THE SUN 281 



A second peculiarity about the sun that is not true of 

 the earth is, that the former exhibits no oblateness of 

 figure whatsoever, but presents at all times a sensibly cir- 

 cular disc. Were the sun as rigid as the earth, he would 

 be flattened at his poles, but, because of Ms inflation, his 

 rotundity is being perpetually retrimmed. The ball of 

 our planet lacks elasticity and, as in the case of a ball of 

 putty, its settling and flattening become more and more 

 confirmed as time goes on. Were a close physical exami- 

 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 his 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 



