A treatise on land-surveying; comprising the theory developed from five elementary principles; and the practice with the chain alone, the compass, the transit, the theodolite, the plane table, &cIllustrated by four hundred engravings, and a magnetic chart . S 0 (267) The Compass itself may be used to plat bearings. Forthis purpose it must be attached to a square board so that the Nand S Hne of the compass box may be parallel to two oppositeedgesof the board. This is placed on the paper, and the box isturned till the needle points as it did when the first bearing wastaken. Then a Une drawn by o
A treatise on land-surveying; comprising the theory developed from five elementary principles; and the practice with the chain alone, the compass, the transit, the theodolite, the plane table, &cIllustrated by four hundred engravings, and a magnetic chart . S 0 (267) The Compass itself may be used to plat bearings. Forthis purpose it must be attached to a square board so that the Nand S Hne of the compass box may be parallel to two oppositeedgesof the board. This is placed on the paper, and the box isturned till the needle points as it did when the first bearing wastaken. Then a Une drawn by one edge of the bDard will be in aproper direction. Mark off its length, and plat the next and thesucceeding bearings in the same manner. -+ (268) When the plat of a survey does not close, it may becorrected as follows. Let Fig. i83. ABODE be the boundarylines platted according tothe given bearmgs anddistances, and suppose thatthe last course comes to E,instead of ending at A, asit should. Suppose alsothat there is no reason tosuspect any single greaterror, and that no one of the lines was measured over very rough 11. A<<1 162 COMPASS SURVEYIIVG. fPART ;iJ ground, or was specially uncertain in its direction wlien inaccuracy must then be distributed among all the lines in?proportion to their length. Each point in the figure, B, C, D, E, mustbe moved in a direction parallel to EA, by a certain distance whichis obtamed thus. Multiply the distance EA by the distance AB,and divide by the sum of all the courses. The quotient ydYL be thedistance BB. To get CC, multiply EA by AB + BC, and dividethe product by the same sum of aU the courses. To get DD, mul-taply EA by AB + BC + CD, and divide as before. So for anycourse, multiply by the sum of the lengths of that course and of allthose preceding it, and divide as before. Join the pomts thusobtained, and the closed polygon ABCDA will thus be formed,and wiU be the most probable plat of the given survey.* The method of La
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectsurveying, bookyear18
