158 



HYDROGRAPHICAL SURVEYING [chap. v. 



Example XVII. — Triangulation of a low ivooded coastline by 

 means of the ship and floating beacons, landing being imprac- 

 ticable. 



Detailed description of this is unnecessary ; it need only be 

 remarked that the beacons should be laid down so as to form 

 equilateral triangles, and that very satisfactory results can be 

 obtained. Long stretches of the Liberian seaboard on the West 

 Coast of Africa have been triangulated in this manner, observa- 

 tion spots on shore being selected at intervals of about 50 or 60 

 miles, where landing could be effected, and true bearings 

 obtained of objects as distant as possible wherever practicable. 



Advantage should be taken of any favourably situated con- 

 spicuous mountain-peak to revert to the methods described in 

 former examples. 



Example XVIII. — This illustrates the survey of the bar of a 

 river on the West Coast of Africa, such as that of the River Brass, 

 the ship and two observers only being available. 



In Fig. 41, A is a theodolite /t^ on the shore, so placed as to 

 see as far as possible along the coast in the direction of B, and 

 visible from D on the opposite entrance point of the river. 



Fig 41. 



A D will form the base for continuing the triangulation up the 

 river. B is a conspicuous tree about 6 miles distant, and 

 clearly recognisable from A, and also from the ship's stations 

 at E, F, G. C is another tree, also recognisable from the ship's 

 stations. 



