AFTER-SHOCKS AND SPACE-DISTRIBUTION OF SEISMIC WAVES. ,5 



If the latter weie the case, it would not be wholly incon- 

 ceivable that au overstrained portion of the earthcrust recovers 

 gradually after its stress has been removed by the geological 

 disturbance which caused the original earthquake. In such a 

 case, to be sure, this phenomenon of recovery might be the prime 

 cause of the after-shocks of the original earthquake, since the 

 ultimate result of this phenomenon must be equal to that which 

 may be produced by an oppositely directed stress. 



Experimental Researches. 



From an investigation by F. D. Adams and J. T. Nicolson,^* 

 it is evident that even such a comparatively rigid rock as marble 

 may become wholly plastic under suitable conditions. For in- 

 stance, the diamter of a cylinder increased by 1.388 times its 

 initial, bulged out under endpressure. Another instance where 

 a plate of marble, resting horizontally on four posts at the 

 corners, in the course of about half a century, was considerably 

 bent by its own weight, is reported by T. J. J. See.^^ 



As to yielding and recovery in the case of torsion of rocks, 

 the author published some experimental results two years ago,'*^ 

 and proposed a logarithmic formula to express the amount of 

 yielding and recov^ery from it at any instant. To cite some 

 of the results : — (1) The amount of yielding increases propor- 

 tionally to the logarithm of the time during which the couple 



1) An t'XpeiiiiientMl investigation into tlie flow of marble. Pliil. Tran.s. of the K. S. 

 A. Vol. 195. 1901. 



2) The secular liending of a tiiurbie slab under its own weiglit. Nature, Nov. 20, 1901. 

 3j Pub. ..f the E. I. C. in ¥. L. No. 14, 1903. Tokyo. This journal, Vol. XIX, Art. 



6. 1903. 



