The great Tuscan astronomer is best known as the first telescopic observer, the fortunate discoverer of the Medicean stars (so Jupiter’s satellites were first named): and what discovery more fitted to immortalize its author, than one which revealed new worlds, and thus gave additional force to the lesson, that the universe, of which we form so small a part, was not created only for our use or pleasure! Those, however, who consider Galileo only as a fortunate observer, form a very inadequate estimate of one of the most meritorious and successful of those great men who have bestowed their time for the advantage of mankind in tracing out the hidden things of nature.

Galileo Galilei was born at Pisa, February 15, 1564. In childhood he displayed considerable mechanical ingenuity, with a decided taste for the accomplishments of music and painting. His father formed a just estimate of his talents, and at some inconvenience entered him, when nineteen years old, at the university of his native town, intending that he should pursue the medical profession. Galileo was then entirely ignorant of mathematics; and he was led to the study of geometry by a desire thoroughly to understand the principles of his favourite arts. This new pursuit proved so congenial to his taste, that from thenceforward his medical books were entirely neglected. The elder Galilei, a man of liberal acquirements and enlarged mind, did not require the devotion of his son’s life to a distasteful pursuit. Fortunately the young man’s talents attracted notice, and in 1589 he was appointed mathematical lecturer in the University of Pisa. There is reason to believe that, at an early period of his studentship, he embraced, upon inquiry and conviction, the doctrines of Copernicus, of which through life he was an ardent supporter.

Galileo and his colleagues did not long remain on good terms. The latter were content with the superstructure which À priori reasoners had raised upon Aristotle, and were by no means desirous of the trouble of learning more. Galileo chose to investigate physical truths for himself; he engaged in experiments to determine the truth of some of Aristotle’s positions, and when he found him in the wrong, he said so, and so taught his pupils. This made the “paper philosophers,” as he calls them, very angry. He repeated his experiments in their presence; but they set aside the evidence of their senses, and quoted Aristotle as much as before. The enmity arising from these disputes rendered his situation so unpleasant, that, in 1592, at the invitation of the Venetian commonwealth, he gladly accepted the professorship of mathematics at Padua. The period of his appointment being only six years, he was re-elected in 1598, and again in 1606, each time with an increase of salary; a strong proof of the esteem in which he was held, even before those astronomical discoveries which have immortalized his name. His lectures at this period were so fully attended, that he was sometimes obliged to adjourn them to the open air. In 1609 he received an invitation to return to his original situation at Pisa. This produced a letter, still extant, from which we quote a catalogue of the undertakings on which he was already employed. “The works which I have to finish are principally two books on the ‘System or Structure of the Universe,’ an immense work, full of philosophy, astronomy, and geometry; three books on ‘Local Motion,’ a science entirely new, no one, either ancient or modern, having discovered any of the very many admirable accidents which I demonstrate in natural and violent motions, so that I may, with very great reason, call it a new science, and invented by me from its very first principles; three books of mechanics, two on the demonstration of principles, and one of problems; and although others have treated this same matter, yet all that has been hitherto written, neither in quantity nor otherwise, is the quarter of what I am writing on it. I have also different treatises on natural subjects—on Sound and Speech, on Light and Colours, on the Tides, on the Composition of Continuous Quantity, on the Motions of Animals, and others besides. I have also an idea of writing some books relating to the military art, giving not only a model of a soldier, but teaching with very exact rules every thing which it is his duty to know, that depends upon mathematics, as the knowledge of castrametation, drawing up of battalions, fortification, assaults, planning, surveying, the knowledge of artillery, the use of instruments, &c.” Out of this comprehensive list, the treatises on the universe, on motion and mechanics, on tides, on fortification, or other works upon the same subjects, have been made known to the world. Many, however, of Galileo’s manuscripts, through fear of the Inquisition, were destroyed, or concealed and lost, after the author’s death.

In the same year, 1609, Galileo heard the report, that a spectacle-maker of Middleburg, in Holland, had made an instrument by which distant objects appeared nearer. He tasked his ingenuity to discover the construction, and soon succeeded in manufacturing a telescope. His telescope, however, seems to have been made on a different construction from that of the Dutch optician. It consisted of a convex and concave glass, distant from each other by the difference of their focal lengths, like a modern opera-glass; while there is reason to believe that the other was made up of two convex lenses, distant by the sum of their focal lengths, the common construction of the astronomical telescope. Galileo’s attention naturally was first turned to the moon. He discovered that her surface, instead of being smooth and perfectly spherical, was rough with mountains, and apparently varied, like the earth, by land and water. He next applied to Jupiter, and was struck by the appearance of three small stars, almost in a straight line, and close to him. At first he did not suspect the nature of these bodies; but careful observation soon convinced him that these three, together with a fourth, which was at first invisible, were in reality four moons revolving round their primary planet. These he named the Medicean stars. They have long ceased to be known by that name; but so highly prized was the distinction thus conferred upon the ducal house of Florence, that Galileo received an intimation, that he would “do a thing just and proper in itself, and at the same time render himself and his family rich and powerful for ever,” if he “named the next star which he should discover after the name of the great star of France, as well as the most brilliant of all the earth,” Henry IV. These discoveries were made known in 1610, in a work entitled “Nuncius Sidereus,” the Newsman of the Stars: in which Galileo farther announced that he had seen many stars invisible to the naked eye, and ascertained that the nebulÆ scattered through the heavens consist of assemblages of innumerable small stars. The ignorant and unprejudiced were struck with admiration; indeed, curiosity had been raised so high before the publication of this book, as materially to interfere with the convenience of those who possessed telescopes. Galileo was employed a month in exhibiting his own to the principal persons in Venice; and one unfortunate astronomer was surrounded by a crowd who kept him in durance for several hours, while they passed his glass from one to another. He left Venice the next morning, to pursue his inquiries in some less inquisitive place. But the great bulk of the philosophers of the day were far from joining in the general feeling. They raised an outcry against the impudent fictions of Galileo, and one, a professor of Padua, refused repeatedly to look through the telescope, lest he should be compelled to admit that which he had predetermined to deny. In the midst of this prejudice and envy, Kepler formed a brilliant exception. He received those great discoveries with wonder and delight, though they overturned some cherished theories, and manifested an honest and zealous indignation against the traducers of Galileo’s fame.

In particular his wrath broke out against a protÉgÉ of his own, named Horky; who, under the mistaken notion of gaining credit with his patron, wrote a violent attack on Galileo, and asserted, among other things, that he had examined the heavens with Galileo’s own glass, and that no such thing as a satellite existed near Jupiter. The conclusion of the affair is curious and characteristic. Horky begged so hard to be forgiven, that, says Kepler, “I have taken him again into favour, upon this preliminary condition, to which he has agreed,—that I am to show him Jupiter’s satellites, and he is to see them, and to own that they are there.”

It was not long before Galileo had new, and equally important matter to announce. He observed a remarkable appearance in Saturn, as if it were composed of three stars touching each other; his telescope was not sufficiently powerful to resolve into them Saturn and his ring. Within a month he ascertained that Venus exhibits phases like those of the moon,—a discovery of great importance in confirming the Copernican system. The same phenomenon he afterwards detected in Mars. We close the list with the discovery of the revolution of the sun round his axis, in the space of about a lunar month, derived from careful observation of the spots on his surface.

About this time (1610–11) Galileo took up his abode in Tuscany, upon the invitation of the Grand Duke, who offered to him his original situation at Pisa, with a liberal salary, exemption from the necessity of residence, and complete leisure to pursue his studies. In 1612 he published a discourse on Floating Bodies, in which he investigates the theory of buoyancy, and refutes, by a series of beautiful and conclusive experiments, the opinion that the floating or sinking of bodies depends on their shape.

Neither Copernicus nor his immediate followers suffered inconvenience or restraint on account of their astronomical doctrines: nor had Galileo, until this period of his life, incurred ecclesiastical censure for any thing which he had said or written. But the Inquisition now took up the matter as heretical, and contrary to the express words of Scripture; and in 1616, Copernicus’s work ‘De Revolutionibus,’ Kepler’s Epitome, and some of Galileo’s own letters, were placed on the list of prohibited books; and he himself, being then in Rome, received formal notice not to teach that the earth revolves round the sun. He returned to Florence full of indignation; and considering his hasty temper, love of truth, and full belief of the condemned theory, it is rather wonderful that he kept silence so long, than that he incurred at last the censures of the hierarchy. He did, however, restrain himself from any open advocacy of the heretical doctrines, even in composing his great work, the ‘Dialogue on the Ptolemaic and Copernican Systems.’ This was completed in 1630, but not printed till 1632, under licence from officers of the church, both at Rome and Florence. It is a dialogue between Simplicio, an Aristotelian, Salviati, who represents the author, and Sagredo, a half convert to Salviati’s opinions. It professes “indeterminately to propose the philosophical arguments, as well on one side as on the other:” but the neutrality is but ill kept up, and was probably assumed, not with any hope that the court of Rome would be blinded as to the real tendency of the book, but merely that it would accept this nominal submission as a sufficient homage to its authority. If this were so, the author was disappointed; the Inquisition took cognizance of the matter, and summoned him to Rome to undergo a personal examination. Age and infirmity were in vain pleaded as excuses; still, through the urgent and indignant remonstrances of the Grand Duke of Tuscany, he was treated with a consideration rarely shown by that iniquitous tribunal. He was allowed to remain at the Florentine ambassador’s palace, with the exception of a short period, from his arrival in February, until the passing of sentence, June 21, 1633. He was then condemned, in the presence of the Inquisitors, to curse and abjure the “false doctrines,” which his life had been spent in proving; to be confined in the prison of the Holy Office during pleasure, and to recite the seven penitential psalms once a week during three years. The sentence and the abjuration are given at full length in the Life of Galileo, in the ‘Library of Useful Knowledge.’ “It is said,” continues the biographer, “that Galileo, as he rose from his knees, stamped on the ground, and whispered to one of his friends, ‘e pur si muove,’ (it does move though.”)

Galileo’s imprisonment was not long or rigorous; for after four days he was reconducted to the Florentine ambassador’s palace: but he was still kept under strict surveillance. In July he was sent to Sienna, where he remained five months in strict seclusion. He obtained permission in December to return to his villa at Arcetri, near Florence: but there, as at Sienna, he was confined to his own premises, and strictly forbidden to receive his friends. It is painful to contemplate the variety of evils which overcast the evening of this great man’s life. In addition to a distressing chronic complaint, contracted in youth, he was now suffering under a painful infirmity which by some is said to have been produced by torture, applied in the prisons of the Inquisition to extort a recantation. But the arguments brought forward to show that the Inquisitors did resort to this extremity do not amount to anything like direct proof. In April, 1634, Galileo’s afflictions were increased by the death of a favourite, intelligent, and attached daughter. He consoled his solitude, and lightened the hours of sickness, by continuing the observations which he was now forbidden to publish to the world; and the last of his long train of discoveries was the phenomenon known by the name of the moon’s libration. In the course of 1636–7 he lost successively the sight of both his eyes. He mentions this calamity in a tone of pious submission, mingled with a not unpleasing pride. “Alas, your dear friend and servant Galileo has become totally and irreparably blind; so that this heaven, this earth, this universe, which with wonderful observations I had enlarged a hundred and thousand times beyond the belief of by-gone ages, henceforward for me is shrunk into the narrow space which I myself fill in it. So it pleases God: it shall therefore please me also.” In 1638 he obtained leave to visit Florence, still under the same restrictions as to society; but at the end of a few months he was remanded to Arcetri, which he never again quitted. From that time, however, the strictness of his confinement was relaxed, and he was allowed to receive the friends who crowded round him, as well as the many distinguished foreigners who eagerly visited him. Among these we must not forget Milton, whose poems contain several allusions to the celestial wonders observed and published by the Tuscan astronomer. Though blind and nearly deaf, Galileo retained to the last his intellectual powers; and his friend and pupil, the celebrated Torricelli, was employed in arranging his thoughts on the nature of percussion, when he was attacked by his last illness. He died January 8, 1642, aged seventy-eight.

It was disputed, whether, as a prisoner of the Inquisition, Galileo had a right to burial in consecrated ground. The point was conceded; but Pope Urban VIII. himself interfered to prevent the erection of a monument to him in the church of Santa Croce, in Florence, for which a large sum had been subscribed. A splendid monument now covers the spot in which his remains repose with those of his friend and pupil, the eminent mathematician Viviani.

In 1618, Galileo published, through the medium of Mario Guiducci, an Essay on the Nature of Comets. His opinions (which, in fact, were erroneous) were immediately attacked under the feigned signature of Lotario Sarsi. To this antagonist he replied in a work entitled ‘Il Saggiatore,’ the Assayer, which we select for mention, not so much for the value of its contents, though, like the rest of his works, it has many remarkable passages, as for the high reputation which it enjoys among Italian critics as a model of philosophical composition. The “Dialogues on Motion,” the last work of consequence which Galileo published, contain investigations of the simpler branches of dynamics, the motion of bodies falling freely or down inclined planes, and of projectiles; determinations of the strength of beams, and a variety of interesting questions in natural philosophy. The fifth and sixth are unfinished; the latter was intended to comprise the theory of percussion, which, as we have said, was the last subject which occupied the author’s mind. For a full analysis of this and the other treatises here briefly noted, and for an account of Galileo’s application of the pendulum to the mensuration of time; his invention of the thermometer, though in an inaccurate and inconvenient form; his methods of discovering the longitude, and a variety of other points well worth attention, we must refer to the Life of Galileo already quoted. The numerous extracts from Galileo’s works convey a lively notion of the author’s character, and are distinguished by a peculiar tone of quaint humour. For older writers we may refer to the lives of Viviani, Gherardini, and Nelli; and to the English one by Salusbury, of which however the second volume is so rare that the Earl of Macclesfield’s copy is the only one known to exist in England. Venturi has given to the world some unpublished manuscripts, and collected much curious and scattered information in his “Memorie e Lettere de Gal. Galilei.” Of Galileo’s works several editions exist: the most complete are those of Padua, in four volumes quarto, 1744, and of Milan, in thirteen volumes octavo, 1811.

In conclusion, we quote the estimate of Galileo’s character, from the masterly memoir from which this sketch is derived. “The numberless inventions of his acute industry; the use of the telescope, and the brilliant discoveries to which it led; the patient investigation of the laws of weight and motion, must all be looked upon as forming but a part of his real merits, as merely particular demonstrations of the spirit in which he everywhere withstood the despotism of ignorance, and appealed boldly from traditional opinions to the judgment of reason and common sense. He claimed and bequeathed to us the right of exercising our faculties in examining the beautiful creation which surrounds us. Idolised by his friends, he deserved their affection by numberless acts of kindness; by his good humour, his affability, and by the benevolent generosity with which he devoted himself, and a great part of his limited income, to advance their talents and fortunes. If an intense desire of being useful is everywhere worthy of honour; if its value is immeasurably increased when united to genius of the highest order; if we feel for one, who, notwithstanding such titles to regard, is harassed by cruel persecution, then none deserve our sympathy, our admiration, and our gratitude, more than Galileo.”