752 



EXPLORATION GEOPHYSICS 



where /> is a parameter. It can be shown that the time required by the 

 wave in traveling from the shot-point to the point A is 



n 



hi 



^^ Vic cos aje 



Furthermore, the horizontal distance from to ^ is 



n 



Xn = ^ hk tan afc 



fc=i 



Fig. 457. — Path of a refracted ray through n horizontal layers. 



The case of interest in refraction prospecting is that wherein the angle 

 a„ + 1 has a value of 90° so that 



P = 



1 



and 



sina&= pVjc = 



Vn + l Vn+1 



Vk 



F„+i 



The total time from to a point 5 at a distance x on the surface is ob- 

 viously 



T 



Vn + l Vn + 1 itx \VTcCOSaT, Vn + lJ 



^ + 2 > — 



Vn + \ i^^Vjc COS aif 



(1 — sin^ofc) 



