en. x. THE RATE OF FALLING BODIES. 81 



strange at first, namely, that if you let two weights, one 

 light and the other heavy, drop from the same height, they 

 will both take exactly the same time in falling to the ground. 

 Galileo could not make the learned men of Pisa believe 

 this, because Aristotle had said that a ten-pound weight 

 would fall ten times as fast as a one-pound weight ; so to 

 convince them he carried different weights up to the top of 

 the Tower of Pisa, and let them fall before their eyes. 

 Still, though they saw them reach the ground at the same 

 moment, they would not believe, so obstinately were they de- 

 termined to think with Aristotle ; and they actually annoyed 

 Galileo so much on account of his opinions that he left Pisa 

 and became a professor at Padua in 1592. 



The best way for you to convince yourself that Galileo 

 was right and they were wrong will be to take some large 

 soft clay balls, say five, each exactly the same weight, and 

 let them drop at the same moment from the same height 

 you can see at once that they will all reach the ground 

 together. Then press four of the balls one against the 

 other so that they stick together. They will now be four 

 times heavier than the remaining ball, and yet if you let 

 them drop from the same height again, there is no reason 

 why the four should fall any faster merely because they are 

 stuck together than when they were separate, and so the five 

 will reach the ground together as they did before. I have 

 said take large balls, because if they are not tolerably heavy 

 the air will interfere with their falling accurately ; indeed, to 

 make the experiment very truly it ought to be made in a 

 vacuum, that is, a space from which the air has been pumped 

 out, for it is easy to see that air, like water, will buoy up a 

 light body more than a heavy one, and so would cause it to 

 be longer in falling. But air-pumps were not invented in 



