FLUID METHODS OF SURVEYING BOREHOLES 



105 



parallel motion just mentioned. The phial is revolved in its 

 sheath, and the arm is moved along the arc by the tangent 

 worm, until the embedded plummet is made perpendicular 

 from each point of view, or parallel with the vertical lines of 

 reference just described, as viewed through the two cross 

 telescopes. The phial is now at the same angle of inclina- 

 tion at which its contents solidified, and its lower bulb will 



Fig. 54. — The Swedish clinometer-goniometer. 



be found nearly in the axis of the revolving arm and an inch 

 or more above the center of a horizontal circular mirror hav- 

 ing a system of parallel lines engraved across its face. 

 Reflected in the mirror will be seen the image of the 

 embedded needle which pointed north before it was fixed by 

 congelation in the borehole. If we now revolve the mirror 

 until the 270 deg. of the graduated circle is opposite the 

 north (or notched) end of the needle and until the reflected 

 image of the needle is sensibly parallel with the engraved 



