Implements. 4 i 



The foresight to station 2 is 2 feet, that is 2 feet less than 

 17, or 15 feet, which is the actual height of station 2. 

 The instrument having been shifted to b, the backsight to 

 station 2 is 8 feet, namely 8 feet higher than the actual 

 height of that station, or 23 feet, which is the height of 

 the instrument in the new position. The foresight to sta- 

 tion 3 is 1 foot, that is 1 foot less than the height of the 

 instrument ; the actual height of station 3 is therefore 22 

 feet. All the rest is calculated in the same manner. 

 Finally, foresights and backsights are summed up; if 

 the sum of the foresights is larger than that of the back- 

 sights, the last station is so much below the first one, and 



OU p.,j / " ; i ._j 



FIQ. 14.— HOW TO PLACE GRADE STAKES BY MEANS OF WATER-LEVEL. 



vice versa. In the present example, station 6 is 3 feet 

 higher than station 1. All the readings are here supposed 

 to be in even feet, something never occurring in actual 

 practice, but it makes the example easier to comprehend. 

 Very often the whole line can be levelled from one point, 

 and this greatly simplifies the matter. 



The water-level is also used in fixing grade stakes. 

 Supposing the continuous line in Figure 14 to represent the 

 rugged surface of an ill-made road, and the dotted line the 

 suggested improvement. A is a plane of reference or 

 " bench mark," and all stakes are placed so much higher or 

 lower than this mark as the dotted line indicates. Placing 



