82 DEEP BOREHOLE SURVEYS AND PROBLEMS 



upper base plate I. Its lower end ni is enlarged and 

 hollowed round to make an all-round contact on the 

 hemispherical cap k. A helical spring o about n presses 

 under I and against n. The upper end of n passes up 

 through lever p which is hinged at q and has a cross pin at 

 r to facilitate disengagement of n from k. On releasing p 

 the spring o pushes plunger n down on to cap nut k, fixing 

 the cone and needle in position. This release is provided 

 by the clockwork in frame s by means of flexible wire or 

 cord t, from the alarm spindle u. After winding up, the 

 alarm is set at any chosen instant for release and in this 

 state is lowered into the borehole. When release occurs 

 t is unwound from u, freeing spring o and pushing n down, 

 thus fixing the cone and magnet in the position in which 

 they have come to rest. The hermetical seal is completed 

 by means of the cap piece w. Other mechanical or electrical 

 means for release may be adopted. 



The magnet is secured so that its center line lies in the 

 central plane of the cone passing through the to 180-deg. 

 mark. A gage is used to get the inclination of the highest 

 and lowest points of the rim base of the cone above the base 

 plate e, and the graduations give the azimuth. The angle 

 of dip is got by the said difference of heights divided by 

 the base diameter of the cone. 



The scribers 4 at the foot of the tube are for marking 

 the core by raising and lowering the tube. Then when 

 brought to bank the dip of the strata in amount and direc- 

 tion can be obtained by noting these marks and the bedding 

 Unes, if any. 



The apparatus while strong and reliable, given its peculiar 

 conditions of application, has the following disadvantages : 



1. Clockwork mechanism is likely to err under the effects 

 of shock on insertion and extraction. 



2. The device has to be separately used to give good 

 results; this means much loss of time in changing tools, etc. 



3. If used as a deviation recorder there is no continuous 

 record. Each record is a separate insertion and with- 

 drawal. 



