88 Prof. C. G. Knott on Reflexion and Refraction of 



The energy which escapes into the air is so small that 

 practically the whole energy remains in the rock. The 

 general behaviour of the phenomenon is very similar to what 

 was found in the case of rock and water, the differences 

 being differences of degree and not of kind. Thus we may 

 make the graphs for rock and water serve in a rough way 

 for rock and air by imagining a few slight changes to be 

 made. In the graph for the incident condensational wave, 

 imagine the distortional-energy carve, B l5 to run up into 

 practical contact with A when the angle of incidence is about 

 B0°, to remain very near to it till about 75°, and then to fall 

 rapidly away to zero at 90°. At the same time, because of 

 the great minuteness of the refracted energy, A', the reflected 

 condensational energy A] begins, at zero incidence, with 

 practically unit value and is to a very close approximation 

 the inversion of B lt In like manner, the incident distortional 

 wave is, for incidences between C and the critical angle 

 35° 13', practically represented by the two reflected waves. 

 The distortional energy begins and ends with value unity, 

 passing through a small minimum value immediately before 

 the critical angle is reached ; while the condensational energy 

 begins and ends with zero and passes through a maximum 

 which is practically unity just before. the critical angle is 

 reached. The refracted condensational energy, A', is very 

 small throughout, and could not be shown graphically with 

 the others unless it were drawn to a scale of at least 1000 to 1. 

 Immediately after the critical angle is past the condensational 

 energy in the air rises abruptly to the greatest value it ever 

 attains, and falls off steadily with increasing incidences until 

 it vanishes at grazing incidences. Practically the whole 

 energy is retained in the solid in the purely distortional form . 



5. JBehavioar of Waves at the Plane Surface of Rock and 

 Fluid, whose Density and Comjyressibility are equal to those 

 of the Rock. 



(1) Distortional Wave incident in the Rock. 



<p- 



B. 



B l . 



e. 



A r 



9'. A'. 







1 



1 









14° 2' 



1 



•725 



25° 



•144 



18° -131 



26° 34' 



1 



•318 



51° 



•261 



35° -421 



35° 13' 



1 



1 



90° 







48° 



45° 



1 



•147 



inif 



ginary. 



66° -853 



50° 44' 



1 



1 







90° 



Higher in- 



'i 











cidences 



I 1 



1 





>> 



imaginary. 



