COMPASS AND PLUMB-BOB METHODS 



125 



When a portion of the core of a boring has been broken 

 off and removed the apparatus is lowered down into the 

 borehole, and when it reaches the bottom the clockwork i 

 is arranged to arrest the motion of the magnetic needle I 



a 



c; 



m 



u — u 



Fig. 69. 



Fig. 70. 



and to raise the spring n. The plumb line is thereby 

 lowered, a mark is made on the wax or hke disc u, and, 

 should the position of the boring tool be inclined, the mark 

 is outside the center of the disc. The apparatus is removed 

 from the borehole and the direction in which the magnetic 

 needle I has been arrested indicates the north and south 



