16 



GENERAL SCIENCE 



of the earth was unknown to the rest of the world and 

 afterwards forgotten. Not until about the time of 

 Columbus was it regained, and since that time many 

 people have sailed around the earth. Wonderful dis- 

 coveries have been made concerning the earth, and almost 

 every part of its surface has been explored. 



Men who have made careful measurements of the 

 shape of the earth tell us that it is an oblate spheroid, 



that is, a sphere which 

 is somewhat flattened at 

 two opposite points. An 

 orange is an oblate sphe- 

 roid, but the flattening of 

 an orange is much greater 

 in proportion to its di- 



FIG. 14. The Earth is an Oblate Spheroid. 



ameter than is that of 

 the earth (Figure 14). 

 The polar diameter of 

 the earth is only twenty- 

 seven miles shorter than 

 the equatorial diameter, 

 and twenty-seven miles 

 is a very small amount when compared to the average 

 diameter of the earth, which is about 8000 miles. 



When we look at the very high mountains on the sur- 

 face of the earth and think of the depressions on the floor 

 of the ocean, which are more than five miles deep, we 

 wonder how a body with such great irregularities can be 

 called a sphere at all. However, we must remember 

 that this notion is due to our nearness of view, and that, 

 when compared to the great size of the whole earth, 

 these irregularities are less, in proportion, than the slight 

 ridges on the surface of the orange. 



