138 DEEP BOREHOLE SURVEYS AND PROBLEMS 



Figure 2 is a view of Fig. 1 turned on its long axis 90 deg. 

 with cover on. 



Figure 2a is a view of Fig. la turned on its long axis 90 

 deg. partly in section and partly in elevation with cover on. 



Figure 4 is an enlarged view of the plumb bob controlling 

 and clamping device g in the inner casing and the compass 

 set free with it, Fig. 5 being a sectional view of Fig. 4 on 

 line XX. It is possible to have three operative positions 

 of the fixing and clamping arrangements for the plumb bob 

 and compass, i.e., 



a. Compass needle fixed from independent movement 

 with its compass case and plumb bob free to move about 

 their pivots. 



b. Compass needle and plumb bob both free with com- 

 pass case held against movement on its pivot. 



c. Compass needle and plumb bob both fixed with com- 

 pass case free to move on its pivot. 



Figure 6 shows Fig. 4 when condition c above is obeyed. 

 Figure 7 shows an enlarged view of the inner casing with 

 compass / and that part of the clamping device which 

 directly operates it. Figure 8 shows a cross section of the 

 inner casing with compass and compass-clamping device. 



In the assembled view (Fig. 3) the upper pivot h and 

 bearing are of non-magnetic material, like phosphor bronze, 

 as also are the nearest rod connections. In small holes the 

 apparatus is placed on the end of the drill rods; in large 

 ones it is let down by a flexible wire. Both inner case b 

 and outer case a are cast in brass or other non-magnetic 

 metal. The inner case is suitably weighted to cause it to 

 turn on the end pivots, bringing the registration device 

 under the inspection cover windows. The weighting means 

 are the lower and heavier portions of the controlling and 

 recording elements and the base plates, their centers of 

 gravity lying below the center line of the end pivots and 

 opposite the inspection covers. The clockwork control 

 i (Fig. 1), near the pivot end, consists of a lever escape- 

 ment, a train of wheels j, and their cooperating pinions k 

 and main spring barrel I. The clock itself d is provided with 



