186 HYDROGRAPHICAL SURVEYING [cHAr. \ ii 



Instru- If conveniently situated marks are plentiful^ the coast- 



mUre"* liner will only want his theodolite or sextant, or both, to take 

 his angles, and a station pointer and tracing-paper for plotting, 

 with protractor, etc. But if the coast has no objects off it 

 to seaward, and landmarks are also short or invisible from 

 the shore, he will require, very probably, a pole of measured 

 length, whereby to ascertain, by observing the angle subtended 

 by its extremities, the distance of points, etc., from one 

 another. 



A convenient form of this pole is described under " Ten- 

 Foot Pole," p. 40. 



Each assistant should have a copy of the Ten-Foot Pole 

 Table,* on a piece of cardboard, always in his angle-book, 

 ready for reference in the field. 

 General Let US suppose an officer landed with his board of points to 



Method of fio coast-hne. 

 Coast - 



Lining. He will start at some point already plotted on the chart, 



and will take angles from it to all the objects he can distin- 

 guish between him and the next fixed point, and beyond, if 

 necessary. 



He will then walk on to another spot, where he will make a 

 supplementary station, fixing liimseK by angles to known 

 points, either by theodolite or sextant, according to circum- 

 stances. 



He will then plot this, his No. 2 A, on his board, by station 

 pointer or tracing-paper, taking care to check his position 

 by his line from the first A, or by a third or " check " angle 

 from his present position. His No. 2 plotted, he will sketch 

 in on the board, the coast-hne between that and the first, 

 having noted any peculiarities as he walked along. 



The scale of the chart will largely influence the distance 

 betw^een the subsidiary stations to be made by the coast- 

 finer, as will also the character of the shore-line, and the 

 intended nature of the chart as to exactitude of detail. 



If the work is to be plotted on return on board, the system 

 is precisely the same, only the detail of coast between the 

 stations must be sketched in the angle-book, instead of directly 

 on to the board. 



Coast-hne may occasionally have to be sketched from a 

 * Appendix R. 



