72 DEEP BOREHOLE SURVEYS AND PROBLEMS 



type but somewhat different in construction. ^ In Fig. 37 

 the tube Ri Hes inside a wide tube R2 (moved by the rods 

 with nuts and spring) and carries in its upper part the closed 

 compass box B filled with oil. The rinsing current escapes 

 by way of the holes 0, 0, in the head of the core, tube Ri. 

 When a determination is being made the external tube is 

 lifted up so far that these openings are covered by the 

 internal projections V of the external tube. In this way 

 an excess pressure of water is set up which actuates a spring- 

 loaded piston k a little further up through the bores n,n. 

 This causes the rod S to free the needle which was hitherto 

 fixed. After the needle has settled down, the external 

 tube is lifted higher and when the water holes 0, are 

 passed by Vi they are again free and the piston k is unloaded. 

 Then the spring F again comes into operation and the needle 

 is fixed orientated. It can now be drawn further so that 

 the core, broken off by the core breaker on the external 

 tube, can be raised to bank. 



The apparatus is in many ways similar to that of Meine 

 or Gothan in principle and construction, but the needle 

 is freed by the rinsing water pressure by moving the tubes 

 relative to one another. The needle is also brought to rest 

 in a similar way. There are two advantages in these varia- 

 tions over the other methods. First, there is a slight saving 

 of time in that the needle does not follow the turning 

 movement of the rods but after adjustment can rotate with 

 them and swing back before coming to rest. Second, 

 there is the by no means small advantage that the needle 

 is always ready for measurement and cannot be thrown off 

 through unavoidable thrusts on the pin. Unintentional 

 freeing of the needle is absolutely impossible, since the 

 rinsing current is suited as long as the wider openings 0, 

 are free and should a throttling of the passage through 

 0, occur the piston k will soon be influenced. Such a 

 throttling, however, cannot occur if the outer tube is 

 raised. 



^ German Patent No. 168,596; also Osterr. Z. Berg-Hiittenw., No. 43, p. 

 561, 1906. 



