CHAP, v.] USE OF THE SHIP FOR TRIANGULATION 157 



In Fig. 40, A, B, C, D, E, F, G are stations along the coast, 

 of which B and C are visible from each other. H, J, K, L, M, N 

 are ship's stations, at each of which simultaneous angles are 

 observed between the four theodohte stations nearest to the 

 ship from which she is at that moment shot up. The essential 

 conditions are that the two first and the two last ship stations 

 shall include observations to and from the first four and the 

 last four theodolite stations, and that proper care and judg- 

 ment are exercised in placing the ship so as to secure the best 



Fig. 40. ^ 



results, as explained in Example XIV. The method of cal- 

 culation is precisely the same as in that example, the principle 

 being the same in both cases. 



Having obtained by calculation the lengths of the sides, and 

 the angles connecting the shore stations, they may be plotted 

 without further calculation on an assumed scale which may 

 be verified later, when the astronomical positions of the 

 extremes of the survey are obtained. 



As the ship moves from one position to another, the officer 

 in the leading boat selects his next station, and occupies it 

 while the remainder close up in succession to the vacated 

 stations in readiness for shooting up the ship at the next 

 position. On vacating a station, the officer should leave a 

 note for the information of his successor, giving a description 

 of the zero he has used. 



