Εικόνες σελίδας
PDF

SECTION IV. of OFF-SETs.

IN taking surveys it is unnecessary and unusual to make a station at every angular point, because , the field work can be taken with much greater expedition, by using offsets and intersections, and with equal certainty; especially where creeks, &c. bound the survey.

Off-sets are perpendicular lines drawn or measured from the angular points of the land, that

lie on the right or left hand to the stationary distance, thus :

PL. 11...fig. 2.

Let the black lines represent the boundaries of a farm or township: and let 1 be the first station;

then if you have a good view to 2, omit the angular points between 1 and 2, and take the bearing

and length of the stationary line 1, 2, and insert them in your field-book: but in chaining from 1 to 2, stop at d opposite the angular point a, and in your field-book insert the distance from 1 to d, which admit to be 4C. 25L. as well as the measure of the off-set ad, which admit to be 10. 12L. thus: by the side of your field-book in a line with the first station, say at 4C. 25L. L. 10. 12L.

that is, at 4C. 25L. there is an off-set to the left. hand of 10. 12L.

[ocr errors]

This done, proceed on your distance line to e opposite to the angle b, and measure ob, supposing then I e to be 7C. 40L, and eb 3.C. 40L, say (still in a line with the first station in your field-book) “ at 70.40L. L. 3C 40L.” That is, at 70.40L. there is an off-set to the left of 3C. 40L, proceed then with your distance line to f opposite to the * c, and measure fe : suppose then I f to be 13C. and felC. 25L. say in the same line as before, at 13C. L. 10. 25L. Then proceed from f to 2, and you will have the measure of the entire stationary line 1, 2, which insert in its proper co

lumn by the bearing.

In taking offsets, it is necessary to have a perch chain, or a staff of half a perch, divided into links for measuring them; for by these means the chain in the stationary line is undisturbed, and the number of chains and links in that line from whence, or to which, the offsets are taken, may be readily known. . . . .

Having arrived at the second station, if you find your view will carry you to 3, take the bearing from 2 to 3, and in measuring the distacce line, stop at l opposite g; admit 2l to be 40. 10L. and the offset lg 1C. 20L. then in a line with the second station in your field-book, say at 4C. 10L. R. 1C. 20L. that is, the offset is a right hand one of 1C. 20L. Again at m, which suppose to be 10C. 25L. from 2; take the off-set mb of IC. 15L, and in a line with the second station, say at 10C. 25L. R. 10. 15I. In the same line when you come to the boundary at i, insert the distance 2i, 13C. 10L. thus, at 13C. 10L. 0; that is, at 13C. 10L. there is no off-set. At n, which is 15C. from 2, take the off-set mk 45L. and still opposite to the second station say at 15C. I. 45. L.

Let the line, 3, 6, represent the boundary, which by means of water, briers, or any other impediment, cannot be measured. In this case make one or more stations within or without the land, where the distances may be measured, and draw a line from the beginning of the first to the end of the last distance, thus; make stations at 3, 4, and 5, taking the bearings, and measuring the distances as usual, which insert in your field-book, and draw a mark like one side of a parenthesis, from the third to the fifth station, to show that a line drawn from the third station to the farthest end of the fifth stationary line will express the boundary. . Thus,

No. Sta. Deg. Ch. L.

s 3 172; 5.45

4 200 13.25

U5 250 3.36 Suppose the point p of the boundary to be inaccessible by means of the lines 6p or p7, being overflowed, or that a quarry, furze, &c. might prevent your taking their lengths: in this case take the bearing of the line 6, 7, which insert opposite to the sixth station in your field-book with the other bearing; then direct the index to the point p, and insert its bearings on the left side of the field-book, opposite to the sixth station, annexing thereto the words Int, for boundary ; and having measured and inserted the distance 6, 7, set the index in the direction of the line 7p, and insert its bearing on the left of the seventh station of the field-book, annexing thereto the words Int. jor boundary: the crossing or intersection of these two bearings will determine the point p, and of

course the boundary 6p? is also determined. If your view will then reach in the first station,

[ocr errors]

take its bearing, stationary line, and off-sets as before, and you have the field-book completed. Thus,

[merged small][graphic][subsumed][ocr errors][ocr errors][ocr errors][ocr errors][subsumed][subsumed][ocr errors][subsumed]

If you would lay down a tower, house, or any other remarkable object in its proper place; from any two stations, take bearings to the object, and their intersection will determine the place where you are to insert it, in the manner that the tower is set out in the figure, from the intersection taken at the first and second stations of the above

field book.

A protraction of this will render all plain, on which lay off all your offsets and intersections, and proceed to find the content by any of the methods in section the 4th.

[merged small][ocr errors][ocr errors][ocr errors][graphic]
« ΠροηγούμενηΣυνέχεια »