Mr Sang on Optimum Surveying. SSI 



would need to be added to the equation depending on dx ; 

 and so of any others. As now the sum of the equations would 

 no longer be zero, and as absolute terms would now be intro- 

 duced, there would be no need of, nor any room for, arbitrary 

 conditions. 



Again, for example, if several distances have been measured 

 at various parts of the survey, these also could be introduced. 

 Thus, if the distance, among others, from A to B had been 

 measured and found to be AB, with a chance of error a (3, the 

 terms 



2cosBA r . , „ , ) 



2 sin BA f , , , ) 



^^^''-^^ iN/(K-^B)^ + (2'A-2/B)^)-AB} 



. 2cosAB f ^^^^ > 



^ 2sinAB f ^ ^ > 



^y^;—--! same. J 



would need to be added to the proper equations. 



In this way there would be no distinction between the Base 

 and a base of verification. The computations would not be 

 carried on in one district from one base, in anotlier district from 

 another, there would be no particular set of trigons selected for 

 computation, and not a single observation would be omitted, or 

 even have too much or too little importance attached to it. 



There are still other cases in which this same method might 

 be useful ; one in particular, on account of its frequent occur- 

 rence in practice, I cannot omit to mention. 



When engaged in coast surveys, we have often to find the 

 position of a station by angles observed at the station itself. 

 For this purpose, a line of signals is made along the coast, and 

 the angles subtended by these are observed with a reflecting 

 circle. This is particularly useful in obtaining soundings, but 

 being susceptible of a great degree of precision, it is often used 

 for finer purposes. It is a matter of regret that, from the obli- 

 teration of the surveyors' marks on the hill tops, we are de- 

 prived of great facilities in fixing geographically the positions 

 of places. 



