It was rare for the citizens of Florence to see anything of their lord, Grand Duke Francesco de' Medici. He spent most of his time isolated in his villa in Pratolino with his extremely unpopular former mistress, now the Grand Duchess Bianca. Rumours in the city had it that they experimented with poisons which Bianca was to use in her murderous projects. The worst suspicions seemed to have been borne out when both of them died suddenly, on the same day in October 1587.
In fact, it was malaria that had killed them. At all events, that was the story of his brother and successor, and since Ferdinando was of a different stamp to Francesco, he was believed. Ferdinando de' Medici had been made a cardinal at the age of fifteen and had then spent many years in Rome, where he proved himself to be a womaniser of a somewhat unseemly sort for a churchman, but also a brilliant administrator and an avid collector of antique statues. He bought a large house on the slopes of Monte Pincio in order to have somewhere to store his collection. It was called the Villa Medici. But now he had to return home to Florence and his grand ducal title.
On the whole Ferdinando was a good ruler. He left the Church and married a distant relative. She was Christina of Lorraine, the granddaughter of King Henri II, a woman who was to be of great significance to Galileo. But more important for the mathematician's immediate future was Ferdinando's choice of his successor as cardinal.
It was generally accepted that a powerful family like the Medicis had to maintain their representation within the College of Cardinals. But now there was no suitable family member available. Instead, Grand Duke Ferdinando sought the election of a man he trusted - Francesco Maria del Monte.
The new Cardinal was not notably interested in questions of theology. Del Monte was a well educated aesthete, a man with a taste for the good life, but also seriously interested in poetry, art, music and science. He was well versed in Vincenzio Galilei's musical theory. Cardinal del Monte was not opulently rich, but lived very comfortably in the Palazzo Madama near the Piazza Navona. He liked latching on to promising young men and helping them - he was the first to discover Caravaggio's unruly artistic genius.
The Cardinal had a brother. His name was Guidobaldo and he was a mathematician.
During his visit to Rome, Galileo had become acquainted with Guidobaldo del Monte, although it did not help him very much in his quest for a position. Now, suddenly, the situation had drastically altered: Guidobaldo's brother was not only a cardinal, but was the Grand Duke's trusted man in Rome.
Galileo spoke to Guidobaldo, Guidobaldo to the Cardinal, the Cardinal to Grand Duke Ferdinando. The result was that in the autumn of 1589, Galileo could again return to his birthplace, Pisa, now as the 25-year old professor of mathematics.
But before leaving Florence, he gave a lecture in the city's prestigious Academy, founded to promote Tuscan as the foundation for the common Italian written language. He had been set the task of describing the location and dimensions of Dante's Hell. Florence was not a city to take its famous authors lightly. A well-known dramatist had once been exiled because he had announced that the sainted Catherine of Siena was a better writer than Florence's own Boccaccio!
The young freelance mathematician took his listeners by storm.
He was intimately versed in The Divine Comedy and the universe that was depicted there. Galileo explained the precise construction Dante had calculated for his Hell. It was shaped like a broad funnel, with its opening up on the surface of the earth. In each of its descending circles ever worse punishments were meted out to ever worse sinners, and using his skill in geometry, Galileo worked out the diameter of the various diabolical departments, in which various devils tortured the unhappy sinners for all eternity. The circles got narrower and narrower until they ended up at the centre of the Earth, where Lucifer himself reigned and everything was everlasting frost and ice - as far away from Heaven, light and warmth as it was possible to get.
Lucifer was at the centre of a sphere. Galileo did not need to produce arguments for this. His educated audience knew only too well that the earth was round. Every scholar had known that since antiquity. Eratosthenes of Alexandria had with fair accuracy calculated the circumference of the Earth 200 years before Christ - admittedly with a bit of luck in his assumptions. Thus Galileo had a starting point for estimating the relative dimensions.
In the matter of the relationship between the Earth and the rest of the universe, Dante, and all other learned men, held to a model that had been perfected by Ptolemy, another Greek from Alexandria, in the second century AD. Very briefly it can be described as follows: the Earth is the fixed and stable centre of the universe. Around it revolve the heavenly bodies at various distances, attached to invisible spherical shells - spheres - which propel them in circular orbits.
This Ptolemaic model seemed hardly more than plain and self-evident common sense - after all, that was how one experienced the Sun, Moon and stars. But Dante's universe was also a marvellous, ingenious alloy of cosmology and theology. Throughout the Middle Ages Ptolemy's thoughts had combined with theological ideas to form a mighty construction, in which God and his angels inhabited the different spheres - or heavens. The interplay between theology and astronomy was extremely intricate. For example, the tilt of the Earth's axis was explained by the Fall: as we know, this ended the state of paradise and brought transition and death into the world. God introduced the seasons and thus "the passage of time" by the simple expedient of tipping the Earth slightly out of its formerly "perfect" position.
But Galileo's subject was Hell. According to Dante, these funnel-shaped circles were created when Lucifer was thrown out of the upper reaches of Heaven, hit the Earth with great force - quite literally as a fallen angel - and then bored into the soil right to the centre of the sphere.
However, the young mathematician who had so impressed his fellow citizens with his understanding of Hell's dimensions, knew something that very few of his listeners had appreciated. An obscure canon by the name of Copernicus from the faraway Baltic coast, had developed a new theory. This theory was slowly permeating educated European circles. It was recklessly daring and could demolish the entire ingenious Ptolemaic edifice.
Galileo did not utter one word about this to the Academy in Florence, because something else was quite clear to him: such a huge cosmological and theological structure would never fall without resistance.
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