82. The bolt was then passed through the hole and threaded through
the nut, with its inner end bearing against the rod. The disk could thus
be held at any desired position by tightening up the bolt. A piece of
white paper was now pasted over the disk. The paper was marked off into
quarters, and opposite quarters were painted black so that it would be
easy to sight, from a distance, the exact center of the target.
[Illustration: Fig. 80. Cutting Out a Disk.]
[Illustration: Fig. 81. The Sighting Disk.]
[Illustration: Fig. 82. Nut Fastened in Block.]
A Simple Method of Surveying.
[Illustration: Fig. 83. Diagram of Our First Lesson in Surveying.]
Of course, none of us had studied trigonometry, but Uncle Ed devised a
very simple method by which we could determine distances quite accurately
without much figuring.
"If you will tell me the length of one side of a triangle and the angles
it makes with the other two sides," said Uncle Ed, "I'll tell you the
length of the other two sides and the size of the third angle. This is how
I will do it:
"Say the line is 6 inches long and one angle is 35 degrees, while the
other is 117 degrees. Let us draw a 6-inch straight line. This we will
call our base line.
Pages:
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74