114 DEEP BOREHOLE SURVEYS AND PROBLEMS 



The zenith angle or angle between the borehole axis at 

 a given point and the vertical = 6. 



The apsidal plane or vertical plane containing the major 

 axis of the ellipse. 



The north angle or angle made by the section of the apsidal 

 plane with the horizontal and measured from the true 

 north = a. 



The apsidal angle or angle between the apsidal plane and 

 the plane through the borehole centrum and a generatrix 

 scribed on the lining = \p. 



The relation between the variations of the north angle 

 Aa and those of the apsidal angle Ai/' is 



Aa = Ai///cos 9 (8) 



Thus it is possible to survey drill holes, for the change 

 of the north angle can be calculated from point to point 

 after the angles 6 and \p have been measured. Thus the 

 positions of the tangents to the center line of the hole are 

 obtained at a number of points and the course of the hole 

 can be determined approximately by calculating the open 

 traverse of which these tangents are component parts. 

 The angles are determined by electrolytic registration. 

 This is done by sinking a cylindrical vessel containing a 

 galvanic bath down the hole and precipitating a metallic 

 coating on a cathode immersed in the bath. The outline 

 of this coating shows the position of the cathode in relation 

 to the horizontal plane and if the cathode is of cylindrical 

 form we get either a circle or an ellipse. 



Figure 62 shows the registering device consisting of the 

 electrolytic vessel A and the anode connected with it, 

 the electrolyte (CUSO4) and the cathode B which is a 

 carefully polished glided copper cylinder on which precipita- 

 tion is made. 



The cylindrical glass electrolytic tube has its long axis 

 coinciding with that of the hole at the spot to be surveyed. 

 The current is supplied from a surface battery through a 

 base contact connected with the anode by means of a pin 

 through the glass. The thin copper sheet anode (not shown 



