THE SUN 283 



minerals, providing man with the ores, which niay not 

 inaptly be termed cosmic pig metal. How these ma- 

 terials reach the earth we shall presently discover; for 

 that they do, and that they have reached her in compara- 

 tively recent times is sufficiently attested, not only by the 

 fact that these heavy ores are to be found here in "veins' ' 

 and "pockets", but that they are to be found on the sur- 

 face. Had the earth been originally her present size, and 

 molten, the heavier materials must inevitably all have 

 sunk toward her center and only froth and scum re- 

 mained to blanket her. 



Though I have spoken of the sun's strata, both in 

 discussing his differential rotations and the chemical con- 

 stitution of his shell, and shall yet continue so to speak, 

 yet I wish the reader to understand that there are no 

 sharp lines of demarcation between them, but that the 

 changes up and down, though certain and pronounced, 

 melt imperceptibly into each other. The reason lies, of 

 course, in the great variety of the natural chemical ele- 

 ments and compounds, and in their abundance in the 

 solar economy. Assuming that the graded temperatures 

 of the shell, level by level, are invariable, and that the 

 pressures are equally so, it follows that every element 

 and compound regularly explodes every time it reaches 

 its particular critical depth. Such explosions necessarily 

 cause eruptions through the photosphere, giving rise to 

 jets, geysers, fountains, or prominences, whichever the 

 reader may think best to call them. In proportion to 

 their deep-seatedness and severity, these explosive gases 

 not only change places themselves, but they carry before 

 them in their outward rush great quantities of debris 

 from the intervening layers to greater or less heights 

 beyond the photosphere, whence, being normally con- 

 densed and turned back by the cosmic cold, they rain 

 down upon the photosphere in a ceaseless hail of slag 

 and cinder only to begin the same process over again. 



Briefly, then, the solar process consists in the con- 

 tinuous explosive conversion of the sun's interior sub- 

 stances into gases by virtue of the pressure of the super- 



