What exactly was said during those six audiences, has been another subject-matter of conjecture and controversy. Only a few points have been established with certainty: first, that in spite of Galileo's attempts at persuasion, Urban refused to revoke the decree of 1616; secondly, that Galileo's impression derived from the six long audiences was that he could write pretty well anything he pleased in support of Copernicus so long as he avoided theological arguments, and stuck to speaking ex hjpothesi.
Thirdly, Urban himself made a suggestion how to get around the difficulty of arguing in favour of the Copernican system without asserting it to be true. The suggestion was this: assuming that a hypothesis explains satisfactorily certain phenomena, this does not necessarily mean that it is true, for God is all-powerful and may have produced the said phenomena by some entirely different means which are not understood by the human mind. This suggestion of Urban's, on which he laid great store, played a crucial part in the sequel.
Thus encouraged, and in the full sunshine of papal favour, Galileo, who was now past sixty, felt the road at last free to embark on his great apologia of Copernicus, which, as we know, he intended to call Dialogue on the Flux and Reflux of the Tides. It took him nevertheless four years to write it 10a ; for nearly three, from 1626 to '29, he seems to have laid it aside, under various excuses and against the urging of his friends. He probably felt that the favour of princes is shortlived as the tide itself, and that his powerful enemies were working against him. One may also suspect that he was hampered by a recurrent psychological blockage, a repressed doubt in the soundness of his "conclusive proof ".
But once again he could not retreat. In January, 1630, the Dialogue was completed.
4. Dialogue on the Great World Systems
The Dialogue is carried on by three characters. Salviati, the brilliant savant, is Galileo's mouthpiece; Sagredo, an intelligent amateur, plays second fiddle to him under the guise of neutrality, and Simplicio, the good-humoured simpleton, defender of Aristotle and Ptolemy, fulfills the role of the clown who is kicked in the pants. Salviati and Sagredo had been friends of Galileo, and were now both dead; Simplicio, Galileo claimed, derived his name from Simplicius, the sixth century commentator on Aristotle, but the double meaning is evident. It is Simplicio who, after being shown up as an ass over and again, trots out at the very end Pope Urban's argument as coming "from a most eminent and learned person, and before whom one must fall silent": whereupon the other two declare themselves silenced by "this admirable and angelic doctrine", and decide "to go and enjoy an hour of refreshment in the gondola that awaits us". And thus the Dialogue ends with what can only be described as a rude noise at the Pope – with the consequences that one may expect.
The Dialogue is divided into four days. The first is devoted to the refutation of the Aristotelian view of the cosmos in general. Passages of witty journalism alternate with others which suddenly ascend to an aloof and majestic vision, and the language assumes breath-taking beauty. In attacking the Platonic dualism of earthly corruption – heavenly perfection, Sagredo explains:
"I cannot without great wonder, nay more, disbelief, hear it being attributed to natural bodies as a great honour and perfection that they are impassible, immutable, inalterable, etc.: as, conversely, I hear it esteemed a great imperfection to be alterable, generable, and mutable. It is my opinion that the Earth is very noble and admirable by reason of the many and different alterations, mutations, and generations which incessantly occur in it. And if, without being subject to any alteration, it had been all one vast heap of sand, or a mass of jade, or if, since the time of the deluge, the waters freezing which covered it, it had continued an immense globe of crystal, wherein nothing had ever grown, altered, or changed, I should have esteemed it a wretched lump of no benefit to the Universe, a mass of idleness, and in a word superfluous, exactly as if it had never been in Nature. The difference for me would be the same as between a living and a dead creature. I say the same concerning the Moon, Jupiter, and all the other globes of the Universe. The more I delve into the consideration of the vanity of popular discourses, the more empty and simple I find them. What greater folly can be imagined than to call gems, silver and gold noble, and earth and dirt base? For do not these persons consider that, if there were as great a scarcity of earth as there is of jewels and precious metals, there would be no king who would not gladly give a heap of diamonds and rubies and many ingots of gold to purchase only so much earth as would suffice to plant a jessamine in a little pot or to set a tangerine in it, that he might see it sprout, grow up, and bring forth such goodly leaves, fragrant flowers, and delicate fruit?
It is scarcity and plenty that make things esteemed and despised by the vulgar, who will say that here is a most beautiful diamond, for it resembles a clear water, and yet would not part with it for ten tons of water. These men who so extol incorruptibility, inalterability, and so on, speak thus, I believe, out of the great desire they have to live long and for fear of death, not considering that, if men had been immortal, they would not have had to come into the world. These people deserve to meet with a Medusa's head that would transform them into statues of diamond and jade, that so they might become more perfect than they are." 11
The battle for and against Copernicus is really joined on the second day, on which the objections against the earth's motion are refuted in terms of terrestrial physics. The central part of the argument concerns the relativity of motion. The classic objections had all been variations on the same theme: that if the earth rotated, everything not firmly attached to it would be left behind – cannon balls, falling stones, birds, clouds, and so forth. In his refutation, Galileo comes very near to a correct theory of impetus, and to Newton's First Law. He shows that a stone dropped from the top of a moving ship's mast would not be left behind because the stone shares the ship's momentum; and by analogy, that a stone dropped from a tower, or a cannon ball in flight, shares the earth's momentum.
But he could not entirely break loose from the Aristotelian dogma about circular motion. He postulates that if a body is left to itself, it will continue, under its initial momentum, to move, not in a straight line, but in a circular orbit through eternity. The reason for this Galileo explains in the opening part of the first day, and repeats over and again:
"... straight motion being by nature infinite (because a straight line is infinite and indeterminate), it is impossible that anything should have by nature the principle of moving in a straight line; or, in other words, towards a place where it is impossible to arrive, there being no finite end. For nature, as Aristotle well says himself, never undertakes to do that which cannot be done, nor endeavours to move whither it is impossible to arrive." 12
This belief contradicts Galileo's intimate knowledge of centrifugal forces, the tendency of an object moving in a circle to fly off at a tangent in a straight line. On the second day another classic objection against the earth's rotation, that bodies not attached to the earth would fly off into space, is admitted by Galileo as valid in theory, but negligible in practice, because the centrifugal force is so much smaller than the earth's attraction. 13 He thus asserts in one passage that a stone lying in a field has a natural tendency to persist in its circular motion, and in another that it has a natural tendency to fly off in a straight line. Similarly, he believed that freely falling bodies describe a circular path. 14 Thus even this most determined opponent of Aristotelianism could not rid himself of the old circular obsession – which partly explains Galileo's rejection of Kepler's Laws.
The second day ends, on Galileo's own admission, in a stalemate. He has refuted the objection that on a rotating earth detached bodies would be left behind, etc.; but he has not proved that the earth does rotate. On either hypothesis, whether she moves or stands still, stones would fall and birds would fly as they do.
The third day is concerned with the astronomical arguments for and against Copernicus, and here Galileo is downright dishonest. He first shows that the Copernican system is supe
rior to the Ptolemaic by the familiar arguments from the Jupiter moons and the phases of Venus. He then explains that to "save" the planets' apparent stations and retrogressions, Ptolemy had to introduce "very great epicycles" which Copernicus was able to dispense "with one single motion of the earth". But he breathes not a word about the fact that Copernicus, too, needs a whole workshop full of epicycles; he keeps silent about the eccentricity of the orbits, the various oscillations and librations, the fact that the sun is neither in the centre of the motions, nor lies in their plane; in a word, he deliberately evades the real problems of astronomy which had started Tycho and Kepler on their quest. The planets all move in perfect circles at uniform linear velocities around the sun (which, for instance, would make Saturn's period twenty-four years instead of thirty). 15 All problems appear solved "with admirable facility"; for "in the Ptolemaic hypothesis there are the diseases, and in the Copernican their cure." 16
It is true that Galileo was writing for a lay audience, and in Italian; his account however, was not a simplification but a distortion of the facts, not popular science, but misleading propaganda. Even his latest, admiring biographer is prompted to the remark:
"A drastic simplification of Copernicus may have seemed to him an easier didactic device. This is, at least, the charitable hypothesis. But the problem remains of how Galileo could commit the capital error, against which he had warned others so many times, of constructing theories in defiance of the best results of observation." 17
Even so, the arguments are again inconclusive, for all that Salviati succeeds in proving against Simplicio is that the heliocentric system saves the phenomena more elegantly than the geocentric, but not that it is true. Moreover, he keeps silent about the fact that the Tychonic system fits the phenomena equally well.
To break the stalemate, the famous theory of the tides is brought out on the fourth day. But before that, at the end of the third, a new and unexpected argument makes its appearance. It is derived from the sunspots, and is introduced with a flourish:
"Hearken then to this great and new wonder. The first discoverer of the solar spots, as also of all other celestial novelties, was our Lincean academician, and he discovered them anno 1610..." 18
The "Lincean academician" is the expression by which the Galileo in the Dialogue refers to himself.
After thus reasserting his spurious claim, he proceeds to claim another discovery of Scheiner's: that the sun, and with it the spots, rotate on an axis which is tilted against the plane of the ecliptic. As a result of this, the spots also travel round the sun in "tilted" circles (as seen from the earth); and their curve changes according to the earth's position – just as the curvature of a tilted spinning top changes to the eye as we walk around it. Ergo, Galileo concludes, the changing curves along which the sunspots travel prove, in a manner "so solid and rational as never before", that the earth moves round the sun. 19
At this point poor Simplicius turns into a relativist and correctly observes that the curves of the spots would look just the same whether the sun travelled round the earth or the earth round the sun. Salviati proceeds to demolish this objection: if we assume that the sun travels round the earth, the spots will look the same only if we also assume that the sun's axis always remains parallel to itself; and this he finds "very hard and almost impossible to believe". 20 Simplicius, intimidated, pipes down; Sagredo exclaims "that amongst all the ingenious subtleties I ever heard, I have never met with anything of greater admiration to my intellect or that has more absolutely captivated my judgement." 21
One simply gapes. Salviati wins his case by pretending that it was virtually impossible for one heavenly body to travel round another while its axis remains parallel to itself. Yet that is, of course, what the earth does while travelling round the sun: its axis remains parallel to itself at a constant tilt of 23 1/2 degrees. If it was impossible to believe that the sun could move thus, then it was equally impossible that the earth should move thus. Yet in a later section Galileo discusses at great length the reasons why the earth moves thus, and explains that the preservation of the fixed tilt of its axis "is far from having any repugnance or difficulty in it." 22
The changing faces of the sunspot-paths were as obvious a consequence of the tilt in the sun's axis as the changing seasons are a consequence of the tilt in the earth's axis. It was as simple as that. But the two pages in which Galileo argues the point against Simplicius 23 are among the most obscure and incomprehensible in the book. He employs his usual tactics of refuting his opponent's thesis without proving his own; in this case not by sarcasm, but by confusing the issue.
There can be no doubt that Galileo's theory of the tides was based on unconscious self-deception; but in the light of the above there can also be little doubt that the sunspot argument was a deliberate attempt to confuse and mislead. To represent the constant tilt of a rotating body as a new and inconceivable hypothesis, when every student since Pythagoras knew that this was the reason why summer followed winter; to obscure this simple issue by the novelty of curving sunspots, while making the complexities of Copernicus appear deceptively simple, was part of a deliberate strategy, based on Galileo's contempt for the intelligence of his contemporaries. We have seen that scholars have always been prone to manias and obsessions, and inclined to cheat about details; but impostures like Galileo's are rare in the annals of science.
The fourth and last day of the Dialogue is taken up almost entirely by the theory of the tides, which is elaborated in more detail. The annual variations in the tides are explained by the tilt of the earth's axis, the monthly variations by monthly changes in orbital velocity. 24 Kepler's explanation of the tides by the moon's attraction is rejected with the remark that "despite his open and penetrating mind" he has "lent his ear and his assent to the moon's dominion over the waters, to occult properties [gravity] and such-like little fancies." 24a
Another surprising thing about the Dialogue is that Galileo not only misrepresented the Copernican system as a beautifully simple affair, but seems to have been himself unaware of its complexities. He had never taken much interest in the tiresome details of planetary theory, and there was no real reason for him to plod through the technical chapters in the Revolutions from cover to cover. If he had done so, he could not have believed that all planets move with the same linear velocity, nor attributed the idea to Copernicus that the moon either shines in her own light or is transparent to the light of the sun. 25 About the insoluble difficulties of the Copernican system we learn only by an aside:
"... how each planet governs itself in its particular revolutions, and how precisely the structure of its circle is framed, which is what is commonly called the Theory of the Planets, we cannot yet undoubtedly resolve. Mars, that has so much puzzled our modern astronomers, is a proof of this." 26
This was written some twenty years after Kepler's determination of the Martian orbit laid a new foundation for planetary theory. * The truth is that after his sensational discoveries in 1610, Galileo neglected both observational research and astronomic theory in favour of his propaganda crusade. By the time he wrote the Dialogue he had lost touch with new developments in that field, and forgotten even what Copernicus had said.
____________________
*
It will be remembered that the New Astronomy's sub-title is Studies on Mars.
5. The Imprimatur
The manuscript was completed in January, 1630.
Galileo intended to supervise the printing of the book in Rome, but could not go at once. His friends assured him that there would be no difficulty, and that all was sunshine. Faithful Father Castelli, who now lived in Rome, wrote that Urban VIII had assured Campanella in an audience that "if it had depended on him, the prohibition of 1616 would never have been passed." 27 Another member of the old guard, Monsignor Ciàmpoli who was now Papal Secretary, wrote that at the Vatican "they were longing for Galileo more than for any beloved damsel." 28
He
arrived in Rome at the beginning of May, and was received in a long audience by Urban VIII. The Pope again confirmed that there was no objection against discussing the merits of the Copernican system, provided that it was treated strictly as a hypothesis. He objected, however, to the intended title, Dialogue on the Flux and Reflux of the Tides, which laid too much emphasis on physical proof, and suggested that it should be called a Dialogue on the Great World Systems instead. He was, of course, far too busy to read the book himself, and left this task to the censors.
The function of Chief Censor and Licenser was exercised by the "Master of the Palace", Father Niccolo Riccardi. He was another Florentine, a member of the Castelli-Ciàmpoli clique, and accordingly devoted to Galileo, though he believed that the Ptolemaic and Copernican systems were mere highbrow pastimes since the ultimate truth was that the stars were moved by angels. But this did not prevent him from admiring the ingenuity of men like Galileo who were plotting the courses of these angelic gymnastics. Because of his enormous girth, Riccardi had been called by the King of Spain Il Padre Mostro, the Father Monster, and all his friends referred to him by this affectionate nickname. By a perverse twist of history it was this pure-hearted and lovable man who, by his bungling, became the chief cause of the tragedy.
The Father Monster read through the manuscript of the Dialogue, and came to the conclusion that it was far above his head. He knew that His Holiness had approved of the idea of the book, had showered favours on Galileo, and encouraged him to go ahead. But he also sensed, though unable to follow the argument in detail, that the book was thinly disguised propaganda for Copernicus, and contradicted in spirit and letter the decree of 1616. To escape the dilemma he instructed his assistant, Father Visconti, to work through the text and to make suitable alterations.