474 T. C. CHAMBERLIN 



overbalance their higher content of light original material.^ It was 

 recognized, however, that the inquiry could not be regarded as 

 having covered all the shrinkage phases of this mass-effect until 

 the physical states of the four bodies during their formation were 

 considered. Under the planetesimal hypothesis their formation 

 embraced two phases: (i) the progressive concentration of those 

 portions of the solar outbursts that were held together by their 

 mutual attractions so as to act as unit assemblages and thus serve 

 as collecting centers or nuclei; (2) the gathering into these nuclei 

 of such scattered parts of the solar outbursts as were dispersed into 

 planetesimal orbits from which they could be picked up only 

 individually. The first process started with a gaseous body and 

 followed the gaseous line of descent; the second was concerned with 

 individual bodies and orbital dynamics. This paper is confined to 

 the first of these. 



THE SUCCESSIVE PHYSICAL PHASES ASSUMED BY THE NUCLEI IN 



PASSING EROM THEIR ORIGINAL CONDITION TO THEIR 



FINAL STATES AS PLANETARY CORES 



There is a wide range between the largest planet and the smallest 

 planetoid. There may also be wide differences of view respecting 

 the probable sizes of the nuclei. As I wish to leave the question 

 of the nuclear masses freely open for the present, it seems best 

 to treat broadly the whole group of solar dependents, including 

 planets, planetoids, and satellites. There is the additional reason 

 that their gradations, their likenesses, and differences, as well as 

 the contrasts of their extreme developments, form the natural 

 background for the special cases with which we are particularly 

 concerned in this discussion. 



It is assumed that each one of the present planets, planetoids, 

 and satellites started from a nucleus inherited from a solar out- 

 burst. It is held that some of these nuclei were formed from the 

 central portions of the solar outbursts, while others were merely 

 segments detached from these. Some of the detached segments 

 are supposed to have remained under the control of the central 

 portions and become satellites, while others pursued orbits of their 



'"Selective Segregation of the Earth and Its Neighbors," Jour. Geo/., Vol. 

 XXVIII (1920), pp. 126-57. 



