482 T. C. CHAMBERLIN 



changed as time went on. In the smallest order of bodies this pre- 

 cipitation, together with the escape of such molecules as remained free, 

 went so far ultimately that the residues were reduced to clouds of 

 precipitates which condensed in a way of their own. 



IV. Almost as soon as cores began to form, differential stresses, 

 more intense below than above, were brought to bear upon them by 

 external agencies which aided in working the lighter and more mobile 

 materials toward the surface, thus developing increasing density and 

 solidity in the central parts. 



In discussing these co-operating factors it will be helpful to 

 have in mind concrete pictures of the deployment of the matter 

 under study, fashioned in the form of spheres of control, for these 

 best bring out the dynamics of the organizing work. The matter 

 in spheres of control may be very differently distributed, but it is 

 to be regarded as occupying in some measure, however scant, the 

 whole space. In adult organizations, usually the matter is highly 

 concentrated toward the center and very sparsely distributed in the 

 outer part. In the initial stages the distribution is likely to be 

 heterogeneous with less difference between the outer and inner 

 parts. Uniform distribution therefore becomes the most conven- 

 ient standard of reference, though probably never realized in fact. 

 Table II gives data from which selections may be made at pleasure 

 in forming representative pictures. 



The primitive earth-mass, before sifting began, should have 

 included (i) the light gases that later escaped and were never 

 recovered, (2) the planetesimals that temporarily escaped and were 

 later recovered, (3) the nuclear portion that remained under 

 self-control, and (4) minor factors that may be neglected. Let the 

 whole be taken as having a mass about twice that of the present 

 earth, without prejudice to a higher or lower final estimate. It 

 would then, if properly distributed, have a sphere of control of the 

 order of 1,500,000 miles in diameter and a mean density for the 

 whole sphere of about 0.00 11 on the air standard, or, let us say, 

 approximately 1/1,000 of the density of the air at sea-level. As 

 loss by sifting went on the sphere of control should have shrunk to 

 a minimum, after which, when planetesimal accretion began to 



