PRIMARY TRAVERSES. 



75 



llEoDETir < 'ooKOINATES. 



Computation of Azimuth a, in Book 67, page 4. 



Spherical angle and distance = K, in Book 04. page 12, lnangle No. 3. 

 Station; Computed by H. M. W. 



When the lines are not more than twenty miles in length, the equation 

 for latitude may be simplified without appreciable error by dropping the 

 last two terms. 



TRAVERSE LINES FOR PRIMARY CONTROL. 



In level country, especially if it is covered with forests, it is very expen- 

 sive to carry on triangnlation, and in some cases practically impossible to 

 do so. Under such circumstances the only means of obtaining an adequate 

 control for maps is by means of traverse lines. 



A traverse line consists of a series of direction and distance measure- 

 ments. Each course, as the direction and the accompanying distance are 

 called, depends upon the one immediately preceding it, and a continuous 

 chain is thus formed. Traverse lines are largely used in the topographic 

 work proper for making minor locations. The primary traverse differs 

 from these only in the fact that it is much more elaborately executed. 



The initial point of a primary traverse must be located either by 

 triangnlation or by astronomic, determinations. The end of the line should, 



