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 . om the platto the same scale, in the manner explained in the next chapter, theresult must be multiplied by 10 times 10. Tliis is called by oldSurveyors Raising the scale, or Restoring true measure. (52) Sectoral Scales. The Sector, (called by the French Compass of Proportion), is an instrument sometimes convenientfor obtaining a scale of eq
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 . om the platto the same scale, in the manner explained in the next chapter, theresult must be multiplied by 10 times 10. Tliis is called by oldSurveyors Raising the scale, or Restoring true measure. (52) Sectoral Scales. The Sector, (called by the French Compass of Proportion), is an instrument sometimes convenientfor obtaining a scale of equal parts. It is in two portions, turningon a hinge, like a carpenters pocket rule. It contains a greatnumber of scales, but the one intended for this use is lettered at itsends L in Enghsh instruments, and consists of two lines runningfrom the centre to the ends of the scale, and each di^dded into tenequal parts, each of which is again subdivided into 10, so that eaclileg of the scale contains 100 Fg- 24. equal parts. To illustrateits use, suppose that a scaleof 7 chains to 1 inch is re-quued. Take 1 inch in thedividers, and open the sec-tor till this distance will justreach from the 7 on one legto the 7 on the other. Thesector is then set for this. CHAP. Ill] Drawing the Map. 87 scale, and the angle of its opening must not be again let a distance of 580 links be required. Open the div-ideratill the J reach from 58 to 58 on the two legs, as in the dotted linein the figure, and it is the required distance. Again, suppose thata scale of 2| chains to one inch is desired. Open the sector sothat 1 inch shall extend from 25 to 25. Any other scale may beobtained in the same manner. Conversely, the length of any known line to any desired scalecan thus be readily determined. (53) Whatever scale may be adopted for platting the survey, itshould be drawn on the map, both for convenience of reference,and in order that the contraction and expansion, caused by changesin the quant
Size: 1779px × 1404px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1870, booksubjectsurveying, bookyear18
