Elastic Waves, ivith Seismological Applications. 



87 



which the reflected condensational wave vanishes, 90 per cent, 

 of the whole initial energy is transferred to the second medium 

 in the distortional form. The curious fall in the B' curve, 

 and the corresponding abrupt rise in the A' or A x curves (or 

 in the B t curve) are very characteristic. Meanwhile the 

 energy of the reflected distortional wave remains very small ; 

 and not until the condensational derivatives have become 

 imaginary does it attain any appreciable value. It then 

 increases, for the higher incidences, at an acceleratinglv rapid 

 rate, finally becoming equal to unity — at grazing incidence 

 in the one case, at the critical angle of 49° 43' in the other. 



It is obvious that, with greater divergences among the 

 values of the constants than those here chosen, the con- 

 densational waves in cases (1) and (2) and the distortional 

 waves in cases (3) and (4) would have become relatively 

 more important ; but the example brings out very clearly the 

 complex nature of the whole phenomenon of reflexion at the 

 plane interface of two elastic solids. 



4. Behaviour of Waves at the Plane Interface of Rock and 

 Air, the Elastic Constants of the rock being taken as on p. 68, 

 with the exception of the Density, which is taken 2000 times 

 that of air. 



(1) Distortional Wave incident in Rock. 



<p. 



B. 



B r 



«, 



K 



0'. 



A'. 







1 



1 











14° 2' 



1 



•534 



25° 



•466 



l°-6 



■00002 



26° 34' 



1 



■025 



51° 



•975 



3° 



•00006 



33° 40' 



1 



003 



74° 



•997 



3° -7 



•00006 



35° 13' 



1 



1 



9U° 







3° -8 



000000 



39° 48' 



1 



1 



imaginary 



4° -3 



•00019 



45° 



1 



1 







4°-7 



•00016 



59° 2' 



1 



1 







5°7 



•00014 



73° 18' 



1 



1 







6°3 



•00014 



84° 17' 



1 



1 





" 



6° 6 



•00006 



(2) Co 



nden 



sational Wave 



incident in Rock. 



e. 



A. 



Ax- 



0'. 



A' r 



f. B t . 







1 



1 





•00013 





14° 2' 



1 



•828 



0°-9 



•00013 



8° -172 



26° 34' 



1 



•464 



l°-7 



•00011 



15° -536 



45° 



1 



•079 



2° -7 



•00009 



24° -921 



59° 2' 



1 



•0002 



3°3 



•00007 



30° 1 



73° 18' 



1 



•003 



3° -7 



•00006 



34° -997 



84° 17' 



1 



•091 



3°-8 



•00005 



35° -909 



