THE AUTHOR'S THEORIES OUTLINED 57 



compulsorily as a matter of equilibration, so that we 

 are under no temptation to gloze the plain facts. 



It is reasonable to suppose the sun and the earth to 

 be composed, not only of the same kinds of materials, 

 but also in about the same proportions. Then why, re- 

 membering the vastly greater self-compressive power 

 of the sun, is his density only one-fourth that of our 

 planet? Heretofore the reason given has been, that the 

 sun is " contracting " in size and that he is in process of 

 transmuting his original "energy of position" into 

 "kinetic energy". No one, strange to say, has ever sug- 

 gested the plain, common- sense view that the sun is dis- 

 tended because he is hot; for what physical fact is better 

 known than that heat expands? In my conception the 

 sun is a mechanical furnace in which his power of self- 

 compression by gravity is constantly churning his sub- 

 stances over and over again from fluid into gas, and, with 

 the help of the cold of space, from gas back again into 

 fluid. The more massive he becomes, then, the hotter 

 he grows. Moreover, the hotter he grows, the more 

 abundant the internal gases he generates within himself ; 

 the more he becomes distended; the greater the number 

 of his elements kept in a perpetually gaseous state; the 

 more refractory the average constitution of his shell, and 

 the thinner, more fluid and well-mixed it is ; the freer his 

 surface ebullitions, and finally, the nearer he approaches 

 the climax of bursting into the nebular state. 



Again. To assert that the sun is, by growth, becom- 

 ing hotter, is equivalent to saying that he is also increas- 

 ing in brightness. But in the case of the sun (or any 

 star, of course) here is this special reason: The more 

 refractory to volatilization a substance, the more in- 

 tensely bright is it when raised to incandescence; and 

 since, by premise, the shell gradually becomes more and 

 more refractory in constitution, while at the same time 

 the ebullitions in it become more rapid, mere brightness 

 accentuates into brilliance. 



Let it not be supposed, however, that our sun can ex- 

 plode but once, or that he cannot undergo explosion until 



