76. By holding the straight edge of this protractor against the
base of the tripod, and noting the number of degrees between the 90 degree
mark and the plumb line, we could tell at a glance at what angle from the
horizontal the instrument was tipped.
[Illustration: Fig. 73. The Tripod Head.]
[Illustration: Fig. 74. The Tripod Leg.]
[Illustration: Fig. 75. The Surveying Instrument Complete.]
[Illustration: Fig. 76. The protractor.]
Surveyor's Chain.
[Illustration: Fig. 77. The Surveyor's Chain.]
[Illustration: Fig. 78. Forming the Links.]
[Illustration: Fig. 79. A Double-Ringed Link.]
We made a surveyor's chain of wire links, each 12 inches long, instead of
7.92 inches, which is the length of a standard surveyor's link. The wire
we used was No. 16 galvanized iron, which was rather stiff and difficult
to bend. In order to make all the links of exactly the same size and shape
we used a form, around which they were bent. The form consisted of a
1-inch board in which two 1/2 inch holes were drilled, just 11-1/2 inches
apart, measured from their centers. An oak pin, 1/2 inch in diameter, was
driven into each hole and projected about an inch above the board. Two
blocks of oak were secured to the baseboard, just before each pin, as
shown in Fig.
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