84 



DEEP BOREHOLE SURVEYS AND PROBLEMS 



for the rod to slide in and as the rod p has a sliding fit in 

 the tool head its vertical movement causes the dog to engage 

 or disengage the teeth on dial k. On 

 engaging it locks the dial against rotation 

 and it can seat within a groove of a 

 stationary rim member of the compass 

 frame h securing the arm of rod o from 

 lateral movement. Normally the dog is 

 urged to engage the teeth by a spring r 

 to lock the dial. 



The gyroscopic compass possesses the 

 feature of indicating the astronomical 

 north direction regardless of the proxim- 

 ity of magnetic masses and similar 

 disturbances. This feature will be more 

 fully described in Chap. IX. 



In operation, the core drill rotates 

 continuously in one direction to form 

 the core s, and, with the drill in drilling 

 position the projecting lower end of the 

 rod being in contact with the bottom 

 of the well, holds the rod in elevated 

 position against the action of the spring 

 r to retain the dog out of engagement 

 with the dial k. After the core has been 

 completely formed the drill is brought to 

 rest, after the lapse of a few seconds, 

 during which the sensitive element of 

 the compass can function to actuate the 

 dial k so as to indicate due north. 



It will be seen that on raising the drill 

 Fig 44— The Hall- ^^'oi^i the Well the lower end of rod o is 

 Armentrout gyrostatic. pulled out of coutact with the Well base 



core orientator. .... . ,„ ,. ,,, , 



pernuttmg sprmg r to function and the dog 

 to lock the dial. This gives the direction. The core drill is 

 now taken out, care being taken not to turn the drill pipe 

 or disturb the recording elements by shocks and bumps. 

 The sleeve t is unscrewed from drill head u keeping the latter 



