CHAP, v.] USE OF THE SHIP FOR TRIANGULATION 161 



and the summit of the island G are shot up and fixed on two 

 lines. 



The ship taking up a position at C and fixing herself on the 

 three points F, A, and B, a third shot is obtained to fix E. 



Taking up a position at D,. and fixing on the three points 

 E, A, and B, third shots are obtained to fix F and G. 



G/ 



Fig-- 43- 



The conspicuous summit of the island B is also shot in from 

 A, C, and D. 



It will be noted that the positions of the ship at C and D 

 are so placed that F and E are respectively nearly in line with 

 A in each case, and therefore, however acute may be the first 

 two lines to those peaks, the ship's position is not materially 

 affected by any uncertainty in their exact positions arising 

 therefrom. 



Example XXI. — Survey on large scale of a shoal from which 

 a distant conspicuous peah is in sight. 



In such a case, if the shoal happens to be a long narrow 

 ridge, the usual method of anchoring on it and starring round 

 the ship is inapplicable. 



11 



