470 



Irrigation and Drainage 



of the instrument into the ground until it stands firmly, 

 and removing the corks, the water will come to a level 

 at once, so that if the operator stands back about 

 four feet he may sight across the two surfaces to 

 determine differences of level. If one uses this instm- 



Fig. 153. Four forms of drainage levels, with target-rods. 



ment with care, avoiding too long ranges, good work 

 may be done with it. 



A carpenter's level is sometimes mounted in a 

 similar manner and used, but it is not as safe a 

 device, because the level itself is liable to be in error 



