136 



DEEP BOREHOLE SURVEYS AND PROBLEMS 



apparatus does not escape all the defects of MacGeorge's 

 apparatus but it is more convenient to handle and more 

 robust. Its great disadvantage is that its action is not 

 continuous up and down the hole, it having to be extracted 

 for every reading. 



Hillmer's Apparatus.^ — Hillmer also adopted the prin- 

 ciple of a plumb-bob point let down on to a prepared base, 

 as shown in Fig. 83. The cylindrical housing a (Fig. 83) is 

 filled with a fluid and is let down on hollow 

 rods into the borehole. It consists of a fluid- 

 filled cylinder a with a pendulum P sup- 

 ported on ball bearings in such a way that it 

 will also maintain its upright position when the 

 housing is inclined. Above the point S of 

 the pendulum is a soft plate G which can- 

 not turn and bears a spring F in such a way 

 that it keeps off the pendulum point. On 

 the upper surface of the plate, freely swing- 

 ing on a point, is a magnetic needle N which 

 has an attachment A pointing downward. 

 A piston K is provided over the needle in the 

 housing the rod of which is carried through a 

 central opening in the housing top and carries 

 on its top end a piston Ki. There is a spring 

 Fi between the latter and the top of the hous- 

 ing which by its pressure keeps piston K 

 in the highest position. In using the device proceed as 

 follows : After having lowered the apparatus to the spot to 

 be measured, and both pendulum and needle have come 

 to rest, a means of pressure (water, compressed air, or the 

 like) is conducted through the hollow rods on to piston Ki. 

 This presses down K and plate G. The attachment A 

 on the magnetic needle and the point S of the pendulum 

 now bore into the soft plate and both are thus fixed. After 

 raising the apparatus to bank, the position of the two marks 

 can be used to get the inclination of the borehole. 



1 Freise, F., " Stratameters and Borehole Dip Measurers," p. 53, Aix-Ia- 

 Chapelle, 1906. 



^T 



Fig. 



