i6 T. C. CHAMBERLIN 



An inspection of the mean densities themselves gives some hint 

 of the general nature of the compression: 3 .34 for the moon, 3 . 58 

 for Mars, 3.69 for meteorites, 4.85 for Venus, and 5.53 for the 

 earth. It is notable that the mean density of meteorites falls 

 between the two bodies suspected of deep porosity and the two 

 bodies in which wash, solution, and cementation are effective. 



The results given in Table II bear an analogous import: 725 

 miles radial shrinkage for the lunar parity-earth; 618 miles for 

 the Martian parity-earth; 572 miles for the meteorite parity-earth; 

 and 177 miles for the Venus parity-earth. However, these shrink- 

 ages represent quite different ranges of growth; to be strictly 

 comparable they must be reduced to a common basis. A conven- 

 ient unit is an increase equal to i per cent of the mass of the earth. 

 This is equal to the weight of about 14 billion cubic miles of water. 

 Reducing the several shrinkages to this unit of mass increase, they 

 become: for the mean rate of shrinkage between the moon stage 

 and the mature earth, 7 .44 radial miles per unit increase of mass; 

 between the Mars stage and the mature earth, 6.90 radial miles 

 per unit; and between the Venus stage and the mature earth, 

 9.17 miles per unit. This brings to attention the very suggestive 

 fact that the rate of shrinkage per unit of mass increase is greatest 

 in the last stage. Next to this, it is greatest in the growth from 

 the stage represented by the moon, the body suspected of being 

 the most porous, and the least affected by wash, solution, and 

 cementation. The first seems to imply that massiveness is the 

 dominant influence. Next to this porosity seems to be influential. 



These inferences will appear to be still more strongly suggested 

 if we reduce all the four natural bodies to parity-bodies, using mean 

 meteoritic material as the basis. The results appear in Table HI. 



The third column shows that if the moon had been built up to 

 its present mass with material of the mean density of meteorites, 

 its radius would fall short of what it actually is by 35 miles; if Mars 

 had been built up in a similar way its radius would be 22 miles 

 short, while the radius of Venus built in the same way would be 367 

 miles greater than it actually is, and the radius of the earth under 

 like conditions 572 miles greater than it is. If all these bodies 

 were actually built up of mean meteoritic material the figures 



