222 DEEP BOREHOLE SURVEYS AND PROBLEMS 



unit, the gyroscope itself (Fig. 4). These three units are 

 assembled, screwed tight, in a high steel jacket 5^ in. 

 external diameter, the apparatus itself being about 43-^ in. 

 in diameter. The lower joints carry dry batteries operating 

 the gyroscope and illuminating the film camera. The top 

 joint ends in a ball-bearing swivel which enables the appara- 

 tus to be sent into the hole either on the drill stem or on a 

 wire line. It is thus independent of many of the objection- 

 able torsional features which render the results of so many 

 devices unacceptable for accuracy. This latter feature 

 plus the north orientating tendency of the gyroscope (and 

 here the special restraining appliances) make this class of 

 instrument independent of the effects due to twist on 

 insertion and extraction of the apparatus. It is claimed 

 that the casing of steel will withstand the mud pressures 

 encountered in holes down to 10,000 ft. deep. The gyro- 

 scope, maintaining the features of rigidity and precession 

 discussed mathematically at the beginning of this chapter, 

 offers great revsistance to any attempt to alter the direction 

 of its axis by being caused to spin, by means of the electric 

 motor self-contained, at a very high speed, as in the case 

 of Anschiitz model and that of the Kiel Nautical Instru- 

 ment Company previously described. The direct-trans- 

 mitting motor rotates the gyroscopic disc at about 10,000 

 r.p.m., and this latter is specially balanced to maintain 

 its axis in the geographical meridian^ when once set there. 

 A pointer coinciding with and controlled by the gyroscope 

 (Fig. 5) is set above the gyroscope on its axis over a grad- 

 uated arc. To this latter is attached a non-magnetic 

 watch with large minute and second hands giving readings 

 to }i sec. This enables computations of depth to be made 

 for each site recorded in the hole. A thermometer may 

 also be added here for reading the temperatures encountered 

 which yields data not only on direct thermal conditions 

 but for computation corrections if desired. 



1 See Rawlings, op. cit., p. 124, for mathematical discussion on balancing 

 the disc. 



