244 FKOM NEBULA TO NEBULA 



nation of the sun humanly possible, it would be found 

 that the northern end, or base, of his shell is appreciably 

 thicker and heavier than its southern, but this in no way 

 affects his external symmetry, inasmuch as his interior 

 buoyancy maintains his shell exactly centered upon his 

 center of mass. 



THE SOLAR PROCESS 



Without pausing at this juncture to point out the 

 source of the sun's heat, save to assert that it is a func- 

 tion of his mass, and judging him simply by analogy with 

 the earth, whose temperature increases with the depth, 

 we are justified in assuming that Ms temperature, too, 

 rises steadily from his photosphere to his center. This 

 naturally prompts the query as to what effect this con- 

 dition has upon the character of the shell 's chemical com- 

 position at the various depths. A preliminary illustra- 

 tion may assist in clarifying the answer : 



Suppose you were handed a mixed pailful of finely 

 pulverized, insoluble materials known to contain equal 

 parts of ten different minerals, all evenly graded in an 

 ascending scale according to specific gravity ; how would 

 you go about the task of separating them? Without 

 bothering to cast about in our minds for an artificial way, 

 let us put the burden on Nature and see how she would do 

 it. We will search for a very deep and narrow well and, 

 finding it, we will dump on its surface, as abruptly but as 

 gently as possible, the entire contents of the pail, then 

 with the eye of imagination, to which all things are trans- 

 parent, watch the result. We will suppose, further, that 

 the water in the well is just 10 fathoms deep. Clearly, 

 there would ensue an interesting race between the ten 

 substances for the bottom, in which contest the test of 

 fitness would, of course, be that of weight, or more tech- 

 nically speaking, specific gravity; and when the affair 

 has been concluded we shall find, piled up on the bottom, 

 a column of ten thin layers ranged in the order of their 

 heaviness. But what of the status of the race at its 

 various stages? In the first fathom, beginning at the 



