COMMON 



CHAPTER ONE 



GRAVITATION 



SECTION i. A real place where things weigh nothing 

 and where there is no up or down. 



Why is it that the oceans do not flow off the earth? 



What is gravity ? 



What is " down," and what is " up "? 



There is a place where nothing has weight; where 

 there is no " up " or " down " ; where nothing ever 

 falls ; and where, if people were there, they would float 

 about with their heads pointing in all directions. This 

 is not a fairy tale; every word of it is scientifically 

 true. If we had some way of flying straight toward 

 the sun about 160,000 miles, we should really reach 

 this strange place. 



Let us pretend that we can do it. Suppose we have 

 built a machine that can fly far out from the earth 

 through space (of course no one has really ever invented 

 such a machine). And since the place is far beyond 

 the air that surrounds the earth, let us imagine that 

 we have fitted out the air-tight cabin of our machine 

 with plenty of air to breathe, and with food and every- 

 thing we need for living. We shall picture it something, 

 like the cabin of an ocean steamer. And let us pretend 

 that we have just arrived at the place where things, 

 weigh nothing: 



When you try to walk, you glide toward the ceiling 

 of the cabin and do not stop before your head bumps. 



