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LAND

a

a

triangle, is always determined; but the position of the second side hj, does not become determined, till the third side jb is measured; then the position of both is determined, and the triangle may be constructed.

At the beginning of a line, to fix a loose line to the mark or place measured from, the sign of turning to the right or left hand must be added, as at k in the second, and ; in the third line; otherwise a stranger, when laying down the vork, may as easily construct the triangle hjb on the wrong side of the line ab, as on the right one: but this error cannot be fallen into, if the sign above named be carefully observed.

In choosing a line to fix a loose one, care must be taken that it does not make a very acute or obtuse angle; as in the triangle por, by the angle at B being very obtuse, a small deviation from truth, even the breadth of a point at p or r, would make the error at B, when constructed, very considerable; but by constructing the triangle PBq, such a deviation is of no consequence.

Where the words leave off are written in the field-book, it signifies that the taking of offsets is from thence discontinued, and of course something is wanting between that and the next offset, to be afterwards determined by measuring some other line.

The field-book for this method, and the plan drawn from it, are contained in the four following pages, engraven on copper plates; answerable to which the pupil is to draw a plan from the measures in the field-book, of a larger size, viz. to a scale of a double size will be convenient, such a scale being also found on most instruments. In doing this, begin at the commencement of the field-book, or bottom of the first page, and draw the first line ah in any direction at pleasure, and then the next two sides of the first triangle bhj by sweeping intersected arcs; and so all the triangles in the same manner, after each other in their order; and afterwards setting the perpendicular and other offsets at their proper places, and through the ends of them drawing the bounding fences.

Note. That the field-book begins at the bottom of the first page, and reads up to the top; hence it goes to the bottom of the next page, and to the top; and thence it passes from the bottom of the third page to the top, which is the end of the field-book. The several marks measured to or from, are here denoted by the letters of the alphabet, first the small ones, a, b, c, d, &c, and after them the capitals A, B, C, D, &c. But, instead of these letters, some surveyors use the numbers in order, 1, 2, 3, 4, &e.

OF

OF THE OLD KIND OF FIELD-BOOK. In surveying with the plain table, a field-book is not used, as every thing is drawn on the table immediately when it is measured. But in surveying with the theodolite, or any other instrument, some kind of a úcld-book must be used, to write down in it a register of account of all that is done and occurs relative to the

survey

in hand. This book every one contrives and rules as he thinks fittest for himself. The following is a specimen of a form which has been formerly used. It is ruled in three columns, as below.

Here o 1 is the first station, where the angle or bearing is 105° 25'. On the left, at 73 links in the distance or principal line, is an offset of 92; and at 610 an offset of 24 to a cross hedge. On the right, at 0, or the beginning, an offset 25 to the corner of the field; at 248 Brown's boundary hedge commences; at 610 an offset 35; and at 954, the end of the first line, the o denotes its terminating in the hedge. And so on for the other stations.

A line is drawn under the work, at the end of every station line, to prevent confusion.

Form of this Field-Book.

Stations,
Offsets and Remarks Bearings, Offsets and Remarks
on the left. and on the right.

Distances.

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and the chief lines serve as the bases of such triangles and trapezoids as are necessary to fill up all the interior parts.

The field-book is ruled into three columns, as usual. In the middle one are set down the distances on the chain-line, at which any mark, offset, or other observation, is made; and in the right and left hand columns are entered the off sets and observations made on the right and left hand respectively of the chain-line ; sketching on the sides the shape or resemblance of the fences or boundaries.

It is of great advantage, both for brevity and perspicuity, to begin at the bottom of the leaf, and write upwards; denoting the crossing of fences, by lines drawn across the middle column, or only a part of such a line on the right and left opposite the figures, to avoid confusion; and the corners of fields, and other remarkable turns in the fences where offsets are taken to, by lines joining in the manner the fences do; as will be best seen by comparing the book with the plan annexed to the field-book following, p. 74.

The letter in the left-hand corner at the beginning of every line, is the mark or place measured from; and that at the right-hand corner at the end, is the mark measured to : But when it is not convenient to go exactly from a mark, the place measured from is described such a distance from one mark towards another; and where a former mark is not measured to, the exact place is ascertained by saying, turn to the right or left hand, such a distance to such a mark, it being always understoodthat those distances are taken in thechain-line.

The characters used are, for turn to the right hand, 7 for turn to the left hand, and placed over an offset, to show that it is not taken at right angles with the chain-line, but' in the direction of some straight fence; being chiefly used when crossing their directions; which is a better way of oba taining their true places than by offsets at right angles.

When a line is measured whose position is determined, either by former work (as in the case of producing a given line, or measuring from one known place or mark to another) or by itself (as in the third side of the triangle), it is called a fast line, and a double line across the book is drawn at the conclusion of it; but if its position is not determined (as in the second side of the triangle), it is called a loose line, and a single line is drawn across the book. When a line becomes determined in position, and is afterwards continued farther, a double line half through the book is drawn.

When a loose line is measured, it becomes absolutely recessary to measure some other line that will determine its position. Thus, the first line ah or bh, being the base of a

triangle,

a

a

a

triangle, is always determined; but the position of the second side hj, does not become determined, till the third side jb is measured; then the position of both is determined, and the triangle may be constructed.

At the beginning of a line, to fix a loose line to the mark or place measured from, the sign of turning to the right or left hand must be added, as at h in the second, and j in the third line; otherwise a stranger, when laying down the vork, may as easily construct the triangle hjb on the wrong side of the line ab, as on the right one: but this error cannot be fallen into, if the sign above named be carefully observed.

In choosing a line to fix a loose one, care must be taken that it does not make a very acute or obtuse angle; as in the triangle por, by the angle at B being very obtuse, a small deviation from truth, even the breadth of a point at p or r, would make the error at B, when constructed, very considerable ; but by constructing the triangle pBq, such a deviation is of no consequence.

Where the words leave off are written in the field-book, it signifies that the taking of offsets is from thence discontinued; and of course something is wanting between that and the next offset, to be afterwards determined by measuring some other line.

The field-book for this method, and the plan drawn from it, are contained in the four following pages, engraven on copper plates; answerable to which the pupil is to draw a plan from the measures in the field-book, of a larger size, viz. to a scale of a double size will be convenient, such a scale being also found on most instruments. In doing this, begin at the commencement of the field-book, or bottom of the first page, and draw the first line ah in any direction at pleasure, and then the next two sides of the first triangle bhj by sweeping intersected arcs; and so all the triangles in the same manner, after each other in their order; and afterwards setting the perpendicular and other offsets at their proper places, and through the ends of them drawing the bounding fences.

Note. That the field-book begins at the bottom of the first page,

and reads up to the top; hence it goes to the bottom of the next page, and to the top; and thence it passes

from the bottom of the third page to the top, which is the end of the field-book. The several marks measured to or from, are here denoted by the letters of the alphabet, first the small ones, a, b, c, d, &c, and after them the capitals A, B, C, D, &c. But, instead of these letters, some surveyors use the Bumbers in order, 1, 2, 3, 4, &e.

OF

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