18 AKT. 10. — S. KUSAKABE. 



a smaller modulus of elasticity and, at the same time, less den- 

 sity than those of older periods. The modulus of elasticity of 

 old rocks increases very rapidly, more rapidly, indeed, than is 

 proportional, as the density increases slowly. 



The velocity of propagation for longitudinal waves as shown 

 in the table, also increases with the age of formation of the rock 

 in question. It may here be noted that, in so far as the present 

 experiments go, the curve expressing the relation between the 

 density and the velocity is somewhat concave towards the posi- 

 tive part of the axis along which the velocity is measured. That 

 is to say, the increase of velocity is more rapid than the corres- 

 ponding increase of density as the age of the formation becomes 

 older. 



VI EFFECT OF MOISTURE. 



In the present case, it being impossible to give specimens 

 any desired amount of moisture, it is only intended to test 

 whether the modulus of elasticity is or is not largely affected by 

 the amount of moisture which might be 2:)resent within the 

 specimen. 



To begin with, a specimen of sandstone was clamped in the 

 usual way, and the wire was stretched with a known tension. 

 When the specimen was in the ordinary dry state, it was found 

 that the wire vibrated most violently when the half wave length 

 was 



/= 10-39 cm. 

 Then the specimen was wrapped in a wet cloth in its clamped 

 state and fed with a constant supply of water dropped upon it 



