SCIENCE OF HOME AND COMMUNITY 



heat every living thing on the earth would perish. We 

 naturally wonder how the sun is able to give out so much 

 heat for such long periods of time. We know that it is not 

 by the ordinary process of burning with which we are famil- 

 iar; because if it were so, the sun would have burned up 

 before this. Astronomers tell us that the heat is given out 

 by the contraction of the sun, and that the sun is all the time 

 becoming smaller. The change is so slight, however, that 

 even with the most powerful telescope, man cannot notice 

 any difference in the size of the sun, 



FIG. 207. Spectroscope, an instrument by means of which many things have 

 been learned about the sun and stars. 



Composition of the sun. One very remarkable thing that 

 man has been able to do is to find out some things of which 

 the sun is made, although it is situated at such a great 

 distance. This has been done by means of the spectroscope. 

 This is an instrument for making and viewing a spectrum. 

 When sunlight passes through a glass prism of a certain 

 shape, the ordinary white light is broken up into a number 

 of colored lights, as in the rainbow. When this spectrum 

 is looked at with a telescope, it is found to contain a great 

 many dark lines crossing it. From the number and position 

 of these lines it is possible to tell what substances must be 



