Elements of surveying and leveling

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. 1883 Excerpt: ... might vitiate the whole survey. No angle less than 30 or more than 120 should be used; and even such angles should not be admitted when the locality can be so chosen as to prevent it. 245. If the triangulation is to be over a limited extent of country which has already been covered by a net-work of Primary Triangles, a side of one of these triangles should be used as a base. It is never good practice to measure a base line, when a side of a triangle of a previous survey is available; but if no such side can be obtained, then the selection of a proper site for a base-line forms one of the first objects of the preliminary reconnaissance. It should, if possible, be fixed on an open plain, free from surface encumbrance or freed from such. It must be so chosen that the surrounding signals may be distinctly seen from its extreme points; and hence those signals which mark points of the adjacent triangulation, should be selected with reference to the base. The length of the base should be suited to the magnitude of the survey. 246. In measuring a base-line, every possible precaution should be taken to insure accuracy. The line measured should be straight, to effect which it should be ranged out with the transit. The ends of the base should be marked by a stone sunk in the ground, with a copper bolt let into it and the exact point of beginning and ending fixed by the intersection of two lines cut into the head of the bolt. The measurement may be made with steel tape or rods. If a tape is used, it should be carefully drawn out each time to its standard length, and should be compared with a standard both before and after measurement, and correction made for its variation, if any, from standard. The mean of several measurements should be taken for the correct measurem...