Galileo's supporters in Rome were not looking forward to his visit. They feared that his eagerness and conviction would only make things worse. Far better for him to stay at home, working away quietly at his arguments.
The Tuscan Ambassador who would have to be his host, wrote to the Grand Duke's Secretary of State:
"... this is no fit place to argue about the Moon or, especially in these times, to try and bring in new ideas."34
The Ambassador was quite right, but it made no difference. With gracious permission from Grand Duke Cosimo, Galileo arrived in Rome in December 1615.
To begin with he behaved as if he was still the feted and celebrated observer of Jupiter from four years before. His cock-suredness completely prevented him from absorbing the scepticism and repugnance with which he was met in many quarters. On the contrary, he was in better spirits than he had been for a long time. His visits to leading Romans took the form of lectures and dazzling discussions, as if he was still amongst his admiring students from Padua.
If, during the conversation in these elegant salons, a doubting cleric or nobleman objected that the Earth could not revolve in just one day, that such speed was unthinkable, Galileo would turn the argument around and point out that, according to Ptolemy, the entire constellation revolved in one day, and that was unimaginably larger than this planet. If they took up the old argument that the Earth's motion must at least be noticeable by us, Galileo would invite them to think that they were aboard a ship: let a ball sink slowly in a container of water while the ship is at rest. It will sink straight down, without touching the sides. But if the ship is under way at a constant speed - what happens to the ball then? It still sinks straight down. It is not affected by the even motion of the ship.
These were impressive intellectual demonstrations. But they did not help the matter in hand. People who got thoroughly trounced in such discussions hardly looked on Galileo with any greater good will. Slowly this became apparent to him.
It was time to play his trump card, his irrefutable new argument. In January 1616 he sent a letter to one ofhis adherents in the College of Cardinals, the very young Alessandro Orsini. The letter was a treatise on the tides, the causes of high and low water.
In the days when he had frequently travelled between Padua and Venice, Galileo had noticed the great barges that carried fresh water across the lagoon and into the city. The water was contained in large, open vessels, and when the barges changed speed for any reason, the water moved. If the speed was reduced, the water sloshed forward, rising at the front end of the container and sinking at the back.
As usual, Galileo was amazingly quick to make a connection between a physical observation and an underlying principle: the sea was like the water in the container, and the boat was the Earth. In this way, high and low tide could easily be explained, but only ifone assumed that the Earth moved!
Working out a theoretical justification, did indeed prove difficult, not least because, in discussion, he had so splendidly demonstrated that the Earth's motion did not influence other movements, an absolutely central plank in the argument against opponents of Copernicus. But the tides had to be explained that way, if they were to constitute a directly observable proof that the Earth moved.
He ended up with a complicated reasoning that took into account both the annual movement of the Earth round the Sun and the daily revolution of the Earth round its axis. The theory did have to have several additions bolted on to it, taking account of sea depths, narrow inlets and the like, to explain the large local variations in tides, but these did not shake Galileo's conviction. If one could only follow his reasoning one could, right then and there, and with one's own eyes, see clear proof of Copernican ideas - just the kind of proof that Bellarmine had predicted would never be found.
His theory of tidal movements - which Galileo doggedly clung to until well into his old age - was, however, completely wrong. But that was not the deciding factor in the events that now followed in quick succession.
The Holy Office had at length come to the conclusion that Father Caccini's string of allegations against Galileo were too diffuse. The matter had to be shelved. But at the same time many churchmen looked on with disquiet and distaste at the dazzling way the mathematician carried on his Copernican propaganda right in the heart of Rome, the bastion of Christendom.
And this caused Galileo's "salvaging expedition" to set in train just what he wanted to avoid. The cardinals decided to attack the issue from another direction. It was unnecessary to hit Galileo directly. The ideas of Copernicus were the problem. If they were prohibited, all discussion would cease.
Now things moved at lightning speed. No lengthy investigations were needed, for Copernican ideas were well known. The Inquisition's leaders had a meeting and formulated two assertions which the cardinals believed summed up the Copernican view. They then handed them over to a group of experts for an evaluation and conclusion. The assertions were these:
"That the Sun is the centre of the world and hence immovable of local motion."
"That the Earth is not the centre of the world, nor immovable, but moves according to the whole of itself, also with a diurnal motion."35
The Inquisition's experts took four days over their work. The majority were Dominicans with only one Jesuit. Their expertise lay solely in the theological field, none of them had any qualifications in astronomy. What happened was exactly what Galileo had most feared: Copernicus' theories were condemned from a literal reading of Holy Scripture, without assessing one single material physical or astronomical argument. The conclusion, which the cardinals of the Holy Office unanimously adopted, was this: The first assertion was
"foolish and absurd in philosophy, and formally heretical, since it explicitly contradicts in many places the sense of Holy Scripture (.. .)"36
The other assertion was given
"the same censure [qualification] in philosophy and that in regard to theological truth it is at least erroneous in faith."37
That the assertion concerning the Sun as the world's immobile centre was "formally [formaliter] heretical", did not simply mean that it was a formal mistake to postulate it. On the contrary, the wording implied the grossest possible censure. Anyone who, in the future, maintained that the Sun stood still, would be viewed as a pure heretic - and would have to accept the consequences of it.
This resolution was passed by the Inquisition on 24 February 1616. That same day, Cardinal Orsini tried to advance Galileo's tidal theory to Paul V. The timing was the worst imaginable, and the offensive failed completely. The Pope said that the best thing Orsini could do was to rid Galileo of his delusions. When the Cardinal continued to argue, the Pope cut him off abruptly. No sooner had Orsini left the room, than the Pope summoned another cardinal, one with very different views: Robert Bellarmine.
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