His ambitions and problems of course ranged far beyond Rome. He continued to favor the French over the Spanish in their war, and so came to fear Spanish spies in the Vatican. And rightfully so, as there were many of them. He had not been pleased, people said, to learn of Galileo’s attempt to sell the celatone and jovilabe to the Spanish military. And when he was not pleased it could go very badly. Once someone sneezed during a service he was conducting in St. Peter’s, and afterward he decreed that anyone taking snuff in church would be excommunicated. Even more of an eye-opener was his decision to have Archbishop Mark Anthony de Dominis burned at the stake for heresy. De Dominis had already been dead for three months when this happened, having expired in the Castel Sant’Angelo after an interrogation by the Inquisition, but no matter; on the feast day of Doubting St. Thomas, the body was exhumed and taken to Campo dei Fiori and burned at the stake, its ashes then thrown into the Tiber. The offense that had outraged the pontiff to such a degree involved speaking about precisely this matter of atomism and transubstantiation for which Galileo had been secretly denounced.

But a heretic was a heretic, and anything could happen to them. Servants all across Italy were much more shocked by a new story that spread with the speed of amazement; Urban, oppressed by all his worries, had been having trouble sleeping at night, and it seemed to him that it was the chirping and singing of the birds in the Vatican gardens that was keeping him awake, and so he ordered them all killed. “He ordered his gardeners to kill every bird in the Vatican!” people said. “All the birds killed, so he can sleep better in the morning!” This was the man Galileo was trying to reason with.

OFTEN AS HE WROTE HE SIGHED. So many had died. His parents and Marina, Sarpi and Sagredo and Salviati, Cesarini and Cosimo … The world of his youth, and of the years in Padua, seemed to have disappeared into the darkness of a previous epoch. He had lived on into a more troubled time. When he was sick it often seemed to the household that it was sorrow that kept him in bed more than any pains of the flesh.

To comfort himself for two of these losses, Galileo structured his new treatise as a series of dialogues between Filippo Salviati, Giovan-francesco Sagredo, and a third character named Simplicio. Salviati would express the views that Galileo himself was trying to teach, although Salviati also referred from time to time to an “Academician,” which the context made clear was Galileo himself. Sagredo, the man Galileo had eulogized as “my idol,” was then the voice of an intelligent courtier of the time, curious and open-minded, willing to be educated by Salviati’s explanations. This was so much the way they had been in real life—not just patrons to Galileo, but friends, teachers, brothers—like the elder brothers he had never had, and had so much enjoyed having. There had to be someone you could boast to who would enjoy hearing it, who would be proud to hear it of you; and wiser heads who would look after you too. He wrote with his heart full and his throat tight:

Now, since bitter death has deprived Venice and Florence of those two great luminaries in the noon of their years, I have resolved to make their fame live on in these pages, so far as my poor abilities will permit, by introducing them as interlocutors in the present argument. May it please those two great souls, forever cherished in my heart, to accept this public monument of my eternal love. And may the memory of their eloquence assist me in delivering to posterity the promised reflections.

The character Simplicio, on the other hand, was indeed a simpleton, as the name suggested—although there had been a Roman philosopher with such a name centuries before. But his meaning was obvious. He stood for all the enemies Galileo had ever sparred with, the whole crowd mashed together, not only the many who had denounced him openly but also the many more who had spoken in private, or in lectures or sermons all over Italy. Simplicio’s lame arguments would illustrate every one of the logical errors and deliberate misunderstandings, the exaggerations and false syllogisms and irrelevancies, the sheer stubborn stupidity, which Galileo had faced over the years. Often he laughed aloud as he wrote—not his low “huh huh huh huh” of true amusement, but the single bark of his sarcastic laugh.

The book was structured as four days of dialogue between the three men, gathered to talk at Sagredo’s palazzo in Venice, that pink ark where Galileo had spent so many magnificent hilarious nights. The first day’s discussion concerned his astronomical discoveries, including many new observations about the moon that he had made since publishing the Sidereus Nuncius. Along the way he interspersed jokes, wordplay, odd little observations that were mysterious even to him:

From the oldest records we have it that formerly, at the Straits of Gibraltar, Abila and Calpe were joined together with some lesser mountains which held the ocean in check; but these mountains being separated by some cause, the opening admitted the sea, which flooded in so as to form the Mediterranean. Consider the immensity of this….

Well, yes; but this event had happened a million years before, and the “oldest records” he spoke of did not exist. How did Galileo know about it? He himself was not completely sure. His old dreams haunted him; he remembered them in fluctuating detail, sometimes even dreaming he was out in space again. He knew for sure he had unfinished business there, but he was less and less sure what it was. He knew that his mind had been tampered with, and more than once overwhelmed.

Thus he had his Sagredo ask, when they were discussing the telescope,

Will the new observations and discoveries made with this admirable instrument never cease?

And his Salviati answered, If its progress follows the course of other great inventions, one may hope that in time things will be seen which we cannot even imagine at present.

Indeed.

Later in that First Day, he wrote, But we are not keeping track of the flight of time…. a person’s memory becomes so confused with such a multitude of things.

So true.

Later still he wrote, But surpassing all stupendous inventions, what sublimity of mind was his who dreamed of finding means to communicate his deepest thoughts to any other person, though distant by mighty intervals of place and time! Of talking with those who are in India; of speaking to those who are not yet born, and will not be born for a thousand or even ten thousand years …

What sublimity of mind, indeed! People really had no idea. He revised the passage so that it seemed to refer to language and to writing, but for him it also referred to something both more immediate and more mysterious. To speak with people who would not be born for a thousand years….

The Second Day of his dialogues concerned the movement of the Earth—the evidence for it, and the explanations for why it was not immediately evident to those standing on the Earth’s moving surface. This required a detailed description of some parts of his motion studies, and Galileo could not help having Salviati say about this: How many propositions I have noted in Aristotle (meaning always his science) that are not only wrong, but wrong in such a way that their diametrical opposites are true.

Ha! But Simplicio was a stubborn character, in the book as in the world. Sagredo tried to explain to him the concepts of relative motion. He tried everything. He used for an example the effect of backspin on tennis balls; he even proposed a clever thought experiment concerning shooting crossbow bolts from a moving carriage, forward and back, to see if the bolts flew longer or shorter distances if shot in the direction of the carriage’s movement or against it. He pointed out, almost kindly, after the failure of one such Socratic lesson, that Simplicio could not seem to free his mind from his preconceptions enough to perform a thought experiment. None of this made any difference to Simplicio, and the Second Day came to an end without him being illuminated by any new understanding.