270 T. C. Chamberlin — Jones's Criticism of 



120° is about the limit for the transverse waves. Both 

 kinds give increasingly imperfect records as their pene- 

 trations become great, but not equally so. The longi- 

 tudinal waves have a speed about fifty per cent greater 

 than that of the transverse waves, evidence that they are 

 actuated by a more effective elasticity — that of volume — 

 than are the distortional waves, which depend on elas- 

 ticity of form. It seems logical, therefore, that the longi- 

 tudinal waves should maintain themselves longer than the 

 transverse waves. As a matter of fact they do not retain 

 their integrity as much longer than the transverse waves 

 as might be expected from their superior velocity. They 

 grow feeble and doubtful progressively as do the distor- 

 tional waves, and at the depth where the latter cease to 

 be identifiable they have already become dubious. If the 

 distortional waves were strong and gave good records 

 uniformly up to a certain depth and then suddenly ceased, 

 while the longitudinal waves continued on and gave good 

 records up to 180°, the inference of a change from the 

 elastico-rigid to a viscous state would at least be plausi- 

 ble, but as the case now stands, such an interpretation 

 does not seem to be the natural one. This does not 

 invalidate the view of Oldham that there is .a change in 

 the nature of the material at about the half -radius depth, 

 for this is compatible with a solid state. 



The correction of the seismic records for density brings 

 the seismic evidence into general harmony with the tidal 

 and nutational evidences and makes the presumption 

 strong that rigidity and elasticity increase from the 

 surface to the center as held by Schweydar. 14 The fol- 

 lowing quotation from Walker, a seismologist who had 

 unusual experience with instruments and records, lies in 

 the same line : 



"At the present time the evidence in favor of a solid earth is 

 very great but the alternative view that the interior of the earth 

 is fluid retarded for a considerable time the progress of seismo- 

 logical theory which requires the earth to possess the properties 

 of an elastic solid. As astronomical theory agrees with the seis- 

 mological in demanding a solid earth, we accept this as a primary 

 condition." 15 



14 W. Schweydar: "tiher die Elastizitat der Erde," Naturwissenschaf- 

 ten, Part 38, 1917, Potsdam, Germany. 



13 G. W. Walker, Modern Seismology, p. 13. (Longmans, Green and Co., 

 London, New York, Bombay and Calcutta, 1913.) 



