INTRODUCTION. 53 



of the mountains, in the manner of engineers. 

 Many works that treat on surveying, give sufficient 

 information respecting the representation and cha- 

 racteristic indication of the single parts, as trees, 

 woods, rocks, and the best mode of etching 

 mountains. 



To avoid confusion, it is more convenient, in 

 the whole drawing, to pay no regard to the vari- 

 ation of the compass, but to lay down all the 

 rhumbs, according to the uncorrected compass ; 

 when the work is finished, the meridians and pa- 

 rallels, beginning at the centre, are turned as 

 much as the angle of the variation at that part 

 amounts to. 



The survey of bays, roads, and harbours, differs 

 from the general business of surveying a coast, 

 so far only, that the method of land-surveyors may 

 be more applied, and sometimes a base line be 

 measured on shore, from the ends of which the 

 angles to tlie most important points are in like 

 manner taken with sextants. 



Sometimes, too, the distance of a ship lying at 

 anchor, from an object on shore, may be taken as 

 the basis of tlie triangles ; but in this case attention 

 must be paid to the changes which currents and 

 winds produce in the ship's place. 



The above described method of determining the 



o 



situation of the observer, by two or more angles, 

 taken from objects whose position is determined, 

 may be employed with peculiar advantage, when 



E 3 



