CHAIN SURVEYING 29 



a sample of notes of a chain survey. The right-hand page is 

 used for sketches and remarks. The line that is being run is 

 commonly represented by the red center line. In case more 

 room is needed for sketching, the line that is being run may be 

 represented by a line drawn on one side of the center line of 

 the page and parallel to it. In sketching, it is better to face 

 in the direction in which the line is being measured and to rep- 

 resent the line as running from the bottom to the top of the 

 page in the notebook. 



FIELD PROBLEMS 



To Run a Line Over a Hill When the Ends of the Line Are 

 Invisible From Each Other. The points A and B, Fig. 1, are 

 supposed to be on op- 

 posite sides of a hill, 

 and to be invisible from 

 each other. It is desired 

 to run a line between 

 them, or to locate some 

 intermediate points. 



Having set two poles p IG 



at A and B, two flag- 

 men with poles station themselves at C and D, approximately 

 in line with A and B, and in such positions that the poles at B 

 and D are visible from C, and those at C and A are visible from 

 D. The flagman at C lines in the flagrn an at D between C and B, 

 and then the flagman at D lines in that at C between D and A, 

 Then the flagman at C again lines in that at D, and so on, 

 until C is in line between D and A at the same time that D 

 is in line between C and B. The points C and D will then be 

 in line with A and B. 



To Erect a Perpendicular to a Line at a Given Point. Let 

 it be required to erect a perpendicular to the line AB at the 

 point B, Fig. 2. A triangle whose sides are in the proportion 

 of 3, 4, and 5 is a right triangle, the longest side being the 

 hypotenuse; for 5*= I 2 +3*. The following method is based 

 on this principle: Lay off on BA a distance BC of 30 ft. 

 (or li.)- Fix one end of the chain at one of the extremities 



