CORE ORIENTATION 83 



4. If there are no bedding planes visible in the core the 

 apparatus is not so acceptable as otherwise. 



5. Friable strata are against its employment as an 

 orientator. 



Hall and Armentrout's Gyrostatic Method. — ^This device 

 is one of the few known instances of the application of a 

 self-contained gyroscopic compass in borehole investigation ; 

 most other types have their gyromotors actuated by a 

 source of electrical energy aboveground, as will be explained 

 in Chap. IX. This apparatus^ has been adopted in the 

 California oil fields and is suited for employment with any 

 rotary core drill of conventional form. In Fig. 44 it will 

 be seen to be mounted on the bracket a on top of the inner 

 core barrel 5 in a chambered casing c with closed top d. 

 This casing has dividing partitions e and /, housing regis- 

 tering elements. 



In the lowermost compartment is a non-magnetic com- 

 pass g preferably a gyroscopic compass of the Sperry^ 

 type including the conventional frame h having trunnions 

 i by which the compass as a unit is supported from the wall 

 of the casing c. This compass includes a motor j con- 

 stantly driving the sensitive element of the compass, 

 the latter being mounted to actuate a dial k disposed upper- 

 most of the compass. The motor j is of the alternating- 

 current type and current is supplied thereto from an 

 alternating-current generator I driven by a direct-current 

 motor m with current supplied to the motor from a battery 

 n. The dial k has an annular toothed edge adapted to be 

 engaged by a dog fixed to the angular extension of rod o 

 extending to the cutter bit at the base of the barrel to a 

 point between certain of the bits p. Guides q are provided 



1 U. S. Patent No. 1,656,809, Jan. 17, 1928. 



2 British Patents Numbers 15,669/11 for the gyrocompass of E. A. Sperry; 

 also Engineering, Vol. 91, p. 816, and Vol. 93, p. 722; Glazebrook, "Diction- 

 ary of Apphed Physics," Vol. 4, or T. W. Chalmers, "Gyroscopic Compass," 

 pp. 54, et seq., Constable & Co., London, 1920. 



For full mathematical treatment see A. L. Rawlings, "Theory of the 

 Gyroscopic Compass and Its Deviations," p. 38, Macmillan & Co., Ltd., 

 London, 1929. 



