DIASTROPHISM AND THE FORMATIVE PROCESSES 401 
_ the same way, and hence are closely comparable. There might 
_have been some gradation of material, but since the earth is com- 
pared with the next outer and the next inner planet, any such 
gradation is largely equated in combining the results. These 
four bodies may therefore be taken as representing four stages of 
growth of a single body under the conditions that prevail at their 
mean distance from the sun, which is substantially the earth- 
distance. 
34. The giant gaseous planets cannot properly be compared 
with these solid: bodies without radical qualification, for the giants 
were probably gaseous from the start and never underwent the 
_ sifting necessary to cull out material unsuited to form the earth 
and kindred bodies (see 48 below). The evolution of the giant 
planets belongs to a distinctly different category. 
35. Comparing the densities of the earth, Venus, Mars, and 
the moon as they now are, a marked increase of density with 
increase of mass is shown: to wit, the moon, with mass 0.0122 
(earth=1), has a density 3.34 (water=1); Mars, with a mass 
0.1065, has a density 3.58; Venus, with mass 0.807 (?), has a 
density 4.85 (?); and the earth, whose mass is unity, has a mean 
density 5.53.7 . ; 
36. Closer inspection shows not only an increase of density with 
mass but an accelerated rate of increase of density for each increment 
of mass. ‘This clearly implies that their densities arise from their 
Own massiveness, an inference in harmony with No. 4 above.’ 
37. Under the kinetic theory of gases, the larger the mass, the 
greater its ability to hold light molecules. Greater proportions of 
intrinsically light matter were therefore almost certainly gathered 
into the more massive bodies. They became dense in spite of a larger 
proportion of intrinsically light material.s 
38. Let it be noted that the acquirement of high density is 
not held to be a matter of simple mechanical compression; this 
was a conditioning factor in the process, but only that. There 
were probably added (a) progressive rearrangements and reorgani- 
zations of the material into denser forms as the stresses grew, 
including not only simple physical readjustments but the formation 
«Tbrd., p. 10. 2 Tbid., pp. 16-17. 3 [bid., p. 17. 
