PLANE TRlGOtfoME'fllt. 49 
front tliis I subtracted 30 feet, the distance from the Water, and this gave 
me the breadth of the river, 190 feet. 
(3.) In order to measure the breadth of a river I set up a mark, A 
(Fig. 3), close to the water; from this point I measured a base of 200 yardsj 
Fig. 2. 
parallel to the course of the river, and set up another mark, B. The angles, 
subtended by a rock on the opposite bank and each end of the base, were 
A 75°, B 40°. I then computed the breadth of the river by Case 1, 
Table 1L 
0 O 
£. A- 75 180 
ZB 40 115 
Fm."k n 5 Z. c == '65 
