118 DEEP BOREHOLE SURVEYS AND PROBLEMS 



on and passes through an insulated copper wire down the 

 rods. The anode of the lowest apparatus is connected 

 to the rod string. 



In order to control the manner in which the precipitation 

 takes place and to judge the length of time it ought to last, 

 it is advisable to shunt in an extra registering apparatus 

 visible aboveground. 



Fig. 65. 



When sufficient precipitation is obtained, the rod string 

 is removed from the drill hole. The precipitation heights 

 on the cathodes are measured and the angles 6 and 

 \p calculated from the above formulae. This method 

 of surveying with orientation from the surface, however, 

 is slow and comparatively a time-consuming work. There- 

 fore the method of surveying with successive bearings is 

 generally to be preferred, if conditions permit its use. 

 In most cases the two methods of procedure are combined. 

 For instance, when surveying a hole vertically set, orienta- 

 tion from the surface is used down to the point where the 

 zenith angle is large enough to allow surveying with succes- 

 sive bearings. 



The Kiruna method is intended solely to give information 

 as to the courses of drill holes that is sufficiently accurate 

 for practical purposes. The Swedish Diamond Drilling 

 Company has proved this new method fully. 



Good results have been obtained at Kiruna and in the 

 United States with this method. Figure 66 shows several 

 of these, including the 1,300-ft. Oskar borehole. The 

 designers make no pretensions to the great accuracy 

 required in such contracts as freezing shaft holes for 

 instance, but guarantee to survey a borehole put down in 



