132 DEEP BOREHOLE SURVEYS AND PROBLEMS 



of the plumb is taken from a pendulum swinging in a definite 

 rotatable plane with the aid of a vernier and scale on a 

 graduated circular segment. In this way errors in obtain- 

 ing the position of the apparatus are either eliminated 

 entirely or essentially lessened. Figures 1 to 4 (Plate VII) 

 show the interior of Mollmann's apparatus. Through the 

 center of the covers h and 5i of housing a (Fig. 1) go two 

 screws c and Ci bearing a rotatable fork d. Below cover h 

 is a plate / with an attachment e against the one side of 

 which presses a spring ^ in a groove (Fig. 4), and this 

 presses the portion e against a rod h. This rod h can be 

 worked up and down by clockwork from the wheel 2' 

 on its prolonged screwed axis k. According to the lift 

 of the rod h a lug n under disc / engages, through the bore 

 m of disc /, a disc p held by spring pressure. Between the 

 discs / and p there is a plate q which is bridged to the fork 

 d and can move it up and down in a slit. The plate q 

 and its bridge is borne on the upper part of the fork under 

 a constant spring pressure by rod r which at its lower end 

 lies on the nose y which is likewise spring-pressed against 

 lever hi. The latter is connected by lever si to the disc t 

 (seen in end view in Fig. 2) which is displaceable laterally 

 in the fork d and coated with felt H on one side. On 

 the same axis as disc t is the upper end u of the indicator 

 z which is widened here and toothed. The lower end of z 

 carries a millimeter or circular graduated vernier while the 

 primary scale v for this is on the fork d. 



A side weight consisting of little tubes of mercury w is 

 attached under fork d, the purpose of which is to turn the 

 fork and indicator z at every inclined position of the 

 borehole. 



Above the apparatus a clockwork is placed which fixes 

 a magnetic needle k' on one side and can turn toothed wheel 

 z' with spindle k on the other side. This turning screws 

 up rod h turning spring g so far that it brings the bore m 

 over the lug n above the spring pressed plate p. The attach- 

 ment n can now enter bore m of disc /, raising plate q and 

 fixing it between / and p. This fixes the fork on the one 



