Galileo's Daughter: A Historical Memoir of Science, Faith, and Love

Author: Dava Sobel
Translator: Xie Yanguang / Country: United States
Publisher:
Publish Date: 2002-03-01
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Honorable Father: The passing of the beloved sister, our dear aunt, has caused us immense grief; but compared to our concern for you, our sorrow for her loss seems insignificant. Now, in your world, you are truly alone, without a companion, and therefore your pain will be even greater. Since your dearest one has left you, the only thing we can imagine is how severe the trials you have endured from this sudden, completely unexpected blow. When we tell you that we grieve as deeply as you do, perhaps you might consider the universal suffering of humanity, where you might find even greater comfort, for we are all but fleeting passersby in this world, and soon we shall all go to our heavenly home, where alone there is perfect happiness. And we must believe that your sister’s blessed soul has already gone there. Therefore, in God’s name, we beg you, dear father, to seek comfort in God and surrender yourself to Him, for you know very well that it is God’s requirement of you; if you do not, it will only harm you and cause us pain, for we would be deeply grieved to hear that you are troubled and sorrowful: In this world, besides you, there is no one else who can be an example of virtue for us. I do not wish to say any more, but we can only sincerely and fervently pray to God for your comfort, and may God be with you forever, and with our burning love, we send you our warmest regards.
May 10, 1623, written from San Matteo. Deeply loving daughter, Sister Maria Celeste and Livia do not know when they will see their brother Vincenzo again. At least for now, Galileo feels it is best to leave this still-toddling little boy with Marina in Padua. Not long after Galileo left Venice, Marina married a respectable citizen, Giovanni Bartolucci, of similar social standing. Galileo not only approved of their marriage but also helped Bartolucci find a job with a wealthy friend of his in Padua. Galileo continued to send money to Marina for Vincenzo’s living expenses, while Bartolucci supplied Galileo with lens blanks for telescopes, obtained from the famous glassworks on the island of Murano within the Venetian waters, a supply that lasted until Florence was proven to be an even better source of pure glass.
Galileo rented a house in Florence, which had a high flat roof from which one could see the entire sky, where he could observe celestial phenomena and install grinding machines for lenses. During the waiting period for the house to be ready, he lived with his mother and two little girls for several months in a room he rented from his sister Virginia and brother-in-law Benedetto Landucci. Despite recent legal disputes, Galileo’s relatives provided him with a rather warm family environment, though the “harmful air of winter in this city” troubled him greatly. “After being away for so many years,” Galileo sighed, “I have encountered Florence’s thin air again, which is a cruel enemy to my head and the rest of my body. In the past three months, colds, bleeding, and constipation have weakened my body, making it frail and listless, so that I have been practically shut in at home, or more accurately, bedridden, yet I have not been fortunate enough to sleep, nor have I been able to rest.”
With health permitting, he devoted his time to studying the problem of Saturn. Saturn was a planet far more distant than Jupiter, and its distance was clearly at the limit of his best telescope’s resolution. He thought he saw two large, fixed satellites of Saturn. He described what he saw using a Latin phrase with the letters of the alphabet rearranged. If the phrase’s letters were restored to their correct order, it meant, “I have seen a very distant planet with three bodies.” To announce this as his discovery without causing ridicule before it was properly confirmed, he quickly sent this Latin phrase to several famous astronomers. Yet, not one of them could correctly decipher it. In Prague, the great Kepler, though now equipped with a telescope and considering it “more precious than the scepter symbolizing royal authority,” also misinterpreted the message, believing it meant Galileo had discovered two satellites of Mars.
Throughout the autumn of 1610, as Venus appeared in the night sky, Galileo studied the changes in its size and shape. He also kept a telescope trained on Jupiter for a long time, striving to determine the exact orbital periods of its four newly discovered satellites to further confirm their reality. Meanwhile, other astronomers complained that they had exhausted their efforts to see Jupiter’s satellites with inferior instruments but had achieved nothing, so they doubted the existence of these celestial bodies. Despite Kepler’s support, some maliciously accused the satellites of being optical illusions, perhaps even artifacts of Galileo’s lenses. Since these satellites had become a contentious issue for the Grand Duchy of Florence, it was necessary to address this situation immediately to protect the Grand Duke’s honor.
Galileo hurriedly made as many telescopes as possible, not only for the princes and nobles of Italy but also for export to France, Spain, England, Poland, and Austria. “To maintain and enhance the reputation of these discoveries,” Galileo argued, “I thought it necessary to let as many people as possible see the truth with their own eyes and acknowledge it.” Some famous philosophers, including some of Galileo’s former colleagues in Pisa, refused to use a telescope to see these so-called new things in Aristotle’s eternal universe. Galileo deflected their ridicule with a humorous tone: In December 1610, upon learning of one such opponent’s death, he loudly expressed the hope that the professor, though he had once disregarded the Medici stars in his lifetime, might encounter them on his journey to heaven.
To solidify his position as the one who announced this discovery, Galileo felt it wise to go to Rome, the eternal city, to widely publicize his findings. He had already visited Rome once in 1587 to discuss geometric problems with the outstanding Jesuit mathematician Christopher Clavius, who had written some influential commentaries on astronomy and would certainly welcome news of Galileo’s recent work. The Grand Duke Cosimo did not oppose this trip, believing it would enhance his status in Rome, as his brother Carlo held the traditional position of Cardinal of the Medici family in Rome at the time.
For a long time in the autumn of 1618, Galileo resisted the temptation to go outdoors and see any of the three comets, which seemed incredible, and it was especially so because he felt perfectly well and could engage in academic discussions with visitors. However, the air at night in November was terrifyingly dangerous to him, after all, he was in his early fifties, and most of that year he had been fighting one illness after another. Moreover, Galileo undoubtedly knew from his friends’ accounts that even if he risked his life to study these objects personally, he would not see much. Even with the highest-powered telescope, the outlines of comets or “hairy stars” remained blurry. When the telescope filtered out the light of stars, they became mere points of light; if the same treatment was applied to planets, they became small spheres. Comets were different from stars or planets, as they could not be clearly focused. Galileo hesitated because he believed comets were part of Earth’s atmosphere—in this case, he was in agreement with his contemporary Aristotle scholars, though for different reasons.
Galileo thus rejected the discovery of his Danish predecessor Tycho Brahe, who had observed a large comet in 1577 and another in 1585. Tycho was probably the most capable observer of celestial bodies with the naked eye, tracking the comet every night with his enormous measuring instruments to determine its position. Through his study of the position, he found that it was farther than the moon and perhaps as far as Venus, which, for the thinking of the 16th century, meant one of two things: either the comet had crashed into the crystalline heaven as Aristotle had described, or these heavens did not exist. Tycho, being the only European brave enough to take such a risk in this field, chose the latter hypothesis in 1572 to identify a new star, which convinced him that change could occur in the unchanging sky.
Galileo, having personally witnessed the second new star in 1604, supported the late Tycho’s explanation of its nature and importance. However, he despised Tycho’s planetary system, considering it a clumsy compromise between Ptolemy and Copernicus. As for the comet Tycho had meticulously tracked, Galileo also dismissed it as a phantom target. He regarded comets as unusual luminous phenomena in the air—most likely reflections of sunlight by high-altitude water vapor—rather than celestial bodies themselves. Galileo believed that you could not measure the distance of a comet, just as you could not catch a rainbow or control the aurora borealis.
Thus, as if the curtain had risen on a play, several characters had already gathered, and their conversation immediately turned to the topic at hand. The discussion of this day drew a line between the Aristotelian/Ptolemaic and Copernican worldviews. For this, Simplicio presented Aristotle’s view, that the Earth was fundamentally different from all celestial bodies—because it was composed of elements rather than aether. Galileo’s alter ego, Salviati, tried to find a place for the Earth in the sky. And Sagredo, with his usual simplicity, endowed the Earth—“the dregs of the universe, a place of filth and corruption—with a unique power derived from its own peculiar mutability: ‘As for me, I think the Earth is very lofty, great, and admirable, and so it is because of the constant modifications, changes, and generations that occur on it. If the Earth did not undergo any changes, it would be a vast desert or a mountain of jade; or if the great stretches of water that once covered it had frozen during the flood period, making it a huge, lifeless, unchanging ice ball, then I would consider it a dead, worthless piece of the universe, essentially a superfluous, non-existent thing.’”
Regarding how the Sun changes through solar flares and shrinks around its waist in circles, Salviati supported him with evidence from their “friend’s” telescope. He proposed that the Moon and all stars, whether fixed or moving, might also be changing, though such changes had not yet been discovered. Aristotle believed that immutability was the defining attribute of perfect celestial bodies, and this claim was completely turned on its head here.