CHAPTER XIV 

 A LITTLE PHYSICS 



THE law of Universal Gravitation is the prime 

 factor in running the machinery of the universe. 

 It means that each one of the one thousand mil- 

 lion larger bodies composing the universe attracts, 

 and is attracted by each one of all the others, by 

 a pull the force of which is directly as the mass 

 act inversely as the squares of the distances. By 

 this mighty power all these millions of bodies are 

 kept in their exact places, performing their mo- 

 tions from age to age with the regularity and pre- 

 cision of perfect clock work. 



The Earth completes its rotation on its axis at 

 the same instant every day, and performs its revo- 

 lution around the sun with the same precision. 

 All the other planets rotate on their axes, and 

 complete their journeys around the sun, in simi- 

 larly exact times. The sun itself, too, rotates on 

 its axis, and is moving at a rapid rate taking 

 along with it all the planets, comets, asteroids and 

 meteors in its system towards some point in 

 Hercules. 



A hundred million bright stars look down from 

 the night sky. Each one is a sun. Each sun is 

 the center of a solar system. Planets, comets, 

 asteroids, and meteors galore, compose each sys- 



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