GEOLOGY — CHAMBERLIN. 169 



This paper is in essence a mathematical discussion of the more funda- 

 mental factors of the theory that the spiral nebulae were derived from suns 

 through approach to one another and bears radically upon the planetesimal 

 hypothesis discussed in the preceding and following papers. 



Paper III.— On the Growth of the Earth by Accretion under the Planetesimal Hypothesis. 



By T. C. Chamberun. 



The probable character and limitations of the planetary nuclei, the knots 

 of the spiral nebulae, are discussed and the mode of aggregation and the 

 associated temperatures considered. Taking the alternative of a primitive 

 atmosphereless earth as the more extreme, the accession of the atmosphere, 

 followed by that of the hydrosphere, is sketched, leading to the discussion of 

 the origin of the ocean basins and the conditions that controlled the evolu- 

 tion of the continents. The development of interior heat by planetesimal 

 impact, by compression, by atomic and molecular union, and hy radioactive 

 agencies is discussed, together with a theory of the origin and evolution of 

 vulcanism. The possibility of the early introduction of life is noted and the 

 requisite conditions of light and temperature are treated, involving autogenic 

 as well as solar sources of radiant energy. 



Paper IV. — On Certain Applications of Geophysical Theory lender the Planetesimal 



Hypothesis, especially those Relating to Compression and Temperature . 



By Arthur C. Lunn. 



This paper is devoted mainly to a quantitative study of that portion of the 

 earth's internal energy which is supposed to have been derived from the 

 mechanical energy of a primitive system of planetesimals subsequently gath- 

 ered into a planetary mass, and of the transformation of this internal energy 

 into the thermal form during the epoch of accretion, together with a study 

 of its subsequent redistribution by conduction. 



In Part I a theory initiated by Fisher is developed on the basis of the 

 Laplacian law of density, together with certain auxiliary assumptions. 

 Formulas and tables are given showing the variation of dimensions and the 

 internal densities of the mass during the epoch of accretion and the dijEfer- 

 ential effect of the accession of an additional stratum on the size and on the 

 moment of inertia of the mass, together with the deformation of the mass 

 elements accompanying the resulting compression. Determinations under 

 alternative secondary postulates of the original distribution of the temper- 

 ature produced by compression, and of its redistribution by conduction, are 

 found to show the existence of a characteristic zone of rising temperatures 

 during the earliest ages. 



Part II is given to an inquiry as to what changes in the results recorded 

 in Part I are produced by changes in the secondary hypotheses employed, 

 and to a critical examination of the latter. The computed masses of the 

 nucleus at various stages of accretion are compared with the observed masses 



