I most firmly accept and embrace the Apostolic and ecclesiastical traditions and the other observances and constitutions of the Church. I also accept Sacred Scripture in the sense in which it has been held, and is held, by Holy Mother Church, to whom it belongs to judge the true sense and interpretation of the Sacred Scripture, nor will I accept or interpret it in any way other than in accordance with the unanimous agreement of the Fathers.
Galileo’s Letter to the Grand Duchess Cristina indirectly charged his opponents with violating this oath by bending the Bible to their purposes. His opponents, on the other hand, judged Galileo guilty of the same crime. His only hope of winning the argument lay in producing proof positive for the Copernican system. Then, since no truth found in Nature could contradict the truth of Scripture, everyone would realise that the Fathers’ judgment about the placement of the heavenly bodies had been hasty, and required reinterpretation in the light of scientific discovery.
December 1615 thus brought Galileo to Rome brandishing new support for Copernicus – derived from observations of the Earth, not the heavens. The tidal motions of the great oceans, Galileo believed, bore constant witness that the planet really did spin through space. If the Earth stood still, then what could make its waters rush to and fro, rising and falling at regular intervals along the coasts? This view of the tides as the natural consequence of the turning Earth had originally occurred to him nearly twenty years previously, at Venice, when he boarded the barges that carried drinking water into the city from Lizzafusina. Watching the way the large cargoes of water sloshed in response to any changes in the ships’ speed or direction, he had found a model for the ebb and flow of the Adriatic and the Mediterranean.
Now, lodged at the Tuscan embassy in the Villa Medici, Galileo passed the early part of January 1616 setting down in writing for the first time his theory of the tides. His social life during this labour consisted of meeting with fifteen to twenty men at a time in the homes of various Roman hosts, where he argued Copernicus’s cause in his most compelling style. The nervous Tuscan ambassador, Piero Guicciardini, fairly choked through these evenings, for he dreaded the possible cost of Galileo’s actions.
‘He is passionately involved in this fight of his’, Guicciardini complained to the grand duke, ‘and he does not see or sense what it involves, with the result that he will be tripped up and will get himself into trouble, together with anyone who supports his views. For he is vehement and stubborn and very worked up in this matter and it is impossible, when he is around, to escape from his hands. And this business is not a joke, but may become of great consequence, and the man is here under our protection and responsibility.’
Galileo needed the evidence of the tides to support Copernicus because his astronomical findings to date had failed to prove the Earth’s motion. It was all very well to argue, as Galileo did, that a rotating, revolving Earth made for a more rational universe – that asking the innumerable, enormous stars to fly daily around the Earth at fantastic speeds was like climbing to a cupola to view the countryside and then expecting the landscape to revolve around one’s head. Such reasoning, however, said nothing about the way God had actually constructed the firmament.
Even Galileo’s discovery of the phases of Venus, which he had dealt as a death blow to the Ptolemaic system, did not constitute proof of the Copernican. The planetary system of Danish astronomer Tycho Brahe could take Venus by the horns and still enable the Earth to remain immobile. According to the Tychonic order, the five planets orbited the Sun, while the Sun – surrounded by Mercury, Venus, Mars, Jupiter and Saturn – circled the stationary Earth. Although Tycho had based this theory on decades of careful observations, Galileo dismissed his plan as even sillier than the Ptolemaic. Since he could not prove the Copernican system by telescope alone, however, he turned to the tides to cement the case. He required the seas to rise to the rescue, not merely of Copernicus’s reputation or his own, but to preserve Italy’s future scientific pre-eminence and – most important – to protect the honour of the Catholic faith. For if the Holy Fathers banned Copernicus, as rumour predicted they might do at any moment, then the Church would endure ridicule when a new generation of telescopes, probably manned by infidels, eventually uncovered the conclusive evidence for the Sun-centred system.
The waters of the world occupy a moving vessel, Galileo wrote in his ‘Treatise on the Tides’. This vast container of water turns on its axis once every day and travels around the Sun once a year. The combination of the two Copernican motions accounts for all tides. The timing and magnitude of specific tides in different locations, however, depend also on many contingent factors, including the extent of each body of water (this was why ponds and small lakes lacked tides), its depth (and consequently the volume of fluid involved), the way it orients itself on the globe (since an east-west waterway like the Mediterranean experienced more dramatic tides than the nearly north-south Red Sea), and its nearness to other bodies of water (which proximity could cause powerful currents and floods, as at the Straits of Magellan where the Atlantic met the Pacific Ocean). Galileo, who never once left Italy, had gathered reports from far and wide to flesh out his explication.
‘To hold fast the basin of the Mediterranean and to make the water contained within it behave as it does surpasses my imagination,’ Galileo declared, ‘and perhaps that of anyone else who enters more than superficially into these reflections.’
But here, again, the fact that Galileo could not account for the tides without moving the Earth did not prove that the Earth moved. What’s more, his theory of the tides, though carefully crafted and eminently reasonable, was wrong. Throughout his life he ignored the true cause of the tides, which rise and fall by the pull of the Moon, because he failed to see how a body so far away could exert so much power. To him, the concept of ‘lunar influence’ smacked of occultism and astrology. Galileo occupied a universe without gravity.* As for the force that made moons orbit planets and planets orbit the Sun in Galileo’s cosmology, they might as well have been pushed around by angels.
Kepler, Galileo’s German contemporary, made the Moon the centrepiece of his own tidal theory. Kepler’s thinking, however, riddled with mystical allusions to the Moon’s affinity for water, alienated Galileo’s strictly logical mind. (Kepler had even posited intelligent beings on the Moon, as builders of the features observed from Earth.) What’s more, Galileo may have had some trepidation about relying on the testimony of a German Protestant.
Galileo presented his manuscript treatise on the tides to one of the newest cardinals in Rome, twenty-two-year-old Alessandro Orsini, a cousin of Grand Duke Cosimo. Galileo wanted Cardinal Orsini to pass the paper on to the current pope, Paul V, whose endorsement might help settle the issue. The young cardinal dutifully delivered the paper, but the sixty-three-year-old pontiff refused to read it. Instead, His Holiness pushed the moment to its crisis by convening expert consultors to decide once and for all whether the Copernican doctrine could be condemned as heretical.
The pope summoned his theological adviser, Roberto Cardinal Bellarmino, the pre-eminent Jesuit intellectual who had served as inquisitor in the trial of Giordano Bruno. Cardinal Bellarmino, the ‘hammer of the heretics’, had once confided to Prince Cesi of the Lyncean Academy that he personally considered the opinion of Copernicus heretical, and the motion of the Earth contrary to the Bible. (This admission prompted Cesi to wonder whether De revolutionibus would ever have been published had Copernicus lived after the Council of Trent, instead of before it.)
Bellarmino knew Galileo from meetings at social occasions over a period of some fifteen years, had viewed Jupiter’s moons through his telescope in 1611, and highly respected his achievements, which he could appreciate more than most, having studied astronomy himself at Florence. The only fault Cardinal Bellarmino found with Galileo was the man’s insistence on treating the Copernican model as a real-life scenario instead of a hypothesis. After all, there was no proof. The cardinal further opined that Galileo should stick to astronomy in public and not try to tell anyone how to interpret the Bible.
The Council of Trent, Cardinal Bellarmino took pains to point out, prohibited the interpretation of Scripture contrary to the common agreement of the Holy Fathers – all of whom, along with many modern commentators, understood the Bible to state clearly that the Sun travelled around the Earth.