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.
