STADIA AND PLANE-TABLE SURVEYING 111 



table at D, Fig. o; orient it approximately by the eye, and plat 

 the point d and the lines dc', da', and db'. Then move the table 

 to C and. orient it with reference to the line CD by placing 

 the edge of the ruler on the line c'd and directing the telescope 

 to station D. Through any point c" on the line c'd plat the 

 lines of sight to B and A , the intersections of which with da' and 

 db' give, respectively, the points a" and b". The line a"b" is 

 then parallel to AB. Now place the edge of the ruler on the 



Plane r >/e &/C 

 (a) 



FIG. 5 



line a"b" and set in this line a mark at a point at least 500 ft. 

 from C, thereby establishing a long line parallel to AB. The 

 board is now undamped, and, with the edge of the ruler on 

 the line ab, it is turned horizontally until the line of sight 

 bisects the mark, thereby making ab parallel to AB. The table 

 is then again clamped, and, with the ruler edge in contact with 

 a and b in turn, the telescope is directed to the points A and B 

 and the lines ca and cb are drawn. The intersection of these 

 lines will give the platted position of the point c. 



