Stránka:roll 1910.djvu/84

68 BOY SCOUTS OF AMERICA To make a right angle, make a triangle whose sides are ex- actly 6, 8, and lo feet or inches each (or multiples of these). The angle opposite the lo must be a true right-angle. There are many ways of measuring distance across rivers, etc., without crossing. The simplest, perhaps, is by the equi- lateral triangle. Cut three poles of exactly equal length; peg them together into a triangle. Lay this on the bank of the river so one side points to some point on the opposite bank. Drive in three pegs to mark the exact points of this triangle (A,B,C). Then move it along the bank until you find a place (F,E,G) where its base is on line with the two pegs, w^here the base used to be, and one side in line with the point across the river (D). The width of the river is seven-eighths of the base of this great tri- angle. Another method is by the isosceles triangle. Make a right- angled triangle as above, with sides 6, 8, and lo feet (A,B,C) ; then, after firmly fixing the right-angle, cut down the 8-foot side to 6 feet, and saw off the lo-foot side to fit. Place this with the side D B on the river bank in line with the sight object (X) across. Put three pegs to mark the three corner places. Then take the triangle along the bank in the direction of C until C D'