MEASUREMENT OF DISTANCE 



17 



tance a e may be computed by traverse. If a e runs N and 

 S, the distance a e will be the latitude of the traverse, or, 

 stated in other words, it will be the sum of 

 the products of the cosines of the several 

 courses into their respective distances. The 

 departure of such a traverse should be zero. 

 Thus, if e is not visible from a, or if it is not 

 convenient to take the range a e, e may be 

 set when the sum of the departures figures 

 up 0. This process of surveying a lake or 

 river shore is called " meandering." It is the 

 method pursued in the United States land 

 surveys on considerable bodies of water. The 

 same method may also be employed to get 

 round a precipitous hill or some other inac- 

 cessible object. 



An example of the computation necessary 

 for solving a problem of this kind is given on 

 page 33. 



8. Method by 60 Angles. (G) A precipitous bluff or 

 impassable swamp may occasionally be passed most read- 

 ily in the following manner. With 

 the compass at a, lay off a 60 

 angle and run out a c, carefully 

 chaining. Next, making an angle 

 of 60 at c, run out c b to an equal 

 distance. Then, if the work has 

 been done accurately, b is in the 

 line and ab = a c = be. 



In working by any of these 

 methods it is better, if possible, 

 to set b in range by the compass 

 from a rather than to rely for the range on any process of 

 figuring or angulation. 



FIG. F 



6. STADIA MEASUREMENT 



A substitute for chaining, which has to some extent 

 been employed in forest land surveying and which deserves 



