Elastic Constants of Rocks and Velocity of Seismic Waves, 53 



Postscript. — Since the above paper was written a valuable 

 niemoir by Prof. Omori on " Seismic Experiments on the 

 Fracturing and Overturning of Columns" (Publications of 

 the Earthquake Investigation Committee in Foreign Lan- 

 guages, No. 4, Tokyo, 1900, pp. 69-141), has reached this 

 country. At the close of the memoir (pp. 137-141) he gives 

 an " absolute scale of destructive earthquakes," the maximum 

 acceleration corresponding to each degree being 300, 900, 

 1200, 2000, 2500, 4000, and more than 4000 mm. per sec. 

 per sec. respectively. The effects of a shock of each degree 

 on buildings &c. are described in detail. It appears also that 

 the Japanese scale has been modified slightly since 1892. The 

 form given by Prof. Ornori is as follows, the corresponding 

 degrees of the Rossi-Forel scale being added in brackets : — 

 Slight (1, 2), Weak (3 to 5), Strong (6, 7), Violent (8 to 10 

 and above) . 



IV. Elastic Constants of Mocks and the Velocity of Seismic 

 Waves. By H. Nagaoka, Professor of Applied Mathe- 

 matics, Imperial University , Tokyo *. 



THE vibration of the earth's crust has from time to time 

 been a favourite subject of discussion among the elas- 

 ticians, and the propagation of seismic disturbance is a 

 problem whose solution has long been hoped for, both from 

 the theoretical and the empirical point of view. With im- 

 proved instruments, seismologists have recently determined 

 the velocity of propagation with tolerable accuracy, but very 

 little is known of the elastic nature of the medium through 

 which the vibration has travelled. The resources from which 

 physicists and seismologists draw their theoretical inferences 

 are so scanty, that among the numerous rocks which con- 

 stitute the earth's crust, only a few of the most commonly 

 occurring rocks have had their physical properties investigated. 

 The questions of elasticity, having close bearing with the 

 deformation of the earth's crust, have repeatedly been a sub- 

 ject of research by several distinguished elasticians as Lord 

 Kelvin, Boussinesq, Cerruti, and Chree. But we are baffled 

 in our attempt to apply the result of subtle analysis to the 

 actual problem, from the lack of experimental knowledge 

 as regards the elastic nature of the diverse rocks which com- 

 pose the outer coating of our planet. The present experiments 

 were undertaken with a view to fill these gaps, and to supply 

 * Reprinted from the Publications of the Earthquake Investigation 

 Committee in Foreign Languages, no. 4. Communicated by the 

 Author. 



