Though these plans had been carried on in secret, yet Galileo's suspicions were excited; and he obtained leave from Cosmo to go to Rome about the end of 1615.[22] Here he was lodged in the palace of the grand duke's ambassador, and kept up a constant correspondence with the family of his patron at Florence; but, in the midst of this external splendour, he was summoned before the inquisition to answer for the heretical doctrines which he had published. He was charged with maintaining the motion of the earth, and the stability of the sun, with teaching this doctrine to his pupils, with corresponding on the subject with several German mathematicians, and with having published it, and attempted to reconcile it to Scripture, in his letters to Mark Velser in 1612. The inquisition assembled to consider these charges on the 25th of February, 1615; and it was decreed that Galileo should be enjoined by cardinal Bellarmine to renounce the obnoxious doctrines, and to pledge himself that he would neither teach, defend, nor publish them in future. In the event of his refusing to acquiesce in this sentence, it was decreed that he should be thrown into prison. Galileo did not hesitate to yield to this injunction. On the day following, the 26th of February, he appeared before cardinal Bellarmine, to renounce his heretical opinions; and, having declared that he abandoned the doctrine of the earth's motion, and would neither defend nor teach it, in his conversation or in his writings, he was dismissed the court.
Having thus disposed of Galileo, the inquisition conceived the design of condemning the whole system of Copernicus as heretical. Galileo, with more hardihood than prudence, remained at Rome for the purpose of giving his assistance in frustrating this plan; but there is reason to think that he injured by his presence the very cause which he meant to support. The inquisition had determined to put down the new opinions; and they now inserted among the prohibited books Galileo's letters to Castelli and the grand duchess, Kepler's epitome of the Copernican theory, and Copernicus's own work on the revolutions of the heavenly bodies.
Notwithstanding these proceedings, Galileo had an audience of the pope, Paul V., in March, 1616. He was received very graciously, and spent nearly an hour with his holiness. When they were about to part, the pope assured Galileo, that the congregation were not disposed to receive upon light grounds any calumnies which might be propagated by his enemies, and that, as long as he occupied the papal chair, he might consider himself as safe.
These assurances were no doubt founded on the belief that Galileo would adhere to his pledges; but so bold and inconsiderate was he in the expression of his opinions, that even in Rome he was continually engaged in controversial discussions. The following very interesting account of these disputes is given by Querenghi, in a letter to the cardinal D'Este:—
"Your eminence would be delighted with Galileo if you heard him holding forth, as he often does, in the midst of fifteen or twenty, all violently attacking him, sometimes in one house, sometimes in another. But he is armed after such fashion that he laughs all of them to scorn,—and even if the novelty of his opinions prevents entire persuasion, at least he convicts of emptiness most of the arguments with which his adversaries endeavour to overwhelm him. He was particularly admirable on Monday last in the house of signor Frederico Ghisilieri; and what especially pleased me was, that before replying to the contrary arguments, he amplified and enforced them with new grounds of great plausibility, so as to leave his adversaries in a more ridiculous plight, when he afterwards overturned them all."
The discovery of Jupiter's satellites suggested to Galileo a new method of finding the longitude at sea. Philip III. had encouraged astronomers to direct their attention to this problem, by offering a reward for its solution; and in those days, when new discoveries in science were sometimes rejected as injurious to mankind, it was no common event to see a powerful sovereign courting the assistance of astronomers in promoting the commercial interests of his empire. Galileo seems to have regarded the solution of this problem as an object worthy of his ambition; and he no doubt anticipated the triumph which he would obtain over his enemies, if the Medicean stars, which they had treated with such contempt, could be made subservient to the great interests of mankind. During his residence at Rome in 1615 and 1616, Galileo had communicated his views on this subject to the comte di Lemos, the viceroy of Naples, who had presided over the council of the Spanish Indies. This nobleman advised him to apply to the Spanish minister, the duke of Lerma; and, through the influence of the grand duke Cosmo, his ambassador at the court of Madrid was engaged to manage the affair. The anxiety of Galileo on this subject was singularly great. He assured the Tuscan ambassador that, in order to accomplish this object, "he was ready to leave all his comforts, his country, his friends, and his family, to cross over into Spain, and to stay as long as he might be wanted at Seville or at Lisbon, or wherever it might be convenient to communicate a knowledge of his method." The enthusiasm of Galileo seems to have increased the lethargy of the Spanish court; and though the negotiations were occasionally revived for ten or twelve years, yet no steps were taken to bring them to a close. This strange procrastination has been generally ascribed to jealousy or indifference on the part of Spain; but Nelli, one of Galileo's biographers, declares, on the authority of Florentine records, that Cosmo had privately requested from the government the privilege of sending annually t to the Spanish Indies two Leghorn merchantmen free of duty, as a compensation for the loss of Galileo!
The failure of this negotiation must have been a source of extreme mortification to the high spirit and sanguine temperament of Galileo. He had calculated, however, too securely on his means of putting the new method to a successful trial. The great imperfection of the time-keepers of that day, and the want of proper telescopes, would have baffled him in all his efforts, and he would have been subject to a more serious mortification from the failure and rejection of his plan, than that which he actually experienced from the avarice of his patron, or the indifference of Spain. Even in the present day, no telescope has been invented which is capable of observing at sea the eclipses of Jupiter's satellites; and though this method of finding the longitude has great advantages on shore, yet it has been completely abandoned at sea, and superseded by easier and more correct methods.
In the year 1618, when no fewer than three comets visited our system, and attracted the attention of all the astronomers of Europe, Galileo was unfortunately confined to his bed by a severe illness; but, though he was unable to make a single observation upon these remarkable bodies, he contrived to involve himself in the controversies which they occasioned. Marco Guiducci, an astronomer of Florence, and a friend of Galileo's, had delivered a discourse on comets before the Florentine Academy, which was published in 1619.[23] The heads of this discourse were supposed to have been communicated to him by Galileo, and this seems to have been universally admitted during the controversy to which it gave rise. The opinion maintained in this treatise, that comets are nothing but meteors which occasionally appear in our atmosphere, like halos and rainbows, savours so little of the sagacity of Galileo that we should be disposed to question its paternity. His inability to partake in the general interest which these three comets excited, and to employ his powerful telescope in observing their phenomena and their movements, might have had some slight share in the formation of an opinion which deprived them of their importance as celestial bodies. But, however this may have been, the treatise of Guiducci afforded a favourable point of attack to Galileo's enemies, and the dangerous task was entrusted to Oratio Grassi, a learned Jesuit, who, in a work entitled The Astronomical and Philosophical Balance, criticised the discourse on comets, under the feigned name of Lotario Sarsi.
Galileo replied to this attack in a volume entitled Il Saggiatore, or The Assayer, which, owing to the state of his health, was not published till the autumn of 1623.[24] This work was written in the form of a letter to Virginio Cæsarini, a member of the Lyncæan Academy, and master of the chamber to Urban VIII.[25], who had just ascended the pontifical throne. It has been long celebrated among literary men for the beauty of its language, though it is doubtless one of the least important of Galileo's writings.
The succession of the cardinal Maffeo Barberini to the papal throne, under the name of Urban VIII., was hailed by Galileo and his friends as an event favourable to the promotion of science. Urban had not only been the personal friend of Galileo and of prince Cesi, the founder of the Lyncæan Academy, but had been intimately connected with that able and liberal association; and it was, therefore, deemed prudent to secure his favour and attachment. If Paul III. had, nearly a century before, patronised Copernicus, and accepted of the dedication of his great work, it was not unreasonable to expect that, in more enlightened times, another pontiff might exhibit the same liberality to science.