ELECTRICAL METHODS 



493 



the ratio for each a is known and Q2 corresponding to various d/a ratios 

 can be read from the curves. Since the electrode separation, a, is known 



pa 



for each set of vakies, we have corresponding values of Q2 and d for each-p^' 



Fig. 294. — Computed curves showing the relationship between ffj 

 o-j, pjp^, and d/a for various values of Q^. (Tagg, A.I.M.E. Geo- 

 physical Prospecting, 1934.) 



ratio. O2 vs. d can then be plotted for each ^ ratio, or for each electrode 



spacing a. 



The use of these curves for determining the depth to a horizontal strat- 

 um will be illustrated for data taken from an experimental survey conducted 



