links; and not in chains and decimals. Therefore, after the content is found it will be in square links; then cut off five of the figures on the right hand for decimals, and the rest will be acres. These decimals are then multiplied by 4 for roods, and the decimals of these again by 40 for perches.

Example. Suppose the length of a rectangular piece of ground be 792 links, and its breadth 385; to find the area in acres, roods, and perches:

The cross consists of two pair of sights set at right angles to each other, upon a staff having a sharp point at the bottom to stick in the ground.

The cross is very useful to measure small and crooked pieces of ground. The method is to measure a base or chief line, usually in the longest direction of the piece, from corner to corner; and while measuring it, finding the places where perpendiculars would fall on this line, from the several corners and bends in the boundary of the piece, with the cross, by fixing it, by trials, on such parts of the line, so that through one pair of the sights both ends of the line may appear, and through the other pair you can perceive the corresponding bends or corners; and then measuring the lengths of the said perpendiculars.

SECTION II.

THE PRACTICE OF SURVEYING.

PROBLEM I. To measure a line or distance.

To measure a line on the ground with the chain: Having provided a chain, with ten small arrows, or rods, to stick one into the ground, as a mark, at the end of every chain; two persons take hold of the chain, one at each end of it; and all the ten arrows are taken by one of them, who goes foremost, and is called the leader; the other being called the follower, for distinction's sake.

A picket, or station staff, being set up in the direction of the line to be measured, if there do not appear some marks naturally in that direction, they measure straight towards it, the leader fixing down an arrow at the end of every chain, which the follower always takes up, till all the ten arrows are used. They are then all returned to the leader, to use over again. And thus the arrows are changed from the one to the other at every ten chains length, till the whole line is finished; then the number of changes of the arrows shows the number of tens, to which the follower adds the arrows he holds in his hand, and the number of links of another chain over to the mark or end of the line. So, if there have been three changes of the arrows, and the follower holds six arrows, and the end of the line cut off forty-five links more; the whole length of the line is set down in links thus, 3645.

PROBLEM II. To survey a triangular field, A B C.

AP 794

A B=1321

PC 826

Having set up marks at the corners, which is to be done in all cases where there are not marks naturally; measure with the chain from A to P, where a perpendicular would fall

from the angle c, and set up a mark at P, noting down the distance A P. Then complete the distance A B by measuring from P to B. Having set down this measure, return to P, and measure the perpendicular P C. And thus having the base and perpendicular, the area from them is easily found. Or, having the place P of the perpendicular, the triangle is easily constructed.

Or measure all the three sides with the chain, and note them down. From which the content is easily found, or the figure constructed.

PROBLEM III. To measure a Four-sided Field.

Measure along either of the diagonals, as A C; and either of the two perpendiculars D E, B F, as in the last problem; or else the sides A B, B C, C D, D A. From either of which the figure may be planned and computed as before directed.

PROBLEM IV. To survey any Field of an Irregular Form.

Fig. 56.

m

n

C

Having set up marks at the corners, where necessary, of the proposed field A B C D E F G (fig. 56.), walk over the ground, and consider how it can best be divided into triangles and trapeziums; and measure them separately as in the last two problems. Thus fig. 56., is divided into the two trapeziums A B C G, G DE F, and the triangle G C D. Then, in the first trapezium, beginning at A, measure the diagonal A C, and the two perpendiculars G,

F

Bn. Then the base G C, and the perpendicular D q. Lastly, the diagonal D F, and the two perpendiculars p E, o G. All which measures write against the corresponding parts of a rough figure drawn to resemble the figure to be surveyed, or set them down in any other form you choose.

▲ h i k l m n, in fig. 57., being a crooked hedge, or river, &c., from A measure in a straight direction along the side of it to B. And in measuring along this line A B, observe when you are directly opposite any bends or corners of the hedge, as at c, d, e, &c.; and from thence measure the perpendicular

offsets, c h, di, &c., with the offset-staff, if they are not very long, otherwise with the chain itself, and the work is done. The register may be as follows:

The spaces included between offsets are calculated as parallelograms: viz. by adding the two perpendiculars together and multiplying this sum by the base; then take the half of the whole when added together for the area; and the work will stand as below:

When the offsets are long the chain may be used; but short distances are measured with the offset-staff, viz. a pole of ten links in length, and each link marked upon it.

PROBLEM VI. To survey an Estate.

If the estate be large, and contain a number of fields, it cannot well be done by surveying all the fields singly, and then putting them together.

1. Walk over the estate two or three times, in order to get a perfect idea of it, until you can carry the map of it toler