116 DEEP BOREHOLE SURVEYS AND PROBLEMS 



The apsidal angle yp is found by measuring the precipita- 

 tion heights at four generatrixes 90 deg. from each other, 

 beginning at the one to which the apsidal angle refers. 

 The heights found in this way are 



ho, hgo, hiso, hiiQ 



from which we get two zenith angles, dx and 62, showing 

 the dip of the elliptical surface of the fluid in two directions 

 at right angles to one another:^ 



, ^ ^180 — ho /i27o — ho , , 



tan di = - — -J ; tan 62 = ^ (10) 



Knowing now di and 62, the direction of the major axis of the 

 eUipse is also known. 



The precipitation heights are measured by aid of a special 

 microscope with adjustable tube in which is a scale grad- 



FiG. 64. 



uated in tenths of miUimeters (Fig. 64). It is possible to 

 determine the angle 6 to as close as 15 min. which is con- 

 sidered very satisfactory. 



When determining ^^ less accuracy is to be expected, and 

 this accuracy falls off the smaller the zenith angle d, i.e., 

 the more vertical the hole. For a zenith angle of 5 deg. the 



1 From some notes kindly supplied by the Swedish Diamond Drilling 



Company. 



