58 



DEEP BOREHOLE SURVEYS AND PROBLEMS 



5. Great loss of time in boring pilot hole, exchanging rods 

 and extracting cores. 



Vivian's method has had very little usage owing to the 

 small probability of success. 



Kendall's Apparatus. — This apparatus was invented by 

 P. F. Kendall at Owen's College, Manchester, in 1887, 

 and it was arranged to be set in a pilot hole like the Vivian 

 method, but the compass in the case was clamped by 

 lifting off the weight of the setting tool. A core was then 

 taken out with the compass attached to the top of it. The 

 magnetic compass is attached by means of a peg or cement 

 to the top of the core and left standing by the boring tool, 



, c. b 



Fig. 31. — Kendall's apparatus. 



and the needle is automatically locked by the release of a 

 spring when the lowering tool is withdrawn. In Fig. 31 

 is shown the compass box a with its strong screwed-on hd 

 6, and inner glass lid c held by a screw collar. The pillar 

 d bears the compass card e while / is a tube sliding on d 

 flanged and serrated at the top. About this is a spiral 

 spring % pressing the flange upward for its toothed edge to 

 grip the compass card e against the glass lid c. A slot and 

 pin on d prevent rotation of the tube. The catch lever g 

 holds down / by the flange when the apparatus is set ; it 

 turns on pin g' on the box floor. The floor trigger h 

 hinged to g has a flange and spiral spring K for operating the 

 catch lever and permitting / to grip the card bearing the 

 needle. An India-rubber ring under the card aids the teeth 



