Copernicus was succeeded by a number of astronomers, who enriched the science with numerous observations without extending the boundaries of discovery. Rein hold computed the Prussian tables superior in accuracy to those of Copernicus. Gemnia Frisius invented a new method of projection. Nonius suggested the coktrivance which goes by his name for subdividing the divisions of instruments. Appian observed five comets, and. skew ed the method of delineating eclipses on a plane ; and William IV. landgrave of Hesse, erected a splendid ob servatory at Cassel, and made a number of correct ob servations with the assistance of Rothman and Justus Byrgius.
Astronomy now began to receive important additions from the industry and genius of Tycho Brahe. This celebr:ated astronomer was born at Knudstrup in Nor way, in the year 1546, and so early as the 14th year of his age he began to display a passion for astronomy. The coincidence between the calculated and observed times of a solar eclipse in 1560 struck his youthful mind with astonishment, and determined him to the study of a science that was founded on such correct principles. The ardour which he felt for astronomy was checked by his uncle and preceptor, who wished to bend the whole of his attention to the study of jurisprudence ; but this opposition served only to rivet his attachment ; and Tycho was compelled to watch the motions of the stars, when sleep had disarmed the vigilance of his preceptor. During his travels in Germany, Tycho became acquaint ed with the most distinguished astronomers of the age, and particularly with the landgrave of Hesse, one of the most accurate observers of these times. Upon his re turn to Denmark, he formed the project of establishing himself at Basle in Switzerland, where he might pursue, without interruption, the laborious career which he had determined to follow ; but, in consequence of a letter from the landgrave of Hesse to Frederic, king of Denmark, Tycho abandoned his project, and accepted of the island of Hucna as a present from his Danish majesty. In this solitary retreat he built the celebrated observatory which he called Uraniburg, a name sacred in the history of as tronomy from the discoveries of Tycho, and the mass of accurate observations which were there made during the space of 21 years. At the death of Frederic all the pen sions were stopped, and Tycho was commanded to dis continue his observations. The minister \Valchcndorp, who drove the astronomer from Huena, will be loaded with the execrations of posterity, and branded as the enemy of virtue and science. The venerable Tycho, accompanied with his wife and children, and carrying with him his books and instruments, was thus forced to seek in a foreign land for a more permanent and happy asylum. After retiring to Rostoch, he found a steady patron in the emperor Rodolph II., who settled upon him a handsome pension, and erected an observatory for his use in the neighbourhood of Prague. In this new situa tion he had for his disciples Longomontanus and the illustrious Kepler ; but neither the society of these able pupils, nor the kindness of Rodolph, could sooth his agi tated spirit. He longed to revisit his native country. In 'a distant land, and surrounded by new friends, the re membrance of former attachments, which even the op pression of an ungrateful country could not subdue, prey ed upon his spirits, and probably hastened his death. On
the 24th October 1601, this exiled astronomer terminat ed his sufferings and labours.
By means of the large and accurate instruments which he invented, Tycho formed a catalogue of 777 stars, su perior in correctness to those of Hipparchus and Ulugh B.eigh. To this laborious undertaking he was prompted by the sudden appearance of a new star in Cassiopeia in 1572. It shone with the brilliancy of Venus, so as to be visible even in the middle of the day. Its twinkling, like that of Sirius, exhibited the prismatic colours ; and hav ing retained-its lustre for several weeks, its splendour gradually diminished till it disappeared in March 1574. The genius of Tycho, however, is more conspicuous in the improvements which he made upon the lunar theory. He discovered the inequality called the variation, amount ing at a maximum to 37', and depending on the equated distance of the sun from the moon. This equation va nishes at the syzigies and quadratures, and reaches its maximum at the octants. The motion of the moon is subject also to another irregularity, depending on the po sition of the earth in its orbit. This irregularity, which was also discovered by Tycho, has been called the annual equation, and affects also the place of her apogee and nodes. In addition to these important discoveries, he determined, with unusual-accuracy, the greatest and least inclination of the lunar orbit, and represented this varia tion by the motion of the pole of the orbit in a srhall cir cle. We are also indebted to Tycho for a more perfect knowledge of astronomical refractions. He made the horizontal refraction 34 minutes, and supposed it to vanish at an altitude of but he very strangely maintained, that the rays of the moon and stars sustained different re fractions from the atmosphere. This opinion, unworthy of a philosopher, is one of the numerous instances which might be brought, to show that the mind of Tycho was not fitted for the higher efforts of philosophy. His skill in observing phenomena IN as not equalled by his genius in discovering their cause ; and it is to this incapacity for general views, that we must ascribe his rejection of the Copernician system of the world. In the Tychonic system, which bears the name of its author, the earth is stationary in the centre of the universe. The sun, with all the planets and comets revolving round him, performs his revolution about the earth, and, in the course of every twenty hours, the stars are carried round the central body. This arrangement of the heavenly bodies, though completely destitute of that beautiful simplicity which marked the Copernican system, had the merit of giving a sufficient explanation of the various phenomena of the heavens. Notwithstanding the physical absurdity of sup posing the sun and planets revolving round one compa ratively insignificant, we cannot persuade ourselves to believe that Tycho was led to adopt this hypothesis from a spirit of opposition to Copernicus, or from the vanity of giving his name to a new system of the world. The evidence of the senses, the seeming hostility of the scrip tures to the motion of the earth, the apparent diameter of the fixed stars, and the difficulty of supposing the earth's orbit invisible at the nearest of these remote bo dies, were arguments which might have swayed the mind of Tycho to reject the hypothesis of Copernicus.