488 T. C. CHAMBERLIN 



that the Hghter elements form a notable factor, and the spectro- 

 scopic evidence tallies with this. The low densities of the giant 

 planets derived from the sun (Jupiter, i . 25; Saturn, o. 63; Uranus, 

 1.44; Neptune, 1.09) suggest a similar constitution with even 

 more cogency, for they are much less affected by high temperature. 

 If, therefore, solid stony or metallic bodies of high specific gravity 

 were to be formed from outbursts of solar gases, the process must 

 have involved the removal of large quantities of the lighter order of 

 constituents. This sifting is precisely what the kinetic theory of 

 gases applied to small bodies would lead us to expect. The process 

 is essentially a form of evaporation, and so the planetoids and 

 satellites, as well as the terrestrial planets with slight qualification, 

 may be regarded as merely the residues of the selective evaporation 

 of much larger original bodies of mixed gases. 



If the original gases, after they were projected from the sun, 

 occupied some large part of the spheres they could control, as 

 indicated above, the escape of the lighter molecules would be rela- 

 tively easy and prompt, at least from the smaller masses. If the 

 nuclei became much condensed before the sifting was completed, 

 the remaining escape might be slow, for the molecules could then 

 only escape from the outer zone where free paths were open to them 

 when they chanced to rebound in an outward direction with the 

 requisite velocity. In so far as the original gaseous masses were 

 affected by turbulence, or by vortical or other eversive motions 

 derived from their ejection, the escape of the light molecules would 

 be facilitated. 



The motions inherited from the original expulsion were probably 

 such that the dominant tendency, in all but the more massive nuclei, 

 was toward gaseous dispersion. Not only would the light mole- 

 cules be likely to escape from control, but many of all kinds. This 

 is only another form of stating the primary tenet of the planet- 

 esimal hypothesis, viz., that such dispersion was an inevitable 

 effect of the solar eruptions, and a condition precedent to planet- 

 esimal accretion later. There is merely the reservation that 

 enough material was held under self-control to serve as collecting 

 centers of the requisite orders of efficiency, but even this is not 

 essential to an ultra type of planetesimal genesis. It seems, how- 



