Formation of Plantations 



39 



intersecting wire as seen in the eyesight or telescope. The 

 points thus determined on the stave are represented by 

 e and g, and these are termed level-points, or points equally 

 distant from the centre of the earth. Therefore the heights 



FIG. 1. SPIRIT LEVEL. 



a, e, and b, g, being read on the graduated staves, the 

 difference between them will give the relative heights of 

 the ground at a and b. Similar processes are repeated 

 with respect to the points b and c, and c and d, the instru- 



_. e ....... \2 



^ 



^^^ 



FIG. 2. METHOD OF LEVELLING. 



ment being placed at i and m, midway between them. 

 Usually the heights b g, c I and d n are inserted in a 

 column headed " Foresights," and the heights a e, b h, 

 c k and d n in a collateral column headed " Backsights." 



