CH. x. ORIGIN OF THE PENDULUM. 77 



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 Pen- 

 dulum, and of the Kate of Falling Bodies, 15 64-1 6 OO. 

 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 Caesalpinus ; 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, comparing its throbs with each swing of the 

 lamp, found that there was always the same number of beats 

 to every swing. Following up this simple observation he dis- 

 covered that a weight at the end of a cord will always take 

 the same time to swing backwards and forwards so long as 

 the cord is of the same length and the arc through which 

 the weight moves is small. This was the beginning of pen- 

 dulums, such as we have now to our clocks, but at first they 

 were only used by physicians to count the rate at which a 

 patient's pulse beats. 



In 1589 Ferdinand de' Medici, Duke of Tuscany, having 

 heard of Galileo's talents, made him Lecturer on Mathematics 

 at Pisa, and it was while he held this post that he made his 

 next discovery, which was about falling bodies. He ot> 



