14 



GENERAL SCIENCE 



heat and light from it. It has a diameter of 866,000 

 miles and is much larger than all the other planets com- 

 bined. If the earth were placed at its center, thei^ would 

 be room for the moon to revolve in its regular orbit, 



which would still be 

 200,000 miles from 

 the circumference of 

 the sun (Figure 11). 

 The reason for the 

 extremely hot con- 

 dition of the sun 

 is not known. Its 

 interior is thought 

 to be composed of 

 a dense white-hot 

 liquid, and the outer 

 portions are known 

 to be intensely 

 heated gases (Fig- 



FIG. 11. Diagram Showing Comparative Sizes . . 



of the Earth, the Orbit of the Moon, and the Ure 12). 1 he SUn 



is composed of the 



same elements .as the earth, but its condition is so hot 

 that these elements can be recognized only by means of 

 the spectroscope, an instrument used in the study of light. 

 Shape of the Earth. Children, if they are concerned 

 with the question at all, imagine that the earth is a flat 

 place bounded by a few hills or a quantity of water, 

 according to where they live ; they are concerned with 

 no people other than those in their immediate locality 

 and those that they see in their very limited travels. 

 In the childhood of the race, people in general held the 

 same ideas. They imagined the earth as flat, and in 

 sailing their crude vessels were careful not to venture 



