182 DEEP BOREHOLE SURVEYS AND PROBLEMS 



borehole is obtained from about a hundred or so photo- 

 graphs, which may be taken in a comparatively short 

 time. 



According to a recent note from the western oil fields 

 of the United States, this apparatus has yielded valuable 

 information in the region of Signal Hill, in the western 

 mineral field. A suite of very instructive photographs 

 taken by the inventor and showing fissures and natural 

 water veins have appeared.^ 



The device has the advantage that the less expensive 

 percussive boring can under certain conditions be made 

 to yield as valuable geological data as a core-drilling plant. 

 Again for finished holes with no cores available it will 

 provide information which could not otherwise be obtained. 

 When "torpedoing" well bases to increase the yield the 

 shattering effect can be photographed. It can also be 

 used for the inspection of casing as to corrosion, buckling, 

 unscrewing, collapse, etc., and for the examination of 

 cemented linings; also for locating lost or broken tools. 



Its great drawback as a deviation instrument is that in 

 strata thickly bedded or without stratification planes or 

 other marked features it has nothing to photograph. It is 

 Umited to the size of hole it will suit and can only be used 

 for orientation purposes in unlined holes. 



Oehman's Apparatus. — This is a magnetic needle and 

 plumb-bob photographic device which has been extensively 

 employed in the deep reef boreholes of the Rand and else- 

 where. It was first invented by Oehman about 1905 and 

 later improved upon by A. Payne-Gallwey.- 



From Fig. 120 it will be seen to be a non-magnetic tube 

 a in two halves connected by a coupling 0. The magnetic 

 needle b is in the lower half with an independent plumb 

 bob c, each swung over a gimbal d with a small electrical 

 lamp e above each. These are held in position and pressed 

 against a brass insulating rod /in the middle of the coupling 



1 Colliery Engineering, p. 372, August, 1926. 



'■^ Hatch, Dr. F. H., A paper read before the British Association, see 

 Brit. Assoc. Rept., 1905. 



