Rocks and the Velocity of Seismic Waves. 57 



■different from the actual value. When the rook is of stratified 

 structure and shows great difference in its elastic behaviour 

 the formula will require modification, but in studying the 

 elasticity of rocks in its broad features, the modulus of rigidity 

 calculated in the above manner will not be far from the 

 general mean. The calculation of the series involved in the 

 above formula is somewhat tedious. Fortunately, St. Venant 

 has calculated a table of 



/"2n-y\-nc S 2n— 1 X 7 



V 2b J V 26 ) 



2,; 



(in-lf («)- _£=ty 



e +e 



for different values of t. As the section of the prism was 

 o 



nearly square shaped, it was thought advisable to calculate 



the sum of the series at small intervals, when the ratio j is 



nearly unity. As such tables will sometimes be found useful, 

 I give the result of calculation in the following table : — 



K 2b J -\ 2b ) 



Table of -j - - (- J 2 j^=i)« (p£y 6 -(^T =/3 ' 



e +e 



c 

 7/ 



jS. 



c 

 I- 



P. 



1-00 



2-249 



1-15 



2-563 



1-01 



2-272 



1-16 



2-583 



1-02 



2-294 



1-17 



2-602 



103 



2-316 



1-18 



2-621 



104 



2-338 



1-19 



2-639 



105 



2-359 



1-20 



2-658 



1-06 



2-379 



1-21 



2-676 



1-07 



2-402 



1-22 



2-694 



1-08 



2-422 



1-23 



2-713 



1-09 



2-443 



1-24 



2-730 







1-25 



2-748 



1-10 



2-464 







1-11 



2-484 







1-12 



2-504 







113 



2524 







1-14 



2-543 



1 





