138 HYDROGRAPHICAL SURVEYING [f'HAP. v. 



from G and W, and the diff. lat., from which we can obtain 

 the distances G 0, O W, and thence the mercatorial bearing 

 and distance G W. 



Example V. — Tivo inaccessible 'peaks visible from three posi- 

 tions, the intermediate position being visible from the other tivo, 

 which are invisible from each other. 



In Fig. 28, A, C are two stations at the extremes of a survey 

 J3^ng more or less in a meridional direction and invisible from 

 each other. 



Fig. 28 



A 



D 



C 



H is an intermediate station visible from A and C. 



B and D are two inaccessible peaks visible from A, H and C. 



Angles are observed at A, H and C. 



True bearings and latitudes at A and C. 



In A A B H, B H = A H . sin B A H . cosec A B H 

 In A C B H, B H = H C . sin B C H . cosec H B C 



AH sin B C H . sin A B H 



... = = M 



H C sin B A H . sin H B C 



AH sin A C H 

 In A A C H, — - = -— --,",-M 

 H C sin H A C 



Now, ACH+HAC=180°-AHC-a 

 ... ACH = a-HAC 



and sin A C H = sin a — H A C 



sin A C H 



.-. -— . sin HA C = sm a — H AC 



sin HAG 



