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LAND-SURVEYING

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LAND-surveying is the art of measuring, planning, and finding the superficial content, of any field, or parcel of land. In this kind of measuring, the area or superficial content is always expressed in acres, or acres, roods, and perches; and the lengths of all lines, in the field, or parcel of land, are measured with a chain.

A line, or distance on the ground, is thus measured.--Having procured ten small arrows, or iron rods, to stick in the ground at the end of each chain ; also some station-staves, or long poles with coloured fags, to set up at the end of a station-line, or in the angles of a field ; two persons take hold of the chain, une at each end, the foremost, for the sake of distinction, is called the leader, the hindermost the follower.

A station-staff is set up in the direction of the line to be measured, if there be not some object, as a tree, a house, &c. in that direction.

The leader takes the ten arrows in his left hand, and one end of the chain by the ring, in his right hand, and proceeds towards the stationstaff, or other object. The follower stands at the beginning of the line, holding the other end of the chain, by the ring, till it is stretched straight, and laid, or held level, by the leader, whom he directs, by waving his hand to the right or left, till he see him exactly in a line , with the object towards which they are measuring. The leader then sticks an arrow upright in the ground, as a mark for the follower to come to, and proceeds forward another chain, at the end of which he is directed, as before, hy the follower ; or he may now, and at the end of every other cbain, direct himself, by moving to the right or left, till the follower and the object measured from, be in one straight line. Having stuck down an arrow, as before, the follower takes up the arrow which the leader first stuck down. And thus they proceed till all the ten arrows are employed, or in the hands of the follower, and the leader, without an arrow, is arrived at the end of the eleventh chain length. The follower then sends or carries the ten arrows to the leader, who puts one of them down at his end of the chain, and proceeds with the other nine and the chain, as before. The arrows are thus changed from the one to the other, till the whole line is finished, if it exceed ten chains, and the number of changes slows how many times ten chains the line contains. Thus, if the whole line measures 36 chains 45 links, or 3645 links, the arrows have been changed three times, the follower will have five arrows in his hand, the leader four, and it will be forty-five links from the last arrow, to be taken up by the follower to the end of the line.

Of the Surveying Cross, or Cross-staff. The surveying cross, fig. 1, consists of two pair of sights at right angles to each other : these sights are sometimes pierced out in the circumference of a thick tube of brass; and sometimes the cross-staff consists of four sights strongly fixed upon a brass cross, and, when used, is screwed on a staff, having a sharp point to stick in the ground. The accuracy of the cross-staff depends on the sights being exactly at right angles to each other. A cross-staff may be easily inade by a carpenter, thus : take a picce of beech or box, ADBC, of four or five inches in breadth, and three or four inches in depth, and upon ADBC draw two lines, AB and CD, crossing each other at right angles. Then, with a fine saw, make two slits, ABG and CDH, of about two inches in depth ; fix this piece of wood upon a staff S, of about four and a half, or five feet in length, pointed at one end, so that it may easily stick into the ground.

Prob. 1. To nieasure off-sets with a chain and cross-staff.

Let Abcdefg, fig. 2, be a crooked hedge, river, or brook, &c. and AG a base line. First, begin at the point A, and measure towards G; when you come to B, where you judge a perpendicular must be erected, place the cross staff in the line AG in such a position that both G and A may be seen through two of the sights, looking for. ward towards G, and backward towards A. Then look along one of the cross sights, and if it point directly to the corner, or bend at b, the cross-staff is placed right; otherwise move backward or forward along AG till the cross sights do point to b, and measure Bb, which set down in links: proceed thus till you have taken all the off-sets, as in the following field-book.*

Field Book.

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To lay down the Plan. Draw the line AG of an indefinite length : then, by a diagonal scale,

A field-book is usually divided into three columns. The middle columa contains the different distances on the chain-line, and in the right and left. band colmans, the off-srts and remarks are entered. The best method of entering field-notes, thongh perhaps not the most conveniert, is to begin at the buttom of the page, and write towards the top.

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set off AB equal to 45 links, draw Bb perpendicular to AG, and equal to 62 links. Next set off AC equal to 220 links, or 2 chains 20 links; draw Cc perpendicular to AG, and equal to 84 links : then set off AD equal to 340 links, or 3 chains 40 links, and make Dd equal to 70 links : proceed thus till you have completed the figure.

To cast up the Content. ABb must be measured as a triangle ; BCcb, CDde, DEed, &c. must be measured as trapezoids. Some authors direct you to add all the perpendiculars Bl, Cc, &c. together, and divide their sum by the number of them, then multiply the quotient by the length AG; but this method is always erroneous except the off-sets Bb, Cc, &c. be equally distant from each other.

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Calculation,

AB = 45 AC=220 AD=340 AE=510'AE=634|AG=784
Bb = 62 AB= 45 AC=220 AD=340 AE=510 AF= 634

90 BC=175 CD=120 DE=170 EF = 124 GF=151 270

B6 = 62 Cc = 84 Dd = 70 Ee = 98 Ff = 57 2790 Cc = 84 Dd = 70 Ee = 98 Ff = 57 Gg 91

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Sum 146 Sum 154 Sum 168 Sum 155 Sun 148
Bc =175 CD=120 DE= 170 EF = 124FG= 15.

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2)116948 = double area of the who.e in square links.

58474 = area in square links.

-58474 = area in acres = 0 A. 2 R. 13.5584 P

2. Required the plan and content of part of a field, from the following field.book.

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The figure must be laid down, and the content calculated as in the first example. Thus, in fig. 3, you will find the area of the part EdcoaA to be 1 R. 13.4 P. and of the part FfgG to be 30 perches; so that the whole is 2 roods 3:4 perches.

Prob. 2. To measure a field in the form of a trapezium.

Set up station-staves, or long poles, at the corners A, B, C, fig. 4. Then begin at D, and measure along the diagonal DB, in a straight line, till you come to the place of the perpendicular AF, which will be known by looking backward and forward through the siglits of the cross-staff, as before directed. Make a mark at F, and measure the perpendicular AF; then proceed from F towards B, and when you come to E, the place where the second perpendicular will fall, make a mark, and measure the perpendicular EC: lastly, continue your measure from E to B. You may either draw a rough plan of the field by the eye, and write the length of the diagonal and perpendiulars on it, which some writers recommend as the best method, or set them down in a field-book, thus :

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To lay down the Plan. Draw the station-line DB equal to 1360 links, or 13.60 cnains, from D set off DF equal to 600 links, or 6 chains ; draw AF perpendicular to DB, and equal to 342 links, or 3 chains 42 links: make

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