88 A MANUAL OF TOPOGRAPHIC METHODS. 



his tract properly platted upon his plane-table sheet, or, if these can not be 

 furnished, with such descriptions of them as are necessary to (-liable him to 

 recognize them and close his lines upon them or connect with them by tri- 

 angulation. He is furnished with a horse and buggy or buckboard, traverse 

 plane table, and aneroid. He has no rodman, but is expected to sight natural 

 objects. Setting up his instrument at his initial station, he levels it roughly 

 by means of the tripod legs, orients it by turning the table until the com- 

 pass needle is on the zero mark in the compass box, then, marking a point 

 on the paper to represent his initial station, and placing his alidade upon it, 

 he points it to an object selected as his second station, and draws a line in 

 that direction. Driving along the road he passes the point sighted at, noting 

 the distance to it by the reading of the odometer, or the count of the revolu- 

 tions of the wheel, and the height as recorded by the aneroid, and passes on, 

 selecting some point from which he can see the point sighted at, There he 

 stops, sets up his table as before, orients it, and sights upon the same signal 

 which he sighted from his initial station. He plots the distance to the signal 

 along the sight line from his initial station; then from the location of the sig- 

 nal as thus established he plots Ins second station by the distance measure- 

 ment and the reverse of the observed direction. In this way the work pro- 

 gresses, a hundred stations or more being occupied in the course of the day. 

 In this work one should aim to make as few stations and to take as long 

 sights as possible consistent with accuracy. Bends of the road between 

 stations can be sketched with all needful accuracy. 



During the progress of the work all points off the line which are capa- 

 ble of being located by intersection must be located by sights taken from 

 stations, and special care must be taken to connect them with the points 

 located by the secondary triangulation, in order to afford as many checks as 

 possible to the accuracy of the traverse line. 



Traverse lines should close with but trifling error — an eighth of an inch 

 upon the paper in a distance of 10 or 12 miles is as great an error as should 

 be permitted — and all errors of closure should be shown. No line should 

 be arbitrarily closed on the traverse sheet. 



The traverse man should sketch or locate all country houses, should 

 note all road intersections and all railroad crossings, specifying by simple 



