line. Having stretched the chain, and stuck down an arrow, as before, the follower takes up his arrow, and thus they proceed, till the ten arrows are in the hands of the follower, and the leader, without an arrow, is arrived at the end of the eleventh chain's length. The follower then either sends or brings the ten arrows to the leader, who puts one of them down at the end of his chain, and advances with his chain as before. And in this manner the arrows are changed from one to the other at every ten chain's length, till the whole line is finished.

The number of changes shows how many times ten chains the line contains, 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. If the whole line measured 48 chains, 56 links (4856 links), the arrows have been changed four times, the follower will have seven arrows in his hand, and it will be 56 links from the last arrow to be taken up by the follower, to the end of the line.

Besides the chain, the land surveyor would find it convenient to be provided with a staff, divided into ten equal parts, answering to 10 links of the chain, for the purpose of measuring offsets, or short distances at right angles to the chain line. For the purpose of laying off perpendicular offsets to the chain line, to some hedge, pond, or other neighbouring object, the measurer should be provided with a cross, which consists of two pair of sights, set at right angles to each other, or a staff shod with an iron spike at the bottom, to stick in the ground.

When the ground to be measured is bounded by

many sides, it is best to draw the base line within the figure, in such a direction as that all the perpendiculars drawn to it, from the corner of the piece, may fall within the figure.

This instrument is very useful to measure small pieces of ground, with crooked boundaries. To effect this, measure the longest line from corner to corner, and while measuring it, find the places where perpendiculars would fall on this line, from the opposite corners in the boundaries of the figure, with the cross, by fixing it by trials on such parts of the line as that through one pair of the sights both ends of the line may appear, and through the other pair you may see the corresponding corners; then measure the lengths of these perpendiculars. Thus, in the annexed figure, measure

the distance AE, along the line AC, also measure EB; then having measured to F, measure the offset DF, and continue the measurement to C. Then having registered these different dimensions in the field book, or having marked them on a figure drawn on paper to represent the ground to be measured, the content is found by the following rules :

To find the Area of a Four-sided Field. RULE. Multiply the diagonal by the sum of both perpendiculars, and half the product will give the area. EXAMPLE. Let the diagonal be 600 links, and the offsets 300 and 400 respectively; required the area.

300

400

700

600

2)420000

21,0000

4

40000

40

16,00000

A. R. P.
2 0 16

Note.-When either the sum of the perpendiculars or the diagonal is an even number, the sum of the perpendiculars may be multiplied by half the diagonal line, or half the sum of the perpendiculars by the whole diagonal, for the area.

In the present example 700×300=210000 square links, as before.

When the ground to be surveyed is triangular, such as ABC, the area is found by multiplying the base AC by the perpendicular EB, and dividing the product by 2; or by multiplying the base by half the perpendicular, or the perpendicular by half the base.

EXAMPLE. The base AC is 600, and the perpendicular EB 300 links; required the area.

The perambulator is used for measuring roads and other level distances; but is unfit to measure uneven ground. It consists of a wheel, the circumference of which is 84 feet, or half a perch; and is furnished with an index, which indicates the distance measured.

Various scales are used to protract and measure the plan on paper, such as plane scales, protractors, reducing scales, parallel and perpendicular rulers, &c.

The best scales are those used on the Ordnance Survey of Ireland, the Tithe Survey of England, and on the different Railways.

They have their edges, which are bevelled off, divided according to the size intended for the map to be drawn to. All distances are measured on the edge of these scales, without the use of compasses.

The following table, showing the decimals answering to every rood and perch in the acre, will be found useful to the land surveyor :