CHAPTER II 



EARTH 



PROBABLY we have been told several facts about 

 this earth we live on which seem rather sur- 

 prising to us, and I suppose we most of us 

 remember some of them. We have been told 

 that the earth is more or less round, that it 

 travels perpetually through space, that there is 

 a strange force called 'gravity' binding it in 

 some mysterious way to the sun, and drawing 

 all things on the earth to the earth. We prob- 

 ably could not have found out these facts our- 

 selves, and, though we believe them to be true, 

 they hardly enter into our every-day life. We 

 still speak of the sun rising and setting, not of 

 the earth turning towards, or away from, the 

 sun ; nor do we usually recollect that the ground 

 we walk on is moving through space at the rate 

 of something like nineteen miles a second, carry- 

 ing us and everything else, even the very air we 

 breathe, along with it. As we see it, and as we 

 think of it, the earth appears a solid immove- 

 able surface, with ups and downs all over it, 

 which, if they are big, we call mountains and 

 valleys. There is the sky above it ; there is the 



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