490 T. C. CHAMBERLIN 



The minute precipitates thus scattered thraugh the gas would 

 serve as Brownian p:articles, and the increase of these would form 

 a progressive series of Brownian mixtures. The minute precipi- 

 tates would be jostled to and fro much as the free molecules were, 

 except that, on account of their greater sizes and masses, they must 

 have responded rather to combined molecular impacts than to 

 single ones, while their lack of perfect elasticity must also have 

 somewhat toned down these activities. 



An analysis of the conditions makes it clear that the Brownian 

 evolution probably diverged very soon into two rather distinct lines, 

 though they must have been united by numerous intermediate 

 phases. One of these may be regarded as the typal line of gaseous 

 descent; the other as divergent toward an alien type that combined 

 a quasi-gaseous phase with a partially orbital factor. In the first 

 the characteristic feature continued throughout to be that of a 

 jostling assemblage, though the original high proportion of mole- 

 cules gave place more and more to precipitates acting as Brownian 

 particles. The gas in this case is presumed to have passed into the 

 liquid phase and thence into the solid form. In the more divergent 

 line the assemblage lost its free molecules largely, and in the ex- 

 treme cases entirely, and became at best merely quasi-gaseous, 

 with a trend toward orbital behavior. Though truly gaseous at 

 the start, the molecular assemblage soon began to be seriously 

 depleted by the escape of the more active molecules and the passage 

 of the rest into precipitates and thence into aggregates, while these 

 tended to lose their to-and-fro dynamics and take on circulatory, 

 rotatory, or revolutionary dynamics. 



Divergent as these trends were, they were readily reversible. 

 When molecules escaped from a nucleus in which their habit was 

 strictly gaseous, they usually took on a specific orbital habit and 

 beame planetesimals; the accident of an encounter, however, 

 might easily throw them back into to-and-fro oscillation. Notwith- 

 standing such reversals, two quite contrasted systems of dynamics 

 arose and were continually contending with one another in the 

 processes that marked the passage of the nuclei into cores. 



The gaseous line of descent was obviously dominant in the 

 nuclei of the giant planets. Perhaps it was also in the nuclei of the 



