43_AN UNDERGROUND TRAVERSE. 

 By a. E. Payne. 



Two years ago, in a paper which the writer had the honour of 

 reading before this Association in Johannesburg, * reference was 

 made to the apparently simple object of measuring an angle in an 

 underground traverse by means of a transit theodolite. The writer 

 called attention to the care with which the simple operation should 

 be conducted so as to justify the reliance which must later be placed on 

 the results obtained. Since that date it has been brought home to 

 the writer, as a member of the Commission of Examiners for Mine 

 Surveyors' certificates, appointed by the Transvaal Government, 

 that there is a great diversity of opinion amongst the mine surveyors 

 of these fields as to how this operation should be best conducted. 



It would seem, therefore, advisable to follow up the outline of 

 the mine surveyors' work, as sketched in the remarks of two years 

 ago, with a few details of some of the methods employed in con- 

 ducting an underground traverse, and the subsequent calculations 

 connected therewith. 



To obtain the necessary information from an authoritative 

 source, the writer asked the Consulting Engineers of the chief Mining 

 Groups represented on the Witwatersrand fields to furnish him with 

 a copy of the form of calculation, the method of procedure, and any 

 other relative information in general use in that group. The result 

 of this enquiry is tabulated in the following pages : — 



I. Method of Procedure. 



First Method.— Self-explanatory. 



Second Method — (Note to Page 403). — "In the first column the station at 

 which the instrument is set up is noted, the second and fourth columns being 

 for angles observed. In the cokmin marked " mean azimuth " the stations 

 observed are noted, under which also appears the mean reading to that station. 

 Always reading the angles from left to right, it is easy to see which is the 

 back sight and which are foresights. The instrument is set just over 360° 

 and set on the back sight, lower Hmb clamped, upper limb undamped, and 

 the foresight taken ; upper limb undamped, and telescope revolved end for 

 end on its axis and set on back sight ; upper limb undamped and foresight 

 taken, each time reading both verniers." 



" The reason tor setting the instrument just over 360° is to make it 

 necessary to read the angle instead of taking it for granted that the 

 vernier is at zero. The readings are then meaned "B" vernier over "A" 

 vernier, and then again B A and A B, the result of which is the true mean 

 reading. Carrying this process through all the stations sighted, and deducting 

 the mean reading of back sight from the foresights, the true mean horizontal 

 angle is at once obtained. The underground stations are not more than 100 

 feet apart, partly because of chaining and because they are afterwards useful 

 in stope measuring." 



" In levelling the collimation method is used, rail and peg level being 

 taken at each station." 



* " The Mine Surveyor and His Work in the Witwatersrand District," vide 

 report of the South African Association for the Advancement of Science, 

 Johannesburg Meeting, 1904, pp. 393-401. 



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