122 HYDROGRAPHIC SURVEYING 



are determined by means of the tangents of the angles they 

 are making with each other. Let BA, Fig. 16, be a line of a 

 traverse from which an angle of 30 15' is to be turned to the 



left at B. Lay off BC 



A ? f-^ p^- 1 JD equal to any convenient 



distance, say 10 in., and 

 draw CC' perpendicular to 

 the left of BA. From a 

 table of natural functions 

 FlG * lf the tangent of 30 15' is 



taken as .58318, which, multiplied by the distance BC in 

 this case 10 gives the length CC', which is 5.83 in. This 

 length is laid off as CC' and the line BC' gives the desired 

 direction. 



To plat an obtuse angle as DEC', Fig. 16, turned off to the 

 right of ED, produce DB and construct the supplement 

 ABC, which is 180-DJ3C', as before. 



HYDROGRAPHIC SURVEYING 



SURVEY OF THE OUTLINE OF A BODY 

 OF WATER 



Hydrographic surveying is the process of surveying a body of 

 water with a view of obtaining the outline of its shore, the 



FIG. 1 



topography of its bottom, and the volume of the body of 

 water. 



