420 CARNEGIE INSTITUTION OF WASHINGTON. 



intensity. The alternative speculation places the integration in 

 outer space. 



Now, the problem of compression gives no special occasion to urge 

 that any form of atomic integration took place in the heart of the 

 earth, but it is wholesome to recognize the possibility of such 

 action, if for no other reason than as a check on arbitrary importations 

 of heavy material to account for internal density. The recognition 

 of such possible integration is in keeping with the trend of cosmic 

 philosophy under the impulse of recent discoveries and the recognized 

 necessity for revised interpretations that shall extend the cosmic 

 cycles. How far the organizing tendency of concentrated stress may 

 go in the depths of the earth is an open and very stimulating question. 

 In the light of all the considerations offered, it would be hazardous 

 to place any narrow limit upon any constructive tendency that favors 

 the return of runaway energy to a more stable organized form, for 

 this is overwhelmingly the dominant form of the energy of the cosmos. 

 But it would be equally hazardous to rest much on any specific inter- 

 pretation that gets far away from observed evidences. Let us there- 

 fore turn to these evidences. 



AMOUNT OF COMPRESSION IMPLIED BY THE EARTH'S MEAN DENSITY. 



As just noted, the earth problem gives no occasion to push the organ- 

 izing functions of pressure and heat as far as atomic integration ; indeed, 

 that might easily carry the increase of density too far to fit the evidence. 

 If we assume that the specific gravity, 3.69, adopted by Farrington as 

 to the mean density of meteorites, represents the density of the original 

 material of the earth, and compare it with 5.53, adopted by Moulton as 

 the present mean density of the earth, it would follow that the mean in- 

 crease in density is only about 50 per cent. Or, if we assume that com- 

 pression in the central part of the moon is offset by porosity of its outer 

 part, and take its mean density, 3.34, as a not too low figure for the 

 density of the original substance of the earth, the increase in its mean 

 density would still be only a little over 65 per cent. In either case, or 

 on any plausible assumption, some part of this must be assigned to 

 simple mechanical compression, so that the increase of density assign- 

 able to reorganization under pressure and heat can not go very far. 



DENSITY EFFECTS WITHIN THE ZONE OF OBSERVATION. 



After an elaborate discussion of the most reliable data, Dr. H. S. 

 Washington remarks in a recent paper :^ "I am inclined to place 

 the average density of the crust at about 2.75, at least for the upper- 

 most shell, while that of 2.80 would probably be nearer the truth for 

 an average of any considerable depth, say 20 or more miles." The 

 mean depths of these two shells can scarcely be more than 8 or 10 miles 



*H. S. Washington, The chemistry oi the earth's cru&t, Jour. Franklin Inst., p. 804 (Dec. 1920). 



