142 HYDROGRAPHICAL SURVEYING [chap. v. 



Assume A B = 10,000 units. 

 In A D A B, calculate A D. 

 In A C B A, calculate A C. 

 In A D C A, calculate D C. 



Knowing D C in units and also in feet, and A B in units, 

 find A B in feet by proportion. 



Example IX. — In this case it was desired to correct the pub- 

 lished cJiart of Bahia Blanca, and to plot points on the same scale. 



In Fig. 32, A and B were two well-defined summits about 

 20 miles apart, not visible from each other, being the only two 

 points on the chart that were recognisable. It was inconvenient 



Fig. 32. 



to visit B. D was a conspicuous tree. C is a station on a 

 coast-hill, and E a station on a sandbank, from both of which 

 stations all points were visible. At A angles to D, E, and C 

 were observed, and all angles observed at C and E. 



Assuming A D = 10,000 units, 



In A« A D C, D E C, C E B, calculate A C, C B. 

 In A A C B, given C A, C B, and Z A C B ; find /"CAB, 

 CB A. 



All the angles now being known, the points may be plotted 

 on the side A B taken from the published chart. 



