104 DEEP BOREHOLE SURVEYS AND PROBLEMS 



tion of the inclination and azimuth at which it set while, 

 say, 500 ft. deep in the borehole. It is easy therefore, after 

 its withdrawal, to tilt it to the same angle and to the same 

 quarter of the compass as before by simply bringing the 

 embedded plummet to the vertical, and the needle to the 

 meridian. These clinostats are heated, inclosed within 

 their brass protecting tubes and lowered by rods on a line to 

 the desired spot in the borehole. Their contents are allowed 



Fig. 53. — MacGeorge's clinometer. 



to cool and congeal and are then withdrawn for inspection. 

 The phial with its congealed contents is placed in a sheath 

 of brass tubing (Fig. 53) attached to a movable arm which 

 carries the index of a vertical arc. This sheath corresponds 

 with the Y's of a theodolite, and carries the phial firmly 

 upon the same principle as these carry the usual telescope. 

 The upper bulb of the phial is brought into the field of two 

 crossed microscopes, which are carried with the arm round 

 the vertical arc ; these are kept truly in the same plane at 

 every angle of inclination by a parallel motion. There are 

 vertical lines drawn upon the object glass of each micro- 

 scope, these being, of course, kept truly vertical by the 



