Astronomical Discoveries of Newton—Necessity of combined Exertion to the Completion of great Discoveries—Sketch of the History of Astronomy previous to the Time of Newton—Copernicus, 1473–1543—Tycho Brahe, 1546–1601—Kepler, 1571–1631—Galileo, 1564–1642.
From the optical labours of Newton we now proceed to the history of his astronomical discoveries—those transcendent deductions of human reason by which he has secured to himself an immortal name, and vindicated the intellectual dignity of his species. Pre-eminent as his triumphs have been, it would be unjust to affirm that they were achieved by his single arm. The torch of many a preceding age had thrown its light into the strongholds of the material universe, and the grasp of many a powerful hand had pulled down the most impregnable of its defences. An alliance, indeed, of many kindred spirits had been long struggling in this great cause, and Newton was but the leader of their mighty phalanx,—the director of their combined genius,—the general who won the victory, and therefore wears its laurels.
The history of science presents us with no example of an individual mind throwing itself far in advance of its contemporaries. It is only in the career of crime and ambition that reckless man takes the start of his species, and, uncurbed by moral and religious restraint, erects an unholy dynasty upon the ruins of ancient and venerable institutions. The achievements of intellectual power, though often begun by one mind and completed by another, have ever been the results of combined exertions. Slow in their growth, they gradually approximate to a more perfect condition:—the variety111 in the phenomena of nature call forth a variety of intellectual gifts;—the powers of analysis and combination are applied to the humbler labours of observation and experiment, and in the ordeal of rival inquiry truth is finally purified from error. How different is it with those systems which the imagination rears,—those theories of wild import which are directed against the consciences and hopes of man. The fatal upas-tree distils its poison in the spring as well as the autumn of its growth, but the fruit which sustains life must have its bud prepared before the approach of winter, its blossom expanded in the spring, and its juices elaborated by the light and heat of the summer and the autumnal sun.
In the century which preceded the birth of Newton the science of astronomy advanced with the most rapid steps. Emerging from the darkness of the middle ages, the human mind seemed to rejoice in its new-born strength, and to apply itself with elastic vigour to unfold the mechanism of the heavens. The labours of Hipparchus and Ptolemy had indeed furnished many important epochs and supplied many valuable data; but the cumbrous appendages of cycles and epicycles with which they explained the stations and retrogradations of the planets, and the vulgar prejudices which a false interpretation of Scripture had excited against a belief in the motion of the earth, rendered it difficult even for great minds to escape from the trammels of authority, and appeal to the simplicity of nature.
The sovereign of Castile, the generous and noble-minded Alphonso, had long before proscribed the rude expedients of his predecessors; and when he declared that if the heavens were thus constituted, he could have given the Deity good advice, he must not only have felt the absurdity of the prevailing system, but must have obtained some foresight of a more simple arrangement. But neither he nor the astronomers whom he so liberally protected seem to112 have established a better system, and it was left to Copernicus to enjoy the dignity of being the restorer of astronomy.
This great man, a native of Thorn in Prussia, following his father’s profession, began his career as a doctor of medicine, but an accidental attendance on the mathematical lectures of Brudzevius excited a love for astronomy, which became the leading passion of his life. Quitting a profession uncongenial to such pursuits, he went to Bologna to study astronomy under Dominic Maria; and after having enjoyed the friendship and instruction of that able philosopher, he established himself at Rome in the humble situation of a teacher of mathematics. Here he made numerous astronomical observations which served him as the basis of future researches; but an event soon occurred which, though it interrupted for a while his important studies, placed him in a situation for pursuing them with new zeal. The death of one of the canons enabled his uncle, who was Bishop of Ermeland, to appoint him to a canonry in the chapter of Frauenburg, where, in a house situated on the brow of a mountain, he continued, in peaceful seclusion, to carry on his astronomical observations. During his residence at Rome his talents had been so well appreciated, that the Bishop of Fossombrona, who presided over the council for reforming the calendar, solicited the aid of Copernicus in this desirable undertaking. At first he entered warmly into the views of the council, and charged himself with the determination of the length of the year and of the month, and of the other motions of the sun and moon that seemed to be required; but he found the task too irksome, and probably felt that it would interfere with those interesting discoveries which had already begun to dawn upon his mind.
Copernicus is said to have commenced his inquiries by an historical examination of the opinions of113 ancient authors on the system of the universe; but it is more likely that he sought for the authority of their great names to countenance his peculiar views, and that he was more desirous to present his own theory as one that he had received, rather than as one which he had invented. His mind had been long imbued with the idea that simplicity and harmony should characterize the arrangements of the planetary system, and, in the complication and disorder which reigned in the hypothesis of Ptolemy, he saw insuperable objections to its being regarded as a representation of nature. In the opinions of the Egyptian sages, in those of Pythagoras, Philolaus, Aristarchus, and Nicetas, he recognised his own earliest conviction that the earth was not the centre of the universe; but he appears to have considered it as still possible that our globe might perform some function in the system more important than that of the other planets; and his attention was much occupied with the speculation of Martianus Capella, who placed the sun between Mars and the moon, and made Mercury and Venus revolve round him as a centre; and with the system of Apollonius Perg?us, who made all the planets revolve round the sun, while the sun and moon were carried round the earth in the centre of the universe. The examination, however, of these hypotheses gradually dispelled the difficulties with which the subject was beset; and after the labours of more than thirty years, he was permitted to see the true system of the heavens. The sun he considered as immoveable in the centre of the system, while the earth revolved between the orbits of Venus and Mars, and produced by its rotation about its axis all the diurnal phenomena of the celestial sphere. The precession of the equinoxes was thus referred to a slight motion of the earth’s axis, and the stations and retrogradations of the planets were the necessary consequence of their own motions combined114 with that of the earth about the sun. These remarkable views were supported by numerous astronomical observations; and in 1530 Copernicus brought to a close his immortal work on the Revolutions of the Heavenly Bodies.
But while we admire the genius which triumphed over so many difficulties, we cannot fail to commend the extraordinary prudence with which he ushered his new system into the world. Aware of the prejudices, and even of the hostility with which such a system would be received, he resolved neither to startle the one nor provoke the other. He allowed his opinions to circulate in the slow current of personal communication. The points of opposition which they presented to established doctrines were gradually worn down, and they insinuated themselves into reception among the ecclesiastical circles by the very reluctance of their author to bring them into notice. In the year 1534, Cardinal Schonberg, Bishop of Capua, and Gyse, Bishop of Culm, exerted all their influence to induce Copernicus to lay his system before the world; but he resisted their solicitations; and it was not till 1539 that an accidental circumstance contributed to alter his resolution. George Rheticus, professor of mathematics at Wirtemberg, having heard of the labours of Copernicus, resigned his chair, and repaired to Frauenberg to make himself master of his discoveries. This zealous disciple prevailed upon his master to permit the publication of his system; and they seem to have arranged a plan for giving it to the world without alarming the vigilance of the church, or startling the prejudices of individuals. Under the disguise of a student of mathematics, Rheticus published in 1540 an account of the manuscript volume of Copernicus. This pamphlet was received without any disapprobation, and its author was encouraged to reprint it at Basle, in 1541, with his own name. The success of these publications, and the flattering115 manner in which the new astronomy was received by several able writers, induced Copernicus to place his MSS. in the hands of Rheticus. It was accordingly printed at the expense of Cardinal Schonberg, and appeared at Nuremberg in 1543. Its illustrious author, however, did not live to peruse it. A complete copy was handed to him in his last moments, and he saw and touched it a few hours before his death. This great work was dedicated to the Holy Pontiff, in order, as Copernicus himself says, that the authority of the head of the church might silence the calumnies of individuals who had attacked his views by arguments drawn from religion. Thus introduced, the Copernican system met with no ecclesiastical opposition, and gradually made its way in spite of the ignorance and prejudices of the age.
Among the astronomers who provided the materials of the Newtonian philosophy the name of Tycho Brahe merits a conspicuous place. Descended from an ancient Swedish family, he was born at Knudstorp, in Norway, in 1546, three years after the death of Copernicus. The great eclipse of the sun which happened on the 26th August, 1560, while he was at the University of Copenhagen, attracted his notice: and when he found that all its phenomena had been accurately predicted, he was seized with the most irresistible passion to acquire the knowledge of a science so infallible in its results. Destined for the profession of the law, his friends discouraged the pursuit which now engrossed his thoughts; and such were the reproaches and even persecutions to which he was exposed, that he quitted his country with the design of travelling through Germany. At the very commencement of his journey, however, an event occurred in which the impetuosity of his temper had nearly cost him his life. At a wedding-feast in Rostock, a questionable point in geometry involved him in a dispute116 with a Danish nobleman of the same temperament with himself; and the two mathematicians resolved to settle the difference by the sword. Tycho, however, seems to have been second in the conflict, for he lost the greater part of his nose, and was obliged to supply its place by a substitute of gold and silver, which a cement of glue attached to his face. During his stay at Augsburg he inspired the burgomaster of the city, Peter Hainzell, with a love of astronomy. This public-spirited citizen erected an excellent observatory at his own expense, and here Tycho began that distinguished career which has placed him in the first rank of practical astronomers.
Upon his return to Copenhagen in 1570, he was received with every mark of respect. The king invited him to court, and persons of all ranks harassed him with their attentions. At Herritzvold, near his native place, the house of his maternal uncle afforded him a retreat from the gayeties of the capital, and he was there offered every accommodation for the prosecution of his astronomical studies. Here, however, the passion of love and the pursuits of alchymy distracted his thoughts; but though the peasant girl of whom he was enamoured was of easier attainment than the philosopher’s stone, the marriage produced an open quarrel with his relations, which it required the interference of the king to allay. In the tranquillity of domestic happiness, Tycho resumed his study of the heavens, and in 1572 he enjoyed the singular good fortune of observing, through all its variations, the new star in Cassiopeia, which appeared with such extraordinary splendour as to be visible in the daytime, and which gradually disappeared in the following year.
Dissatisfied with his residence in Denmark, Tycho resolved to settle in some distant country; and having gone as far as Venice in search of a suitable residence, he at last fixed upon Basle, in Switzerland.117 The King of Denmark, however, had learned his intention from the Prince of Hesse; and when Tycho returned to Copenhagen to remove his family and his instruments, his sovereign announced to him his resolution to detain him in his kingdom. He presented him with the canonry of Roschild, with an income of 2000 crowns per annum. To this he added a pension of 1000 crowns; and he promised to give him the island of Huen, with a complete observatory erected under his own eye. This generous offer was instantly accepted. The celebrated observatory of Uraniburg was established at the expense of about 20,000l.; and in this magnificent retreat Tycho continued for twenty-one years to enrich astronomy with the most valuable observations. Admiring disciples crowded to this sanctuary of the sciences to acquire the knowledge of the heavens; and kings34 and princes felt themselves honoured by becoming the guests of the great astronomer of the age.
One of the principal discoveries of Tycho was that of the inequality of the moon’s motion, called the variation. He detected, also, the annual equation which affects the place of her apogee and nodes, and he determined the greatest and the least inclination of the lunar orbit. His observations on the planets were numerous and precise, and have formed the data of the present generalizations in astronomy.118 Though thus skilful in the observation of phenomena, his mind was but little suited to investigate their cause, and it was probably owing to this defect that he rejected the system of Copernicus. The vanity of giving his own name to another system was not likely to actuate a mind such as his, and it was more probable that he was led to adopt the immobility of the earth, and to make the sun, with all his attendant planets, circulate round it, from the great difficulty which still presented itself by comparing the apparent diameter of the stars with the annual parallax of the earth’s orbit.
The death of Frederick in 1588 proved a severe calamity to Tycho, and to the science which he cultivated. During the first years of the minority of Christian IV. the regency continued the royal patronage to the observatory of Uraniburg; and in 1592 the young king paid a visit of some days to Tycho, and left him a gold chain in token of his favour. The astronomer, however, had made himself enemies at court, and the envy of his high reputation had probably added fresh malignity to the irritation of personal feelings. Under the ministry of Wolchendorf, a name for ever odious to science, Tycho’s pension was stopped;—he was in 1597 deprived of the canonry of Roschild, and was thus forced, with his wife and children, to seek an asylum in a foreign land. His friend, Henry Rantzau, of Wansbeck, under whose roof he found a hospitable shelter, was fortunately acquainted with the emperor Rodolph II., who, to his love of science, added a passion for alchymy and astrology. The reputation of Tycho having already reached the imperial ear, the recommendation of Rantzau was scarcely necessary to ensure him his warmest friendship. Invited by the emperor, he repaired in 1599 to Prague, where he met with the kindest reception. A pension of three thousand crowns was immediately settled upon him, and a commodious observatory erected for his use119 in the vicinity of that city. Here the exiled astronomer renewed with delight his interrupted labours, and the gratitude which he cherished for the royal favour increased the satisfaction which he felt in having so unexpectedly found a resting-place for approaching age. These prospects of better days were enhanced by the good fortune of receiving two such men as Kepler and Longomontanus for his pupils; but the fallacy of human anticipation was here, as in so many other cases, strikingly displayed. Tycho was not aware of the inroads which both his labours and his disappointments had made upon his constitution. Though surrounded with affectionate friends and admiring disciples, he was still an exile in a foreign land. Though his country had been base in its ingratitude, it was yet the land which he loved,—the scene of his earliest affection,—the theatre of his scientific glory. These feelings continually preyed upon his mind, and his unsettled spirit was ever hovering among his native mountains. In this condition he was attacked with a disease of the most painful kind, and though the paroxysms of its agonies had lengthened intermissions, yet he saw that death was approaching. He implored his pupils to persevere in their scientific labours. He conversed with Kepler on some of the profoundest points of astronomy, and with these secular occupations he mingled frequent acts of piety and devotion. In this happy condition he expired without pain at the age of fifty-five, the unquestionable victim of the councils of Christian IV.
Notwithstanding the accessions which astronomy had received from the labours of Copernicus and Tycho, no progress was yet made in developing the general laws of the system, and scarcely an idea had been formed of the power by which the planets were retained in their orbits. The labours of assiduous observers had supplied the materials for this120 purpose, and Kepler arose to lay the foundations of physical astronomy.
John Kepler was born at Wiel, in Wirtemberg, in 1571. He was educated for the church, and discharged even some of the clerical functions; but his devotion to science withdrew him from the study of theology. Having received mathematical instruction from the celebrated M?stlinus, he had made such progress in the science, that he was invited in 1594 to fill the mathematical chair of Gratz in Styria. Endowed with a fertile imagination, his mind was ever intent upon subtle and ingenious speculations. In the year 1596 he published his peculiar views in a work on the Harmonies and Analogies of Nature. In this singular production, he attempts to solve what he calls the great cosmographical mystery of the admirable proportion of the planetary orbits; and by means of the six regular geometrical solids,35 he endeavours to assign a reason why there are six planets, and why the dimensions of their orbits and the time of their periodical revolutions were such as Copernicus had found them. If a cube, for example, were inserted in a sphere, of which Saturn’s orbit was one of the great circles, it would, he supposed, touch by its six planes the lesser sphere of Jupiter; and, in like manner, he proposes to determine, by the aid of the other geometrical solids, the magnitude of the spheres of the other planets. A copy of this work was presented by its author to Tycho Brahe, who had been too long versed in the severe realities of observation to attach any value to such wild theories. He advised his young friend “first to lay a solid foundation for his views by actual observation, and then, by ascending from these, to strive to reach the causes of things;” and there is reason to think that, by the aid of the whole Baconian philosophy, thus compressed121 by anticipation into a single sentence, he abandoned for a while his visionary inquiries.
In the year 1598 Kepler suffered persecution for his religious principles, and was compelled to quit Gratz; but though he was recalled by the States of Styria, he felt his situation insecure, and accepted of a pressing invitation from Tycho to settle at Prague, and assist him in his calculations. Having arrived in Bohemia in 1600, he was introduced by his friends to the Emperor Rodolph, from whom he ever afterward received the kindest attention. On the death of Tycho in 1601, he was appointed mathematician to the emperor,—a situation in which he was continued during the successive reigns of Matthias and Ferdinand; but what was of more importance to science, he was put in possession of the valuable collection of Tycho’s observations. These observations were remarkably numerous; and as the orbit of Mars was more oval than that of any of the other planets, they were peculiarly suitable for determining its real form. The notions of harmony and symmetry in the construction of the solar system, which had filled the mind of Kepler, necessarily led him to believe that the planets revolved with a uniform motion in circular orbits. So firm, indeed, was this conviction, that he made numerous attempts to represent the observations of Tycho by this hypothesis. The deviations were too great to be ascribed to errors of observation; and in trying various other curves, he was led to the discovery that Mars revolved round the sun in an elliptical orbit, in one of the foci of which the sun itself was placed. The same observations enabled him to determine the dimensions of the planet’s orbit, and by comparing together the times in which Mars passed over different portions of its orbit, he found that they were to one another as the areas described by the lines drawn from the centre of the planet to the centre of the sun, or, in more technical terms, that122 the radius vector describes equal areas in equal times. These two remarkable discoveries, the first that were ever made in physical astronomy, were extended to all the other planets of the system, and were communicated to the world in 1609, in his “Commentaries on the Motions of the Planet Mars, as deduced from the observations of Tycho Brahe.”
Although our author was conducted to these great laws by the patient examination of well-established facts, his imagination was ever hurrying him among the wilds of conjecture. Convinced that the mean distances of the planets from the sun bore to one another some mysterious relation, he not only compared them with the regular geometrical solids, but also with the intervals of musical tones; an idea which the ancient Pythagoreans had suggested, and which had been adopted by Archimedes himself. All these comparisons were fruitless; and Kepler was about to abandon an inquiry of about seventeen years’ duration, when, on the 8th March, 1618, he conceived the idea of comparing the powers of the different members which express the planetary distances, in place of the numbers themselves. He compared the squares and the cubes of the distances with the same powers of the periodic times; nay, he tried even the squares of the times with the cubes of the distances; but his hurry and impatience led him into an error of calculation, and he rejected this law as having no existence in nature! On the 15th May, his mind again reverted to the same notion, and upon making the calculations anew, and free from error, he discovered the great law, that the squares of the periodic times of any two planets are to one another as the cubes of their distances from the sun. Enchanted with this unexpected result, he could scarcely trust his calculations; and, to use his own language, he at first believed that he was dreaming, and had taken for granted the very truth of which he was in search. This brilliant discovery was published123 in 1619, in his “Harmony of the World;” a work dedicated to James VI. of Scotland. Thus were established what have been called the three laws of Kepler,—the motion of the planets in elliptical orbits,—the proportionality between the areas described and their times of description,—and the relations between the squares of the periodic times and the cubes of the distances.
The relation of the movements of the planets to the sun, as the general centre of all their orbits, could not fail to suggest to Kepler that some power resided in that luminary by which these various motions were produced; and he went so far as to conjecture that this power diminishes as the square of the distance of the body on which it was exerted; but he immediately rejects this law, and prefers that of the simple distances. In his work on Mars, he speaks of gravity as a mutual and corporeal affection between similar bodies. He maintained that the tides were occasioned by the moon’s attraction, and that the irregularities of the lunar motions, as detected by Tycho, were owing to the joint actions of the sun and the earth; but the relation between gravity, as exhibited on the earth’s surface, and as conducting the planets in their orbits, required more patience of thought than he could command, and was accordingly left for the exercise of higher powers.
The misery in which Kepler lived forms a painful contrast with the services which he performed to science. The pension on which he subsisted was always in arrears, and though the three emperors whose reigns he adorned directed their ministers to be more punctual in its payment, the disobedience of their commands was a source of continued vexation to Kepler. When he retired to Sagan, in Silesia, to spend in retirement the remainder of his days, his pecuniary difficulties became still more harassing. Necessity at last compelled him to apply124 personally for the arrears which were due; and he accordingly set out in 1630 for Ratisbon; but in consequence of the great fatigue which so long a journey on horseback produced, he was seized with a fever, which carried him off on the 30th November, 1630, in the 59th year of his age.
While Kepler was thus laying the foundation of physical astronomy, Galileo was busily employed in extending the boundaries of the solar system. This distinguished philosopher was born at Pisa in 1564. He was the son of a Florentine nobleman, and was educated for the medical profession; but a passion for geometry took possession of his mind, and called forth all his powers. Without the aid of a master, he studied the writings of Euclid and of Archimedes; and such were his acquirements, that he was appointed by the Grand-duke of Tuscany to the mathematical chair of Pisa in the twenty-fifth year of his age. His opposition to the Aristotelian philosophy gained him many enemies, and at the end of three years he quitted Pisa, and accepted of an invitation to the professorship of mathematics at Padua. Here he continued for eighteen years adorning the university by his name, and diffusing around him a taste for the physical sciences. With the exception of some contrivances of inferior importance, Galileo had distinguished himself by no discovery till he had reached the forty-fifth year of his age. In the year 1609, the same year in which Kepler published his celebrated commentary on Mars, Galileo paid a visit to Venice, where he heard, in th............