calculator that could compute compound interest or monetary exchange rates, extract square roots for arranging armies on the battlefield, and determine the proper charge for any size of cannon. Shipwrights at the nearby Venetian Arsenale also adopted Galileo’s revolutionary compass, to help them execute and test new hull designs in scale models before building them full-size.

Galileo crafted the first few compasses himself, but soon required the services of a full-time, live-in instrument maker to meet the popular demand. The hired craftsman moved into Galileo’s house with wife and children in tow, to work in exchange for salary, room and board for his whole family, all production materials, and a two-thirds share of the price of the finished brass instruments, which sold for five scudi each. Galileo would not have made much money under these conditions, except that he charged every visiting student nearly twenty scudi to learn how to use the compass, and all of this was his to keep. At first he gave out a personally handwritten instruction manual as a learning aid; then in 1603 he hired an amanuensis to help generate enough copies – until three years later, when he hit on the idea of publishing the booklet for sale with the instrument.

He called his treatise Operations of the Geometric and Military Compass of Galileo Galilei, Florentine Patrician and Teacher of Mathematics in the University of Padua. Its 1606 title page notes that the book was printed ‘in the Author’s House’ and cannily dedicated to the future grand duke of Tuscany, Don Cosimo de’ Medici.

‘If, Most Serene Prince,’ Galileo addressed his young patron in the dedication, ‘I wished to set forth in this place all the praises due to your Highness’s own merits and those of your distinguished family, I should be committed to such a lengthy discourse that this preface would far outrun the rest of the text, whence I shall refrain from even attempting that task, uncertain that I could finish half of it, let alone all.’

Cosimo, a lad of sixteen, had become Galileo’s most elite private pupil the previous summer. The heir apparent to the House of Medici, he bore the name of his resolute grandfather, Cosimo I, who had expelled all rival and foreign influences from Florence, annexed the city of Siena to the Duchy of Tuscany, and then pressured Pope Pius V to create for him the title of grand duke in 1569. Thus the self-made Medici family, who had been successful bankers holding high government positions in the old Republic of Florence throughout the fourteenth and fifteenth centuries, assumed the aura and authority of royalty in Galileo’s time.

Galileo, who typically returned to Florence when the University of Padua closed between terms, procured recommendations as a mathematical mentor to the royal household. As young Prince Cosimo’s tutor, Galileo gained status with the boy’s powerful parents: the much beloved Grand Duke Ferdinando I (who had started his career as a cardinal in Rome before being called home to the throne at the sudden death of his lecherous, murderous older brother, Francesco) and his devoutly religious French wife, Grand Duchess Cristina of Lorraine. By dedicating the tract on the geometrical compass to Cosimo, Galileo hoped to pave his way to an appointment as court mathematician – a prestigious position that would not only lighten his financial burden but also bring him home to his beloved Tuscany.

‘I have waited until now to write,’ Galileo said with all requisite deference in his first letter to Cosimo in 1605, ‘being held back by a respectful concern of not wanting to present myself as presumptuous or arrogant. In fact, I made sure to send you the necessary signs of reverence through my closest friends and patrons, because I did not think it appropriate – leaving the darkness of the night – to appear in front of you at once and stare in the eyes of the most serene light of the rising sun without having reassured and fortified myself with their secondary and reflected rays.’

No formal contract bound the prince and the scientist at that point. If and when Galileo’s tutorial services were required, he was summoned, as in the following invitation written by the chief steward of the grand duke and duchess, dated 15 August 1605, and sent from Pratolino, one of the seventeen Medici palaces, a few miles north of Florence: ‘Her Most Serene Highness wishes that you should come here not only that the Prince may receive competent instruction but that your health may be restored. She hopes that the excellent air on the mountain of Pratolino will do you good. A pleasant room, good food, a comfortable bed, and a hearty welcome await you. Messer Leonido will see that you are provided with a good litter whether you wish to arrive this evening or tomorrow.’

The grand duchess again sent her horse-drawn conveyance to fetch Galileo for the wedding of Prince Cosimo, in 1608, to Maria Maddalena, the archduchess of Austria and sister of Emperor Ferdinand II. The nuptials spread along both banks of the Arno, where spectators on grandstands watched a re-enactment of Jason’s capture of the Golden Fleece, sumptuously staged on a specially constructed island in mid-river, with special effects including giant sea monsters that spat real fire.

In January 1609, when Grand Duke Ferdinando lay ill, Madama Cristina implored Galileo to review her husband’s horoscope. Galileo’s early career experience teaching astronomy to medical students had familiarised him with astrology, since doctors needed to cast horoscopes, to see what the stars foretold of patients’ lives, as an aid to diagnosis and treatment, as well as to ascertain reasons for particular illnesses and determine the most propitious times for mixing medications. Galileo had prepared many horoscopes, including one for his daughter Virginia at her birth in 1600, probably for the novelty of playing with astronomical positions, as he never expressed any faith in astrological predictions. In fact he remarked how the prophecies of astrologers could most clearly be seen after their fulfilment.*

Nevertheless, Galileo courteously replied to the grand duchess’s request by return post. Despite his forecast of many more happy years for Ferdinando, the grand duke died of his illness just three weeks later. And so it happened that Galileo’s summertime student, not quite nineteen years old, was suddenly enthroned as His Serene Highness Grand Duke Cosimo II, sovereign of all Tuscany.

Cosimo’s accession gave Galileo the perfect opportunity to petition for the coveted court post, as he had created it in his dreams. ‘Regarding the everyday duties,’ Galileo wrote in his application to Florence, ‘I shun only that type of prostitution consisting of having to expose my labour to the arbitrary prices set by every customer. Instead, I will never look down on serving a prince or a great lord or those who may depend on him, but, to the contrary, I will always desire such a position.’

But he did not obtain the position just then. He continued his teaching at Padua and his research, which focused on establishing the mathematical principles of simple machines such as the lever, and determining how bodies accelerate during free fall – one of the most important unresolved questions of seventeenth-century science. ‘To be ignorant of motion is to be ignorant of Nature,’ Aristotle had said, and Galileo sought to end the general ignorance of Nature’s laws of motion. Later that year, however, in the summer of 1609, Galileo was distracted from his motion experiments by rumours of a new Dutch curiosity called a spyglass, or eyeglass, that could make far-away objects appear closer than they were. Though few Italians had seen one first-hand, spectacle makers in Paris were already selling them in quantity.

Galileo immediately grasped the military advantage of the new spyglass, although the instrument itself, fashioned from stock spectacle lenses, was little more than a toy in its first incarnation. Seeking to improve the spyglass by augmenting its power, Galileo calculated the ideal shape and placement of glass, ground and polished the crucial lenses himself, and travelled to nearby Venice to show the doge, along with the entire Venetian senate, what his contrivance could do. The response, he reported, was ‘the infinite amazement of all’. Even the oldest senators eagerly scaled the highest bell towers of the city, repeatedly, for the unique pleasure of discerning ships on the horizon – through the spyglass – a good two to three hours before they became visible to the keenest-sighted young lookouts.

In exchange for the gift of his telescope (as a colleague in Rome later renamed the instrument), the Venetian senate renewed Galileo’s contract at the University of Padua for life, and raised his salary to one thousand florins per year – more than five times his starting pay.

Still Galileo continued to refine the optical design in subsequent attempts, and when autumn came with its early dark, he chanced to focus one of his telescopes on the face of the Moon. The jagged features that greeted him by surprise there spurred him to improve his skill at lens grinding to build even more powerful models – to revolutionise the study of astronomy by probing the actual structure of the heavens, and to disprove Aristotle’s long unquestioned depiction of all celestial bodies as immutable perfect spheres.

In November 1609 Galileo fabricated lenses with double the power of the glass that had dazzled the doge. Now equipped to magnify objects by a factor of twenty, he spent half of December drafting a series of detailed drawings of the Moon in several phases. ‘And it is like the face of the Earth itself,’ Galileo concluded, ‘which is marked here and there with chains of mountains and depths of valleys.’

From the Moon he journeyed to the stars. Two kinds of stars filled the heavens of antiquity. The ‘fixed’ stars outlined pictures on the night sky and wheeled around the Earth once a day. The ‘wandering’ stars, or planets – Mercury, Venus, Mars, Jupiter and Saturn – moved against the background of the fixed stars in a complex pattern. Galileo became the first to distinguish them further: ‘Planets show their globes perfectly round and definitely bounded, looking like little moons, spherical and flooded with light all over; fixed stars are never to be seen bounded by a circular periphery, but have rather the aspect of blazes whose rays vibrate about them, and they scintillate a very great deal.’*

He pursued this new nocturnal fascination through the winter, plagued by the cold and the difficulty of keeping the instrument steady against the trembling of his hands and the beating of his heart. He needed to wipe the lenses repeatedly with a cloth, ‘or else they become fogged by the breath, humid or foggy air, or by the vapour itself which evaporates from the eye, especially when it is warm’. Early in January, he fell on the most extraordinary discovery of all: ‘four planets never seen from the beginning of the world right up to our day’, in orbit around the planet Jupiter.

Beyond their enormous astronomical significance, the new Jovian planets held special meaning for a friend of the Florentine court. Cosimo I of glorious memory had created a classical mythology for the Medici family when he became duke in 1537 – even before he catapulted to grand dukedom in 1569. Cosimo fashioned himself an earthly embodiment of the cosmos, as his name implied. By this coup, he convinced the Florentine citizenry that it was Medici destiny to usurp power from the other prominent families who had long governed in uneasy coalition. As the head of his de facto dynasty, Cosimo I identified with the planet Jupiter, named after the king of the Roman pantheon, and he filled the Palazzo della Signoria, where he lived and ruled, with frescoes stressing this Olympic theme.

Galileo had given Venice his telescope. Now he would offer Florence the moons of Jupiter.

He quickly set down his discoveries in a new book, entitled Sidereus Nuncius, or The Starry Messenger. As he had done with his earlier work on the geometric compass, he dedicated the text to young Cosimo II. On this occasion, however, Galileo took the time and gave himself enough space properly to extol his prince:

Your Highness…scarcely have the immortal graces of your soul begun to shine forth on Earth than bright stars offer themselves in the heavens which, like tongues, will speak of and celebrate your most excellent virtues for all time. Behold, therefore, four stars reserved for your illustrious name, and not of the common sort and multitude of the less notable fixed stars, but of the illustrious order of wandering stars, which, indeed, make their journeys and orbits with a marvellous speed around the star of Jupiter, the most noble of them all, with mutually different motions, like children of the same family, while meanwhile all together, in mutual harmony, complete their great revolutions every twelve years about the centre of the world…

Indeed, it appears that the Maker of the Stars himself, by clear arguments, admonished me to call these new planets by the illustrious name of Your Highness before all others. For as these stars, like the offspring worthy of Jupiter, never depart from his side except for the smallest distance, so who does not know the clemency, the gentleness of spirit, the agreeableness of manners, the splendour of the royal blood, the majesty in actions, and the breadth of authority and rule over others, all of which qualities find a domicile and exaltation for themselves in Your Highness? Who, I say, does not know that all these emanate from the most benign star of Jupiter, after God the source of all good? It was Jupiter, I say, who at Your Highness’s birth, having already passed through the murky vapours of the horizon, and occupying the midheaven and illuminating the eastern angle from his royal house, looked down upon Your most fortunate birth from that sublime throne and poured out all his splendour and grandeur into the most pure air, so that with its first breath Your tender little body and Your soul, already decorated by God with noble ornaments, could drink in this universal power and authority.

In the continuing paean of the remaining paragraphs of this dedicatory note, Galileo took it upon himself to name the planets the Cosmian stars. But Cosimo, the eldest of eight siblings, preferred the name Medicean stars – one apiece for him and each of his three brothers. Galileo naturally bowed to this wish, though he was thus forced to paste small pieces of paper with the necessary correction over the already printed first pages in most of the 550 copies of The Starry Messenger.

The book created a furore. It sold out within a week of publication, so that Galileo secured only six of the thirty copies he had been promised by the printer, while news of its contents quickly spread worldwide.

Within hours after The Starry Messenger came off the press in Venice on 12 March 1610, the British ambassador there, Sir Henry Wotton, dispatched a copy home to King James I. ‘I send herewith unto His Majesty’, the ambassador wrote in his covering letter to the earl of Salisbury,

the strangest piece of news (as I may justly call it) that he hath ever yet received from any part of the world; which is the annexed book (come abroad this very day) of the Mathematical Professor at Padua, who by the help of an optical instrument (which both enlargeth and approximateth the object) invented first in Flanders, and bettered by himself, hath discovered four new planets rolling about the sphere of Jupiter, besides many other unknown fixed stars; likewise, the true cause of the Via Lactea [Milky Way], so long searched; and lastly, that the moon is not spherical, but endued with many prominences, and, which is of all the strangest, illuminated with the solar light by reflection from the body of the earth, as he seemeth to say. So as upon the whole subject he hath first overthrown all former astronomy – for we must have a new sphere to save the appearances – and next all astrology. For the virtue of these new planets must needs vary the judicial part, and why may there not yet be more? These things I have been bold thus to discourse unto your Lordship, whereof here all corners are full. And the author runneth a fortune to be either exceeding famous or exceeding ridiculous. By the next ship your Lordship shall receive from me one of the above instruments, as it is bettered by this man.

In Prague, the highly respected Johannes Kepler, imperial astronomer to Rudolf II, read the emperor’s copy of the book and leaped to judgment – despite the lack of a good telescope that could confirm Galileo’s findings. ‘I may perhaps seem rash in accepting your claims so readily with no support of my own experience,’ Kepler wrote to Galileo. ‘But why should I not believe a most learned mathematician, whose very style attests the soundness of his judgment?’

The copy of The Starry Messenger that had the greatest impact on Galileo’s life, however, was the one he sent to Cosimo, along with his own superior telescope. The prince expressed his thanks late in the spring of 1610 by appointing Galileo ‘Chief Mathematician of the University of Pisa and Philosopher and Mathematician to the Grand Duke’. Galileo had specifically stipulated the addition of ‘Philosopher’ to his title, giving himself greater prestige, but he insisted on maintaining ‘Mathematician’ as well, for he intended to prove the importance of mathematics in natural philosophy.

In negotiating his Tuscan future, Galileo requested the same salary he had recently been promised by the University of Padua – the figure of one thousand to be paid now in Florentine scudi instead of Venetian florins. Rather than plead for more money, he made the base pay stretch further by seeking official release from responsibility for his brother’s share of their sisters’ dowries.

Galileo also secured a bonus in personal liberty by arranging for his university appointment at Pisa to entail no noisome teaching duties. He would be free to study the world around him for the rest of his days, and to publish his discoveries for the benefit of the public under the protection of the grand duke, who promised to pay for the construction of new telescopes.

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