CHAP. IV.] CALCULATING THE TRIANGULATION 105 



This convergency, and half of it, added respectively to the 

 bearing of B from A, will give the reverse bearing of A from 

 B, and the mercatorial bearing, thus : 



B from A = N. 69° 05' 00" W. 

 AfromB=S. 69° 16' 14" E. 



N. W. 



Mercatorial bearing ^ 69° 10' 37" _-- 



S. E. 



If this differs much from the rough mercatorial bearing, we 

 must recalculate the latitude of B before proceeding further, 

 but this should not be necessary. 



Then to calculate bearing of B E, we have the bearing of A 

 from B, just found, to start from. Adding the three angles, 

 A B H, H B C, C B E, to it, we shall get the bearing of E from 

 B. The convergency for B E is calculated in the same manner 

 as above, and we shall then have mercatorial bearing of B E. 

 Thus: 



A from B S. 69° 16' 14" E. 



A B H 38 51 47 



H B C 59 33 27 



C B E 72 40 31 



E from B S. 240 21 59 E. 



Or N. 60 21 59 W. 



I convergency .... 12 26 



Mercatorial bearing of N. „ W. 



^ — 60° 34' 26" - 



BE S. E. 



In like manner we must calculate the mercatorial bearing Appiica- 

 of all the sides we require, remembering that of the reverse ^°^ °^ 

 bearings, the bearing of the station nearest the pole from the gency. 

 one farthest from the pole is the smallest. In this case, then, 

 being in the northern hemisphere, where a bearing is measured 

 from the north point, the convergency is added to obtain the 

 reverse bearing. 



Having obtained the bearing of each side, we can calculate 

 the relative position of any two stations by working out the 

 traverse between them. 



