284 CHAMBERLIN— THE INTERIOR OF THE [April 24, 



has been given by Dr. Schlesinger. The import of seismic studies, 

 the subject of Dr. Reid's contribution, lends very special support to 

 the view that the interior of the earth is elastico-rigid at least to the 

 extent that distortional waves have been shown to pass through its 

 interior. It seems certain already that this condition prevails 

 throughout much more than half the volume of the earth ; concern- 

 ing the rest, the deep interior, the seismic evidence is perhaps still 

 to be regarded as indeterminate. But on the seismic evidence it 

 does not fall to me to dwell. 



The tidal studies of Hecker, Orloff and others lend support to 

 the tenet of a rigid earth but they fall somewhat short of con- 

 clusiveness. The brilliant experimental determinations of Michel- 

 son and Gale, correlated with the computations of Moulton, have 

 carried the evidence to the point of preliminary demonstration. 

 They need only to be adequately repeated and verified to become 

 final, so far at least as elastic rigidity can be indicated by the re- 

 sponse of the earth-body to solar and lunar attractions. The special 

 feature of most critical value in the demonstrations of Michelson 

 and his colleagues is the high degree of elasticity shown by the 

 almost instantaneous response of the earth to the distorting pull of 

 the tide-producing bodies. This cuts at the very base of concepts 

 founded on the supposed properties of a viscous earth. These tidal 

 determinations of elasticity are in close accord with the seismic 

 evidences of elasticity. The two are happily complementary to one 

 another. The one deals with the earth as a whole under rhythmical 

 series of increasing and diminishing stress-differences springing 

 from external attraction ; the other deals in an intensive partitive 

 way with earth substance by sharp short stresses that call into action 

 its most intimate structural qualities. While it is wise, no doubt, 

 to refrain from resting too much on these early results of relatively 

 new and radical lines of inquiry, until their results shall be more ma- 

 ture, their prospective import is radical and decisive in favor of a 

 soHd earth not only, but of an elastico-rigid earth. Assuming that 

 the present import of these inquiries wih be amply justified by more 

 mature research, it is pertinent to bring into consideration the corol- 

 lary they so distinctly imply, viz. : that the molten and viscous ma- 

 terial in the earth, or at least in its outer half, if not throughout 



