CHAP, v.] USE OF THE SHIP FOR TRIANGULATION 159 



An observer is landed at A, and the ship anchors or moors 

 at F. A base by sound or range-finder is then measured 

 between A and F, and at a given signal the ship is shot up from 

 A, and the angles AFB, AFC, AFD observed at the ship. 



The ship then moves to E, and afterwards to G, simultaneous 

 angles being observed to the same points as before at both 

 stations. 



Calculate A B in A A F B, and G B in A A B G. 



The true bearing of B will be observed from A. 



Intermediate points between D and B and A and C may be 

 shot in from the ship's stations, the observer being careful to 

 use main points as zeros which will give the least change in 

 the angle due to any small movement of the ship whilst the 

 angles are being taken. 



Example XIX. — Triangulation of a strait with good natural 

 objects, by means of the ship under way and one theodolite 

 station on shore. 



The method illustrated by the previous example may be 

 used with good effect in the case of straits, such as Ward Hunt 

 Strait in New Guinea, where the summits of the hills are sharp 

 and well defined, though densely wooded. 



Fig. 42. 



If there are three or four observers on board the ship, the 

 main angles may be taken simultaneously, and the ship need 

 not anchor. A very large area may thus be rapidly triangu- 

 lated, its limitation being practically determined by the dis- 



