1 8 GREAT MEN OF SCIENCE 



positions were made by means of new and very elaborate 

 apparatus invented by himself, and reached the greatest 

 exactitude obtainable without telescopes. For example, he 

 took into account, and determined for the first time, errors 

 in the division of his circles and the refraction of the air. 

 His measurements, which are contained in extensive tables, 

 give us the position of stars with an accuracy of half a minute 

 of arc (one-sixtieth of a full moon diameter) while Copernicus 

 himself had regarded observations twenty times less accurate 

 than these as especially successful. 



Tycho was the son of a Swedish nobleman, and began by 

 studying law in Copenhagen; but then, following his own 

 inclinations and in opposition to the wishes of his family, 

 he turned to astronomy. At the age of sixteen, he went to 

 the University of Leipzig, then to Wittenberg and Rostock; 

 he also carried on studies in alchemy at the same time. It 

 is possible that these enabled him to make the alloy of silver 

 with which he ingeniously replaced the upper part of his 

 nose, which he had lost in a duel. In any case, great experi- 

 ence in the working of metals was very valuable to him in the 

 construction of his instruments. His main life work, to 

 which we have already referred, was rendered possible for 

 him by the favour of princes. King Frederick II of Den- 

 mark, on the recommendation of the Landgrave William IV 

 of Hesse, presented him with the island of Hven in the Catte- 

 gat, and built for him, when he was thirty years of age, the 

 observatory of Uranienburg, as well as the house Sternenburg 

 for him, his assistants, and scientific guests. The observa- 

 tory was splendidly equipped and became very famous. 



He worked here with the greatest energy for twenty-one 

 years. At the end of that time his work was disturbed. 

 Frederick II died; four regents carried on the government 

 during the minority of his successor. Tycho fell out with 

 one of them, and thus made it easy for his enemies, of which 

 so energetic and proud a man must have had a large number, 



