Several years ago there was published in Rome a salutary edict which, in order to obviate the dangerous tendencies of our present age, imposed a suitable silence upon the Pythagorean opinion that the earth moves. There were those who impudently asserted th at this decree had its origin not in judicious inquiry, but in passion none too well informed… Therefore I propose in the present work to show to foreign nations that as much is understood of this matter in Italy, and particularly in Rome, as transalpine d iligence can ever have imagined… To this end I have taken the Copernican side in the discourse, proceeding as with a pure mathematical hypothesis and striving by every artifice to represent it as superior to supposing the earth motionless - not, indeed, ab solutely, but as against the arguments of some professed Peripatetics. These men indeed deserve not even that name, for they do not walk about; they are content to adore the shadows, philosophising not with due circumspection but merely from having memoris ed a few ill-understood principles.

 

With this announcement in the foreword To the discerning reader Galileo thought he had ensured the safety of his Dialogue … where, during the meetings of four days, there is discussion concerning the two Chief Systems of t he World, Ptolemaic and Copernican, propounding inconclusively the philosophical and physical reasons as much for one side as for the other, which was published in Florence in 1632 and dedicated to the new Grand Duke of Tuscany, Ferdinand II de' Medici. Indeed, Galileo's announcement contained the gist of the matter: Copernican theory presented as a mathematical hypothesis; terrestrial motion understood not in the absolute sense but only as methodological criticism of the Peripatetics, who opposed it; the censorship of 1616 defined as a salutary measure against scandal and the scent of heresy; and the whole book presented as a defence of the Roman ecclesiastic milieu, accused of ignorance abroad, where certain prohibitions had never prevented scientific investigation. What more could be asked?

 

Obtaining the imprimatur, however, was not easy. In Florence things had moved rather fast, but in Rome the Master of the Holy Palace, Niccolò Riccardi, a native of Genoa, had inexplicably delayed matters. Galileo had had dealings with him since the time of the Assayer, whose approval he had formalised, and they had met when Galileo visited Rome in 1624. Riccardi was nicknamed Father Monster for his amazing memory, it seems, and even more for his ugliness. He had never been particularly opposed to astronomical discoveries, and had always deemed it necessary to keep science separate from Scripture. But he was not a great intellectual power: 'He is ready to settle for a quiet life by postulating angels who, without difficulty or complications of any kind, direct the known movement of the celestial bodies.' Thus Galileo portrayed him, disconcerted more by Riccardi's mental laxity than by the angels. In 1630 Riccardi had read the manuscript of the Dialogue without raising objections, giving his approval for the Roman edition, which however was not published. It was strange that a year later, having asked to inspect only the preface and the epilogue, Riccardi was still delaying his opinion on the Florentine edition. Francesco Niccolini, the Tuscan ambassador to Rome, took a strong line on this and Riccardi finally gave his authorisation for printing, but demanded a written release relieving him of all responsibility. Clearly, he was under pressure from above, from very high up. In the end, he did not hide the fact that he was acting under the direct instructions of Urban VIII, sending the Florentine Inquisitor a letter with the Pope's demands. In addition to the known provisos, punctiliously included by Galileo in the preface, the Pope desired that, in line with his personal opinions, reference should be made to 'the reasons of Divine omnipotence ... which must calm the intellect.' Moreover, it was strictly forbidden to mention, either in the title or in the main argument, the problem of 'ebb and flow', that is, tidal motion - an extraordinary demand.

 

With official approval and permission, and with some correction to the preface made by Father Monster, the volume was ready within a few months. The Dialogue was the result, not only of Galileo's experience as a scientist, but also of his experience as a man. In his book, Galileo paid homage to two men who had been among his closest friends: the Venetian, Giovanfrancesco Sagredo, represented as a sort of new Copernican Socrates (as Campanella saw him, although it was perhaps only as a projection of himself), and the Florentine Filippo Salviati, depicted as an acute interlocutor, intellectually honest and free from bias. The third figure is an imaginary one: a certain Simplicio, a Peripatetic, a concentrate of all the errors of Aristotle's followers, prey to the most obtuse prejudices. Galileo explained in the preface that he had given this character the same name as that of Aristotle's ancient commentator, but the provocative linkage of his name to the simplicity of his thoughts was obvious to all.

 

The veneer of caution adorned only the preface. For the rest, the Dialogue was a brandishing of the sword against the foundations of the Aristotelian world and the 'unbelievable cowardice' of all those 'servile minds' incapable of rebelling against it. Galileo gathered the fruits of decades of work, reviewing all the stages leading to his Copernican convictions against notions such as: the incorruptibility of the heavens, unmasked by the telescope, with observations of the Moon and of sunspots, whose optical deformation had led him to hypothesise an inclination of the Sun's axis of rotation in respect to the plane in which the Earth orbited; the inconsistency of a single centre of the universe coinciding with that of the Earth, refuted by the knowledge acquired on the motion of falling weights; the static position of the Earth, contradicted, not only by the implausibility of the rapid rotation of the celestial sphere, but also by telescopic observation of the behaviour of the other planets in the solar system and by measurement of their orbits. Age-old myths on the motion of falling bodies, demonstrations claimed to disprove terrestrial movement, were eliminated through a single proof, that of the relativity of motion: inside a moving structure, such as a ship (but it could also be the Earth), the motion imparted to the containing structure is 'common to all the things contained in it and also to the air.' Accordingly, motion inside the structure was unaffected by it. In other words, the flight of a fly inside a ship (or the falling of a body on the Earth) will take place in the same way whether the ship (or the Earth) is moving or standing still.

 

All were castigated - Aristotle, Ptolemy, Tycho Brahe and, by implication, their still living followers, which was to have negative consequences for Galileo. His attack was wide-ranging, launched in a language that was terse and penetrating, occasionally caustic, and at times even lyrical, never trite, where each word had its own precise meaning, going straight to the centre of a problem without idle abstraction and leaving no space for misunderstanding. The Dialogue is thus not only one of the most important texts of modern science but also a literary masterpiece, in which physics is discussed in the language of poetry. There emerges in it, along with a passionate love of truth, a fascination with nature and its phenomena, almost humanised in the descriptions of their appearance and behaviour. That Moon we perceive is full of 'eminences and cavities', similar to our 'highest and steepest mountains', of 'detached and solitary boulders, very steep and precipitous', of plains that contain 'a mountain soaring high' or 'exceedingly dark material.' Its relation to the Earth, to which it always turns the same side, 'almost as if attracted by magnetic power', is ambiguous; and the Earth in recompense, on 'very clear nights', in turn reflects on the Moon the rays of the Sun, a positive effect 'when the Moon has most need of them', only then to respond negatively, by taking light away from it in an eclipse. Those 'flies, butterflies and such little winged animals', those darting 'little fishes', illustrate the principle of the relativity of motion. And there was an almost obsessive observation of daily life, seeking to find links with scientific theories in silk, velvet, mother-of-pearl, diamonds, marble, musical instruments, household items, and petty human limitations among those 'who know all poetry by heart, but are then dismayed to have to compose only four verses' and others who 'know all the precepts of Da Vinci, but are unable to paint a stool.'

 

Galileo's scientific exposition also advanced the bold concept of man, in virtue of his own nature, thirsting for knowledge, in a continuous, inexhaustible search which, truth by truth, comes ever closer to understanding the laws that govern the universe, even if 'there is no effect in nature, however small it may be, that can be entirely understood by even the most speculative intellect.' Galileo may have concluded the preface to the Dialogue by diplomatically reaffirming that he questioned the 'immobility of the Earth' only following a 'mathematical whim', not through ignorance, but through 'the knowledge of Divine omnipotence and awareness of the weakness of the human intellect'; but at the same time he was unable to restrain the enthusiasm that in truth his faith in the capacity of human reason aroused in him. 'My admiration is boundless,' he wrote, 'regarding the way in which reason overcame sound sense in Aristarchus and Copernicus and took charge of their belief.' This is hardly an awareness of human weakness.

 

Many readers, too many, understood immediately that human intellect, despite the best intentions, had by no means subdued itself before Divine omnipotence. To the point of getting their fingers burnt. A good part of the fourth day of the Dialogue was dedicated to discussing the reasons for the infamous 'ebb and flow' of the sea. Galileo had been interested in this problem for many years, probably since his time in Padua, and since 1616 his Discorso sul flusso e reflusso del mare [Discourse on Tides] had been circulating in manuscript form. Unable to determine the true cause of this phenomenon, he had maintained that tidal motion was caused only by the movement of the Earth and had no connection with the attraction of the Moon, as some other scientists, Kepler included, thought, and as is in fact the case. It would have been only a marginal extra element in favour of his hypothesis, and it was moreover debated among the Copernicans themselves. But why was the Pope so afraid of this issue as to bring it to the attention of the Inquisition? Since antiquity, the 'ebb and flow' of the sea had been considered one of the most mysterious and incomprehensible natural events, whose causes man could never understand. In the scholastic tradition, the legend that Aristotle had committed suicide because he had proved unable to discover the cause had persisted for years. In Catholic circles, it was held up as an example of how Divine omnipotence overstretched the feeble talents of man. Confronting the problem by means of science meant not only violating an age-old taboo, but also, in this specific case, going against the beliefs of the Pope. But this was far from all. Tidal ebb and flow, if Galileo had succeeded in his aim, would have sounded the death knell of mathematical hypothesis, since it would have constituted physical proof that the Earth moved. The study of the tides was not, indeed, considered the domain of mathematical sciences such as cosmology, but was regarded as a concern of natural philosophy. So far, Galileo, with his telescopic observations, had succeeded only in proving the falsity of Ptolemy, but not the truth of Copernicus, demonstrable only through geometry, and the danger that he might so succeed, thanks to tidal motion, could not have escaped the shrewd eye of the Pope, Barberini. Galileo, however, had obeyed orders and had not centred his Dialogue on the phenomenon of the tides, nor mentioned the latter in the title. But he had not refrained from explaining in detail his whole theory, indicating tidal motion as one of the most important 'statements of the Copernican system.' He had been careful not to omit mention of the Pope's ideas, and referred to the Pope himself without name, praising the 'most sound doctrine' of Divine omnipotence learned 'from a most erudite and most eminent person … before whom we must necessarily keep silent.' But, singing these praises, between one stupid utterance and another, was the simpleminded Simplicio. It was an unconsidered choice, and one that was to cost him dear.

 

The reading of the Dialogue stunned men of science, not only Galileo's closest followers and not only in Italy. A scene of fervent excitement, amazement and rapture dawned. It was immediately clear that this was a revolution. 'This is new light on ancient truths, of new worlds, new stars, new systems, new nations… it is the beginning of a new age,' cried Campanella with his usual impulsive élan. 'May He who guides all make haste. We for our own small part will follow. Amen.'

 

But not all were friends; and the 'new age', at least in Italy, was still in the future. Just dawning, it was soon to come to an abrupt halt.