CHAP. XX.] FIXING BY STATION POINTER 465 



Latitudes 0° to 65°, together with Methods of using Co- 

 ordinates " (sold by J. D. Potter, agent for sale of Admiralty 

 Charts). These tables, used in connection with the specimen 

 forms suggested for showing compactly the work necessary for 

 determining geodetic positions, greatly facilitates the labour of 

 computation. 



FIXING BY STATION POINTER WHEN ALL OR 

 ANY OF THE OBJECTS USED TO FIX WITH 

 ARE BEYOND THE LIMITS OF THE POINTER. 



By COMMAXDER H. P. DOUGLAS, R.N., Superintendent 

 OF Charts. 



During surveying operations it very often happens that, when 

 plotting positions, one or more of the objects observed fall 

 beyond the limits of the legs of the station pointer. 



The methods usually employed to overcome this difficulty 

 are either to make use of a ruler to align the leg or legs to the 

 distant point or points, or else to draw radiating hues from the 

 distant object, and then align the leg of the pointer to one of 

 these radial Unes. 



Neither of these methods is, at the best, satisfactory, but 

 the following method, which simply means reducing the scale, 

 appears more satisfactory, and is not, it is believed, generally 

 known. 



It is theoretically correct, and the only errors that can creep 

 in are caused by (1) the prolongation of a line, (2) careless plot- 

 ting, and (3) a bad fix. 



(2) and (3) are not recognised by the surveyor, and the error 

 due to (1) should be so small that the fix thus obtained is far 

 more satisfactory than the above-mentioned methods. 



It is generally known, when using certain objects to fix with, 

 whether any of them will fall beyond the limits of the legs of 

 the station pointer, and also approximately how much beyond. 



Therefore, joining the three objects that are being used for 

 fixing, divide the distance between them into |, -|, |, etc., as 

 may be necessary. Then, setting the observed angles on the 

 pointer, plot a position, using the centre object and the two 

 objects obtained by division. 



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