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Galileo had now regained his home but not his freedom, special permission being required before he could go into Florence. He was suffering from several ailments and wished to live within easy reach of his physician. For this purpose he petitioned early in 1634 for leave to move into Florence. The reply was a mandate from the Inquisition forbidding him to ask again, under pain of being at once removed to Rome and actually confined in the prison of the Holy Office. Soon after this his beloved daughter, Sister Maria Celeste, who had almost despaired of seeing him again, owing to serious illness during his long absence, sank under her sufferings and died in April. Galileo was so ill that he expected soon to follow her.

Shortly afterwards he heard definitely, what he might have suspected before, that it was only the fact of his being out of favour with the Jesuits that had brought him into such trouble at Rome. Otherwise he could have held and taught any doctrine he pleased. Perhaps this galvanised him into fresh energy, for he soon set to work again on his projected new "Dialogues on two new sciences". These were Cohesion and Resistance to Fracture, and Uniform, Accelerated, and Projectile Motion, embodying the foundations of Dynamics. The books are full of interesting experiments. The form is similar to that of his forbidden work, the same interlocutors being introduced, and we find them discussing falling bodies, the motion of a pendulum, lines of quickest descent, the parabolic motion of projectiles, and other themes connected with dynamics, the strength of beams, the possible finite velocity of light, the harmonic vibrations of strings, the explanation of concords and discords, and similar subjects, some of them only occurring as digressions.

The MS. was completed in 1636, but the Inquisition had forbidden any of Galileo's work to be published, even reprints of his previous books, to which no exception had been taken. He tried to find a publisher outside Italy, but the presence of Scheiner in Germany and the fear of opposition from him and the Jesuits caused one project after another to be abandoned, until finally Elzevir produced the work at Amsterdam in 1638. Galileo pretended that this was pirated from a MS. copy, in order to observe the letter of the embargo laid on him by the Inquisition.

As soon as the MS. had been completed he projected a fresh series of problems, including the subject of Percussion, and also resumed his plan of determining longitude at sea by observation of Jupiter's satellites. The negotiation with Spain had dragged to an end in 1632, but in 1636, hearing that a prize of 30,000 scudi was offered by Dutch merchants for a sure method, Galileo offered his plan through his friend Diodati at Paris; using this means in order to keep the officials of the Inquisition in ignorance of what he was doing. His sight was failing, and when the Dutch Government sent him a gold chain as a sort of retaining fee, he was found in bed totally blind. He refused to keep the chain, fearing that he would be unable to complete his calculations. As a matter of fact his "Ephemerides" were afterwards completed, but owing to a series of accidents they were not published for two centuries.

His last astronomical discovery before his sight failed altogether was the explanation of what is called the moon's libration, by which we see rather more than half the surface of the moon, as it shows a little more to the north, south, east, or west. He became totally blind in December, 1637, and at length the entreaties of his friends for more liberty began to have greater effect. He had very occasionally been allowed to pay short visits, with precautions as to travelling at night so as not to be seen, but early in 1638 the Pope gave Castelli to understand that a proper petition might now receive consideration. This was sent, but the Pope also required a report from the local Inquisitor as to the reality of the infirmities, and even when Galileo was allowed upon this report being favourable, to move to Florence, his son was set to watch over his movements and to see that his visitors did not stay long, while he himself had to get special permission from Rome even to go to church at Easter.

A few months later Castelli was allowed to come to Florence and visit Galileo, partly in connection with the "Ephemerides" of the Medicean stars, which the Tuscan Lord High Admiral wished to take to Spain. Galileo returned to Arcetri in January, 1639, probably being ordered to do so, as his health had slightly improved. Being now close upon seventy-five years of age and very infirm, it appeared unnecessary to insist upon such close restrictions, and visitors were permitted more freely, including foreigners of distinction, some of whom visited Italy principally with the object of paying their respects to Galileo. It was in that year that the visit took place to which Milton referred when he wrote, "I found and visited the famous Galileo, grown old, a prisoner to the Inquisition for thinking in Astronomy otherwise than the Franciscan and Dominican licensers thought". A few months later the poet returned to Florence after paying a round of visits to other places and wintering in Rome.

In 1639 Viviani, "the last disciple of Galileo," came to live with him at the age of eighteen, and remained on the most intimate terms with him for the rest of the philosopher's life. In 1640 the old man was challenged by one of the Grand Duke's brothers to respond to an argument that the faint light on the "dark" part of the new moon, which Galileo had attributed to earth-shine, was in reality phosphorescence. This Galileo did very effectively with all his old dialectic skill.

Even later he was urged to reply to another argument against the Copernican system, but he had taken to heart the oft-repeated warnings he had received on the subject, and though readily demolishing the point raised against the system, he declared that no good Catholic could doubt the insufficiency of the Copernican doctrine in face of the unanswerable argument of the Divine Omnipotence, but as all the other systems were demonstrably false, it would be necessary to wait for a new one of which both science and theology can approve. It is quite clear that this is only a sarcastic evasion and cannot be understood to mean that he had really changed his mind.

His very last mechanical suggestion was the application of a pendulum to regulate a clock. His son Vincenzio made a drawing of the design from Galileo's dictation, but the plan was interrupted by his mortal illness, and Vincenzio himself also died before completing the clock.

Castelli tried to be with his old master to the end, but had to return to Rome towards the close of 1641. Torricelli, known to fame as the inventor of the barometer, shared with Viviani and Galileo's son the duties of amanuensis, but the sands were now rapidly running out, and the end came on January 8, 1642, when Galileo died after receiving the Pope's blessing.

His enemies were still unappeased, and though they failed in their endeavours to dispute his right to make a will, and to be buried in consecrated ground, they were able to do something, for the Pope, hearing that a public funeral and a marble monument were in contemplation, prevailed by threats upon the Grand Duke Ferdinand to cancel the arrangements.

Nearly a century later the monument in the Church of Santa Croce at Florence was erected by means of funds left for the purpose by Viviani, whose remains as well as Galileo's were removed thither.