106 DEEP BOREHOLE SURVEYS AND PROBLEMS 



lines, an index at the side of the graduated mirror frame will 

 give the exact angle between the needle and the vertical 

 plane of revolution of the phial. This is, in fact, the mag- 

 netic bearing of the inclined phial and of the borehole which 

 it occupied at the time of the application of the test. The 

 same operation is repeated with the other phials which com- 

 plete the set, and then the results are combined and the mean 

 taken in the same manner as if six separate determinations 

 of the same horizontal angle and azimuth had been made 

 with a theodolite or an altazimuth instrument. These six 

 phials — or self-registering compass clinometers as they may 

 be termed — are encased within, and protected by, the 

 cylinder or guide tube. 



Figure 54 shows the more modern clinometer-goniometer 

 now being used in the Swedish iron fields. 



Cylinder or Guide Tube. — This is a strong brass tube, 

 about 6 ft. in length, into which the phials accurately fit 

 (see Fig. 55 which shows part of its upper end with the 

 phials in their brass slide in the act of entering). This 

 tube or cylinder is securely closed against the heaviest 

 water pressure likely to be encountered even in bores of 

 2,000 ft. depth the glass clinostats being too fragile to bear 

 exposure, unprotected, to such a pressure. The guide 

 tube is passed down the bore by means of J^-in. diameter 

 service piping jointed in measured lengths, the effect of the 

 iron being kept from the magnets by the interposition of a 

 distance tube of brass. For use in hot strata, where cold 

 water must be poured down this small piping in order to 

 cool the cylinder below, the upper part of this is pierced 

 with holes out of which the cooling stream from the tubing 

 may issue and flow down the outside of the cylinder, thus 

 congealing its contents. Where the bore is approximately 

 perpendicular and the strata comparatively cool, these 

 may be dispensed with, and the bore surveyed by lowering 

 the guide tube with a small wire rope. Figure 56 shows an 

 actual survey of a 500-ft. borehole by this method at 

 Stawell, Victoria, in the early eighties. The principle 

 of this apparatus is still widely used. The apparatus itself 



