52 



ANGULAR SURVEYING 



forwards, set up, and oriented at the preceding point. The 

 instrumental operations in running this traverse are as follows: 

 The transit is first set up at A and oriented by setting the 

 vernier at 317 24 ' (azimuth of AF) and directing the tele- 

 scope, with the upper plate clamped, along AF, the point F 

 being marked by a flag. The lower clamp is then set, the 

 vernier clamp is loosened, the telescope is turned in azimuth 

 and directed to a flag held at B, and the vernier is read. The 



reading, which in this case is 75 17', is recorded as the azi- 

 muth of AB. As A is the initial point of the survey, com- 

 plete information as to how the instrument is oriented should 

 be described by means of a sketch or a written statement. 

 As a check, the magnetic bearing of AF and that of the last line 

 should be taken and recorded. Suppose the magnetic bearing 

 of AF to be N 40 10' W; as the true bearing is N 42 36' W, 

 the declination is 2 26' west, which should be noted. 



The instrument is now moved forwards, set up at B, and 

 oriented by making the reading of the vernier equal to the 

 azimuth of BA, which is equal to that of AB plus 180; that 

 is, 75 17' 4-180 = 255 17'. The upper clamp being set. the 

 telescope is directed to A; the lower clamp is set, the upper 

 clamp loosened, the telescope directed to C, and the vernier 

 read. The reading is found to be 89 30' which is recorded 

 as the azimuth of BC. The instrument is then moved to C, 



