CHAP, v.] EXAMPLES OF IRREGULAR PLOTTING 133 



The point to be noted is that if the observation spots A and B 

 are plotted on their observed astronomical positions, C laid 

 down from its true bearings from A and B, and the inter- 

 mediate stations D, E, F from the direct shots to them and 

 their true bearings of C (laid down from C as reversed bearings 

 with convergency applied), we shall get an incorrect plot, 

 which will be at once evident on laying down lines to such a 

 point as Z visible from E, F, and B. 



The less the distance between A and B, the greater will be 

 this discrepancy, and the more hopeless will be the situation, 

 owing to the fact that probable errors in the astronomical 

 positions are quantities pecuHar to themselves, and are inde- 

 pendent of distance. 



Example II. — Two inaccessible objects visible from both ter- 

 minal astronomical positions linked by a chain of intermediate 

 stations visible from each other. 



In Fig. 25, A and B are two astronomical positions at the 

 extremes of a survey invisible from each other. C and D 



Fig. 25 



are two conspicuous inaccessible sharp peaks visible from A and 

 B, and from the intermediate stations E and F, which latter 

 are visible from each other and from A and B respectively. 



