128 DEEP BOREHOLE SURVEYS AND PROBLEMS 



mutator H. The current is supplied through the wires 

 K, L, from a battery of known electric motive force having 

 a galvanometer and standard resistance box in the line. 

 In this way the declination of the plumb bob is known, and 

 therefore, by means of the galvanometer, a calibration 

 scale can be constructed. The wire from K is attached 

 to the top pivot screw h, and that from L to the hemi- 

 cylinder B, and so to F and the switch arm G. 



When the casing A is tilted, the weights M, M, on B, 

 cause the latter to revolve on its pivots h, h' and bring it to 

 rest in the position in which G moves in a vertical plane. 



The cable is internally screw-threaded into the instrument 

 at m by means of the plug N (Fig. 74) having a further 

 external thread n' to assist the connection to casing. The 

 cable is also secured in the plug by a screw thread n^, 

 and a cap Q covers the top, holding the gland nut P with 

 its gripping pieces r. 



The instrument is lowered into the hole by a 3^^-in. wire 

 rope containing two insulated conductors inside it. These 

 lead through the connecting plug of Fig. 74 on the lower 

 end, and on the other to contact rings on the sides of the 

 surface drum on which the rope is coiled, and through which 

 a pair of brushes make contact with the current supply. 

 A measuring wheel, over which the rope passes, gives the 

 distance down the hole to the apparatus. The surface 

 recording instrument is attached at the contact rings, 

 and by the galvanometer system of cahbration can be 

 arranged to give a continuous record of the variation 

 in dip of the hole. This instrument does not record the 

 direction of dip. Marriott's second form of this instrument 

 records the amount and direction of dip, but, however, 

 intermittently. 



Marriott's Intermittently Recording Instrument for Direc- 

 tion and Amount of Dip in Deep Boreholes. — Referring to 

 Fig. 75 which illustrates the instrument used in this 

 method, it will be seen that A is a copper or brass tubular 

 vessel having a screw cap B, details of which are shown 

 in Figs. 76 and 77. This screws into the upper end of the 



