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D-T" TTT ^^ 



80 SIXTEENTH CENTURY. pt. hi. 



lowing up this simple observation he discovered 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 pendulums, such as we now have 

 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 of Mathematics 

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

 next discovery, which was about falling bodies. He observed 

 that a stone or any other body, dropped from a height, falls 

 more and more quickly from the time it starts till it reaches 

 the ground, and after many experiments he succeeded in 

 calculating at what rate its falling increases. At the end of 

 the first second it will be falling at the rate of 32 feet per 

 second, at the end of two seconds it will be falling at the 

 rate of 64 feet per second, at the end of three seconds at the 

 rate of 96 feet per second, and so it will continue, falling 32 

 feet faster every second till it reaches the ground. 



Galileo explained this increase of velocity, or quickness 

 of falling, in the following way : It is the weight of the stone, 

 he said, which drags it down ; and when it had been once 

 started downwards by its weight, it would go on moving at 

 the same rate for ever, without any more dragging. But the 

 weight still goes on pulling it down just as much at the end 

 of the first second as it did when it started, and so the stone 

 falls, first with the drag of its start, then with the drag of the 

 first second added, then of the next, and the next all added 

 together, until it reaches the ground. 



This was quite a true explanation, so far as it went, and 

 Galileo went on to prove another fact, which sounds very 



