164 DEEP BOREHOLE SURVEYS AND PROBLEMS 



An apparatus t is arranged in each link tube ri,r2, etc., and 

 called a ''pot head," owing to its first being made pot 

 shaped. On the floor of this head rests a cork-lined base 

 nil (Fig. 5) covered with tin foil and having impressed coor- 

 dinate axes. A tong-shaped device s above the head has 

 one fixed z and one spring-moved limb s (Fig. 2) which 

 carries the plumb weights I. From the latter in each head 

 or top there is a pair of common threads or wires; this 

 common wire is laid over the transom d carried by the 

 tongs. In the base of the little trestle of the tongs is an 

 adjusting piece n between set screws o with two fine holes 

 for guiding the plummet fibers. This permits of a hair 

 adjustment of the plummet points exactly perpendicular 

 over the zero of the coordinate axes arranged under the 

 head on a perfectly horizontal plate. 



The gudgeons of the cross joints/ of the link tubes lie at 

 right angles to one another in their crossing vertical planes. 

 The coordinate axes of the marked plate and of the tin-foil 

 plate have definitely arranged and assured symmetrical 

 positions on the whole of the plumbing heads. Thus in 

 each tube of the linked series we have a separate measuring 

 operation assured independent of its neighbor. It does not 

 matter if the break points between two tubes do not lie on 

 the axis of the borehole, because the preceding and succeed- 

 ing errors compensate for each other. In horizontal pro- 

 jection we then have a simple figure of the deviation of 

 each tube. The metal plumb bobs are not affected by 

 water, chemicals, pressures or mud, thus combating some 

 of the objections to Erlinghagen's and Haussmann's appa- 

 ratuses. The fundamental idea of the apparatus will be 

 clearly seen by considering two equally swinging pendulums 

 side by side, especially when they have a small difference in 

 length. In each apparatus are two plumb bobs on a com- 

 mon string. The string is led over the transom, and when 

 let down in a dipping tube the plummets mark parallel 

 lines on the cross axes at a corresponding distance from the 

 position of rest. Should the line be at any instant at greater 

 or less distance than the normal case provides, an oblique 



