CHAP. VI.] RUNNING SURVEY 177 



Having plotted the positions where astronomical observa- Repiot- 

 tions have been taken, if the intermediate stations are to be smLring 

 put in by bearing and distance, they must be squared in so as in- 

 to agree in total distance and bearing with the astronomical 

 positions. Thus, in Fig. 52, let A be the position from which 

 we start ; B, C, etc., to H, are positions of the ship as plotted 

 by course and distance on the rough chart ; a, h, are the same 

 positions as A, H, but as given by the astronomical observa- 

 tions. 



To bring the intermediate positions to agree with a, h, as 

 plotted on the graduated sheet, we join A H and a h. Drop 

 perpendiculars from B, C, etc., to the normal line A H. With 

 the proportional compasses set to correspond to the different 

 lengths a h, A H, measure the corresponding distances along 

 a h for the points where the perpendiculars will cut, and lay 

 off perpendiculars along which the corresponding distances can 

 be measured, and so we obtain b, c, d, etc. 



If any mountains have been observed both from A and H, 

 their positions should next be put down by their true bearings. 

 The angles taken from the first positions are now laid off, and 

 as objects are fixed, they can be used as checks to the next 

 positions. If we can rely upon the bearings taken to the 

 mountains we shall use them to fix the intermediate positions 

 in preference to course and distance, so that b, c, etc., may be 

 again shifted, especially if the ship has not been accurately 

 steered on her courses, or we have reason to think currents 

 have varied at different parts of our run. 



Nothing will agree exactly in a running survey of this kind. No Ex- 

 but a very fair approximation to the relative positions of expected, 

 conspicuous objects may be got. 



The amount of detail possible will not be very great, but Amount 

 will vary with the quickness and accuracy of eye and hand 

 of the officer sketching it in. There is nothing that requires 

 the knack which distinguishes a good surveyor so much as 

 this sketching in fairly accurately of a coast-line in a running 

 survey, and good judgment as to depth of bays, and other 

 points that must be mainly put in by eye, is most valuable. 



It is well to have one officer aloft, who will be able to get 

 a better view of river-mouths, etc., and make little sketches 

 of bits not seen from deck. He can also take angles to objects 



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