66 INTRODUCTION TO GENERAL SCIENCE 



is spherical, and that its rotation on its axis is what gives the 

 apparent motion to the sun. We have some very certain 

 proofs that the earth is spherical: we know that the earth 

 can be circumnavigated, and, moreover, the shadow of the 

 earth upon the moon, no matter when it occurs, always has a 

 circular shape. Again, if the earth were flat, the time of sun- 

 rise and sunset would be the same everywhere; but we know 

 that such is not the case. The higher we climb upon a hill, 

 or rise in a balloon, the farther we can see. This is true only 

 because the earth is spherical. The amount of curvature of 

 the earth in feet may be found for the first few miles by 

 squaring the number of miles and multiplying by two thirds. 

 The shape of the eartn is not an exact sphere, but is called an 

 oblate spheroid, having a polar axis twenty-seven miles less 

 than the equatorial diameter. Thus the land at the poles is 

 thirteen and one half miles nearer the center of the earth than 

 any point on the equator. 



References : 



1. 1002:114-119. Shape of the Earth. 



2. 1002 : 126-127. Size of the Earth. 



3. 1304 : 1-3. Shape and Size of the Earth, 

 a. 1001 : 46-47. Size of the Earth. 



6. 1001 : 52-53. Methods of Determining the Earth's Form. 



c. 1001 : 56. Shape and Rotation of the Earth. 



d. 1001 : 58. Surface and Volume of the Earth. 



e. 1303 : 1-5. Shape and Size of the Earth. 

 /. 1305 : 38-41. Shape and Size of the Earth. 

 g. 1306 : 3-5. Form and Size of the Earth. 

 h. 1307 : 14-15. Form and Size of the Earth. 



i. 1309 : 18-22. Shape, Size, and Density of the Earth. 



j. 1311 : 1-2. Form of the Earth. 



k. 1312 : 16-18. Shape and Size of the Earth. 



