156 



DEEP BOREHOLE SURVEYS AND PROBLEMS 



2. There is no guarantee of continued alignment of the 

 meridian indexes. 



3. The feeler centering springs are liable to error and they 

 also preclude the adoption of this method 

 in very narrow boreholes. 



4. Springs are objectionable in boreholes 

 holding water under high pressure. 



5. The apparatus becomes too involved 

 if attempts are made to obtain continuous 

 readings. 



Erlinghagen's Apparatus. — This appa- 

 ratus introduced a significant change in 

 the construction of deviation instruments. 

 It is a pendulum apparatus with electrically 

 operated registration mechanism. It con- 

 sists essentially of an electromagnet 

 operated pendulum and a clockwork-driven 

 recording paper strip in which the pendulum 

 pointpricks a set of definitely arranged 

 marks. The clockwork is also released 

 simultaneously with the pendulum by 

 means of drawbars. 



Provided the apparatus keeps from turn- 

 ing on being let down the hole, it is a very 

 suitable apparatus and Chief Engineer 

 Erlinghagen of Nordhausen, the inventor, 

 tried various devices to attain this end. 

 He first employed a longitudinal slit g down 

 the apparatus c (Fig. 95) with the rope a 

 held in the slit. This was not entirely 

 satisfactory. Later he employed telescopic 

 lenses held by counterspring nuts in the apparatus, as in 

 Figs. 96 and 97, which solved the difficulty. 



Figure 96, left, shows the entire apparatus assembled 

 ready for insertion in the hole with the lenses collapsed. 

 Figure 96, right, shows the device in the extended condi- 

 tion. Only electric current is used for the determination 

 apparatus. The tubes can be let out by loosening a brake 



Fig. 95.— Erling- 

 hagen's original 

 centering device. 



