An Underground Traverse. 405 



(4) Fourth Method. — At 614 S backsight on cross-cut plug 604 x. 



&c. 



Note: " Clamp the vernier to zero and set on the back point, 

 unclamp upper plate and sight to forward point and book the 

 reading as " positive angle." 



2. " Clamp the vernier to zero and set on the forward point, 

 unclamp upper plate and sight to back point and book the reading 

 as " negative angle." 



3. " Tape distance to back point and book as " back distance." 



4. " Tape distance to forward point and book as " forward 

 distance. ' ' 



" Repeat operation at every point of traverse." 



" Distances are taped horizontally, the plumb bob being raised 

 or lowered till approximately on a level with the instrument." 



" Measure every line twice, first as a forward distance and 

 then as a back distance; if there is any difference take the mean." 



(5) Fifth Method.— Main Reef West Drive. 5th April, 1905. 



1127 M- 1128 M = ii29 M 



+ 160 22' Length of plumb at 1127 = 2-46 



- 199 38' do. 1128 = 3-76 



Backsight 93 42' do. 1129 = 2-81 



266 18' 



Distance =5396 Rail level at 1127 = 6-75 



do. 1128 = 7-21 



Foresight 89 05' do. 1129 = 6.36 



270 55' 

 Distance = 65 21 



" Set up instrument at say peg 11 28 M and set vernier at 0°. 

 Clamp spindle on back sight (1127 M) and read vertical angle, say 

 93° 42'. Unclamp vernier and read angle 11 27 — 11 28 — 11 29 

 which for convenience call x, also read fore vertical as 89° 05' 



" Now, plunge telescope, set vernier at 0°, and clamp on 

 foresight (11 29), and again read fore vertical as 270° 55. If 

 instrument is in adjustment the sum of both fore verticals will be 



