PREPARATION OF THE DESIGN 83 



same column as the foresights. The actual height 

 of the dumpy 4-9 may be taken in passing as it 

 will indicate that the gradient from C to D is 

 not uniform. This is also an intermediate and 

 should be further remarked as "instrument" 

 with its distance (30 ft.) from C. Revolve the 

 telescope and read D 2-42, which is a foresight. 

 Change the position of the dumpy to 3, leaving 

 staff at D. Take backsight at D 1-2, and foresight 

 at E 9-5, which completes the line. A line paral- 

 lel to this is taken by using E as backsight, and the 

 first of the new line as foresight. In practice it is 

 convenient to plan out the ground in squares 50 ft. 

 each way, and take the levels in lines up and down. 



The field book now shows just the readings from 

 the staff in two columns, backsight and foresights, 

 and any necessary remarks. The next process is 



