The severity of this order was keenly felt by Galileo. While he remained at Arcetri, his seclusion from the world would have been an object of choice, if it had not been the decree of a tribunal; but to be debarred from the conversation of his friends in Florence—in that city where his genius had been idolised, and where his fame had become immortal, was an aggravation of punishment which he was unable to bear. With his accustomed kindness, the Grand Duke made a strong representation on the subject to his ambassador at the Court of Rome. He stated that, from his great age and infirmities, Galileo’s career was near its close; that he possessed many valuable ideas, which the world might lose if they were not matured and conveyed to his friends; and that Galileo was anxious to make these communications to Father Castelli, who was then a stipendiary of the Court of Rome. The Grand Duke commanded his ambassador to see Castelli on the subject—to urge him to obtain leave from the Pope to spend a few months in Florence—and to supply him with money and every thing that was necessary for his journey. Influenced by this kind and liberal message, Castelli obtained an audience of the Pope, and requested leave to pay a visit to Florence. Urban instantly suspected the object of his journey; and, upon Castelli’s acknowledging that he could not possibly refrain from seeing Galileo, he received permission to visit him in the company of an officer of the Inquisition. Castelli accordingly went to Florence, and, a few months afterwards, Galileo was ordered to return to Arcetri.

During Galileo’s confinement at Sienna and Arcetri, between 1633 and 1638, his time was principally occupied in the composition of his “Dialogues on Local Motion,” in which he treats of the strength and cohesion of solid bodies, of the laws of uniform and accelerated motions, of the motion of projectiles, and of the centre of gravity of solids. This remarkable work, which was considered by its author as the best of his productions, was printed by Louis Elzevir, at Amsterdam, and dedicated to the Count de Noailles, the French ambassador at Rome. Various attempts to have it printed in Germany had failed; and, in order to save himself from the malignity of his enemies, he was obliged to pretend that the edition published in Holland had been printed from a MS. entrusted to the French ambassador.

Although Galileo had for a long time abandoned his astronomical studies, yet his attention was directed, about the year 1636, to a curious appearance in the lunar disc, which is known by the name of the moon’s libration. When we examine with a telescope the outline of the moon, we observe that certain parts of her disc, which are seen at one time, are invisible at another. This change or libration is of four different kinds, viz. the diurnal libration, the libration in longitude, the libration in latitude, and the spheroidal libration. Galileo discovered the first of these kinds of libration, and appears to have had some knowledge of the second; but the third was discovered by Hevelius, and the fourth by Lagrange.

This curious discovery was the result of the last telescopic observations of Galileo. Although his right eye had for some years lost its power, yet his general vision was sufficiently perfect to enable him to carry on his usual researches. In 1636, however, this affection of his eye became more serious; and, in 1637, his left eye was attacked with the same disease. His medical friends at first supposed that cataracts were formed in the crystalline lens, and anticipated a cure from the operation of couching. These hopes were fallacious. The disease turned out to be in the cornea, and every attempt to restore its transparency was fruitless. In a few months the white cloud covered the whole aperture of the pupil, and Galileo became totally blind. This sudden and unexpected calamity had almost overwhelmed Galileo and his friends. In writing to a correspondent he exclaims, “Alas! your dear friend and servant has become totally and irreparably blind. These heavens, this earth, this universe, which by wonderful observation I had enlarged a thousand times beyond the belief of past ages, are henceforth shrunk into the narrow space which I myself occupy. So it pleases God; it shall, therefore, please me also.” His friend, Father Castelli, deplores the calamity in the same tone of pathetic sublimity:—“The noblest eye,” says he, “which nature ever made, is darkened; an eye so privileged, and gifted with such rare powers, that it may truly be said to have seen more than the eyes of all that are gone, and to have opened the eyes of all that are to come.”

Although Galileo had been thwarted in his attempt to introduce into the Spanish marine his new method of finding the longitude at sea, yet he never lost sight of an object to which he attached the highest importance. As the formation of correct tables of the motion of Jupiter’s satellites was a necessary preliminary to its introduction, he had occupied himself for twenty-four years in observations for this purpose, and he had made considerable progress in this laborious task. After the publication of his “Dialogues on Motion,” in 1636, he renewed his attempts to bring his method into actual use. For this purpose he addressed himself to Lorenzo Real, who had been the Dutch Governor-General in India, and offered the free use of his method to the States-General of Holland.[36] The Dutch government received this proposal with an anxious desire to have it carried into effect. At the instigation of Constantine Huygens, the father of the illustrious Huygens, and the secretary to the Prince of Orange, they appointed commissioners to communicate with Galileo; and while they transmitted him a gold chain as a mark of their esteem, they at the same time assured him, that if his plan should prove successful it should not pass unrewarded. The commissioners entered into an active correspondence with Galileo, and had even appointed one of their number to communicate personally with him in Italy. Lest this, however, should excite the jealousy of the court of Rome, Galileo objected to the arrangement, so that the negociation was carried on solely by correspondence.

It was at this time that Galileo was struck with blindness. His friend and pupil, Renieri, undertook in this emergency to arrange and complete his observations and calculations; but before he had made much progress in the arduous task, each of the four commissioners died in succession, and it was with great difficulty that Constantine Huygens succeeded in renewing the scheme. It was again obstructed, however, by the death of Galileo; and when Renieri was about to publish, by the order of the Grand Duke, the “Ephemeris,” and “Tables of the Jovian Planets,” he was attacked with a mortal disease, and the manuscripts of Galileo, which he was on the eve of publishing, were never more heard of. By such a series of misfortunes were the plans of Galileo and of the States-General completely overthrown. It is some consolation, however, to know that neither science nor navigation suffered any severe loss. Notwithstanding the perfection of our present tables of Jupiter’s satellites, and of the astronomical instruments by which their eclipses may be observed, the method of Galileo is still impracticable at sea.

In consequence of the strict seclusion to which Galileo had been subjected, he was in the practice of dating his letters from his prison at Arcetri; but after he had lost the use of his eyes, the Inquisition seems to have relaxed its severity, and to have allowed him the freest intercourse with his friends. The Grand Duke of Tuscany paid him frequent visits; and among the celebrated strangers who came from distant lands to see the ornament of Italy, were Gassendi, Deodati, and our illustrious countryman Milton. During the last three years of his life, his eminent pupil Viviani formed one of his family; and in October 1641, the celebrated Torricelli, another of his pupils, was admitted to the same distinction.

Though the powerful mind of Galileo still retained its vigour, yet his debilitated frame was exhausted with mental labour. He often complained that his head was too busy for his body; and the continuity of his studies was frequently broken with attacks of hypochondria, want of sleep, and acute rheumatic pains. Along with these calamities, he was afflicted with another still more severe—with deafness almost total; but though he was now excluded from all communication with the external world, yet his mind still grappled with the material universe, and while he was studying the force of percussion, and preparing for a continuation of his “Dialogues on Motion,” he was attacked with fever and palpitation of the heart, which, after continuing two months, terminated fatally on the 8th of January 1642, in the 78th year of his age.

Having died in the character of a prisoner of the Inquisition, this odious tribunal disputed his right of making a will, and of being buried in consecrated ground. These objections, however, were withdrawn; but though a large sum was subscribed for erecting a monument to him in the church of Santa Croce, in Florence, the Pope would not permit the design to be carried into execution. His sacred remains were, therefore, deposited in an obscure corner of the church, and remained for more than thirty years unmarked with any monumental tablet. The following epitaph, given without any remark in the Leyden edition of his Dialogues, is, we presume, the one which was inscribed on a tablet in the church of Santa Croce:—

Galilæo Galilæi Florentino,
Philosopho et Geometræ vere lynceo,
Naturæ Œdipo,
Mirabilium semper inventorum machinatori,
Qui inconcessa adhuc mortalibus gloria
Cælorum provincias auxit
Et universo dedit incrementum:
Non enim vitreos spherarum orbes
Fragilesque stellas conflavit:
Sed æterna mundi corpore
Mediceæ beneficentiæ dedicavit,
Cujus inextincta gloriæ cupiditas
Ut oculos nationum
Sæculorumque omnium
Videre doceret,
Proprios impendit oculos.
Cum jam nil amplius haberet natura
Quod ipse videret.
Cujus inventa vix intra rerum limites comprehensa
Firmamentum ipsum non solum continet,
Sed etiam recipit.
Qui relictis tot scientiarum monumentis
Plura secum tulit, quam reliquit.
Gravi enim
Sed nondum affecta senectute,
Novis contemplationibus
Majorem gloriam affectans
Inexplebilem sapientiæ animam
Immaturo nobis obitu
Exhalavit
Anno Domini
MCXLII.
Ætatis suæ
LXXVIII.