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GALILEO GALILEI (1564-1642)
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GALILEO GALILEI (1564-1642) , See also:Italian astronomer and experimental philosopher, was See also:born at See also:Pisa on the 15th of See also:February 1564. His See also:father, Vincenzio, was an impoverished descendant of a See also:noble Florentine See also:house, which had exchanged the surname of Bonajuti for that of Galilei, on the See also:election, in 1343, of one of its members, Tommaso de' Bonajuti, to the See also:college of the twelve Buonuomini. The See also:family, which was nineteen times represented in the signoria, and in 1445 gave a gonfalonier to See also:Florence, flourished with the See also:republic and declined with its fall. Vincenzio Galilei was a See also:man of better parts than See also:fortune. He was a competent mathematician, wrote with considerable ability on the theory and practice of See also:music, and was especially distinguished amongst his contemporaries for the See also:grace and skill of his performance upon the See also:lute. By his wife, Giulia Ammannati of See also:Pescia, he had three sons and four daughters. From his earliest childhood Galileo, the eldest of the family, was remarkable for intellectual aptitude as well as for See also:mechanical invention. His favourite pastime was the construction of See also:original and ingenious See also:toy-See also:machines; but his application to See also:literary studies was equally conspicuous. In the monastery of See also:Vallombrosa, near Florence, where his See also:education was principally See also:con-ducted, he not only made himself acquainted with the best Latin authors, but acquired a See also:fair command of the See also:Greek See also:tongue, thus laying the See also:foundation of his brilliant and elegant See also:style. From one of the monks he also received instruction in See also:logic; but the subtleties of the scholastic See also:science were thoroughly distasteful to him. A document published by F. Selmi in 1864 proves that he was at this See also:time so far attracted towards a religious See also:life as to have joined the novitiate; but his father, who had other designs for him, seized the opportunity of an attack of ophthalmia to withdraw him permanently from the care of the monks. Having had See also:personal experience of the unremunerative See also:character both of music and of See also:mathematics, he desired that his son should apply himself to the cultivation of See also:medicine, and, not without some straining of his slender resources, placed him, before he had completed his eighteenth See also:year, at the university of Pisa. He accordingly matriculated there on the 5th of See also:November 1581, and immediately entered upon attendance at the lectures of the, celebrated physician and botanist, See also:Andrea Cesalpino. The natural gifts of the See also:young student seemed at this time equally ready to develop in any direction towards which choice or See also:hazard might incline them. In musical skill and invention he already vied with the best professors of the See also:art in See also:Italy; his personal See also:taste would have led him to choose See also:painting as his profession, and one of the most eminent artists of his See also:day, Lodovico See also:Cigoli, owned that to his See also:judgment and counsel he wasmainly indebted for the success of his See also:works. In 1581, while watching a See also:lamp set swinging in the See also:cathedral of Pisa, he observed that, whatever the range of its oscillations, they were invariably executed in equal times. The experimental verification of this fact led him to the important See also:discovery of the isochronism of the pendulum. He at first applied the new principle to See also:pulse-measurement, and more than fifty years later turned it to See also:account in the construction of an astronomical See also:clock. Up to this time he was entirely ignorant of mathematics, his father having carefully held him aloof from a study which he rightly apprehended would See also:lead to his See also:total See also:alienation from that of medicine. See also:Accident, however, frustrated this purpose. A See also:lesson in See also:geometry, given by Ostilio See also:Ricci to the pages of the See also:grand-ducal See also:court, chanced, tradition avers, to have Galileo for an unseen listener; his See also:attention was riveted, his dormant See also:genius was roused, and he threw all his energies into the new pursuit thus unexpectedly presented to him. With Ricci's assistance, he rapidly mastered the elements of the science, and eventually extorted his father's reluctant permission to See also:exchange See also:Hippocrates and See also:Galen for See also:Euclid and See also:Archimedes. In 1585 he was withdrawn from the university, through lack of means, before he had taken a degree, and returned to Florence, where his family habitually resided. We next hear of him as lecturing before the Florentine See also:Academy on the site and dimensions of See also:Dante's Inferno; and he shortly afterwards published an See also:essay descriptive of his invention of the hydrostatic See also:balance, which rapidly made his name known throughout Italy. His first See also:patron was the Marchese Guidubaldo del See also:Monte of See also:Pesaro, a man equally eminent in science, and influential through family connexions. At the Marchese's See also:request he wrote, in 1588, a See also:treatise on the centre of gravity in solids, which obtained for him, together with the See also:title of " the Archimedes of his time," the See also:honourable though not lucrative See also:post of mathematical lecturer at the See also:Pisan university. During the ensuing two years (1589–1591) he carried on that remarkable See also:series of experiments by which he established the first principles of See also:dynamics and earned the undying hostility of bigoted Aristotelians. From the leaning See also:tower of Pisa he afforded to all the professors and students of the university ocular demonstration of the falsehood of the Peripatetic dictum that heavy bodies fall with velocities proportional to their weights, and with unanswerable logic demolished all the time-honoured See also:maxims of the See also:schools regarding the See also:motion of projectiles, and elemental See also:weight or levity. But while he convinced, he failed to conciliate his adversaries. The keen See also:sarcasm of his polished See also:rhetoric was not calculated to soothe the susceptibilities of men already smarting under the deprivation of their most cherished illusions. He seems, in addition, to have compromised his position with the grand-ducal family by the imprudent candour with which he condemned a See also:machine for clearing the See also:port of See also:Leghorn, invented by Giovanni de' See also:Medici, an illegitimate son of Cosmo I. Princely favour being withdrawn, private rancour was See also:free to show itself. He was publicly hissed at his lecture, and found it prudent to resign his professorship and withdraw to Florence in 1591. Through the See also:death of his father in See also:July of that year family cares and responsibilities devolved upon him, and thus his nomination to the See also:chair of mathematics at the university of See also:Padua, secured by the See also:influence of the Marchese Guidubaldo with the Venetian See also:senate, was welcome both as affording a See also:relief from pecuniary embarrassment and as opening a See also: His See also:appointment was three times renewed, on each occasion with the expressions of the highest esteem on the See also:part of the governing See also:body, and his yearly See also:salary was progressively raised from 18o to l000 florins. His lectures were attended by persons of the highest distinction from all parts of See also:Europe, and such was the See also:charm of his demonstrations that a See also: Discoveries followed upon it with astounding rapidity and in bewildering variety. The Sidereus Nuncios, published at Venice early in 161o, contained the first-fruits of the new mode of investigation, which were sufficient to excite learned amazement on both sides of the See also:Alps. The mountainous configuration of the See also:moon's See also:surface was there first described, and the so-called " See also:phosphorescence " of the dark portion of our See also:satellite attributed to its true cause—namely, See also:illumination by sunlight reflected from the See also:earth .2 All the time-worn fables and conjectures regarding the composition of the Milky Way were at once dissipated by the simple statement that to the See also:eye, reinforced by the telescope, it appeared as a congeries of lesser stars, while the See also:great nebulae were equally declared to be resolvable into similar elements. But the discovery which was at once perceived to be most important in itself, and most revolutionary in its effects, was that of See also:Jupiter's satellites, first seen by Galileo on the 7th of See also:January 161o, and by him named Sidera Medicea, in honour of the grand-See also:duke of See also:Tuscany, Cosmo II., who had been his See also:pupil, and was about to become his employer. An See also:illustration is, with the general run of mankind, more powerful to convince than an See also:argument; and the cogency of the visible plea for the Copernican theory offered by the See also:miniature system, then first disclosed to view, was recognizable in the See also:triumph of its See also:advocates as well as in the increased acrimony of its opponents. In September 16ro Galileo finally abandoned Padua for Florence. His researches with the telescope had been rewarded ' The word telescope, from riPte, far, eKmreiv, to view, was invented by Demiscianus, an eminent Greek See also:scholar, at the request of See also:Prince Cesi, See also:president of the Lyncean Academy. It was used by Galileo as early as 1612, but was not introduced into See also:England until much later. In 1655 the word telescope was inserted and explained in Bagwell's Mysteries of Astronomy, See also:trunk or See also:cylinder being the terms until then ordinarily employed. 2 Leonardo da See also:Vinci, more than a See also:hundred years earlier, had come to the same conclusion.by the Venetian senate with the appointment for life to his professorship, at an unprecedentedly high salary. His discovery of the " Medicean Stars " was acknowledged by his nomination (July 12, 161o) as philosopher and mathematician extraordinary to the grand-duke of Tuscany. The emoluments of this See also:office, which involved no duties See also:save that of continuing his scientific labours, were fixed at r000 scudi; and it was the See also:desire of increased leisure, rather than the promptings of See also:local patriotism, which induced him to accept an offer the original See also:suggestion of which had indeed come from himself. Before the See also:close of 16ro the memorable See also:cycle of discoveries begun in the previous year was completed by the observation of the ansated or, as it appeared to Galileo, triple See also:form of See also:Saturn (the See also:ring-formation was first recognized by Christiaan See also:Huygens in 1655), of the phases of See also:Venus, and of the spots upon the See also:sun. As regards sun-spots, however, Johann See also:Fabricius of Osteel in See also:Friesland can claim priority of publication, if not of actual detection. In the See also:spring of 1611 Galileo visited See also:Rome, and exhibited in the gardens of the Quirinal See also:Palace the telescopic wonders of the heavens to the most eminent personages at the pontifical court. Encouraged by the flattering reception accorded to him, he ventured, in his Letters on the Solar Spots, printed at Rome in 1613, to take up a more decided position towards that See also:doctrine on the See also:establishment of which, as he avowed in a letter to Belisario Vinta, secretary to the grand-duke, " all his life and being henceforward depended." Even in the time of See also:Copernicus some well-meaning persons, especially those of the reformed persuasion, had suspected a discrepancy between the new view of the solar system and certain passages of Scripture—a suspicion strengthened by the See also:anti-See also:Christian inferences See also:drawn from it by See also:Giordano See also:Brune; but the question was never formally debated until Galileo's brilliant disclosures, enhanced by his formidable See also:dialectic and enthusiastic zeal, irresistibly challenged for it the attention of the authorities. Although he had no desire to raise the theological issue, it must be admitted that, the discussion once set on See also:foot, he threw himself into it with characteristic impetuosity, and thus helped to precipitate a decision which it was his See also:interest to avert. In See also:December 1613 a See also:Benedictine See also: He was a man of vast learning and upright piety, but, although personalty friendly to Galileo, there is no doubt that he saw in his scientific teachings a danger to See also:religion. The year 1615 seems to have been a period of suspense. Galileo received, as the result of a See also:conference between Cardinals Bellarmin and Del Monte, a semi-See also:official warning to avoid See also:theology, and limit himself to physical reasoning. " Write freely," he was told by See also:Monsignor Dini, " but keep outside the
See also:sacristy." Unfortunately, he had already committed himself to dangerous ground. In December he repaired personally to Rome, full of confidence that the weight of his arguments and the vivacity of his eloquence could not fail to convert the entire pontifical court to his views. He was cordially received, and eagerly listened to, but his imprudent ardour served but to injure his cause. On the 24th of February 1616 the consulting theologians of the Holy Office characterized the two propositions—that the sun is immovable in the centre of the See also:world, and that the earth has a diurnal motion of rotation—the first as " absurd in See also:philosophy, and formally heretical, because expressly contrary to Holy Scripture," and the second as " open to the same censure in philosophy, and at least erroneous as to faith." Two days later Galileo was, by command of the See also:pope (See also:Paul V.), summoned to the palace of Cardinal Bellarmin, and there officially admonished not thenceforward to " hold, See also:teach or defend " the condemned doctrine. This See also:injunction he promised to obey. On the 5th of See also: He brought with him, for the refutation of calumnious reports circulated by his enemies, a written certificate from Cardinal Bellarmin, to the effect that no See also:abjuration had been required of or See also:penance imposed upon him. During a prolonged See also:audience he had received from the pope assurances of private esteem and personal See also:protection; and he trusted to his dialectical ingenuity to find the means of presenting his scientific convictions under the trans-See also:parent See also:veil of an See also:hypothesis. Although a sincere See also:Catholic, he seems to have laid but little stress on the See also:secret admonition of the Holy Office, which his sanguine temperament encouraged him gradually to dismiss from his mind. He preserved no written memorandum of its terms, and it was represented to him, according to his own deposition in 1633, solely by Cardinal Bellarmin's certificate, in which, for obvious reasons, it was glossed over rather than expressly recorded. For seven years, nevertheless, during which he led a life of studious retirement in the See also:Villa Segni at Bellosguardo, near Florence, he maintained an almost unbroken silence. At the end of that time he appeared in public with his Saggiatore, a polemical treatise written in reply to the See also:Libra astronomica of Padre Grassi (under the See also:pseudonym of Lotario Sarsi), the Jesuit astronomer of the Collegio Romano. The subject in debate was the nature of comets,. the conspicuous appearance of three of which bodies in the year 1618 furnished the occasion of the controversy. Galileo's views, although erroneous, since he held comets to be See also:mere atmospheric emanations reflecting sunlight after the evanescent See also:fashion of a See also:halo or a See also:rainbow, were expressed with such triumphant vigour, and embellished with such telling sarcasms, that his opponent did not venture upon a reply. The Saggiatore was printed at Rome in October 1623 by the Academy of the Lincei, of which Galileo was, a member, with a See also:dedication to the new pope, See also:Urban VIII., and notwithstanding some passages containing a covert See also:defence of Copernican opinions, was received-with See also:acclamation by ecclesiastical, no less than by scientific authorities. Everything seemed now to promise a close of unbroken prosperity to Galileo's career. Maffeo See also:Barberini, his warmest friend and admirer in the Sacred College, was, by the election of: the 8th of August 1623, seated on the pontifical See also:throne; and themarked distinction with which he was received on his visit of congratulation to Rome in 1624 encouraged him to See also:hope for the realization of his utmost wishes. He received every See also:mark of private favour. The pope admitted him to six See also:long audiences in the course of two .months, wrote an enthusiastic letter to the grand-duke praising the great astronomer, not only for his distinguished learning, but also for his exemplary piety, and granted a See also:pension to his son Vincenzio, which was afterwards transferred to himself, and paid, with some irregularities, to the end of his life. But on the subject of the decree of 1616, the revocation of which Galileo had hoped to obtain through his personal influence, he found him inexorable. Yet there seemed See also:reason to expect that it would at least be interpreted.in a liberal spirit, and Galileo's See also:friends encouraged his imprudent confidence by eagerly retailing to him every papal utterance which it was possible to construe in a favourable sense. To Cardinal See also:Hohenzollern, Urban was reported to have said that the theory of the earth's motion had not been and could not be condemned as heretical, but only as rash; and in 163o the brilliant Dominican monk Tommaso See also:Campanella wrote to Galileo that the pope had expressed to him in conversation his disapproval of the prohibitory decree. Thus, in the full anticipation of added renown, and without any misgiving as to ulterior consequences, Galileo set himself, on his return to Florence, to See also:complete his famous but ill-starred work, the Dialogo dei due massimi sistemi del mondo. Finished in 163o, it was not until January 1632 that it emerged from the presses of Landini at Florence. The book was originally intended to appear in Rome, but unexpected obstacles interposed. The Lincean Academy collapsed with the death of Prince Federigo Cesi, its founder and president; an outbreak of See also:plague impeded communication between the various Italian cities; and the imprimatur was finally extorted, rather than accorded, under the pressure of private friendship and powerful interest. A tumult of See also:applause from every part of Europe followed its publication; and it would be difficult to find in any See also:language a book in which animation and elegance of style are so happily combined with strength and clearness of scientific exposition. Three interlocutors, named respectively Salviati, Sagredo, and Simplicio, take part in the four dialogues of which the work is composed. The first-named expounds the views of the author; the second is an eager and intelligent listener; the third represents a well-meaning but obtuse Peripatetic, whom the others treat at times with undisguised contempt. Salviati and Sagredo took their names from two of Galileo's early friends, the former a learned Florentine, the latter a distinguished Venetian See also:gentleman; Simplicio ostensibly derived his from the Cilician commentator of See also:Aristotle, but the choice was doubtless instigated by a sarcastic regard to the See also:double meaning of the word. There were not wanting those who insinuated that Galileo intended to depict the pope himself in the See also:guise of the simpleton of the party; and the See also:charge, though preposterous in itself, was supported by certain imprudences of expression, which Urban was not permitted to ignore. It was at once evident that the whole See also:tenor of this remarkable work was in flagrant See also:contradiction with the edict passed sixteen years before its publication, as well as with the author's personal See also:pledge of conformity to it. The ironical submission with which it opened, and the assumed indetermination with which it closed, were hardly intended to See also:mask the vigorous assertion of Copernican principles which formed its substance. It is a singular circumstance, however, that the argument upon which Galileo mainly relied as furnishing a physical demonstration of the truth of the new theory rested on a misconception. The ebb and flow of the tides were, he asserted, a visible See also:proof of the terrestrial double See also:movement, since they resulted from inequalities in the See also:absolute velocities through space of the various parts of the earth's surface, due to its rotation. To this notion, which took its rise in a confusion of thought, he attached See also:capital importance, and he treated with scorn Kepler's suggestion that a certain occult attraction of the moon was in some way concerned in the phenomenon. The theological censures which the book did not fail to incur were not slow in making themselves See also:felt. Towards the end of August the See also:sale was prohibited; on the 1st of October the author was cited to Rome by the Inquisition. He pleaded his See also:age, now close upon seventy years, his infirm See also:health, and the obstacles to travel caused by See also:quarantine regulations; but the pope was sternly indignant at what he held to be his ingratitude and insubordination, and no excuse was admitted. At length, on the 13th of February 1633, he arrived at the residence of Niccolini, the Tuscan See also:ambassador to the pontifical court, and there See also:abode in retirement for two months. From the 12th to the 3oth of See also:April he was detained in the palace of the Inquisition, where he occupied the best apartments and was treated with unexampled See also:indulgence. On the 3oth he was restored to the hospitality of Niccolini, his warm See also:partisan. The See also:accusation against him was that he had written in contravention of the decree of 1616, and in See also:defiance of the command of the Holy Office communicated to him by Cardinal Bellarmin; and his defence consisted mainly in a disavowal of his opinions, and an See also:appeal to his See also:good intentions, On the 21st of June he was finally examined under menace of See also:torture; but he continued to maintain his assertion that after its condemnation by the Congregation of the Index, he had never held the Copernican theory. Since the publication of the documents See also:relating to this memorable trial, there can no longer be any doubt, not only that the See also:threat of torture was not carried into See also:execution, but that it was never intended that it should be. On the 22nd of June, in the church of Santa Maria See also:copra See also:Minerva, Galileo read his recantation, and received his See also:sentence. He was condemned, as " vehemently suspected of See also:heresy," to incarceration at the See also:pleasure of the tribunal, and by way of penance was enjoined to recite once a See also:week for three years the seven See also:penitential See also:psalms. This sentence was signed by seven cardinals, but did not receive the customary papal ratification. The See also:legend according to which Galileo, rising from his knees after repeating the See also:formula of abjuration, stamped on the ground, and exclaimed, " Eppur si muove!" is, as may readily be supposed, entirely apocryphal. Its earliest ascertained appearance is in the See also:Abbe Irailh's Querelles litleraires and he was engaged in dictating to his disciples, See also:Vivian and See also:Torricelli, his latest ideas on the theory of impact when he was seized with the slow See also:fever which in two months brought him to the See also:grave. On the 8th of January 1642 he closed his long life of triumph and humiliation, which just spanned the See also:interval between the death of See also:Michelangelo and the See also:birth of See also:Isaac See also:Newton. The See also:direct services which Galileo rendered to astronomy are virtually summed up in his telescopic discoveries. To the theoretical perfection of the science hecontributed little or nothing. He pointed out indeed that the so-called " third motion," introduced by Copernicus to account for the See also:constant See also:parallelism of the earth's See also:axis, was a superfluous complication. But he substituted the equally unnecessary hypothesis of a magnetic attraction, and failed to perceive that the phenomenon to be explained was, in relation to absolute space, not a movement but the See also:absence of movement. The circumstance, however, which most seriously detracts from his scientific reputation is his neglect of the discoveries made during his lifetime by the greatest of his contemporaries. Kepler's first and second See also:laws were published in 16oq, and his third ten years later. By these momentous inductions the geometrical theory of the solar system was perfected, and a hitherto unimagined symmetry was perceived to regulate the mutual relations of its members. But by Galileo they were passed over in silence. In his Dialogo dei massimi sistemi, printed not less than thirteen years after the last of the three laws had been given to the world, the epicycles by which Copernicus, adhering to the See also:ancient postulate of See also:uniform circular motion, had endeavoured to reduce to theory the irregularities of the planetary movements, were neither expressly adopted nor expressly rejected; and the conclusion seems inevitable that this grave defection from the cause of progress was due to his perhaps unconscious reluctance to accept discoveries which he had not originated. His name is nevertheless justly associated with that vast See also:extension of the See also:bounds of the visible universe which has rendered modern astronomy the most See also:sublime of sciences, and his telescopic observations are a See also:standing See also:monument to his sagacity and acumen.
With the sure See also:instinct of genius, he seized the characteristic features of the phenomena presented to his attention, and his inferences, except when distorted by polemical exigencies, have been strikingly confirmed by modern investigations. Of his two capital errors, regarding respectively the theory of the tides and the nature of comets, the first was insidiously recommended to him by his passionate desire to find a physical confirmation of the earth's double motion; the second was adopted for the purpose of rebutting an anti-Copernican argumentfoundedonthe planetary analogies of those erratic subjects of the sun. Within two years of their first discovery, he had constructed approximately accurate tables of the revolutions of Jupiter's satellites, and he proposed their frequent eclipses as a means of determining longitudes, not only on See also:land, but at See also:sea. This method, on which he laid great stress, and for the facilitation of which he invented a See also:binocular glass, and devised some skilful mechanical contrivances, was offered by him in 1616 to the See also:Spanish See also:government, and afterwards to that of Tuscany, but in each See also:case unsuccessfully; and the close of his life was occupied with prolonged but fruitless negotiations on the same subject with the states-general of See also: He pointed out that they were limited to a certain defined See also:zone on the sun's surface; he noted thefaculae with which they are associated, the See also:penumbra by which they are bordered, their slight proper motions and their rapid changes of form. He inferred from the regularity of their general movements the rotation of the sun on its axis in a period of little less than a See also:month;, and he grounded on the varying nature of the paths seemingly traversed by them a plausible, though inconclusive, argument in favour of the earth's See also:annual revolution. Twice in the year, he observed, they seem to travel across the solar disk in straight lines; at other times, in curves. These appearances he (vol. iii. p. 40, 1761). Galileo remained in the custody of the Inquisition from the 21st to the 24th of June, on which day he was relegated to the Villa llIedici on the Trinita de' Monti. Thence, on the 6th of July, he was permitted to depart for See also:Siena, where he spent several months in the house of the See also:archbishop, Ascanio See also:Piccolomini, one of his numerous and trusty friends. It was not until December that his See also:earnest desire of returning to Florence was realized, and the remaining eight years of his life were spent in his villa at Arcetri called " I1 Giojello," in the strict seclusion which was the prescribed See also:condition of his See also:comparative freedom. Domestic afflictions combined with numerous and painful infirmities to embitter his old age. His See also:sister-in-See also:law and her whole family, who came to live with him on his return from Rome, perished shortly afterwards of the plague; and on the 2nd of April 1634 died, to the inexpressible grief of her father, his eldest and best-beloved daughter, a See also:nun in the See also:convent of See also:San Matteo at Arcetri. Galileo was never married; but by a Venetian woman named Marina Gamba he had three children—a son who married and See also:left descendants, and two daughters who took the veil at an early age. His prodigious See also:mental activity continued undiminished to the last. In 1636 he completed his Dialoghi delle nuove scienze, in which he recapitulated the results of his early experiments and mature meditations on the principles of See also:mechanics. This in many respects his most valuable work was printed by the Elzevirs at See also:Leiden in 1638, and excited admiration equally universal and more lasting than that accorded to his astronomical See also:treatises. His last telescopic discovery—that of the moon's diurnal and monthly librations—was made in 1637, only a few months before his eyes were for ever closed in hopeless See also:blindness. It was in this condition that See also:Milton found him when he visited him at Arcetri in 1638. But the See also:fire of his genius was not even yet See also:extinct. He continued his scientific See also:correspondence with unbroken interest and undiminished logical acumen; he thought out the application of the pendulum to the regulation of clock-work, which Huygens successfully realized fifteen years later; referred with great acuteness to the slight inclination of the sun's axis of rotation to the See also:plane of the See also:ecliptic. Thus, when the earth finds herself in the plane of the sun's See also:equator, which occurs at two opposite points of her See also:orbit, the spots, travelling in circles parallel with that plane, necessarily appear to describe right lines; but when the earth is above or below the See also:equatorial level, the paths of the spots open out into curves turned downwards or upwards, according to the direction in which they are seen. But the explanation of this phenomenon is equally consistent with the See also:geocentric as with the See also:heliocentric theory of the solar system. The idea of a universal force of See also:gravitation seenis to have hovered on the See also:borders of this great man's mind, without ever fully entering it. He perceived the See also:analogy between the power which holds the moon in the neighbourhood of the earth, and compels Jupiter's satellites to circulate See also:round their See also:primary, and the attraction exercised by the earth on bodies at its surface; 1 but he failed to conceive the See also:combination of central force with tangential velocity, and was disposed to connect the revolutions of the See also:planets with the axial rotation of the sun. This notion, it is See also:plain, tended rather towards See also:Descartes's theory of vortices than towards Newton's theory of gravitation. More valid instances of the anticipation of modern discoveries may be found in his prevision that a small annual See also:parallax would eventually be found for some of the fixed stars, and that extra-Saturnian planets would at some future time be ascertained to exist, and in his conviction that See also:light travels with a measurable, although, in relation to terrestrial distances, See also:infinite velocity. The invention of the See also:microscope, attributed to Galileo by his first biographer, Vincenzio Viviani, does not in truth belong to him. Such an instrument was made as early as 15ea by See also:Zacharias See also:Jansen of Middleburg; and although Galileo discovered, in 161o, a means of adapting his telescope to the examination of See also:minute objects, he did not become acquainted with the See also:compound microscope until 1624 when he saw one of Drebbel's instruments in Rome, and, with characteristic ingenuity, immediately introduced some material improvements into its construction. The most substantial, if not the most brilliant part of his work consisted undoubtedly in his contributions towards the establishment of mechanics as a science. Some valuable but isolated facts and theorems had been previously discovered and proved, but it was he who first clearly grasped the idea of force as a mechanical See also:agent, and extended to the See also:external world the conception of the invariability of the relation between cause and effect. From the time of Archimedes there had existed a science of See also:equilibrium, but the science of motion began with Galileo. It is not too much to say that the final triumph of the Copernican system was due in larger measure to his labours in this See also:department than to his direct arguments in its favour. The problem of the heavens is essentially a mechanical one; and without the mechanical conceptions of the dependence of motion upon force which Galileo familiarized to men's minds, that problem might have remained a sealed book even to the intelligence of Newton. The interdependence of motion and force was not indeed formulated into definite laws by Galileo, but his writings on dynamics are everywhere suggestive of those laws, and his solutions of dynamical problems involve their recognition. The extra-See also:ordinary advances made by him in this See also:branch of knowledge were owing to his happy method of applying mathematical See also:analysis to physical problems. As a pure mathematician he was, it is true, surpassed in profundity by more than one among his pupils and contemporaries; and in the wider imaginative grasp of abstract geometrical principles he cannot be compared with See also:Fermat, Descartes or See also:Pascal, to say nothing of Newton or See also:Leibnitz. Still, even in the region of pure mathematics, his 1 The passage is sufficiently remarkable to deserve See also:quotation in the original:—" Le parti della Terra See also:hanno tal propensione at centro di essa, the quando See also:ella cangiasse luogo, le dette parti, benche lontane dal globo nel tempo delle mutazioni di esso, to seguirebbero per tutto; esempio di cio sia it seguito perpetuo delle Medicee, ancorche See also:separate continuamente da Giove. L'istesso si deve dire della See also:Luna, obbligati a seguir la Terra."—Dialogo dei massimi sistemi, Giornata terza, p. 351 of Alberi's edition.powerful and original mind left notable traces of its working. He studied the properties of the See also:cycloid, and attempted the problem of its See also:quadrature; and in the " infinitesimals," which he was one of the first to introduce into geometrical demonstrations, was contained the fruitful germ of the See also:differential calculus. But the method which was peculiarly his, and which still forms the open road to discoveries in natural science, consisted in the combination of experiment with calculation—in the transformation of the See also:concrete into the abstract, and the assiduous comparison of results. The first-fruits of the new system of investigation was his determination of the laws of falling bodies. Conceiving that the simplest principle is the most likely to be true, he assumed as a postulate that bodies falling freely towards the earth descend with a uniformly accelerated motion, and deduced thence that the velocities acquired are in the direct, and the spaces traversed in the duplicate ratio of the times, counted from the beginning of motion; finally, he proved, by observing the times of descent of bodies falling down inclined planes, that the postulated law was the true law. Even here, he was obliged to take for granted that the velocities acquired in descending from the same height along planes of every inclination are equal; and it was not until shortly before his death that he found the mathematical demonstration of this not very obvious principle. The first law of motion—that which expresses the principle of inertia—is virtually contained in the idea of uniformly accelerated velocity. The recognition of the second—that of the See also:independence of different motions—must be added to form the true theory of projectiles. This was due to Galileo. Up to his time it was universally held in the schools that the motion of a body should cease with the impulse communicated to it, but for the " reaction of the See also:medium " helping it forward. Galileo showed, on the contrary, that the nature of motion once impressed is to continue indefinitely in a uniform direction, and that the effect of the medium is a retarding, not an impelling one. Another commonly received axiom was that no body could be affected by more than one movement at one time, and it was thus supposed that a See also:cannon See also:ball, or other projectile, moves forward in a right See also:line until its first impulse is exhausted, when it falls vertically to the ground. In the fourth of Galileo's dialogues on mechanics, he demonstrated that the path described by a projectile, being the result of the. combination of a uniform transverse motion with a uniformly accelerated See also:vertical motion, must, apart from the resistance of the air, be a See also:parabola. The establishment of the principle of the composition of motions formed a conclusive answer to the most formidable of the arguments used against the rotation of the earth, and we find it accordingly triumphantly brought forward by Galileo in the second of his dialogues on the systems of the world. It was urged by anti-Copernicans that a body flung upward or See also:cast downward would, if the earth were in motion, be left behind by the rapid See also:translation of the point from which it started; Galileo proved on the contrary that the reception of a fresh impulse in no way interfered with the movement already impressed, and that the rotation of the earth was insensible, because shared equally by all bodies at its surface. His theory of the inclined plane, combined with his satisfactory See also:definition of " momentum," led him towards the third law of motion. We find Newton's theorem, that " See also:action and reaction are equal and opposite," stated with approximate precision in his treatise Della scienza meccanica, which contains the substance of lectures delivered during his professorship at Padua; and the same principle is involved in the axiom enunciated in the third of his mechanical dialogues, that " the propensity of a body to fall is equal to the least resistance which suffices to support it." The problems of percussion, however, received no definitive See also:solution until after his death. His services were as conspicuous in the statical as in the kinetical See also:division of mechanics. He gave the first satisfactory demonstration of equilibrium on an inclined plane, reducing it to the level by a See also:sound and ingenious See also:train of reasoning; while, by establishing the theory of " virtual velocities," he laid down the fundamental principle which, in the See also:opinion of See also:Lagrange, contains the general expression of the laws of equilibrium. He 41I studied with attention the still obscure subject of molecular See also:Galilee, son peaces, sa condemnation, published in 1867 in the Revue See also:des questions hisloriques. He was followed by M. Karl von Gebler, who, in an able and exhaustive but somewhat prejudiced work, Galileo Galilei and See also:die romische See also:Curie (See also:Stuttgart, 1876), sought to impeach the authenticity of a document of See also:prime importance in the trial of 1633. He was victoriously answered by Signor Domenico Berti, in Il Processo on See also:finale di Galileo Galilei (Rome, 1876), and by M. de 1'Epinois, with See also:Les pieces du peaces de Galilee (Rome, See also:Paris; 1877). The touching letters of Galileo's eldest daughter, Sister Maria See also:Celeste, to her father were printed in 1864 by Professor Carlo Arduini, in apublication entitled La Primogenita di Galileo Galilei. The issue of a " See also:national edition " of the Works of Galileo, in 20 large volumes, was begun at Florence in 189o. It includes a See also:mass of previously inedited correspondence and other documents, collected by the indefatigable director, Professor See also:Antonio Favaro, among whose numerous publications on Galilean subjects may be mentioned: Galileo e lo studio di Padova (2 vols., 1883); Scampoli Galileani (12 series, 1886–1897); Nuovi Studii Galileani (1891); Galileo Galilei e Suor Maria Celeste (1891). See also Th. See also:Henri See also: Wegg-Prosser in Galileo and his See also:Judges (1889), and in two articles published in the See also:American Catholic Quarterly for April and July 190E (A. M. Additional information and CommentsThere are no comments yet for this article.
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