146 HYDROGRAPHICAL SURVEYING [chap. v. 



attained by using the true bearing resulting from the astro- 

 nomical positions. 



Intermediate points may be shot in from other ship's posi- 

 tions fixed on theodolite lines from A and D or from D and B, 

 with a third shot back from C derived from the calculated 

 angle through either station. 



The observed astronomical positions should be adjusted to 

 the results by triangulation in respect to bearing. 



Example XII. — Two inaccessible objects visible from both 

 astronomical positions, irivisible from each other, and at such 

 distance apart that the ship cannot see both from a single position. 



In Fig. 35, A, B are the two terminal astronomical positions ; 

 C, D, two inaccessible objects visible from A and B ; E, F, ship's 

 positions visible from A and B respectively. The ship being 



Fig- 35- 



A 



shot up in her two positions, and angles at the ship being ob- 

 tained simultaneously between the shooting-up station and 

 C and D, we have sufficient data for calculation from which 

 the main points may be subsequently plotted. 



Assume B F = 10,000 units. 



(1) In A BFD, findDB, FD. 



(2) In A B F C, find C B, F C. 



