Part 11

Eratosthenes, born at Cyrene, succeeded Aristarchus, being invited by Ptolemy Euergetes. This professor is said to be the inventor of the Armillary sphere, an instrument or machine composed of moveable sides, representing the equator, the two colures, with the meridian; all of which turned round on an axis directed to the two poles of the world, each of which circles were anciently called armilla, and the whole machine, astrolabus. All instruments which could be contrived for the promotion of this science, were furnished at the public expense, and placed within the observatory of Alexandria. Assisted by these instruments, Eratosthenes first undertook to measure the obliquity of the ecliptics, or rather the double of that obliquity, that is, the distance from the tropics, which he made to be about 47 degrees; the obliquity, or half of this distance, 23½ degrees. This grand attempt was to ascertain the exact distance of a degree of the meridian, and thus to determine the circumference of the earth; which he accomplished with wonderful exactness, considering the period at which he lived; and he performed this by the same method since adopted by the moderns who have succeeded him. He is also said to have discovered the true distance of the sun from the earth.

The great Archimedes lived contemporary with Eratosthenes, that eminent geometrician of Syracuse, whose inventive genius in mechanics had constructed engines which protracted the fall of that capital, with its Island Sicily, to the almost omnipotent power of Rome for a considerable period.

The most illustrious astronomer which had as yet appeared at Alexandria was Hipparchus, who flourished between one hundred and sixty and one hundred and twenty-five years before Christ. He first brought this science into a tangible elementary form, rendering it systematic. He discovered, or was the first who observed the difference between the autumnal and the vernal equinox; the former being seven days longer than the latter, which proceeds from the eccentricity of the earth’s orbit, first discovered from observing the inequality of the solar motion. He framed tables for what is called equation of time, or to ascertain the difference between the shade on a well constructed dial and a perfectly regulated clock. He made great progress in explaining the motions and phases of the moon; however, he was not so successful with respect to the planets.

His greatest work was his ascertaining the number of the stars, marking their distances, and arriving at the means by which their precise places on the hemisphere of Alexandria could be known. He marked one thousand six hundred stars, in seventy-two signs, into which the heavens were divided. Pliny says this was a labour which must have been difficult even to a god. The appearance of a new star induced him to set about and accomplish this work, which he did in a catalogue for the benefit of future observers.

Hipparchus does not mention comets, whence it has been conjectured he had never seen any; it has also been suggested, that he considered them with meteors, which are not objects of astronomical observation. He divided the heavens into forty-nine constellations, viz., twelve in the ecliptic, twenty-one in the north, and sixteen in the south. To one of these he gave the name of Berenice’s Hair, in honour of the wife of Ptolemy Soter, who had consecrated her hair, which was very beautiful, to Venus Urania, if her husband should return from a war in Asia victorious; it being hung up in the temple of the goddess, soon after disappeared, and is said to have been carried off by the gods.

Hipparchus likewise constructed a sphere, or celestial globe, on which all the stars visible at Alexandria were depicted; and thought to have been similar to the Faranese globe at Rome, still extant. In his observations on the stars, he discovered that, when viewed from the same spot, their distance always appeared the same from each other; but he discovered the distance of the moon to be different in various parts of the heavens; for instance, in the horizon and zenith. This he conceived to be owing to the extent of the globe; he, therefore, contrived a method of reducing appearances of this kind, to what they would be if viewed from the centre of the earth, which is called a parallax; and the discovery of it was of the greatest importance to astronomy. He took this idea from observing that a tree, in the middle of a plain, appeared in different parts of the horizon, when viewed from different situations; so does a star appear in the various points of the heavens, when viewed in different parts of the globe. Hipparchus was the first who connected geography with astronomy, and this fixed both the sciences on certain principles.

After the overthrow of the Roman empire, the first encourager of learning was Charles the Great, or Charlemagne; but little could be done in his time; after his death the former ignorance prevailed. Beda, or Bede, from his piety and modesty termed _venerabilis_, and his scholar, Alcinius, both Englishmen, greatly excelled in general literature; among other qualifications they were eminent in the astronomy of the preceding period. The first step towards the revival of knowledge, or the translation of the Astronomical Elements of Alfergan, the Arab, by order of Frederick II., chosen Emperor of Germany in 1212. About the same time Alphonso X., King of Castile, assembled from all parts the most famous astronomers, who at his desire, composed what are called the Alphonsine Tables, founded on the hypothesis of Ptolemy.

About the same period John Sacrobosco, of Holywood, a native of Halifax, in Yorkshire, who was educated at Oxford, and taught mathematics and philosophy at Paris, made an abridgment of the amalgamist of Ptolemy, and of the commentaries of the Arabs, which was long famous as an elementary book under the title of “De Sphira Mundi.” He died at Paris, in the year 1235. In the same year, Roger Bacon, an English Franciscan friar, made astonishing discoveries in science for the time he lived. He perceived the error in the Kalendar of Julius Cæsar, and proposed a plan, for the correction of it, to Pope Clement IV. in 1267. He is presumed from his writings to have known the use of optical glasses, and the composition and effects of gunpowder. He believed in planetary influence on men’s fortunes, and the transmutation of metals. On account of his vast knowledge in astronomy, mathematics, and chemistry, he was called Doctor _Mirabilis_; but, for the same reason, he was suspected of magic. Under this pretext, whilst at Paris, he was put in prison by order of the Pope’s legate; and after a long and severe confinement, he was at last, by the interest of several noble persons, liberated, returned to England, and died at Oxford in 1292, in the seventy-eighth year of his age.

In the fifteenth century two events happened which changed the face of the sciences; the invention of printing, about 1440, and the taking of Constantinople by the Turks in 1453. The learned men of that city having escaped from the cruelty of the victors, fled into Italy, and again introduced the taste for classical literature; which was greatly promoted by the munificence of the Emperor Frederick III., Pope Nicholas V., and particularly of Cosmo de Medici, who justly merited the title of Father of his Country, and Patron of the Muses.

The restoration of astronomy began in Germany. The first who distinguished himself, was George Purbach, born at Purbach, on the confines of Austria and Bavaria, in 1423, who was cut off in the flower of his age--only thirty-eight years old. He was succeeded by a scholar more skilful than himself, John Muller, born at Konigsberg, in 1436, who taught mathematics and astronomy with great reputation at Vienna. In February, 1471, appeared a comet, on which he published his observations. Being called to Rome by Pope Sextus IV., to assist in correcting the Kalender, he was cut off by the plague, in 1476. Bernard Waltherus, a rich citizen of Nuremberg, his friend and associate, succeeded him, who is said to have first made use of clocks in his astronomical observations, in 1484, and to have been the first of the moderns who perceived the effects of the refraction of light.

Fracastorius, born at Verona, in 1483, was a celebrated astronomer, and an eminent poet and good philosopher; he made considerable discoveries in this science, and with all his abilities may be considered as the precursor of the celebrated Copernicus.

Nicholas Copernicus, the restorer of the Pythagorean philosophy, and the modern discoverer of the rational and true system of astronomy, as now universally received, under the title of his name, was born at Thorn, a city of Royal Prussia, 19th February, 1473. Having learnt the Latin and Greek Languages in his father’s house, he was sent to Cracow, to be instructed in philosophy and physic, where he was honoured with the degree of doctor; showing a greater predilection for mathematics than medicine. His uncle by his mother’s side was a bishop, who gave him a canonry upon his return from Italy, whither he had gone to study astronomy, under Dominic Maria, at Bologna, and had afterwards taught mathematics with success at Rome. In the repose and solitude of an ecclesiastical life, he bent his chief attention to the study of astronomy. Dissatisfied with the system of Ptolemy, which had prevailed fourteen centuries, he laboured to form a juster one. What led him to discover the mistakes of Ptolemy was his observations on the motions of Venus; he is said to have derived his first notion on this subject from various passages in the classics, which mention the opinions of Pythagoras and his followers, as, indeed, he himself acknowledges in his address to Pope Paul III. He established the rotation of the earth round its axis, and its motion round the sun; but to explain certain irregularities in the motion of the planets, he retained the epicicles and eccentrics of Ptolemy. His work was first printed at Nuremberg, in 1543, a short time before his death.

The doctrines of Copernicus were not at first generally adopted. The most eminent professors in Europe adhered to the old opinions.

Among the astronomers of this period, the Landgrave of Hesse deserves particular praise, who erected a magnificent observatory at the top of the Castle of Cassel, and made many observations himself, in conjunction with Christopher Rothman and Justus Burge, concerning the place of the sun, of the planets, and of the stars.

But the person who enriched astronomy with the greatest number of facts of any modern who had yet appeared, was Tycho Brahe, a Dane of noble extraction, born in 1546, designed by his parents for the study of the law; but attracted by an eclipse of the sun in 1560, at Copenhagen, whither he had been sent to learn philosophy, he was struck with astonishment in observing that the phenomenon happened at the very moment it had been predicted.

He admired the art of predicting eclipses, and wished to acquire it. At first, for want of proper instruments, he fell into several mistakes, which, however, he afterwards corrected. Having early perceived his future improvements must depend on instruments, he caused some to be constructed larger than usual, and thus rendered more exact. On the 11th November, 1572, he perceived a new star in Cassiopeia, which continued without changing its place till spring 1574, equal in splendour to Jupiter or Venus. It last it changed colours and entirely disappeared. Nothing similar to this had been observed since the days of Hipparchus.

Tycho, in imitation of that illustrious astronomer, conceived a design of forming a catalogue of the stars. To promote his views, the King of Denmark ordered a castle to be built in Hueun, an island between Seonia and Zealand, which Tycho called Uranibourg, “the city of heaven,” and where he placed the finest collection of instruments that had ever yet appeared; most of them invented or else improved by himself. He composed a catalogue of seven hundred and seventy-seven stars, with greater exactness than had ever been done before; and constructed tables for finding the place of the most remarkable stars at any given time. He was the first who determined the effect of refraction, whereby we see the sun or any star above the horizon, before it is so in reality; as we see the bottom of a vessel when filled with water, standing at a distance, which we could not see when empty. He made several other improvements and important discoveries, which he published in a work entitled “Progymnasmata.” The labours of Tycho attracted the attention of Europe; the learned went to consult him, and the noble to see him. James VI. of Scotland, when he went to espouse the sister of Frederic, King of Denmark, paid Tycho a visit, with all his retinue, and wrote some Latin verses in his praise.

But these honours were of short continuance. After the death of his protector, King Frederic, the pension assigned him was withdrawn, and he was compelled to exile himself from his native country. Having hired a ship, he transported his furniture, books, and instruments to a small place in Hamburgh, in 1597. The Emperor Rodolphus invited him into his dominions, settled a large pension upon him, gave him a castle near Prague, to prosecute his discoveries, and appointed him Longomatus, a native of Jutland, and the celebrated Kepler, to assist him. But Tycho was not happy in his new situation; he died 14th October, 1601, repeating several times, “I have not lived in vain.”

Kepler was one of the greatest philosophers that ever lived, and ought to be considered as the discoverer of the _true_ system of the world. He was born in Germany, at Wiel, near Wirtemberg, 27th December, 1571. He early imbibed the principles of Copernicus. After the death of Tycho, he was employed to finish the tables which he had begun to compose from his observations. Kepler took twenty years to finish them. He dedicated them to the emperor, under the title of the “Rodolphine Tables.”

Kepler united optics with astronomy, and thus made the most important discoveries. He was the first who discovered that the _planets move not in a circle, but in an ellipse_; and that altogether they move sometimes faster and sometimes slower, yet that they describe equal areas in equal times; that is, that the spaces through which they move in different parts of their orbit, are of equal times, though of unequal length; yet when two straight lines are drawn from the extremity of either space to the centre of the sun, they form triangles which include equal areas. He likewise demonstrated that the squares of the periodical times of the revolution of the planets round the sun, are in proportion to the cubes of their distance from him; a theorem of the greatest use in astronomical calculations: for having the periodical times of two planets given, and if the distance of one of them be known, by the rule of proportion, the distance of the other can be ascertained.

Kepler is said to have used logarithms in framing his “Rodolphine Tables.” This great man died in poverty, 15th November, 1631, at Ratisbon, whither he had gone to solicit the arrears of his pension, which had been very ill paid: he left nothing to his wife and children but the remembrance of his virtues.

Contemporary with Kepler was Galileo, born at Pisa, in Italy, in 1564; illustrious for his improvements in mechanics, for his application of the effects of gravity, and for the invention, or at least, the improvement of telescopes.

The use of spectacles, or reading glasses (convex for long-sighted; and concave for short-sighted persons,) had been invented by one Spina, a monk at Pisa, in 1290; or, as some say, by our countryman Roger Bacon. The use of telescopes or glasses for viewing objects at a distance, was invented by Zachary Janssen, a spectacle-maker, at Middleburg, or rather, as it is said, from the accidental discovery of a child. The honour of this invention is also claimed by others. It is certain that Galileo first improved them so as to answer astronomical purposes. He also first made use of the single pendulum for measuring time in making his observations; to which he was led, by considering one day the vibrations of a lamp suspended from the vaulted roof of a church. He likewise discovered the gravity of the atmosphere from the rising of water in a pump, by the action of a piston, which led the way to the invention of the barometer, by his scholar Toricelli.

The use of telescopes opened, in a manner, a new world to Galileo. He observed with astonishment the increased magnitude and splendour of the planets and their satellites, formerly invisible: which afforded additional proofs of the veracity of the Copernican system, particularly the satellites of Jupiter, and the phasis of Venus. He discovered an innumerable multitude of fixed stars, which the naked eye could not discern, and what greatly excited his wonder, without the least increase in their size or brightness.

About the same time, John Napier, of Merchiston, in Scotland, invented what are called “Logarithms,” first published at Edinburgh in 1614, afterwards improved by Mr. Briggs, Professor of Geometry, at Oxford, in which, by a very ingenious contrivance, addition is made to answer for multiplication, and subtraction for division; an invention of the greatest utility in astronomical calculations.

Galileo was not afflicted with poverty, but with persecution. At seventy years of age he was called before the Holy Inquisition, for supporting opinions contrary to Scripture,--and was obliged, on the 11th of June, 1633, formally to abjure them, to avoid being burnt as a heretic. The system of Copernicus had yet gained but few converts; and the bulk of professions and learned men in Europe, attached to the philosophy of Aristotle, supported the old doctrine. Galileo was condemned to prison, and confined to the small city of Arcem, with its territory, where he consoled himself by the study of astronomy. He contrived a method of discovering the longitude by the satellites of Jupiter, which, however, has not been productive of all the advantages he expected. He died in prison, or rather in exile, in 1642.

Although there were a great number of astronomers contemporary with Kepler and Galileo, none made any conspicuous figure. John Bayer, of Augsburg, introduced the Jewish method of marking the stars with letters of the Greek and Latin alphabets; this the Jews use because their law does not permit the use of figures, the produce of fancy.

In 1732, astronomers were very attentive to observe the transit of Venus over the disc of the sun, which Kepler had predicted, as a confirmation of the system of Copernicus. Mercury was observed by Gassendi in France, and some others; but the transit of Venus did not then take place for their inspection.

The transit of Venus was first seen by Jeremiah Horrox, of Hoole, an obscure village, fifteen miles north of Liverpool, on the 24th of November, 1639, and at the same time by his friend, William Crabtree, at Manchester. Horrox was born in 1619, and died in 1641, in the twenty-third year of his age. He wrote an account of his observations, which were published after his death, under the title of “Venus in Sole visa,” by Hevelius.

The Copernican system was first publicly defended in England, by Dr. Wilkins, in 1660; in France, by Gassendi, the son of a peasant in Provence, who published many valuable works on Philosophy. He was born in 1592, and died in 1655. He was violently opposed by Morin, a famous astrologer.

Descartes, descended from a noble family, the son of a counsellor of Brittany, in France, born at Haye, in Tourraine, 31st of March, 1596, early distinguished himself by his knowledge in algebra and geometry. He attacked and overturned the philosophy of Aristotle, in his own country. He attempted to establish certain principles, which, though founded in theory, he took for granted, by which he accounted for all appearances. Like Mochus and Democritus, he imagined all space to be filled with corpuscules, or atoms, in continual agitation, and denied the possibility of a vacuum. He explained everything by supposing vortices, or motions round a centre, according to the opinions of Democritus, and thus discovered the centrifugal force in the circular motion of the planets. But the system of Descartes not being founded on facts or experiments, did not subsist long: although at first it had many followers. His astronomical opinions were much the same with those of Copernicus.

Although the lively notions of Descartes led him into error, yet his exalted views greatly contributed to the improvement of science. Men were led to observation and experiments, in order to overturn his system, and astronomy was cultivated by persons of ability; viz., Bouillard, at Paris; Ward, at Oxford, 1653; and by Helvelius, at Dantzic, 1643, who constructed a fine observatory, and collected a great many facts by his long assiduous observation, for fifty years, during which he made many discoveries concerning the planets, fixed stars, and particularly comets. Colbert, in the name of Louis XIV., sent him a sum of money and a pension. Hevelius published a catalogue of fixed stars, entitled, “Firmamentum Sobieskianum,” dedicated to John Sobieski, King of Poland, at that time justly famous for having raised the siege of Vienna, when attacked by the Turks, 1683. In honour of whom Helvelius formed a new constellation between Antinonus and Serpenterius, called _Sobieski’s Shield_.

But the most distinguished astronomer of that time was Christian Huygens, son to the secretary of the Prince of Orange, born at the Hague, 14th of April, 1629, and educated at Leyden, under Schooten, the commentator on Descartes,--famous for the application of pendulums to clocks and springs to watches, for the improvement of telescopes and microscopes, and for the great discoveries he made, in consequence of these improvements in astronomy.

The establishment of academies, or societies, at this time, contributed greatly to the advancement of science.

The Royal Society, in London, was begun in 1659, but did not assume a regular form till 1662. Its transactions were first published in 1665. The Academy of Sciences, at Paris, was founded in 1686, by Louis XIV., who invited to it Rœmer, from Denmark, Huygens and Cassini from Italy.

Cassini was born at Perinaldo, in the county of Nice, on the 8th of June, 1625, and was appointed first professor in the Royal Observatory at Paris, where he prosecuted his discoveries till his death, in 1712, and was succeeded by his son. He was assisted by Picard, Auzoul, and La Hire.

By the direction of the Academy of Sciences at Paris, a voyage was undertaken by Riecher and Meurisse, at the king’s expense, to the island of Caienne, in South America, almost under the equator, in 1672, to ascertain several philosophical facts;--the refraction of light, the parallax of Mars, and of the Sun, the distance of the tropics, the variation in the motion of the pendulum, &c.

The parallax of the sun is the angle under which an observer at the sun would see the earth: this Cassini fixed at 9½ seconds, and the angle under which we see the sun, at 16 minutes and 6 seconds, or 966 seconds; hence he concluded that these semi-diameters, are as 9½ to 966, or as 10 to 1932. So that, according to Cassini, the semi-diameter of the earth is one hundred times less than that of the sun; and consequently the sun is a million times larger than the earth.