CHAP. VII.] COAST-LINING 187 



boat pulling -along the shore, fixing and shooting up any 

 natural object on the beach from positions at anchor. Care 

 is necessary to select suitable points as zeros, so that any small 

 movement of the boat will produce the least amount of 

 error (see p. 168). 



When the coast-liner sees that at the next station he will Using 

 not be able to fix himself by angles, he must use his ten-foot poJ^^°°* 

 pole, sending a man on ^vith it with instructions where to 

 stand, or going on himself to some selected point to which he 

 will first take the angle ; leaving the pole behind with a man 

 at his present station, with directions, when signalled, to hold 

 the pole horizontal, and at right angles to the observer. 



To ensure the latter, either a rough pointer of some kind can 

 be attached to the centre of the pole, so as to project at right 

 angles, in which case the holder will be directed to point this 

 to the observer, or he will be told to sway it gently backwards 

 and forwards, and the observer will read the largest angle he 

 can measure. 



The angle observed, and the corresponding distance looked 

 out of the table, the latter is measured on the scale of the 

 chart, and applied by a pair of compasses, as a distance from 

 the last station along the line laid off from that last station 

 in the direction of the required station. 



If necessary, the whole coast can be carried on in this way ; 

 but if the marks are a long way apart, great care must be 

 taken in observing the angles on to the positions to be measured, 

 as there is no check on the work, and each error Avill be accumu- 

 lative. In this case the man must be sent on, and must mark 

 the exact place he stood when the angle was observed to him, 

 and the coast-liner must make his next station precisely on 

 that spot. 



A distant station or well-fixed object, not many degrees 

 from the line of coast, should, if possible, be used as a zero 

 at each position for shooting up the ten-foot pole. Errors in 

 bearing resulting from faulty distances are thus minimised. 

 A range-finder is preferable to a ten-foot pole for long distances. 



The azimuth compass may sometimes be employed in this 

 work with advantage. Any little error, when a properly fixed 

 station is reached, can be squared in. 



It will be understood that this ten-foot pole method is only 



