THE SUN 279 



i find the chief cause of volcanic eruptions and earth- 

 quakes, and the solar eruptions. 



Now, explosiveness is characterized by the abrupt- 

 ness of its happening. When the critical condition with- 

 in the bowels of the earth is well advanced, but not yet 

 altogether ripe for a spontaneous letting go, the impend- 

 ing catastrophe may be precipitated by some foreign 

 agency, as, for example, by a great solar eruption how 

 will be explained later. The point to be impressed in this 

 place is, that the exploding crisis is not indefinitely de- 

 ferable, and that, sooner or later, the explosive tendency 

 within the sphere catches up to and finally overwhelms 

 the repressive forces. The effect of these belchings out 

 of the earth's interior is to relieve the distension of her 

 crust in the neighborhood of the orifices of escape and 

 allow subsidence to the normal level; following which 

 event the gases go on accumulating again, until the like 

 action is repeated a sort of earth-breathing, one might 

 say. This alternate subsidence and elevation of the 

 earth's crust is a long-standing scientific curiosity, and 

 has heretofore been sought to be explained by the so- 

 called principle of Isosta-sy; meaning, that the various 

 areas of the earth's crust are equilibrated against each 

 other. That this principle of isostasy is fundamentally 

 sound, it seems to me, should go without saying; only it 

 requires to be treated, not so much as a prime cause as a 

 concomitant one of minor potency. 



THE ANATOMY OF THE SUN 



Returning again to the sun, my conception of him is 

 that of an enormous bounding shell of molten matter en- 

 closing and mightily compressing an inner spherical 

 chamber of superheated gases, whose buoyancy, in turn, 

 supports the shell. In short, the sun is, in principle, con- 

 structed on the order of the soap-bubble, only his walls 

 are proportionally far thicker. How thick ? 



It can be shown by a very simple calculation, based 

 on the rule that the volumes of spheres are to each other 

 as the cubes of their diameters, that were the third-of-a- 



