Fig. 75. The Surveying Instrument Complete. tacked a cord to the center of the tripod head, and attached a good-sized sinker to its lower end. In connection with this plumb line we occasionally used a protractor consisting of a semicircle of cardboard 5 inches in diameter, on which the degrees of the circle
Fig. 76. The Protractor. were marked off with radiating lines, as illustrated in Fig. 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.
Surveyor’s Chain.
Fig. 77. The Surveyor’s Chain.
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
