investigation of a complicated subject, and acuteness of discrimination between the true and the fallacious.

TYCHO BRAHE.

OF eminent astronomers, the next in point of time was Tycho Brahe, who, though adopting the Ptolemaic notion of the earth being the fixed and immovable centre of the universe, yet did good service to the progress of the science by his numerous observations and discoveries. Descended of an ancient and noble family, originally of Sweden, but settled in Denmark, Tycho was born December 14, 1546, at Knub Strup, in the bailiwick of Schönen, the jurisdiction of which was then held by his father. When seven years old, he commenced the study of the classics, his education, as well as that of his brothers, being intrusted to private tutors. His father dying, his uncle sent him, in 1559, to study philosophy and rhetoric at Copenhagen, where it was intended to train him for some civil employment. The great eclipse of the sun on the 21st August 1560, happening at the precise time the astronomers foretold, he began to look upon astronomy as something divine; and purchasing the tables of Stadius, gained some notion of the theory of the planets. His thoughts were now wholly engrossed with astronomy; and though sent by his uncle, in 1562, to study jurisprudence at Leipsic, mathematics, and not law, were the subject of his private labors. It is told of him, that, having procured a small celestial globe, he was wont to wait till his tutor had gone to bed, in order to examine the constellations and learn their names; and that, when the sky was clear, he used to spend whole nights in viewing the stars. He abandoned the amusements and pleasures fitting for his age, and devoted his pocket-money to the purchase of mathematical and astronomical books, the perusal of which he persisted in, in spite of the remonstrances and rebukes of his preceptor. About this time he also began to apply himself to chemistry, less perhaps for the cause of the science, than with a view to discover the Philosopher's Stone and the grand Elixir of Life-a digression from his astronomical career, prompted no doubt by the natural supersition and enthusiasm of his constitution.

In 1571 he returned to Denmark; and was favored by his mother's brother, Steno Belle, a lover of learning, with a convenient place at the castle of Herritzvad, near Knub Strup, for conducting his observations and building a laboratory: but marrying a peasant girl beneath his rank, such a violent quarrel ensued between him and his relations, that Frederick II, king of Denmark, was obliged to interpose to reconcile them. In 1575, he began his travels through Germany, and proceeded as far as Venice, meeting with the kindliest attention from various philosophers and crowned heads. This attention, conjoined with certain offers made him by the Landgrave of Hesse, and the greater facility of procuring better apparatus, induced him to think of removing his family to Basil; but Frederick of Denmark, being informed of his design, and unwilling to lose such an ornament to his country, promised (to enable him to pursue his studies) to bestow upon him for life the island of Hveen in the Sound, to erect an observatory and laboratory there, and to defray all the expenses necessary for carrying on his designs. Tycho Brahè readily embraced this proposal; and, accordingly, the first stone of the observatory was laid in August

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1576. The king also bestowed on him a pension of two thousand crowns, a fee in Norway, and a canonry, which brought him one thousand more. In this retreat he was visited by various princes; among others, by James VI of Scotland, when proceeding to Denmark to marry the princess Anne. This monarch, of literary memory, made the astronomer several presents, and with his own hand wrote some verses in his praise. In Uranienborg, for such he had styled his new erection, he framed that system of the universe which is yet known by his name; namely, that the earth remains fixed and immovable as the grand centre, and that the sun and all the heavenly bodies revolve around it—a doctrine the reverse of that of Copernicus, which all succeeding astronomers have adopted. But though mistaken in this conception, we are indebted to him for a more correct catalogue of the fixed stars; for several important discoveries respecting the motions of the moon and comets, and the refraction of the rays of light; and for valuable improvements in astronomical instruments. Tycho was likewise a skillful chemist, and found in poetry his recreation from severer studies. His Latin poems are said to exhibit considerable merit; but his chemical manipulations partook too much of the alchemy of his day to be of use to future inquirers.

Happy might our philosopher have been in the castle of Uranienborg, had not his impetuous character, and his fondness for satire, made him many enemies, who prejudiced Christian IV, the successor of Frederick II, against him. On the death of his patron, he was deprived of his pension, fee, and canonry; and finding himself incapable of bearing the expenses of his observatory, he went to Copenhagen, whither he brought some of his instruments, and continued his observations in the city, till Valkendorf, chamberlain to Christian, commanded him, by the king's orders, to discontinue them. He then removed his family to Rostock, and afterwards to Holstein, to solicit Henry Ranzon to introduce him to the Emperor Rodolphus, who was a great friend to astronomy and astrology. Succeeding in his wishes, he was received by the emperor with the greatest civility and respect; provided with a magnificent house, till he could procure one more fit for astronomical observations; allotted a pension of three hundred crowns; and promised, upon the first opportunity, a fee for himself and his descendants. Unluckily he did not long enjoy this happy situation; for, being suddenly taken ill with a fatal disease, he was cut off on the 24th of October 1601, in the fifty-fifth year of his age. He was interred with great pomp and ceremony in the principal church of Prague, where a noble monument was erected to his memory; thus like many other men of eminence, receiving in a strange land the honors that had been denied him in his own.

Tycho was, notwithstanding his faults and weaknesses, a remarkable man for the age in which he lived; his errors and misjudgments being to a great extent those of his era. His skill in astronomy is universally admitted; and though failing to establish his system over that of Copernicus, yet no one can deny him the merit of advancing by his labors the progress of the science. That he was addicted to astrology, presages, and the occult sciences, is true; but these were features of the age more than of individuals that he was impetuous, sarcastic, and unamiable, is to be regretted; but it must also be admitted that the grossest injustice was done him and the cause of science by the successor of his patron. Most of his works,

which were numerous, and written in Latin, are still extant. The Emperor Rodolphus purchased his expensive astronomical and other instruments; but they were mostly destroyed after the battle of the Weisseberg, near Prague, in 1620. A large sextant alone remains in Prague. The famous brass celestial globe, which was six feet in diameter, and cost about a thousand pounds, returned to Copenhagen after various adventures, but perished in the great fire of 1728. The castle of Uranienborg, where he nightly watched and pondered, has long been in ruins, leaving scarcely a trace of its structure and character. All, however, has not perished, nor been fruitless. 'It was the friendship of Tycho,' says an eminent authority, which formed Kepler, and directed him in the career of astronomy. Without this friendship, and without the numerous observations of Tycho, of which Kepler found himself the depositary after the death of his master, he would never have been able to discover those great laws of the system of the world which have been called Kepler's Laws,' and which, combined with the theory of central forces, discovered by Hüygens, conducted Newton to the grandest discovery which has ever been made in the sciences that of universal gravitation.'

GALILEO.

THE Copernican theory, which Tycho had labored in vain to supersede, was next received and supported by an Italian philosopher, whose name and history are inseparably interwoven with the progress of astronomy. That illustrious individual, Galileo Galilei, usually known by his Christian name, was born at Pisa in 1564. His father, a Tuscan nobleman of small fortune, caused him to be educated for the profession of medicine at the university of his native city. While studying there, he became deeply sensible of the absurdities of the philosophy of Aristotle, as it had then come to be taught, and he became its declared enemy. That spirit of observation for which he was so distinguished was early developed. When only nineteen years old, the swinging of a lamp suspended from the ceiling of the cathedral in Pisa, led him to investigate the laws of the oscillation of the pendulum, which he was the first to employ as a measure of time. He left it incomplete, however, and it was brought to perfection by his son, Vincenzo, and particularly by Huygens, the latter of whom must be regarded as the true inventor of the pendulum. About this period Galileo devoted himself exclusively to mathematics and natural science, and in 1586 was led to the invention of the hydrostatic balance. In 1589, his distinction in the exact sciences gained for him the chair of mathematics in his native university, where, immediately on his installation, he began to assert the laws of nature against a perverted philosophy. In the presence of numerous spectators, he performed a series of experiments in the tower of the cathedral, to show that weight has no influence on the velocity of falling bodies. By this means he excited the opposition of the adherents of Aristotle to such a degree, that, after two years, he was forced to resign his professorship. Driven from Pisa, he retired into private life; but his genius being appreciated in another part of Italy, he was, in 1592, appointed professor of mathematics in Pudua. He lectured here with unparalleled success. Scholars from the most distant regions of Europe crowded round

him. He delivered his lectures in the Italian language instead of Latin, which was considered a daring innovation.

During eighteen years which he spent at Padua, he made many discoveries in natural philosophy, which he introduced into his lectures, without regard to their inconsistency with the doctrines previously taught. Among these may be mentioned his discovery of the rate of descent in falling bodies; certain improvements on the thermometer; some interesting observations on the magnet; and a number of experiments relative to the floating and sinking of solid bodies in water. In 1609, hearing that one Jansen, a Dutchman, had made an instrument by which distant objects were made to appear near, Galileo, whose mind was prepared for the discovery, instantly conceived on what principle it was constructed, and, without losing a day, he fashioned a similar instrument with many improvments: such was the origin of the telescope, the most interesting of all instruments connected with science.

Turning his optical tube towards the heavens, Galileo perceived the moon to be a body of uneven surface, the elevations of which he computed by their shadows; and the sun to be occasionally spotted; and from the regular advance from east to west of these spots, he inferred the rotation of the sun, and the inclination of its axis to the plane of the ecliptic. From a particular nebula, which his rude instrument enabled him to resolve into individual stars, he even conjectured, what Lord Rosse has but recently proved, that the whole Milky Way was but a vast assemblage of stars and systems. He discovered that the planet Venus waxed and waned like the moon, that Saturn had something like wings by its sides (afterwards found to be a ring), and that Jupiter was surrounded by four satellites. It is now altogether impossible to imagine the wonder and delight with which these discoveries must have filled the mind of a philosopher like Galileo, who had perhaps long surmised that all was not as it seemed in the heavens, but despaired of ever being able to penetrate the mystery. In the year 1611, while entering upon his investigations, he was induced, by the invitation of his prince, the Grand Duke of Tuscany, to return to Pisa, and resume the chair of mathematics there, with a large salary. It was consequently at that city that he first gave his discoveries to the world. That persecution which had only been suspended by accident in the case of Copernicus, now fell with full weight on the head of the Italian philosopher. Having openly declared, in a work which he published, that his discoveries proved the truth of the Copernican theory, he was denounced by the clergy as a heretic, and obliged, in 1615, to proceed to Rome, and appear before the court of Inquisition, who obliged him to promise that he would never more broach such dangerous doctrines. It has been stated, but is not quite certain, that he was on this occasion imprisoned by the Inquisition for five months, and that he would have suffered still more severely if the Grand Duke had not interceded for him.

For several years he observed the silence enjoined upon him, but continued to pursue the study of the true theory of the heavens. Panting to make known to the world a complete account of the system of Copernicus, yet dreading the prejudices of his enemies, he fell upon the expedient of writing a work, in which, without giving his own opinion, he introduces three persons in a dialogue, of whom the first defends the Copernican system, the second the Ptolemæan (or that of Aristotle), and the third

weighs the reasons of both in such a way, that the subject seems problematical, though it is impossible to mistake the preponderance of arguments in favor of Copernicus. With this great work, which is still held in reverence, Galileo went to Rome in 1630, in the sixty-sixth year of his age, and, by an extraordinary stretch of favor, received permission to print it. Scarcely had it appeared at Rome and Florence, when it was attacked by the disciples of Aristotle, and most violently of all by the teacher of philosophy at Pisa. A congregation of cardinals, monks, and mathematicians, was appointed to examine his work, which they unhesitatingly condemned as highly dangerous, and summoned him before the tribunal of the Inquisition. This blow fell heavily on the head of Galileo, now an old man, and left defenseless by the death of his friend and patron, Cosmo II. He was compelled to go to Rome in the winter of 1633, and was immediately immured in a cell in one of the prisons of the Inquisition. There he remained for several months, when, being brought before an assembly of his judges, he was condemned to renounce, kneeling before them, with his hand upon the gospels, what were called the 'sinful and detestable errors and heresies' which he had maintained. The firmness of Galileo gave way at this critical moment of his life: he pronounced the recantation. But at the moment he rose, indignant at having sworn in violation of his conviction, he exclaimed, stamping his foot, ‘E pur si muove!'-(It still moves!') Upon this dreadful relapse into heresy, he was sentenced to imprisonment in the Inquisition for life, and every week for three years was to repeat the seven penitential psalms; his Dialogues' were also prohibited, and his system utterly condemned. Although Galileo was in this manner sentenced to confinement, it appeared to those who judged him that he would not be able, from his age, to endure such a severe punishment, and they mercifully banished him to a particular spot near Florence.

Here Galileo lived for several years, employing his time in the study of mechanics and other branches of natural philosophy. The results are found in two important works on the laws of motion, the foundation of the present system of physics and astronomy. At the same time he tried to make use of Jupiter's satellites for the calculation of longitudes; and though he brought nothing to perfection in this branch, he was the first who reflected systematically on such a method of fixing geographical longitudes. He was at this time afflicted with a disease in his eyes, one of which was wholly blind, and the other almost useless, when, in 1637, he discovered the libration of the moon. Blindness, deafness, want of sleep, and pain in his limbs, united to embitter his declining years; still his mind was active. In my darkness,' he writes in the year 1638, 'I muse now upon this object of nature, and now upon that, and find it impossible to soothe my restless head, however much I wish it. This perpetual action of mind deprives me almost wholly of sleep.' In this condition, and affected by a slowly-consuming fever, he expired in January, 1642, in the seventy-eighth year of his age. His relics were deposited in the church of Santa Croce, at Florence, where posterity did justice to his memory by erecting a splendid monument in 1737.

Galileo is represented by his biographers as of diminutive stature, but strong and healthy, of agreeable countenance, and lively conversation and manner. He preferred living in the country, where his relaxations con