64 



INTRODUCTION TO GENERAL SCIENCE 



the atmosphere and the supply of water. They all rotate on 

 axes, and revolve around the sun. Thus they have day and 

 night, and seasons, although all these periods are entirely 

 different from those of the earth, in length, in degree, and 

 frequency of changes. 



Since we live on the earth, we do not think of it as a sphere 

 revolving through space, for it is so large that the small part 

 we see at one time seems flat, while the sun and the stars ap- 

 pear to move around the earth. Nevertheless, the earth 

 behaves like the other planets, and is, after all, one of the 

 smallest ones, Mars and Mercury, only, being smaller. 



References : 



Size of the Sun and Distances of the 



Planets. 



The Earth as a Planet. 

 The Planets in General. 

 Revolution of the Earth around the Sun. 

 Structure of the Solar System. 

 The Planets. 

 The Earth as a Globe. 

 Relation of Earth to Other Planets. 

 The Earth as a Planet. 

 Rotation of the Earth. 

 Revolution of the Earth. 

 The Relation of the Earth to the Planets 



and the Sun. 

 k. 1307 : 10-14. The Earth among Planets. 



46. AGE OF THE EARTH 



The age of the earth must be very great, so great as to be 

 reckoned in millions of years. We know that this is so, for the 

 changes which have taken place upon the surface of the earth 

 could not have been accomplished in any short period of time. 



