COMPASS AND PLUMB-BOB METHODS 



131 



only dip in amount continuously and the second, though it 

 gives both amount and bearing of dip, is intermittent. 

 These are the only drawbacks to this clever device, which is 

 independent of torsion in the rods or lowering rope. 



Boifom of Hole 



Surface of Ground 



4165 Esfimafed 

 depfh of Reef 

 veriiocilly below 

 Mouth of Borehole 



Fig. 80. 



Mollmann's Apparatus. — This device,^ invented in Dort- 

 mund in 1904, is an improvement on previous pendulum 

 or plumb-bob apparatuses in that the vertical position 



1 German Patent No. 155,849, Oct. 22, 1904. 



