48 
HINTS TO TRAVELLERS. 
(1.) Wishing to ascertain the height of a point C (Fig. 1), which could 
not be approached nearer than B, I observed the angle of altitudo 
C B D = 46°, and measured the distance from B to A= 200 feet, at which 
place I found the angle CAB- 29°. 
Having found the Z A C B as above, I then computed the length of B C 
by Case 1, Table II. Then, as the Z C I) B = 90°, I computed the height 
C D by Case 1, Table I . 
Fig. 1 . 
c 
(2.) To measure the breadth of a river when standing at B (Fig. 2), a 
short distance from it, I sent on a man with a staff to a distance which I 
judged to be greater than the breadth of the river. I then motioned him 
to the right and left until he was in such a position that the reflected image 
of the staff was shown exactly over a tree on the opposite bank (as seen 
directly), when I had 90° on the arc of my sextant: having set my sextant 
to 45°, I walked in a straight line towards the staff until I reached a 
position, A, where, on looking through my sextant, I saw the reflected 
image of the tree shown exactly over a mark set up at B (as seen directly ). 
I then measured the distance from A to B, which I found to be 220 feet; 
