156 T. C. CHAMBERLIN 



crystals in the midst of the gaseous molecules would mark the turn 

 of the tide in the history of the smaller nuclei for the molecular 

 losses would speedily grow less and a definite centralizing move- 

 ment would set in which would increase the power of self-control. 

 Molecular losses would be lessened and the capture of planetesimals 

 increased relatively. 



The question of the temperatures and the physical states that 

 would follow this stage in the smaller nuclei is important and 

 difficult but must be deferred. 



4. It remains only to consider the selective action of the success- 

 ful nuclei in the process of gathering in planetesimals, but this 

 need not detain us for the principles would be essentially those 

 already emphasized sufficiently. The smaller order of nuclei 

 could not capture and hold the Hghter free molecules as such, though 

 they could perhaps capture and retain the very heavy molecules. 

 They could quite certainly hold most of the planetesimal aggregates 

 that they encountered but would have little power to draw them to 

 themselves. The nuclei of medium mass could ^hold some of the 

 free molecules but not the lightest, and so their accessions would 

 be greater in mass, but lower in mean specific gravity. 



SUMMARY 



It seems clear, then, from the foregoing considerations that, in 

 general, the planets, planetoids, and satellites, if built up by the planet- 

 esimal method, would be composed of inherently heavy material in 

 inverse proportion to their masses, and hence that the inherent 

 specific gravity of the matter of the moon would be somewhat 

 greater than that of Mars, that of Mars somewhat greater than 

 that of Venus, and that of Venus greater than that of the earth. 



There is still need to consider (i) what were the physical 

 states of the nuclei while they were gathering in the planetesimals, 

 (2) what masses the planetesimals attained, and (3) what was the 

 effect of their infall on the later stages of the growing bodies. This 

 last will obviously involve the frequency of the fall of the planet- 

 esimals upon the nuclei. The discussion of these points must be 

 deferred to the next article. 



