THEORY OF SEISMIC PROSPECTING 39 
Without going through all the steps in the simple deductions we 
may write down the following formulae for the positions of the center, 
foci, and vertices of the iso-time ellipses. S is the origin. Distances to 
the right of S are positive and to the left are negative. 

HIG 
Distance from S to center 
= p(1)=—(—~_-_+_) jist ) 
Mig og Nik (a—d) sin (a+v) ( Vi a 
—V,T cosasin’? A cos? asin’ 
sin? a—sin? 3 sin? a—sin? & 
—cos a sin ? 
= (Vil 18 BOE G9): 
sin? a—sin? 3 
Distance from S to right vertex 
Vi 2H cosa 
sin (a+) Vi 
283 
