i: HKATVM— Continued. 



Select an object C on tlu- horizon so that AC=90° as nearly 

 as possible. 



Select an object D on the horizon so that BD = 90° as nearly 

 as possible. 



Then A'C=AC' and in>. Bl). 



Measure CD. 



Then A'C+CB- B'D-^A'R', the angle required. 



Or AC+CD-BD-A'B' 



In practice the ideal conditions required are seldom or ever 

 found, and a few degrees divergence from 90° in selecting the 

 horizon marks will introduce error. The method can there- 

 fore only be regarded as an expedient which may be occasionally 

 useful. If the horizon marks shall be on opposite sides of the 

 elevated object, the same reasoning would apply, but the 

 angle between the horizon marks being in that case very large, 

 it M^ould have to be measured by means of an intermediate 

 mark. If forced to use the sextant for triangulation another 

 means mav be used. 



