DIASTROPHISM AND THE FORMATIVE PROCESSES 671 



so simple and instructive. The orbits in this case were distributed 

 through greater space and more irregularly, and hence their 

 coalescence with one another and their capture by the planetary 

 nuclei, as a rule, required greater changes in the forms, dimensions, 

 and attitudes of their orbits. We will turn to concrete specifica- 

 tions and numerical values presently. 



THE SIZE or PLANETESIMALS NOT IMPORTANT IN RESPECT TO 

 MELTING EFFECTS 



Lest we stress the growth of planetesimals too much, it is 

 prudent to observe at once that the sizes of the planetesimals 

 were not matters of vital moment so far as the total energy-effect 

 of their infall was concerned, for whatever was gained by concen- 

 tration of mass was lost by less frequent infalls. On the whole, 

 less energy available for conversion into heat was carried into the 

 earth by the united planetesimals than by the same mass ununited, 

 for in coming together, energy of motion was converted into heat 

 and this was dissipated at the point of union in open space; the 

 combined mass carried so much less energy into the earth-core. 

 However, whenever combination took place, there was relatively 

 less resistance and heating of the atmosphere in plunging through 

 it, and so relatively more heating of the surface of the earth. As 

 we shall see a little later, however, the chief effect at the earth's 

 surface was lateral dispersion and an elastic or explosive reaction, 

 resulting in a great scattering of debris with little obvious melting. 

 None the less, we shall consider the melting effects of large planet- 

 esimals as well as small ones. 



THE LIGHT SHED ON SIZE BY EXISTING PLANETESIMALS 



It has been shown in previous papers' that the union of mole- 

 cules and the growth of small aggregates could take place with 

 more or less facility up to a certain order of size, but that beyond 

 such order conditions unfavorable to further growth arose and 

 increased relatively, so that indefinite growth was probably limited, 

 as a general rule. It appeared that chemical, electrical, and 



' Article X, this Journal, Vol. XXVIII, No. 2 (February-March, 1920), 

 pp. 140-44. 



