CHAP, v.] USE OF THE SHIP FOR TRIANGULATION 149 



is required to fix another station, C, further along the coast, 



no inshore points being available to carry on the triangulation, 



and C being visible from B. 



To find D, the best position for placing the ship, D B should 



ABC 

 roughly bisect angle ABC; and A D C= 180° — , or 



180°-AB D. 



Observers being stationed at A, B, C, the observer at B puts 

 up transit marks, if necessary, to give the ship the direction 

 of BD. 



The bearing of A B and D B being known, angle A B D is 

 the difference of those bearings, and the position on the line 

 D B can be picked up by the ship. 



Fig. 36. 



The ship hoists flag and dips in the usual manner when 

 simultaneous observations are made at A, B, and C, and 

 repeated as often as necessary. B C is calculated from A B 

 through D B, using the calculated angles at D. 



In the case of the station C, which it is required to fix, being 

 situated between the fixed stations A and B, as in Fig. 37, the 

 ship should be placed at D, so that D C bisects A C B and 

 A D B = 90°. 



Example XIV. — Illustrating the triangulation of a low wooded 

 coastline destitute of natural features, and of a general convex 

 form, by means of the ship and one floating beacon. 



In Fig. 38, A, B, C, D are A^ on the coastline, the general 

 convex form of which prevents their being visible from each 

 other, except in the case of A and B. 



