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 . to four times their true proportional dimensions. Fis. 67. B 1500 0 1250 20 0 1000 0 30 750 5040 5002500A (116) The plat and Field-notes lA the position of two nouses,determined by offsets, are given below on a scale of 2 chains to 1inch. I I Fig. 68. B 250 to B 30 20 185150 Frojn A. 9050 0 10 ^ 10 ^ 30 (117) Double offsets are sometimes co
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 . to four times their true proportional dimensions. Fis. 67. B 1500 0 1250 20 0 1000 0 30 750 5040 5002500A (116) The plat and Field-notes lA the position of two nouses,determined by offsets, are given below on a scale of 2 chains to 1inch. I I Fig. 68. B 250 to B 30 20 185150 Frojn A. 9050 0 10 ^ 10 ^ 30 (117) Double offsets are sometimes convenient; and sometimestriple and quadruple ones. Below are given the notes and theplat, 1 chain to 1 inch, of a road of varying width, both sides ofwhich are determined by double offsets. It will be seen that theline AB crosses one side of the road at 160 links from A, and theother side of it at 220. CHAP. III.] Offsets. 77 Two methods of keeping the Field-notes are given. In the ifirstform, the offsets to each side of the road are given separately andconnected by the sign +. In the second form, the total distanceof the second offset is given, and the two measurements connectedby the word to. This is easier both for measuring and platting. Fig. 69. B 260 240 0 220 20 200 40 180 45 160 50+ 0 140 65+ 5 120 60+20 100 45+15 80 50+10 60 50+20 40 55+20 20 60+ 0 A 30+6010+705030100 B 260 240 0 220 20 200 40 180 45 160 50 to 0 140 60 to 5 120 70 to 20 100 60 to 15 80 60 to 10 60 70 to 20 40 75 to 20 20 60 to 0 A 30 to 9010 to 805030100 (118) These offsets may generally be taken with suflficient accura-cy by measuring them as nearly at right angles to the base line as theeye can estimate. The surveyor should stand by the chain, facingthe fence, at the place which he thinks opposite to the comer towhich he wishes to take an offset, and measure square to it bythe eye, which a little practice will enable him to do with muchcorrectness. 78 CHAIN SURVEYING. [part II The offsets may be measu
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectsurveying, bookyear18
