HINTS TO TftAtELLEM 
50 
(4.) To ascertain the height of an inaccessible point, A (Fig. 4), abof @ 
my position C, I measured its angle of elevation with a theodolite, and 
Fig. 4. 
D 
found it to be 40°: as a river behind me prevented my taking a base in 
that direction, I measured one of 200 yards to the left of 0 and set up a 
