134 DEEP BOREHOLE SURVEYS AND PROBLEMS 



hand, and on the other hand, by the simultaneous raising 

 of the bar r attached to q, the nose y of lever hi is liberated. 

 This is drawn away by the pressure of a spring action on 

 the head of lever s' and the felt-faced disc t is thus pressed 

 against the widened part u of the indicator z. In this way 

 it is brought to rest and permits of a direct reading when 

 the whole is brought to the surface. 



Though the device of MoUmann constitutes a progressive 

 step in the science of borehole surveying it is intermittent 

 in action. Owing to the pendulum being only allowed to 

 swing in the plane normal to the fork beams it rapidly 

 comes to rest, hardly 8 to 10 sec. being needed. It is also 

 very easily read by the ordinary boring personnel. The 

 accuracy of the scale readings is read in 20-min. arcs for 

 10 deg. being thus far superior to previous devices; but even 

 this accuracy is unnecessarily high owing to its being 

 greater than that of the compass. This apparatus is 

 accurate, rapid, reliable and sure in action but unfortunately 

 it is unreliable in respect to orientation of the deviation. 



Bawden's Apparatus. — This device, invented in Kalgoor- 

 lie. West Australia, in 1905 by Wm. R. Bawden, contains 

 many features which are to be seen in Gallacher's apparatus 

 of 13 years later. 



The inner tube A (Fig. 81) has head joint covers k and ki 

 with counterweight sectors g, gi on the loaded axial pivots 

 which support the tube A. Tube A is attached by further 

 attachments to the counterbalance sectors g, g\. The mag- 

 netic needle n is likewise enclosed by a loaded spherical 

 housing d and by means of Cardan suspensions all round 

 is thus so mobile that its pin always stands vertical. The 

 spherical housing d has an opening for filling with fluid 

 gelatine and is closed from above by a screw cover and 

 hardwood plate. 



For obtaining the dip of the hole two pendulums pi and 

 P2 are provided and are rotatable with graduated arcs e and 

 / on metal plates. On both sides of the plates are reading 

 glasses. The tube A is connected to the plate by a bow. 

 Before using the apparatus the pendulum housing and 



