EXTEMPORARY MEASUREMENTS, 
53 
Extemporary Measurements. 
To set off a Bight Angle from any point on the ground by means 
of a Hope, 
To set off, from any point A, a line at right angles to a given direction, 
as A E, measure an equal distance on each side of A, in the same 
straight line as A E, this equal distance being 
about one-fourth of the length of the rope . Let C 
and D be these points. Fasten the ends of the 
rope at C and D, and having ascertained the 
centre of the rope by doubling it, the centre 
should be drawn out towards B, until D B and 
0 B are tight. Then E A B will be a right 
angle; therefore, as we are thus able to set off 
a right augle to any line, the distance of any o 
inaccessible object may be obtained by either of 
the three following ways 
To find the Distance of an inaccessible object 
with a Measuring Line. 
By Fig. 1, p. 54.—From the line A D 
measure off the perpendiculars A C, D E, 
ranging the point 0 in line with E B, then 
AB s 
AC x AD 
D E ~ A O’ 
By Fig. 2, p. 54.—Fix any convenient points H and K. Join H K and 
bisect it in J; make J L = J F, and range I in line with H L and with 
J G; then L I - F G. 
By Fig. 3, p. 54.—Set off 0 M at right angles to 0 P* and M N at 
0 M 2 
right angles to M P; then 0 P ~ . 
Rough Methods of Measuring. 
Rough angular measurements may be taken by the span at arm’s 
length. From the end of the thumb to the end of the middle finger 
gubtepds an angle of 15°; the full span to the end of the little finger 
