PENDULUM METHODS 161 



The pendulum, being very sensitive to shocks and taking 

 about 20 min. to subside, has a hair brush damping device 

 h which brings it to its position of rest in about 45 sec. 



For working the measuring apparatus a horseshoe magnet 

 m on the floor of the apparatus is switched in so that con- 

 nection is made by way of the bearing plate e which is 

 attracted downward. Plate e is connected by drawbars to 

 the clockwork. The weight of the clockwork is taken by 

 springs / so that the magnet has very little force to over- 

 come. The point of the pendulum sticks up into the paper 

 strip when measuring, and at the same time four points t, 

 arranged in the center ring and which lie on concentric 

 circles on the periphery of the guard tube, mark four points 

 on the paper strip, by which we are able to recognize the 

 center point of the measuring figure at that instant. 



The conductor wire for the magnet coils goes along one 

 of the long drawbars to a clamp for current rod u. The 

 head here is specially sealed against entry of water under 

 high pressure, thus preserving the clockwork and magnet. 

 This is done by means of opposed nuts c and copper 

 rods k on floor h bushed to the insulating plate I and slip 

 rings d,d. 



The direction line of the paper may be noted on the out- 

 side of the tube with the whole apparatus above it, so that 

 on letting it into the hole one knows how it stands. The 

 conductor and lowering rope are all in one, the conductor 

 being insulated with cement, bitumen and tape. 



The inventor gives details^ of surveys carried out with 

 the apparatus, which did not turn on extraction or insertion, 

 and these facts were checked by an investigation in a blind 

 shaft between two levels belonging to the German Solvey 

 Works in Bernburg. The results of two surveys at Solvey- 

 hall with the apparatus and a later normal instrumental 

 survey check are to be seen in Fig. 101. A series of 160- 

 mm. tubes were arranged for the apparatus test; the normal 

 survey shows a constant survey traverse distance from the 

 apparatus survey. Erlinghagen's apparatus marked a new 



1 Gluckauf, p. 743, June 15, 1907. 



