KTNETrC MEASUREMENT OF THE ELASTICITY OF ROCKS. 3 



causing the motion. Hence for the apparent modukis of elasticity 

 during one complete vibration, we must take the mean value of 

 the moduli at all different phases. 



For a j)iece of sandstone, e.g., when the maximum bending 

 force during the cycle was equal to that due to J/=^3000 grams- 

 weight, we had a mean value 3.67 times greater than that taken 

 at the state of no bending. In other words, the mean kinetic 

 modulus for this specimen, provided the vibration be assumed to 

 take place at as slow a rate as in this case, is nearly three and 

 a half times greater than the static modulus. 



Possibly sound-experiments furnish the best means of ascer- 

 taining the kinetic modulus of elasticity. The results deduced 

 from such infinitely small strains as occur in sound vibration is 

 no doubt of great significance as regards the elastic property of 

 rocks. The fact that it seems strange to speak of the vibration 

 of such loose rocks as sandstone, shows at once that the measure- 

 ment of the kinetic modulus of elasticity in them is much more 

 defficult than in metallic substances. 



The method to be adopted here is a new application of 

 Melde's experiment*, combined with the principle of resonance. 

 The number of specimens examined amounts to one hundred and 

 fifty eight, collected from various lacalities in the main islands of 

 Japan, containing 23 Archœan, ß5 Palaeozoic, 12 Mesozoic and 58 

 Cainozoic rocks. This whole series of experiments is but a begin- 

 ning in this field of inquir}^ and may be thrown aside as a wreck 

 in the path of progress ; yet the author ho^^es it may prove a help 

 to later investigators. 



* Melde. Phil. Mag. Vol. 47, 1874. Lowery. Ibidem. Vol. 48, 1874. 



