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.