CHAP, v.] USE OF THE SHIP FOR TRIANGULATION 155 



the first station was made. For this purpose a rough plot may 

 be made to get the approximate distances, from which, as 

 explained on p. 92, the " false station " can be calculated 

 and the necessary corrections applied to the angles obtained 

 at the ship to the beacons at each of her positions. 



Similarly, the ship in each position may be referred to the 

 original spot that the beacon occupied, and the necessary 

 correction applied to each of her angles. 



Thus the ship's angles to the beacons will receive a double 

 correction — (1) that due to small movement of the beacons ; 

 (2) that due to the angles at the ship not having been observed 

 at the original positions of the beacons. 



The ship's angles between the shore stations will require 

 correction for the latter cause only. 



The more frequently pairs of stations along the coast are 

 visible from each other, the less troublesome and more correct 

 the calculation becomes. 



True bearings observed from one coast station to another on 

 those occasions when they are visible, compared with the true 

 bearings of those stations worked up from former true bearings 

 through the calculation, will keep a satisfactory check upon 

 the work. 



Having corrected the angles for " false station " and tested Caicuia 

 all the complete triangles, the calculation may be proceeded with. *^°^- 



Assuming the stations B and C to be intervisible, and the 

 side B C= 10,000 units, 



In A B J C, find B J, C J. 



In A H J A, find H A. 



In A H B J, find H B, H J. 



In A H A B, given H A, H B, and Z A H B, find Z « H A B, 



H B A, and A B. 

 In A J C K, find J K, C K. 

 In A J K D, find K D. 

 In A C K D, given K C, K D, Z C K D, find Z « K C D, 



K D C, and C D. 

 In A D K L, find K L, D L. 

 In A K L E, find L E. 

 In A D L E, given L D, L E, Z D L E, find Z « L D E, 



LED, and D E. 

 In A L E M, find L M, M E. 



