ART. 10. — H. KUSAICABE. 



I. INTRODUCTION. 



As to the elastic constants of several rocks wliicli compose the 

 so-called outer-crust of our planet, we have already a valuable 

 paper joublished by Professor H. Nagaoka,* in which the elastic 

 constants for one hundred specimens are given, with some notes 

 relating to seismology. The author also has reported some ex- 

 perimental researches relating to the hysteresis and the variation 

 of the constants under different conditions.^ A little considera- 

 tion, however, will make it evident that the values of elastic 

 constants determined by a statical method may be far from what 

 ought to be used in the discussion of seismic waves. 



The importance of measuring them again by a kinetic 

 method may thus be readily recognized. Not only are the rapid 

 a,lterations of state concerned in the propagation of a wave attended 

 with a thermal effect, which goes to change the elastic constants 

 beyond their value statically obtained ; but also in the case of 

 rocks, the phenomenon of yielding may have great influence in 

 making them deviate further from one another. 



In the author's papers above cited it has been shown that 

 the modulus of elasticity varies, during one cycle of strain, ac- 

 cording to a definite law. When a piece of rock is bent by a 

 force and unbent by virtue of its own elasticity, it is not, evidently, 

 the modulus of elasticity at any particular state, which determines 

 the vibratory motion of the rock. Afoduli of elasticity at all 

 the different phases of the vibratory motion equally take part in 



* H. Nagaoka.. The Pub. of the E.I.C. in RL. No. 4, 1900, and Phil. ]\Iag. 

 1900. 



t S. KusAKABE. This Journal. Vol. XIX., Art. 6. and Vol. XX., Art. 9. The Pub. 

 of the E.I.C. in F.L. Nos. 14 and 17. 



