CH. x. THE RATE OF FALLING BODIES. 79 



noyed 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 air buoys up bodies as water does, and this 

 would retard the falling of a light body, especially if it had 

 much surface, while it would be inappreciable in heavier 

 ones. But air-pumps wer,e not invented in Galileo's time, 

 so he could not make the experiment very accurately. 



In the year 1592 Galileo established another law in 

 mechanics which is of great value, namely, that any force 

 which will lift a weight of two pounds up one foot will lift a 

 weight of one pound up two feet> or in other words, just as 

 much as you make a weight lighter, so much higher the 

 same force can lift it. If you double the weight, the same 

 force will only lift it half as high ; if you treble the weight, 

 it will only lift it one-third as high, and so on. This law is 

 of immense value in determining the balance of machines, 

 but we cannot examine it further here. At about the same 



