152 HYDROGRAPHICAL SURVEYING [chap. v. 



rection found in a similar manner should be applied to the 



angle E H B. 



With these precautions considerable accuracy should be 



attained. 



In order to ensure that no mistakes have been made in the 



angles, it is advisable to repeat the observations three times at 



each position. 

 Caicuia- Having corrected and tabulated each set of angles taken 

 tion. £qj. pacii position, three separate values of the final results 



for plotting A, B, C, and D can be deduced, and the mean 



adopted. 



In A A B E, given A B or B E as a base, find E B. 



In A E B F, find E F, B F. 



In A E F C, find E C, F C. 



In A B C F, given B F, F C, and Z B F C, find B C, 



Z ^ F B C, B C F. 

 In A E B G, find G E, G B. ] Compare G B found in 

 In A B G C, find G C, G B. J different triangles. 



At B, the angle to C being known, and at C the angle to B 

 also being known, we can test the angles in the triangle B H C, 

 which affords a good check ; similarly, A B G C can be 

 tested. 



In A E G C, given Z « E G C, E C G, and E C, find G C. 



Compare G C with the value found in A B G C. 

 In A E H C, given E C, Z « E C H, E H C, find C H, 



E H. 

 In A E H B, given EH, Z « E H B, E B H, find B H. 

 In A B H C, given B C and the angles, find B H, C H. 



Compare values of B H, C H found previously. 

 In A G C H, given C G, C H, and Z G C H, find G H. 



Z « C G H, C H G. 



We have now the means of testing A D G H, haAnng all its 

 angles. 



In A D G H, given G H, and the angles, find H D, 



GD. 

 In A H C D, given C H, H D, and Z C H D, find C D 



and Z « H C D, H D C. 



