CH. x. ORIGIN OF THE PENDULUM. 79 



of which he catalogued 777. He built there a magnificent 

 observatory, which he called Uraweriburg, or the City of the 

 Heavens, and filled it with instruments of every kind, which 

 enabled him to keep a register of the different positions of 

 the heavenly bodies night after night. 



When Frederick II. died, Tycho was persecuted and 

 driven into exile by some envious people who grudged him 

 the pension he was receiving. He then went to Bohemia, 

 under the protection of the Emperor Rudolph II., and here 

 he drew up the valuable astronomical tables called the 

 Rudolphine tables, which, as we shall afterwards see, were of 

 immense use to Kepler. Tycho died in 1601, before Galileo 

 and Kepler made their greatest discoveries. 



Galileo's discovery of the principle of the Pendulum, 

 and of the rate of Falling Bodies, 1564-1600. Galileo dei 

 Galilei was born at Pisa in 1564. His father, though of 

 good family, was poor, but being himself a man of talent 

 and education, he made great exertions to send his son to 

 the University of Pisa, meaning to educate him as a doctor. 

 Here Galileo studied medicine under the famous botanist 

 Csesalpinus ; but having also begun to learn geometry, he 

 became so wrapt up in this pursuit that his father found it 

 was useless to check him, and therefore wisely let him follow 

 his natural bent. It was while he was still at the University, 

 and before he was twenty years of age, that Galileo made his 

 first discovery. When watching a lamp one day which was 

 swinging from the roof of the cathedral, he noticed that, 

 whether it made a long or a short swing, it always took the 

 same time to go from one side to another. To make quite 

 sure of this he put his finger on his own pulse, and, compar- 

 ing its throbs with each swing of the lamp, found that there 

 was always the same number of beats to every swing. Fol- 



