116 UNIVERSITY OF MISSOURI BULLETIN 



matter to themselves. We do find nebulous regions in the 

 sky where such a process seems to be going on. 



In regard to the future of the solar system, all agree 

 that the sun and planets are cooling and that eventually they 

 will all be perfectly dark and cold bodies. In that case, star- 

 light alone would illuminate the earth, day and night. One 

 of the puzzling things is how the sun maintains its heat as 

 well as it does. This is partly accounted for by its own 

 shrinkage. A shrinkage means that the outer layers are 

 slowly falling in toward the center, thereby producing heat, 

 and the doctrine of the conservation of energy tells us that 

 the shrinkage necessary to produce heat as fast as the sun 

 radiates it would be too small to detect in less than 6,000 years. 

 However, the sun could not have maintained its heat at this 

 rate for more than twenty million years, whereas geologists 

 tell us that the earth must have received heat from it at about 

 the present rate for about one hundred million years. It 

 has been suggested that the difference may be caused by the 

 presence of radium in the sun. The disintegration of a com- 

 paratively small amount of radium would explain the facts 

 satisfactorily. 



The theory of the tides shows us that the speed of rota- 

 tion of the earth is slowly decreasing, so that the day will 

 finally be as long as the month, or a little longer. When this 

 occurs, the moon will gradually approach the earth and finally 

 reunite with it. So far as I know, there is no evidence to 

 show that the planets will reunite with the sun, unless some 

 outside star actually collides with the sun, in which case 

 another great nebula may be formed which will extend out 

 to the planets and absorb them. 



Life on Other Spheres. Next to the question of cos- 

 mogony, the question of most interest to the average mind is 

 this: Are any of the other heavenly bodies inhabited? In 

 recent years the popular magazines have contained many 

 articles by an earnest advocate of the theory that Mars at least 



