94 DEEP BOREHOLE SURVEYS AND PROBLEMS 



holds the inner barrel firmly on the core at all times, so that 

 the core is not parted if the outer barrel raises up because of 

 vibration or chattering. Circulation fluid passes between 

 the barrels and discharges at the cutters to provide cooling 

 action. Exact dimensions of construction are important 

 to secure best results. 



Photographs can be made at 1-, 2-, 4- or 8-min. intervals 

 from the time the instrument is set to go into a well. About 

 75 exposures can be made (in 4>^ hr. at 4 min. each) so 

 that the 4-min. interval is suitable to 6,000 ft. depth. 

 Incidentally, the course of the well is surveyed at the same 

 time. 



