AUXILIARY REGISTRATIONS IN BOREHOLE SURVEYS 33 



to the place noted and then extracting and reading. Or, 

 as said before, a continuous pump pressure record is 

 kept. 



The borehole depths read from the rod are entered as 

 abscissae and the computed deviations from the horizontal 

 as ordinates, as shown in Fig. 11a above. We thus get a 

 line showing the course of the borehole. When the 

 actual borehole is not intended to be horizontal the depths 

 are projected, otherwise we get foreshortening errors. To 

 lessen errors we may plot true borehole lengths against 

 measured pressures direct. These methods are not affected 

 by the smallness of the hole.^ 



Brigg's "Clinoscope." — This is another and more recent 

 method of measuring the deviation of horizontal boreholes. 

 It consists of a mercurial transmitter and Wheatstone 



d- e" d'' ^ J 



Fig. 12. — Brigg's clinoscope, vertical section of transmitter. 



bridge recorder, the tilting of the mercury into the horizon- 

 tal position varying resistances which are measured by the 

 bridge. 



^ 



,^7V 



~TT1I 

 m j u 



Fig. 13. — Brigg's horizontal clinoscope. Plan of transmitter. 



In Figs. 12 and 13 is shown the transmitter which is a 

 fiber box half filled with mercury g in the container d. 

 Two circular pits at ^, i (Fig. 13) are connected by a slot 

 s, the surface of the mercury, when the transmitter is level, 



1 Thiele, p., Verfahren zur Ermittlung der Abweichung von Horizon tal- 

 bohrungen in der Vertikalebene, Kali, p. 32, Jan. 15, 1913. 



