144 DEEP BOREHOLE SURVEYS AND PROBLEMS 



the outer case and having terminals tN,tE,ts and tw (Figs. 1, 

 2). A fifth terminal t is connected to line A and therefore 

 H. The strands c are led to the five terminals. The 

 cable C goes out to the surface outside the rods. Cup E 

 can be inserted in only one position and is replaced by a 

 wooden clamping plug when not in use. A tail piece is 

 hung 30 ft. below the transmitter to aid centering. Figure 

 84 shows the receiver connections which are in a wooden 

 box 11 by 10 by 7 in. The cell h is an ordinary pocket torch, 

 4-volt refill, hence the claim to cheapness, and Z is a small 

 induction coil, its secondary connected to condenser C2 for 

 clearing the telephone note. The five strands of the cable 

 are attached to terminals Tn,Te,Ts,Tw and T (the last is 

 the plummet strand, the others the above mentioned t,y, 

 tE,ts and tw of Figs. 1 and 2, Plate IX) and from there to the 

 respective electrodes of the transmitter cup. Needle a 

 is held by the operator and loose flexed to the dish Ei 

 which holds salt solution (say, NaS04) and has four plati- 

 num electrodes e'^, e's, e's, e'w. It has a glass floor with a 

 dial scale the concentric circles of which are minutes of arc 

 and the radial lines 5-deg. bearing each. The operator 

 wears a low-resistance headphone R, one receiver of which 

 is coupled to the terminals 1 and 2, giving NS deflections, 

 the other to 3 and 4, giving EW deflections. The rods have 

 a special orientating coupling by external scribing in relation 

 to the vulcanite cup E.^ 



It will be seen from the wiring diagram (Fig. 85) that the 

 wiring system involves two applications of the Wheatstone 

 bridge connections to the liquid resistances of the earphone 

 indicators. Needle a is moved about the receiving dish 

 base until the noise in both earphones is a minimum, when 

 a occupies the same position in the dish as plummet needle 

 H (Plate IX) in the transmitting cup, and this is read on 

 the cup base dial. The receiver connections are reversed, 

 as in Fig. 85, because H will occupy a position diametrically 

 opposite to the hole dip. The bob must be at rest in the 

 hole to get a clear minimum sound and it takes about 10 



1 Brydon, a. D., op. cit., p. 437. 



