by Mario Livio
Initially, Galileo refused to believe that the Balance was written by Grassi, especially because of its sharp sarcasm pointed directly at Galileo. Blind to his own deficiencies when it came to manners and the treatment of others, Galileo felt that this attack was unwarranted, since Guiducci never mentioned Grassi by name. His doubts were quickly dispelled, however, by a letter he received at the beginning of December from his Lincean friend Ciampoli: “I see that you cannot bring yourself to believe that Father Grassi is the author of ‘The Astronomical Balance,’ ” he wrote, “but I repeat to assure you once again that His Reverence and the Jesuit Fathers want you to know that it is their work, and they are so far from the judgment that you make about it that they glory in it as a triumph.” Ciampoli added that Grassi himself had usually spoken about Galileo in a much more reserved manner than the other Jesuits did, and that therefore he [Ciampoli] was rather surprised to see Grassi use “so many biting jokes.” As we shall see later, judging from Grassi’s subsequent behavior, it is hard to avoid the impression that Grassi’s “more reserved manner” may have been nothing but an act, to conceal more sinister intentions.
Grassi’s Balance contained a few valid criticisms. For instance, he pointed out the self-contradiction concerning the absence of a detected parallax, which Galileo used to infer the comets’ distances while separately arguing through his avatar Guiducci that parallaxes could not be applied to comets. Grassi also remarked that a few of the ideas advanced by Galileo in Guiducci’s “Discourse” were, in fact, not original but rather closely resembled those expressed by the sixteenth-century polymath Gerolamo Cardano and the philosopher Bernardino Telesio. In general, Grassi demonstrated an excellent command of optics and an up-to-date familiarity with all the relevant scientific publications. This was hardly surprising, since even from the little known about him, Grassi was exceptionally knowledgeable. He not only experimented with and wrote about optics and vision, about the physics of light, and about atmospheric pressure, but he was also a great architect who designed the Church of St. Ignatius at the Collegio Romano, as well as a church in Terni and a Jesuit college in Genoa. He even staged an opera, in addition to his accomplishments as a mathematician.
On the other hand, Grassi’s essay came with its own set of problems. First, it included a surprisingly naïve reliance on ancient, imaginary tales. Second, it contained an internal self-inconsistency, and third, it directed some underhanded jabs at Galileo. For example, in trying to prove Aristotle’s claim that friction with the air could heat bodies to incandescence (which is true in the case of meteorites and artificial satellites reentering Earth’s atmosphere), Grassi seemed to trust bizarre stories from antiquity, such as one describing how the Babylonians cooked their eggs by swirling them on slings. Astonishingly, the inconsistency in Balance was associated with the declared purpose of the essay itself. Grassi wrote: “I wish to say that here my whole desire is nothing less than to champion the conclusions of Aristotle.” This was a strange assertion, given that his own theory located the comets far beyond the Moon, contrary to Aristotle’s notion of immutable heavens. It may be that the insertion of this statement, endorsing Aristotle unequivocally, reflected advice from higher-up Jesuit circles rather than Grassi’s own intentions. Finally, there were the “biting jokes,” the slyest of which changed Guiducci’s phrase “some other cause for the apparent deviation” [of the comet’s path from the zenith toward the north] to read “some other motion.” Grassi then wrote this viciously cunning paragraph:
What is this sudden fear in an open and not timid spirit which prevents him from uttering the word that he has in mind? I cannot guess it. Is this other motion which could explain everything and which he does not dare to discuss—is it of the comet or of something else? It cannot be the motion of the circles, since for Galileo there are no Ptolemaic circles. I fancy I hear a small voice whispering discreetly in my ear: the motion of the Earth. Get thee behind me thou evil word, offensive to truth and to pious ears! It was surely prudence to speak it with bated breath. For, if it were really thus, there would be nothing left of an opinion which can rest on no other ground except this false one.
Then, delivering a parting blow, Grassi added a line strikingly similar to Marc Anthony’s recurring, sarcastic pronouncement “And Brutus is an honorable man” in William Shakespeare’s Julius Caesar: “But then certainly Galileo had no such idea, for I have never known him otherwise than pious and religious.”
How can we reconcile these insidious remarks with Ciampoli’s statement that Grassi had always spoken about Galileo with respect? A few Galileo scholars suggested that maybe these passages were the work of Scheiner, whose well-known animosity toward Galileo was constantly increasing. At any rate, Galileo had to consider how to react without worsening his relations with the mathematicians of the Collegio Romano. For his part, Mario Guiducci, whose name was, after all, listed as the author of the Discourse, responded to Grassi’s Balance by sending a letter to his former professor of rhetoric at the Collegio Romano, Tarquinio Galluzzi. He did not attempt to address the physical arguments, declaring only that while he had different views on comets from those of the “Reverend Mathematician,” he had no intention of offending Father Grassi or any other of the Jesuit mathematicians.
As for Galileo himself, after consulting with his Roman friends Cesi, Ciampoli, Cesi’s cousin (and Lincean Academy member) Virginio Cesarini, and another founding member of the academy, Francesco Stelluti, it was decided that Galileo should send his response to Cesarini. In addition to not wanting to further muddy the water, Galileo’s friends judged that it would be improper for him to answer directly to Grassi, since the latter had chosen to hide behind the fictional disciple Sarsi.
Virginio Cesarini was an excellent choice to receive Galileo’s manuscript, since he was known to be a true believer (he was later chamberlain to two Popes) and also an informed intellectual and a poet, who served as a conduit between scientists working in different cities. His open-mindedness and intellect were perfectly demonstrated in a letter he sent to Galileo in 1618, in which he urged the master to create and spread a new logic “based on natural experiments and on mathematical demonstrations,” since he believed that such a “more certain logic… will at once open the intellect to consciousness of the truth and shut the mouths of some vain and pertinacious philosophers whose science was opinion and, what is worse, other people’s and not their own.”
These very sentiments were echoed in a pronouncement by philosopher and mathematician Bertrand Russell more than three hundred years later: “Philosophy is to be studied, not for the sake of any definite answers to its questions… but rather for the sake of the questions themselves; because these questions enlarge our conceptions of what is possible, enrich our intellectual imagination, and diminish the dogmatic assurance which closes the mind against speculation.”
As it turned out, recurring illnesses, preoccupation with his literary interests, and a series of historically consequential events delayed Galileo’s response until October 1622, when he finally sent a manuscript to Cesarini. On the literary side, Galileo returned to his lifelong, almost obsessive fascination with comparing poets Ariosto and Tasso. The significant historical incidents included the deaths of Pope Paul V, Cardinal Roberto Bellarmino, and, even more impactful for Galileo, his greatest supporter, the Grand Duke Cosimo II, all in 1621. Since Cosimo’s son Ferdinando was only ten years old at the time of his father’s death, the Grand Duchess Christina and her daughter-in-law, Maria Maddalena of Austria, both singularly religious women, were appointed as regents of the duchy.
Galileo’s manuscript, when eventually completed, was entitled The Assayer, referring to an extremely precise scale that goldsmiths were using, and providing a contemptuous contrast to Grassi’s Balance, which implied a cruder weighing device. As soon as Cesarini received the manuscript, he sent copies of it for comments to Ciampoli, Cesi, and a few other friends. He also informed Galileo that the Jesuit mathematicians, who had he
ard about the manuscript’s arrival, were “eager and anxious, and they even dared to ask me for it; but I have refused them it because they would have been able more effectively to obstruct its publication.”
In spite of these assurances, Cesarini did not resist the temptation to read parts of The Assayer to a few of his acquaintances. One way or another, the Jesuits also heard about those passages—in seventeenth-century Rome, they were the equivalent of Big Brother—and, according to Cesarini, “they have fathomed everything.” There was still the thorny problem of obtaining permission to print the pamphlet. At the time, it was standard practice that a “print approval,” or imprimatur, would have to be obtained from the ecclesiastical authorities for any manuscript to be published. Cesarini managed to have the book examined by the Dominican Niccolò Riccardi, who was a Genoese follower of Galileo. Riccardi did not disappoint. He expressed effusive admiration for the book: “thanks to the subtle and solid speculation of the author in whose days I consider myself happy to have been born, when, no longer with the steelyard [a weighing apparatus] and roughly, but with such delicate assayers the gold of truth is weighed.” This was not the common imprimatur that the Inquisition’s bureaucracy expected. It sounded more like present-day laudatory blurbs that appear on the covers of new books. Cesarini was happy to take it. He rapidly inserted the revisions suggested by about a half dozen members of the Accademia dei Lincei and rushed the work to print.
Figure 8.1. Title page of The Assayer.
Still, unexpected external circumstances further delayed publication. On July 8, 1623, Pope Gregory XV died after only two years of papacy. Then, following exhausting negotiations among the cardinals, Cardinal Maffeo Barberini was elected on August 6 as Pope Urban VIII. After years of the nonerudite (although surprisingly undogmatic in doctrinal matters) Pope Paul V, the election of a relatively young, brilliant, presumably open-minded, and refined intellectual Pope was greeted with hope by Galileo, his friends, and, indeed, all progressive Catholics. As a cardinal, Barberini had shown great admiration for Galileo, even to the point of sending him an ode, “Adulatio Perniciosa,” in which he expressed his esteem for Galileo’s astronomical discoveries. Barberini had also apparently played a role in preventing Copernicanism from being pronounced altogether heretical in 1616. Perhaps most important, shortly before Barberini was elected as Pope, Galileo congratulated him on the occasion of his nephew, Francesco Barberini, having completed his studies. In his reply, Barberini wrote: “assuring you that you find in me a very ready disposition to serve you out of respect for what you so merit and for the gratitude I owe you.”
Given these expressed sentiments and the fact that Pope Urban VIII appointed Galileo’s friends Cesarini, Ciampoli, and Stelluti to master of the chambers, secretary of the briefs, and privy chamberlain, respectively, it should come as no surprise that the Accademia dei Lincei dedicated The Assayer to the Pope. In October 1623 the book was finally ready. Unfortunately, it still contained many typographical errors, but it included a wonderful dedication written by Cesarini himself and signed by all the members of the Lincean Academy. The dedication read, in part: “This we dedicate and present to Your Holiness as to one who has filled his soul with true ornaments and splendors and has turned his heroic mind to the highest undertakings.… Meanwhile, humbly inclining ourselves at your feet, we supplicate you to continue favoring our studies with gracious rays and vigorous warmth of your most benign protection.”
Cesi, the founder of the academy, presented a splendidly bound copy to the Pope on October 27. (Figure 8.1 shows the title page.) Copies of the book were also given to the cardinals. This marked the official approval of The Assayer, a book whose literary verve and intellectual passion were hailed by one of Galileo’s twentieth-century biographers as “a stupendous masterpiece of polemic literature.” Grassi’s opinion was, of course, very different.
CHAPTER 9 The Assayer
Even though The Assayer was formally written as a response to Orazio Grassi’s (Sarsi’s) Balance, the topic of comets became rather peripheral in Galileo’s polemical masterpiece, providing in some sense only a pretext for an exposition of Galileo’s thoughts about various aspects of science, and a platform for him to attack Tycho Brahe’s system.
Right from the start, Galileo presents two of his principal viewpoints: first, his disdain for blind reliance on authority and, second, his philosophy on the nature of the cosmos. The following passage has become one of Galileo’s most memorable manifestos:
In Sarsi I seem to discern the firm belief that in philosophizing one must support oneself upon the opinion of some celebrated author, as if our minds ought to remain completely sterile and barren unless wedded to the reasoning of some other person. Possibly he thinks that philosophy is a book of fiction by some writer, like the Iliad or Orlando Furioso, productions in which the least important thing is whether what is written is true. Well, Sarsi, that is not how matters stand. Philosophy is written in this grand book, the universe, which stands continually open to our gaze. But the book cannot be understood unless one first learns to comprehend the language and read the letters 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 proclamation about the mathematical nature of reality is particularly striking. We should remember that he made this statement at a time when very few mathematical “laws of nature” had been formulated (mostly by him!). Yet he somehow anticipated what Nobel laureate Eugene Wigner would call in 1960 “the unreasonable effectiveness of mathematics”—the fact that the laws of physics, which the entire universe seems to obey, are all stated in the form of mathematical equations. Even earlier, in 1940, Einstein turned this fact into the definition of physics: “What we call physics comprises that group of natural sciences which base their concepts on measurement, and whose concepts and propositions lend themselves to mathematical formulations.” But what is it that gives mathematics such powers?
With very little evidence to base this opinion upon, Galileo thought in 1623 that he knew the answer: the universe “is written in the language of mathematics.” It was this dedication to mathematics that raised Galileo above Grassi and the other scientists of his day, even when his specific arguments fell short of convincing—and even though he assigned to geometry a more important role than it seemed to deserve at the time. His opponents, he wrote, “failed to notice that to go against geometry is to deny truth in broad daylight.”
Impressively, together with his conviction that nature was geometrically structured, Galileo also understood that all scientific theories are only tentative and provisional. That is, science has to be constantly reappraised as fresh observational evidence becomes available. By admitting that everything he said had been “set forth tentatively as a conjecture… open to doubt and, at best, only probable,” Galileo introduced the revolutionary departure from the medieval, ludicrous notion that everything worth knowing was already known. Instead, Galileo expressed only one near certainty: that to decipher any of nature’s secrets would require the language of mathematics.
The Assayer offered its author the opportunity to exhibit some of his most witty sarcasm. For example, he and Grassi differed in their understanding of the origin of heat. Whereas Grassi, following the Aristotelians, thought that heat was caused entirely by motion, Galileo attributed heat also to the detachment of matter particles via friction forces, or to compression. In modern terms, heat is a form of energy transferred, for example, due to a temperature difference between two systems, with the temperature being determined by the average speed of the random motion of atoms or molecules. The problem with Grassi’s concept was that because of his trust in ancient authors, he committed the naïve error of believing legendary tales, such as that mentioned earlier of the Babylonians cooking eggs through whirling them on slings. Galileo pou
nced on this fallacy like a cat on a slow mouse:
If Sarsi wishes me to believe, on the word of Suidas [Greek historian], that the Babylonians cooked eggs by whirling them rapidly in slings, I shall believe it; but I shall say that the cause of this effect is very far from the one he attributes to it. To discover the true cause, I reason as follows: “If we do not achieve an effect which others formerly achieved, it must be that we lack something in our operation which was the cause of this effect succeeding, and if we lack one thing only, then this alone can be the true cause. Now we do not lack eggs, or slings, or sturdy fellows to whirl them, and still they do not cook, but rather cool down faster if hot. And since we lack nothing except being Babylonians, then being Babylonian is the cause of the egg hardening.”
Another interesting and consequential discussion in The Assayer concerned the very nature of matter and the role of the senses. Following a distinction that dated all the way back to the Greek philosopher Democritus in the fifth century BCE, Galileo identified two types of properties: those that were intrinsic to physical bodies, such as shapes, numbers, and motions, and those that were, in his view, associated with the existence of conscious, sentient observers, such as tastes and odors. He wrote:
“To excite in us tastes, odors, and sounds, I believe that nothing is required in external bodies except shapes, numbers, and slow or rapid movements. I think that if ears, tongues, and noses were removed, shapes and numbers and motions would remain, but not odors or tastes or sounds. The latter, I believe, are nothing more than names when separated from living beings.”
Galileo’s reintroduction of these concepts from antiquity into the conversation of early seventeenth-century philosophy may have later inspired and affected similar ideas of Descartes and especially of the empiricist philosopher John Locke. In his influential 1689 treatise Essay Concerning Human Understanding, Locke specifically distinguished between what he regarded as properties that are independent of any observer (dubbed “primary qualities”), such as number, motion, solidity, and shape, and “secondary qualities”: those that produce sensations in observers, such as color, taste, odor, and sound. As we shall see later, even this seemingly innocuous discussion of those qualities that Galileo regarded as being subjective, and representing mere names in the external object, was about to contribute, to some extent at least, to his subsequent troubles with the Church.