78 CHARLES S. SLICHTER 



from homogeneity to heterogeneity would result in increased 

 pressure in the interior, and in a decreased magnitude of the 

 earth's volume and surface. 



It is difficult to decide whether or not the minimum value of 

 the eccentricity used above is too high to correspond with that 

 uncertain date "the beginning of geological time." The rota- 

 tion period of the heterogeneous spheroid would, probably, be 

 shorter than for the homogeneous spheroid, and the shorter 

 period may not be consistent with theories regarding the moon- 

 earth couple. If we are required to assume a value of the eccen- 

 tricity less than that used above, the changes in pressures I 

 have given must be reduced. On the other hand, it must be 

 remembered that there are causes at work which may augment 

 the effects of a change in the internal pressure, and may even 

 produce large results from what seem to be small causes. For 

 example, if we suppose a contest in a given region in the interior 

 between extreme heat on the one hand, and extreme pressure on 

 the other hand, as to whether the material, or a single constit- 

 uent of the material, will take on the crystalline form or not, 

 we have a case in point. It may happen that a very slight 

 increase in pressure may materially extend the zone in which 

 crystallization may take place and thus result in a considerable 

 increase in density ; it is not impossible to believe that such a 

 zone may exist in the region near the center, where pressures 

 may be dominant on account of their enormous magnitude, and 

 also in a region near the surface, where pressure may again be 

 dominant owing to the lower temperature. 



Charles S. Slichter. 



