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by the churchmen, and the partisans of the Aristotelian philosophy.
Being thus placed in a situation of independence, and in possession of uninterrupted leisure, Galileo devoted himself with ardour to the study of philosophy; and it must be admitted, that if there be others to whom physical science is indebted for more profound investigations, and researches of greater difficulty, there is, perhaps, no one whose writings have more contributed to its general progress, or whose name is associated with a greater number of brilliant discoveries.
Galileo's astronomical discoveries were the natural, it may be said the necessary, consequences of the invention of the telescope. With respect to the instrument itself, it is not easy to pronounce with certainty on the exact degree of merit be can claim in the invention. The received story is, that while at Venice in 1609, he heard accidentally of an instrument having been constructed in Holland, which possessed the property of causing distant objects to appear nearer to the observer; that on reflecting on the means by which this effect could be produced, he found, after a night's consideration, the explanation in the principle of refraction; and that by applying two spectacle glasses of a particular kind to a leaden tube, he was immediately in possession of a telescope which magnified three times. According to this account, Galileo was a re-inventor of the telescope. He himself claims no other merit than that of divining the construction, and improving the instrument. He affirms that he had never seen any of the Dutch telescopes; and although, as remarked by Sir David Brewster, there is no reason to doubt his assertion, it appears from various evidence that more than one telescope had previously been brought from Holland to Italy ; whence it has been conceived to be quite possible that, without having actually seen the instrument, he may have received such information with respect to its construction, as would render the discovery of the principle not altogether independent. But whether his merit in the re-invention of the telescope be great or small, he is entitled, beyond all question, to the honour of first applying it to the examination of the Heavens; and displaying, to the astonished gaze of mankind, new worlds and wonders, of the existence of which, till that time, no one had formed a conception.
The invention of the telescope was followed almost immediately by a crowd of astronomical discoveries, which, though, from our familiarity with them at the present day, they cease to be regarded with wonder, could not fail, on their first announcement, to excite very great admiration and astonishment. The
first object he examined was the moon, whose rugged and irregular surface, presenting so many points of resemblance to our own earth, supplied him
with arguments against the Aristotelian doctrine of the perfection, absolute smoothness, and incorruptible essence of the heavenly bodies; of which he was not slow to take advantage. He next observed and pointed out the remarkable difference between the telescopic appearances of the planets and fixed stars; and the innumerable multitude of small stars that become visible in the milky way, the pleiades, and other nebulæ and clusters. But, of all his telescopic discoveries, that which was regarded as the most astonishing and incredible, (for their existence was denied, and cause shown why they could not possibly exist,) was the satellites of Jupiter. Four small planets revolving about a central body, and presenting so palpable and striking an analogy to the primary planets revolving about the sun, furnished an argument in favour of the Copernican theory, to which even the most bigoted followers of Aristotle could scarcely withhold their assent. The ring of Saturn also attracted his notice; but, in this case, he mistook the nature of the phenomenon, and supposed the planet to be triple. He remarked the horned appearance of Venus, and thereby removed a difficulty which had occurred to Copernicus himself, who perceived that, if his theory were true, the inferior planets ought to have phases like the moon. His discovery of the spots on the sun has occasioned much controversy; having been claimed by Fabricius, Scheiner, and our countryman Harriott. Galileo's claim to priority seems now generally admitted; and he deduced from the phenomena the important conclusion, that the sun revolves on its axis in a period of about twenty-eight days.
Greatly as these discoveries have contributed to the fame of Galileo, it cannot be said that they occupied a large portion of his time—having been all published within three years after he was in possession of the telescope. Viewing them with relation to the present state of knowledge, their intrinsic merit is not very great. They are nothing beyond what an ordinary observer, with a tolerably good telescope, would be expected to make out in the course of a few evenings; excepting, perhaps, the phenomena of the solar spots, and the motions of Jupiter's satellites, which require time for their development. After the invention of the telescope, they imply no great merit; and could not long have escaped observation, although Galileo had never lived. In fact, with the exception of the phases of Venus, and the triple appearance of Saturn, they were all claimed by other observers even in his own lifetime. But, in order to appreciate them correctly, we must go back to the period at which they were made; and consider them with reference to the ideas universally entertained in that age. In this light, their importance assumes a very different character; and it will appear that to Galileo must be conceded the honour, not only of having made an immense addition to the existing knowledge of the heavens, but of having prepared men's minds for the reception of the true Theory of the Universe, by beating down and overthrowing the prejudices by which they had been kept enthralled for so many generations.
The researches of Galileo, in some of the other departments of natural philosophy, were of more importance than bis telescopic discoveries. Since the days of Archimedes, no advance had been made in the theory of mechanics. In determining the law of the acceleration of falling bodies, and thereby laying the foundation of dynamics, Galileo gave it an immense extension, While yet a student at Pisa, he remarked the extremely impor: tant fact of the isochronism of the pendulum; and being then engaged in medical studies, he proposed to apply that property as a means of ascertaining the rate of the pulse. At a more mature aye, he had an idea of making use of a pendulum as a regulator of clock-work; but he was ignorant of the theory of the isoehronism, which was first given by Huygens. The three (so called) laws of motion, though they are not distinctly enunciated, are virtually involved in the reasoning which he employs in his · Dialogues on Mechanics,' published in 1638. The principle of virtual velocities has usually been ascribed to him: the germ is, however, to be found in the anterior writings of his first patron and early friend, Guido Ubaldi. In mathematics he was not an inventor; and it would seem that his acquirements in this department were scarcely equal to the state of knowledge at the time. Delambre has remarked as extraordinary, that in his long calculations (published in 1632) to prove that the new star of 1572 had no parallax, he made no use of Logarithms, although the tables of Napier, Kepler, Ursinus, and Briggs, were then in existence, and would have greatly abridged his labour. In a letter to the Grand Duke, written in 1609, he mentions several mathematical treatises on which he was engaged ; among others, one on the composition of continuous quantity. It is not very clear that the works alluded to 'ever existed elsewhere than in his own mind; but it is supposed that many of his writings have been lost, and that with reference to the one just mentioned, Cavalleri long refused to publish his own theory, in the hope that Galileo's would be given to the world. On these very insufficient grounds, Libri gives him the credit of having imagined the calculus of indivisibles.
It is not our purpose to enumerate the specific services which Galileo rendered to the physical sciences; and still less to enter into any account of the long and prolix discussions with which the announcement of the greater part of his discoveries was followed. His claim to the gratitude of posterity consists not so much in his actual discoveries, important though they were, as in the revolution which he contributed to effect in philosophy, by applying geometrical reasoning to experimental facts, and teaching mankind to reject the dogmas of the schools, and to appeal from the authority of Aristotle to reason and observation. cannot, indeed, be said that he was either the first who followed the inductive method of reasoning, or who perceived and denounced the worthlessness of the scholastic philosophy; but the credit which he had gained by the telescope, and the wonders it revealed, and, above all, the extraordinary elegance and perspicuity of his writings, threw the merits of others into the shade; and gave an impulse and currency to his opinions, which they would not have obtained without these accessory advantages. Considering the frequency with which his name occurs in all the scientific productions of the seventeenth century, and that it stands at the head of so many important discoveries both in astronomy and mechanics, we may admit the remark of his countryman Libri, that in science he was the master of Europe.
(The circumstances which entitle Galileo to be regarded as a martyr of science, are the persecutions he sustained on account of his assertion of the earth's motion; his trial, condemnation, and imprisonment, by the Inquisition ; and his constrained abjuration, in his old age, of the Copernican doctrine, which it had been the principal business of his life to establish. (This episode in his history has been represented in very different colours by his biographers; some ascribing his persecution to the jealousy with which the Romish Church has always been disposed to regard the propagation of physical knowledge; while others have considered that it was provoked, if not altogether compelled, by his own imprudent conduct ;) which left the heads of the Church no alternative but to reduce him to silence, or abandon their pretensions to spiritual authority. Sir David Brewster has treated this subject with fairness and moderation. He is no apologist of the Inquisition; yet, on perusing his narrative, we cannot fail to see that its conduct, in this particular case, was not without circumstances of palliation; and that Galileo himself, like many others who have had the credit of suffering for the cause of truth, had no small share in stirring up the persecution by which his last years were embittered.
Galileo had adopted the Copernican theory at an early period;
and as it was not the disposition of his mind long to cherish any opinion in silence, keen discussions on the subject had taken place between himself and the Peripaticians during his residence at Padua. Defeated in argument, they invoked the aid of religion, and attempted to silence him by the authority of Scripture. The heads of the Church, though disliking the innovation, were reluctant to commit themselves by a formal condemnation of the doctrine, and desirous that it should be viewed in the light of a mere mathematical hypothesis. In fact, the theory of the earth's motion, so far from having met with opposition on its first promulgation, had been received with favour by some of the most eminent cardinals and churchmen; and Copernicus, himself a priest, had dedicated his great work, De Revolutionibus, to the Pope. But when Galileo, who had no spiritual character, began to disseminate the same doctrine, the Dominicans took alarm, and forced the Church into a reluctant declaration of its sentiments. In replying to the objections which his opponents drew from certain texts of Scripture, Galileo, in a letter to his friend and pupil Castelli, endeavoured to prove that the expres. sions employed in the sacred writings were not intended to have reference to astronomical systems; and that there was, in fact, as much difficulty in reconciling the language of Scripture with the Ptolemaic as with the Copernican theory; and in 1615 he published a letter, addressed to the mother of the Grand Duke, in which the same arguments were stated at greater length, and enforced with quotations from the ancient fathers, and instances of the former practice of the Church. The publication of these letters gave great offence to the court of Rome; for, however favourably it might be disposed to the new doctrines, it could not submit to see the interpretation of the Scriptures wrested from the hands of the priesthood by a layman. Galileo having reason to apprehend that the doctrine would be formally condemned, proceeded to Rome for the purpose of endeavouring to avert, if possible, this consequence. Here, he was brought before the tribunal of the Inquisition, charged with maintaining the doctrine of the motion of the earth and the immobility of the sun, teaching it to his pupils, and attempting to reconcile it to Scripture. In February 1616, a congregation of cardinals, having considered the charges, decreed that Galileo should be enjoined to renounce the obnoxious doctrines, and to pledge himself, under the penalty of imprisonment, that he would neither teach, defend, or publish them in future. Galileo, says Sir David Brewster, 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 ;