484 T. C. CHAMBERLIN 



to dispersion naturally assigned to simple explosion and that would 

 be unfavorable to self-control.' We are here concerned only with 

 those differential impulses that affected the relations of one part 

 of an ejected mass to other parts. It is assumed that these differ- 

 ential impulses were so graded that (i) they scattered into planetesi- 

 mals a notable part of the projected mass, (2) they tore away 

 from the central portions segments that were massive enough to 

 hold themselves together, but not very firmly, while (3) the main 

 central masses retained a higher degree of self-control.^ Such a 

 partition of effects seems the natural result of the mechanics of 

 eruption. It seems also to fit the requirements of the bodies that 

 now make up the planetary system. The masses that retained their 

 self-control were the nuclei of the organizations that were to 

 follow, and constitute the theme to which we are here confined. 



Under such a range of impulses the nuclei probably graded from 

 the largest and most strongly held down to small diffuse ones on 

 the very limit of self-control, beyond which complete dissipation 

 into planetesimals set in. They are therefore to be dealt with as 

 a graded series rather than a single type. The question of control, 

 however, was not so much a matter of mass as of balance between 

 the force of gravity and of the motions involved. 



Three types of inherited motions need recognition : the turbulent, 

 the vortical, and the rotatory. Turbulent motions were not only 

 inherited directly from the sun, but must have been generated by un- 

 balanced thrusts and drags incident to eruption. Eruptive actions 

 almost inevitably give rise to more or less of vortical motion, or at 

 least some form of eversive motion. In free interplanetary space, 

 and in such tenuous bodies as those under discussion, motions of 

 this type might persist long and be specially effective in discharging 

 internal heat. All unbalanced differences of thrust and drag in the 

 ejection of eru*^ted masses would ultimately appear in the form of 

 rotation and so rotation of some order could scarcely have failed 



^ Jour. Geol., Vol. XXVIII (February-March, 1920), pp. 145-49, or the original 

 article by Pettit, Astrophys. Jour., Vol. L (October, 1919), pp. 206-19. 



^ In addition, the least projected parts fell back to the sun, while doubtless some 

 particular parts received cumulative impulses and were thrown into anomalous 

 courses, but these are neglected throughout this discussion. 



