HISTORY OF SCIENCE. 



thus freighted conveyed also Tycho himself, his wife, his five sons, his 

 four daughters, his men-servants, and his women-servants, and landed 

 all safely at Rostock. Surely never before was such an exodus ! ffe-f S 



It was in 1597, when Tycho was fifty-one years of age, that he tlius 

 found himself at Rostock, which place he soon left with all his family, 

 to accept the hospitality of his friend Count Rantzan at the chateau 

 that nobleman possessed near Hamburg. It was here that he com- 

 pleted his work entitled " Astronomies instaurata Mechanics? and, in 

 order to secure a new patron, he dedicated it to the Emperor Rudolph, 

 who was known to be particularly fond of alchemy, astrology, mecha- 

 nics, and the sciences. The project was successful. Tycho was in- 

 vited to Prague, where he was handsomely received by the Emperor 

 (1599), who settled upon him a handsome annual pension, gave him 

 houses for his residence, observatories, and a laboratory. Tycho soon 

 resumed his astronomical observations at Prague ; but it was only in 

 the beginning of the year 1601 that he had received his larger instru- 

 ments from Huen, and that his family had joined him. In October 

 of the same year, however, his life was cut short by a brief illness in 

 the fifty-fifth year of his age. 



The collection of instruments which Tycho caused to be constructed, 

 and which he used in his observations, included every contrivance 

 that had been devised for the study of the heavenly bodies; and 

 the improvements which he effected in the construction of those instru- , 

 ments have contributed largely to his reputation. His instruments 

 surpassed in size and workmanship all that had been before con- ' 

 structed. The larger dimensions afforded space for more minute sub- 

 divisions of the graduated limbs, and by employing in addition the 

 method of reading small divisions, which is now so well known as the 

 Diagonal Scale, Tycho was enabled to read off his instruments to the 

 three hundred and sixtieth part of a degree, whereas Hipparchus could 

 not come nearer than the sixth part of a degree. Tycho made a cata- 

 logue of the fixed stars surpassing in accuracy the catalogues of Ptolemy \ 

 and of the Arabian astronomers; but though he considered that the 

 errors could not exceed one minute of arc, this accuracy is not found 

 to be maintained throughout the catalogue. Perhaps, however, with- 

 out the advantages afforded by the telescope and by the use of exact 

 time-keepers, it was hardly possible to attain greater precision. Tycho 

 had tried to improve upon the clepsydra of the Greeks by substituting 

 mercury for the water, and as this did not answer his expectations, ' 

 he endeavoured to make clocks with wheels which would answer his 

 purpose. The pendulum had not yet been applied to clocks, which 

 at this period were controlled by the oscillations of a weighted bar, 

 which swung horizontally in alternate directions. Tycho had four 

 clocks, which indicated hours, minutes, and seconds. His largest 

 clock had only three wheels, but one of them was 3 feet in diameter, 

 and had 1,200 teeth. 



