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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1873 Excerpt: ... Theoretically, the most accurate manner of using the Theodolite for this purpose, is that in which we are altogether independent of the magnetic needle. In this system, the direction of all the forward angles has reference to the triangulation, and the side of the triangle to which they are referred is termed the "zero line," or directing line. In illustration of this method, a page of a Field Book, and the corresponding plan drawn to the scale of 12 inches to a mile, are shown in Plate VI. The different points at which the Theodolite has to be set up in traversing to observe the forward angle, are prefixed in the Field Book with the sign (c), and in describing the process of traversing here, they will be alluded to by that sign. In order to avoid confusion, the whole of the triangulation is not shown, but only the Stations A, T, and M. Having elected to commence the traversing at a convenient Station A, and selected the side A T as the "zero line" set up the Theodolite exactly over that Station, adjusted to read horizontal angles (Page 37), and send an assistant to hold a pole or flag at (c) I., where the road changes its direction. Adjust the cross hairs of the Theodolite on T (zero line), by lower clamping and micrometer screws, release the vernier plate and bisect the foot of the pole at 0 I.; the angle recorded by the vernier on the horizontal circle is 251 15'. This is entered in the chain column as the forward angle. Perpendicular offsets are then measured with the chain (or wand used for the purpose), the sides of the road being distant 10 links on the left, and 98 on the right. We then measure forwards in a direct line towards (c) I., at 150 links distance we are opposite the corner of an enclosure on the left, and
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