KINETIC MEASUREMENT OF THE ELASTICITY OF EOCKS. 11 



Tr=ll-0B5 

 w =5-67x10-' 

 / =12-47 

 whence 7ii=175'o 



??2=--0-2 

 n =351-0 

 ^ = 2-034x10'- c.g.s. unit. 



IV. PRELIMINARY EXPERIMENTS AND THE PROCESS 

 OF CALCULATION. 



Although the above testings gave satisfactory result, preli- 

 minary experiments with sandstone aud tuff were so very ambiguous 

 as to wholly confound the observer. At first sight, there seems 

 to be no definite length with which the string may vibrate witli 

 maximum amplitude. In the case of sandstone, e.g., lengths 

 corresponding to maximum amplitude were as follows : — 



The small numbers in brackets are the number of loops contained 

 in the segment. Those marked with ^r correspond to a peculiar 

 mode of vibration. 



It may be argued prima facie that the elasticity of such 

 loose materials as rocks which compose the earthcrust is not 

 unique and therefore, as the facts prove, that the velocity of the 

 propagation of seismic waves is diverted between wide limits. If 

 we assume that all these lengths equally correspond to the proper 

 vibrations of the specimen, then the velocity of longitudinal waves 



