ASTRONOMY 121 



Surrounding the brilliant part of the sun there is a layer 

 of gases through which the light must shine, and it is the 

 absorption by these gases which produces the dark gaps in 

 the spectrum of sunlight. By noting the positions of these 

 gaps and comparing them with the light given out by luminous 

 bodies on the earth we find that this atmosphere of the sun 

 contains the gases of about thirty-nine of the same elements 

 as we find in the earth. 



Outside of this layer of gases, there is another layer 

 called the chromosphere, consisting mainly of hydrogen gas. 

 This gives out a reddish light, but it cannot be seen ordinarily 

 on account of the much more brilliant light from the main 

 body of the sun. But when the sun goes behind the moon 

 in a total eclipse, we see the chromosphere standing out as a 

 bright rosy ring around the dark moon. Outside of the 

 chromosphere we find the corona, a faint bright mass, prob- 

 ably gaseous, extending very far out beyond the sun's surface. 



Dissipation of Energy . If we believe that energy cannot 

 be destroyed or created, we are naturally led to ask : What be- 

 comes of the great amount of energy continually being sent out 

 by the sun? If the stars do extend to infinite distances in 

 all directions, then all energy radiated from the sun must 

 eventually reach some other star, but otherwise much of it 

 must be sent radiating out through limitless space and so be 

 lost to the stellar universe. This means that finally everything 

 must cool down to absolute zero. Whether this is so or not, 

 we know that the hot bodies are losing heat and the cold 

 bodies presumably gaining heat, so that the general tendency 

 is for all to reach the same temperature. Now, the sun's heat 

 is the ultimate source of practically all the energy of our 

 bodies, as well as of all artificially constructed machines. 

 Moreover, there is a law of physics, known as the second law 

 of thermodynamics, which states that we can change heat 

 energy into mechanical energy only by trans fering some heat 

 from a hot body to a colder body. Consequently, if every- 



