124 DEEP BOREHOLE SURVEYS AND PROBLEMS 



The whole is enclosed in a casing / capable of being 

 hermetically sealed, the casing being secured to a plate e 



Fig. 68. — The Otto-Gothan apparatus. 



screwed into the bore cylinder ab. The indicating device 

 can be removed from the casing as a whole by undoing the 

 screw. The action of the device is as follows : 



