Galileo’s Daughter by Dava Sobel

(Walker Publishing Co., 1999;
reprinted Penguin Books, 2000. 420 pages)

On the Shoulders of Giant edited by Stephen Hawking
(Running Press, 2002. 1264 pages.)

Although the Sobel book is some five years old, I thought it should be reviewed because of its probable interest to readers of this journal and because the companion book, edited by Hawking, can very profitably be read in conjunction with it.

Let me begin with Galileo’s Daughter. Its title notwithstanding, this is really a book about Galileo Galilei. It does contain the (translated) texts of a large number of letters written to him by his daughter, a nun née Virginia, who assumed the name Suor Maria Celeste.1 Galileo’s replies have never been found, and presumably were destroyed by the Mother Superior of Maria Celeste’s convent after her death (since Galileo had been declared a heretic by the Church). These letters are valuable in that they help portray the human side of Galileo, and give the reader insight into the inner torments he suffered as the conflict between his strong religious beliefs and his scientific persona exacerbated. They also, collaterally, give a finely drawn picture of convent life in 17th century Italy, making one wonder realize the intense religiosity of any woman who would be willing to suffer the associated tribulations.

Galileo was born on Feb. 15, 1564 in Pisa, to which city his father, Vincenzio Galilei2 along with his wife Giulia, had translocated from Firenze shortly before. Vincenzio was a musician; in fact after returning to Firenze in 1572 he became a member of the famous Florentine Camerata, the group of musicians whose ideas led eventually to the introduction of baroque music and thus of opera.3

Galileo, after studying in a Florentine grammar school and then in a Benedictine monastery, enrolled in the University of Pisa in 1581, leaving in 1585 without a degree.4 Despite his academic failings, Galileo was appointed to the faculty in Pisa in 1589, where he taught physics and mathematics and began the researches into mechanics which much later led Albert Einstein to refer to him as the father of not only modern physics but of modern science altogether.

Three years later Galileo was appointed professor of mathematics at the University of Padua, a post he held for 18 years until, in 1610, he became chief mathematician and philosopher to Cosimo II, grand duke of Tuscany, and moved to Firenze thus attaining closure. (Everyone familiar with the Italian life style knows that Italians are never contented until they are able to live in their hometowns.) While in Padua, Galileo had been very active. First of all, he produced three illegitimate children by Marina Gamba, a woman whose lower class stations precluded her from becoming his wife.5 The first child, born in 1601, was the fore-mentioned Virginia. Livia was born a year later and then, in 1606, his son Vincenzio followed.

But Galileo was also active outside the bedroom during his time in Padua. It was here, in 1609, that he constructed his first telescope, based on a recent Dutch invention. He visualized it initially as military device, but then, in the winter of 1610, Galileo was inspired to look towards the heavens, and the story of the world changed instantaneously. He first viewed the moon, finding that it was not the perfect sphere postulated in Aristotelian-Ptolemaic cosmology. The discovery of the moons of Jupiter followed shortly, and the revelation that other "planets" existed led ultimately to his rejection of the geocentric cosmology. He named the Jovian moons the "Medicean planets" in a successful effort to curry favor with Cosimo II. His appointment to the Florentine court followed shortly after the publication of his book Sidereus Nuncius (i.e., the Starry Messenger).

Galileo tried unsuccessfully to use the observation of the Jovian satellites to measure longitude, a long-standing navigational problem that was actually not solved until the development of the chronometer in the next century. (Dava Sobel is also the author of the definitive work on this subject, Longitude, first published in 1996.) Further observational information for the heliocentric model included his Galileo’s discovery of the phases of Venus and the rotation of the sun itself (from tracking sunspots). His publication Sunspot Letters appeared in 1613.

Copernicus, in 1545, had published his heliocentric model of the universe in the book De revelutionibus. (This book is usually referred to in English, for example by Hawking, as On the Revolution of Heavenly Spheres.) Nobody had paid much attention to Copernicus’ work, not even the Inquisition, because nobody took it seriously, there being no observational data. But now things changed, and in 1616 Galileo published Treatise on the Tides (in Italian, rather than Latin, the normal language of scholars, in order to make it accessible to the people). His idea was that ocean tides were caused by the earth’s rotation (he of course knew nothing about gravity). There was a germ of truth in his ideas--the fact that there are two high and two low tides every 24 hours is certainly due to the earth’s rotation (although admittedly it could equally well be due to the moon’s rotation around the earth).

But trouble was just around the corner. The Church, scandalized that any one might believe that the earth rotated had just finished placing Copernicus’ work on the index of forbidden books.6 The Treatise was not banned, but Galileo was summoned before the Inquisition and admonished to desist from defending the earth’s revolution as fact, a decision which Galileo accepted. This seemed to leave leeway for using geocentricism as a computational model, in many ways like the Bohr atom. But when Galileo was called before the Inquisition again, in 1633, this time to defend his major work Dialogue on the Two Chief World Systems, Ptolemaic and Copernican, he was found guilty of heresy despite his protests that the book made it very explicit that the heliocentric model was nothing but a computational tool.

In 1633 the Church was embroiled in the Thirty Years’ war (1618-1648) and Pope Urban VIII had come under considerable pressure to support the Spanish who, while traditional political enemies of the Papal States, were nonetheless Catholics and hence on the Pope’s side in the war (which pitted Catholic against Protestant in Germany and adjacent lands). As a gesture of confirmation of his strong pro-Catholic leanings7 the Pope, who at one time (as Cardinal Barberini) had been a close friend of Galileo’s, led the anti-Galileo faction in the Vatican. (One can think, by way of analogy, Pres. Eisenhower’s sacrifice of the Rosenbergs in 1953, designed in all probability to confirm his own anti-Communist credentials.)

Sobel’s book gives a wonderfully complete account of Galileo’s trial for heresy, including much of the testimony. I have never seen this anywhere before, and it is simply not to be missed. The verdict of heresy meant that all of Galileo’s works, not only the Dialogue, were placed on the index. They remained there until 1835 (although in 1822 the Church permitted publication of new books that taught that the earth moved). Evolution, anyone?8 It also makes very clear the workings of a theocracy. Catholics were not only forbidden to write books about the earth’s revolution, they were forbidden to believe in it. Amazingly, only 143 years elapsed between Galileo’s trial and the American Revolution. This compares with the 144 years between the outbreak of the American civil war and today. This is the space of two lifetimes.9 One can understand the Founding Fathers’ insistence on separation of church and state. And the idea that something like half the world today either has theocratic governments or is predisposed towards them gives one pause for reflection.

Galileo was forced to recant at his trial, and sentenced to house arrest for the remainder of his life. (He lost his eyesight in 1637 and died in 1642.) He had first lived in the family homestead in Firenze after taking his position in the Medici court in 1610, but in 1617 moved south across the Arno a short distance to a new home, Bellosguardo. In 1631, desiring to be closer to his daughters in the Convent of San Matteo in Arcetri, he took a home there known as Il Gioello (the Jewel), and lived there until his death. Arcetri, which is close enough to downtown Firenze to be reached by city bus (ATAF), is now the location of the physics department of the University of Firenze (located on Largo Enrico Fermi). Il Gioello is still around, and is used as a sometime conference center. Directly opposite it is one of the best restaurants in the Firenze area, Omero, where my wife and I once had our Easter dinner. The Convent of San Matteo, nearby, is still in use, but today it houses Franciscan friars rather than nuns.

After the trial, Galileo wrote another book, Two New Sciences. It should have been non-controversial, since there was no discussion of cosmology, only basic science and mathematics. (The topics included strength of materials and motion, both free fall and projectile). But because all of Galileo’s works were on the forbidden index, no publisher would touch the book. Finally a publisher in the Netherlands (a Protestant country), Louis Elzevir, agreed to undertake its publication. Of course, the book was a sensation, even in Catholic countries; its success carried the Elzevir family on to a successful career in scientific publishing. The firm is still flourishing today, under the name Elsevier. In fact, Marcel Dekker, Inc., publisher of this journal, is a spin-off of Elsevier; the founder of the company, Maurice Dekker, worked at Elsevier. Just before World War II he was sent to the U.S. to establish an American branch of the company; eventually it separated from Elsevier.

I have already mentioned that the letters from Suor Maria Celeste to her father give a deeply personal picture of Galileo’s trials and tribulations. They also provide compelling insight into the cloistered life of 17th century Italy. The nuns in those days were primarily of the upper classes, because a dowry was required of all postulants, just as it was for marriage. Young women around the age of 15 who were not considered "marriageable" would be banished to the convent. Frequently "marriageability" had to do with physical appearance, but Galileo’s daughters were not considered marriageable because they were illegitimate. (Galileo’s son, Vincenzio, was "legitimized" by Grand Duke Cosimo II in 1619; this allowed Vincenzio to pursue a university education and, ultimately, a career.)

The Poor Clares, the order of nuns associated with the Franciscans, led a particularly Spartan life as they took a vow of poverty (they were supposed to beg if they needed money). Their day began at midnight with the first of the eight canonical hours, Prime, followed almost immediately by Matins. They were then allowed to go back to bed (they always slept in their clothes in case God called them in the middle of the night) rising around dawn for Terce. Sext followed at noon, then Nones in midafternoon. Around sunset they attended Vespers and then Compline before retiring. Somewhere in between Terce and Sext they also attended Mass, and received communion (a nearby priest celebrated the Mass). They filled in the rest of their spare time working in the convent and its gardens where they grew most of their own food. Somehow Suor Maria Celeste also found the time to write all those letters to her father whom she adored (despite the fact that he had banished her to the convent. She died shortly after the trial, at age 33, and shares a sarcophagus with her father in Firenze’s Santa Croce church. The interment there did not come until 1737, since for many years after his death Galileo was still considered a heretic.

Now let me briefly describe the Hawking book. It consists of English translations of the works of five authors that made seminal impacts on modern physics and astronomy. (Each translation is accompanied by a brief discussion entitled "His Life and Work" written by Hawking.)

The works included in the book are Copernicus’ On the Revolution of Heavenly Spheres; Galileo’s Dialogue Concerning two Sciences; Newton’s Principia; Kepler’s Harmony of the World; and selections from Einstein’s The Principle of Relativity (including both special and general). The works of Copernicus and Galileo are obviously a useful adjunct to the study of the Sobel book. The excruciating detail of these two works (covering over 600 pages between them) makes it unlikely that anyone but the most dedicated historian of science would read them in detail but even a casual skimming of selected portions will add considerably to the understanding of Renaissance cosmology.

All of the selections in the book merit inclusion in the library of scientists interested in the historical backgrounds of their profession. For example, I found it very helpful when reading Sobel’s description of Galileo’s Diaologue to refer to the relevant portion of Hawking’s book in order to clarify what Sobel ad written and to carry the subject further than she was able to do in her short book. In a similar manner I found the Copernicus section quite helpful. The Einstein section I read for enjoyment (discovering that the many writers on relativity since Einstein cannot match the master in clarity and vitality of expression. The sections on Kepler and Newton I found pretty hard going, and so far I have just skimmed them.


1. "Celeste" to honor her father’s astronomical research.

2. It was not uncommon in those days for eldest sons to receive a first
name derived from the family name; "Galileo," incidentally, derives
from "Galilee."

3. The first opera, Dafne (lost) was written by Jacopo Peri sometime before 1600. Baroque music differs from the polyphonic Renaissance style (as in the music of Palestrina, for example) in that it involves a dominant, monodic, musical line accompanied by a bass part (usually realized on a keyboard and/or low stringed instrument). This (presumably) made it possible for the listener to understand the words. Modern opera companies, appreciating the word "presumably," now make a practice of displaying supertitles even for operas performed in the vernacular. Although polyphonic music was still written during the Baroque era and even after (for example, the fugues of J.S. Bach) vocal music was almost always monodic.
4. Thus Galileo became, up until the time of Bill Gates, history’s most distinguished drop out.

5. Perhaps he objected to the fact that she has sex with a man to whom she wasn’t married!

6. After all, the bible in numerous citations tells the faithful that the earth is stationary. For example, Psalm 96, verse 10: Say among the heathen that the  Lord reigneth: the world also shall be established that it shall not be moved…(KJV).

7. That the Pope of all people had to make such a statement really says a lot about the politics of the time.

8. The Catholic Church’s position on evolution has actually been irreproachable to a scientist. It is the fundamentalist denominations that object to it.

9. When I was in high school I knew a woman, born in 1860, who had seen Sherman burn Columbia, SC, in 1865. By the same token, it is quite within the  realm of possibility that Ben Franklin (b. 1706) had met someone who had known Galileo.