40 SYLVAIN J. PIRSON 
constant in any horizontal direction due to the continuity of char- 
acter of sedimentary formations parallel with the bedding surfaces. 
Thus we have: 
Pih P2h 
—=a, and —=wm 
Piv P2v 
Suppose that the current is introduced at the surface at two 
points C, and C2 (Fig. 1). The densities of current across surfaces 
V 
e, Y Keres RTE TP OE RED C. 
aa 
‘ z& ! a - = 
Sh 
ie 
, ee 
Sev 
Fic. 1.—Gish-Rooney electrode set-up and resistivity vectors. 
perpendicular to the axes OX, OY, and OZ are respectively: 

I OV, 
Iz i ee Saba 4 
Pih Ox 
I OV: 
yp 2 PS 
Ph oy 
' I OV: 
AN ) 
piv 02 
when the axis OZ is chosen perpendicular to the bedding plane XOY 
in which the axes ox and oy may have any particular position. V, is 
the electrical potential at any point in medium 1 and 2,, zy and 7, the 
densities of current perpendicular to the directions x, y, and z at 
that point. 
The total current at the point considered is then given by 
I = tig + jiy + bi, 
700 
