A complete treatise on practical land-surveying, in seven parts; . hen, will the groove b d pointto another at n. Reverse the direction of the grooves, so that b d may be inthe direction of m; then, if a c be in the direction of n, theinstrument is correct. THE OFFSET-STAFF. The Offset-Staff is an instrument used to measure shortdistances ; and may be in length. 10, 12, or 15 links. It wouldbe advisable to number the links from each end, on oppositesides, with the figures, 1, 2, 3, Sec. as the staff, thus marked,will be more convenient for use. Note.—As the Cross-Staff is sometimes thought inc
A complete treatise on practical land-surveying, in seven parts; . hen, will the groove b d pointto another at n. Reverse the direction of the grooves, so that b d may be inthe direction of m; then, if a c be in the direction of n, theinstrument is correct. THE OFFSET-STAFF. The Offset-Staff is an instrument used to measure shortdistances ; and may be in length. 10, 12, or 15 links. It wouldbe advisable to number the links from each end, on oppositesides, with the figures, 1, 2, 3, Sec. as the staff, thus marked,will be more convenient for use. Note.—As the Cross-Staff is sometimes thought incommodious, a smallpocket-cross may be so contrived as to be readily fixed, upon occasion, to theOffset-staff. This may be most expeditiously accomplished by means of a holemade through the cross, admitting the top of the staff, to the eighth link,counting from the bottom or piked end ; at which place there must beattached a small shoulder, upon which the cross will rest. Plate I. and/ ///r ? //>,//,////////sv/f// ^ Part II) LAND-SURVEYING. 35 THE COMPASS. The Compass is an instrument used by surveyors, to pointout the range or direction of lines; and also to shew the bear-ings of objects. The circumference of the card of the compasscontains 360°, and is divided into thirty-two equal parts, calledPoints, each containing 11° 15. Of these, the four principal (namely East, West, North, andSouth) are called Cardinal Points; from which the names ofthe others are derived. To the under-side of the card, and in the direction of its northand south lines, is attached a magnetic bar of hardened steel,called the Needle, by which the north-point is directed towardthe northern part of the horizon; and the other points, conse-quently, to their corresponding ones in the heavens. The card and needle are suspended on an upright pin, calledthe Supporter, which is fixed in the bottom of a brass, orwooden, box ; and the whole is covered with a plate
Size: 1582px × 1579px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, booki, bookpublisheretcetc, booksubjectsurveying
