SEARCHERS AFTER NATURE'S TRUTHS 303 



Galileo. It is Sir Isaac Newton, who was born in 

 England the very year that Galileo died. 



Perhaps you have heard the story of Sir Isaac 

 Newton sitting under the apple tree, and asking him- 

 self the question any child might ask: ''What makes 

 an apple fall to the ground?" And this searcher for 

 truth thought about that falUng apple and other 

 motions of bodies on the earth and of the planets out 

 in space, until he found an answer. He said there 

 was an invisible force everywhere pulling particles of 

 matter toward each other, moving smaller bodies 

 toward larger ones. This force he called gravitation. 

 He knew that if he was right about the pull of that 

 force, he could prove it from the movement of the 

 moon around our earth, and of the planets around 

 the sun. 



Do you think that was easy to do? Oh, no! Even 

 after his keen mind had thought out a reason for 

 what he saw, Newton had to work very hard to prove 

 his law. He covered whole pages with figures. How 

 long do you think his patience lasted? One year? 

 Two? Three? For seventeen years Newton kept on 

 thinking and trying, and still he had not proved what 

 he believed to be true. 



One day he heard that another scientist had found 

 a new measurement for the curve of the earth's sur- 

 face, more accurate than before, which would give a 

 different number for the mass or weight of the earth. 

 Newton hurried home, put that new number into 

 his pages of figures, worked his long problem all over 

 again, — and this time it was right. He had proved 

 his great law of gravitation, and helped people to 



