214 DEEP BOREHOLE SURVEYS AND PROBLEMS 



This take-up motor turns the measuring box with the 

 mercury vessel and contact springs to the rotations of the 

 gyrocompass, for the bead is only out of contact when it 

 hangs free between the contact springs on the mercury 

 vessel. Consequently, the measuring box is always in a 

 definite position with respect to the gyrocompass and 

 thus also to the meridian. In Fig. 2 (Plate XIII) the lower 

 bearing of the compass box is shown at I and in Fig. 3 L 

 is the upper bearing of it. The box itself is shown in Fig. 4. 



The east-west pendulum a swings in the picture plane 

 and the north-south pendulum h at right angles to this. 

 Under each pendulum is a registering casket kk with a 

 registering strip running close under the points. Over 

 the pendulum points lie the cores or armatures dd of two 

 small electromagnets as broad as the strips. When taking 

 measurements the current is sent into the electromagnet 

 by a telegraph key on the surface; the core strikes the 

 pendulum and presses a fine needle on the end of the pendu- 

 lum into the registering paper thus perforating it. Break- 

 ing the circuit the electromagnet operates a catchwork 

 driving the registering strip 5 mm. forward ready for the 

 next measurement. 



On opening the apparatus at bank and taking the strips 

 out from the casket and reading the deflection of the several 

 holes from the midline of the paper, two separate tables are 

 entered up with the data from the two strips. The sum 

 of the entries in the two tables, east-west and north-south, 

 gives the displacement at the depth concerned. 



Figure 1 shows the head of the apparatus; the various 

 leads of the cable are tightened with India-rubber the 

 winding cable itself being of medium steel and held by bolts 

 h. Eight lines encased in gutta-percha and jute yarn 

 take the current to the wheel, take-up motor and electro- 

 magnets. The rope is also covered with gutta-percha to 

 distribute the load at the bearing guide roll. 



The cable drum and motor are in a special lorry as also 

 are the current source and transformer for the direct- 

 current portion and also the necessary controls for the gyro- 



