66 DEEP BOREHOLE SURVEYS AND PROBLEMS 



the needle I is pressed up against the stay m and fixed. 

 Simultaneously the stud o is freed from lever p and the 

 spring t presses the lever end pi against the balance, thus 

 stopping the clock. 



The core is broken off now and the whole raised to the sur- 

 face. The boring cylinder, provided below with two marks 

 A and B, is now unscrewed and the core top is free. The 

 core is marked with a diamond or in color and then it is 

 adjusted on a disc chuck v (Fig. 4) which has a shell u 

 so that the marks coincide with the diametrically opposite 

 marks Ai and Bi on the shell u and turntable v. The com- 

 pass is now placed on this (usually on a top core shell Ui) 

 and being still fixed is turned to occupy the same vertical 

 plane as A, B or Ai, Bi (Fig. 3). On releasing the needle 

 and letting it come to rest in its north meridian, the whole 

 table is turned until the north end of the needle registers 

 the previously noted time. The position thus indicated 

 is that which the core had previously in the hole and thus 

 the strike is obtained. 



Gothan's apparatus was the first to meet the demands 

 of durability, simplicity and rapidity in manipulation with 

 any measure of success. It has been used at great depths 

 and experimentally tested to 100-atm. pressure for more 

 than 2 hr. 



The casing mentioned above has a further non-magnetic 

 rod connection of 4 m. above and about 2 m. of bronze core 

 barrel below to protect it from local magnetic influences. 

 Very satisfactory data on its application have been obtained 

 by Professor Schneider, of the Berlin School of Mines, in 

 Upper Silesia and Galicia.^ It has been used in depths of 

 over 3,500 ft. 



It is a surer apparatus and greater time saver than 

 Koebrich's method, because it brings the orientation 

 marks and the core to the surface. It does not depend on 

 chisel marks like the latter and also the check is made 

 aboveground. Further, in Koebrich's method the core has 



1 Mitt. Markscheiderwesen, Heft 4, p. 40, 1902; also O. Erlinghagen, 

 Gliickanf, No. 23, 1907, for tests at Aix-la-Chapelle. 



