CANAL CONSTRUCTION. 



59 



taken with two rods to save time, the locator making 

 a sketch and estimating roughly his distance at the 

 same time. Having gone down the river far enough 

 to satisfy himself as to its fall, he turns at right angles 

 as nearly as may be and continues to level hillward 

 across the valley until he records the elevation assumed 

 as the head of the works. He will now be able to fix 



FIG. 7 — THE JACKSON LEVEL. 



the location of any chosen grade upon the line of his 

 cross levels according to his estimated distance, and is 

 therefore also in a position to estimate approximately 

 the rate of his grade. He knows from his sketch and 

 estimated distance what area of the valley is behind him 

 on the up-stream side bounded by the river, by the 

 canal, and by the line of his cross levels. 



The next operation is to turn again at right angle 

 and continue leveling down the valley more or less upon 



