straight on the line, and for fixing it in the original pofition.

Of shifting the Paper on the Plain Table.

When one paper is full, and you have occafion for more; draw a line in any manner through the farthest point of the last station line, to which the work can be conveniently laid down; then take the fheet off the table, and fix another on, drawing a line upon it, in a part the most convenient for the reft of the work; then fold or cut the old sheet by the line drawn on it, apply the edge to the line on the new sheet, and, as they lie in that pofition, continue the last station line upon the new paper, placing upon it the rest of the measure, beginning at where the old fheet left off. And so on from sheet to sheet.

When the work is done, and you would faften all the fheets together into one piece, or rough plan, the aforefaid lines are to be accurately joined together, as when the lines were transferred from the old sheets to the new ones.

But it is to be noted, that if the faid joining lines, upon the old and new fheet, have not the fame inclination to the fide of the table, the needle will not point to the original degree when the table is rectified; and if the needle be required to refpect ftill the fame degree of the compafs, the eafieft way of drawing the lines in the fame pofition, is to draw them both parallel to the fame fides of the table, by means of the equal divifions marked on the other two fides.

The theodolite is a brazen circular ring, divided into 360 degrees, and having an index with fights, or a telescope, placed upon the center, about which the index is moveable; alfo a compafs fixed to the center, to point out courses and check the fights; the whole

4

being

being fixed by the center upon a ftand of a convenient height for ufe.

In ufing this inftrument, an exact account, or fieldbook, of all measures and things neceffary to be remarked in the plan, must be kept, from which to make out the plan upon your return home from the ground.

Begin at fuch part of the ground, and measure in fuch directions, as you judge moft convenient; taking angles or directions to objects, and measuring fuch distances as appear neceffary, under the fame reftrictions as in the use of the plain table. And it is fafest to fix the theodolite in the original pofition at every ftation by means of fore and back objects, and the compafs, exactly as in using the plain table; registering the number of degrees cut off by the index when directed to each object; and, at any station, placing the index at the fame degree as when the direction towards that station was taken from the last preceding one, to fix the theodolite there in the original pofition, after the fame manner as the plain table is fixed in the original pofition, by laying its index along the line of the laft direction.

The best method of laying down the aforefaid lines of direction, is to describe a pretty large circle, quarterit, and lay upon it the feveral numbers of degrees cut off by the index in each direction; then, by means of a parallel ruler, draw, from ftation to ftation, lines parallel to lines drawn from the center to the refpective points in the circumference.

4. OF THE CROSS.

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

The crofs is very ufeful to measure fmall and crooked pieces of ground. The method is to measure a bafe or chief line, ufually in the longest direction of the

L1

upon

the piece from corner to corner; and while measuring it, finding the places where perpendiculars would fall this line from the feveral corners and bends in the boundary of the piece, with the crofs, by fixing it, by trials, upon fuch parts of the line as that through one pair of the fights both ends of the line may appear, and through the other pair you can perceive the correfponding bends or corners; and then measuring the lengths of the faid perpendiculars.

REMARK S.

Befides the fore-mentioned inftruments, which are moft commonly ufed, there are fome others; as the circumferentor, which refembles the theodolite in fhape and ufe; and the femi-circle, for taking angles, &c. But of all the inftruments for measuring, the plain table is certainly the beft; not only because it may be used as a theodolite or femi-circle, by turning uppermoft that fide of the frame which has the 360 degrees upon it; but because it is, in its own proper ufe, by much the easiest, safest, and most accurate for the purpofe; for by planning every part immediately upon the fpot, as foon as meafured, there is not only faved a great deal of writing in the field-book, but every thing can alfo be planned more eafily and accurately while it is in view, than it can be afterwards from a field-book, in which many little things must be either neglected or mistaken; and befides, the opportunities which the plain table afford of correcting your work, or proving if it be right, at every ftation, are fuch advantages as can never be balanced by any other method. But although the plain table be the most generally useful inftrument, it is not always so; there being many cafes in which fometimes one inftrument is the propereft, and fometimes another; nor is that furveyor mafter of his bufinefs who cannot in any cafe diftinguifh which is the fitteft inftrument or method,

and

and use it accordingly: nay, fometimes no inftrument at all, but barely the chain itself, is the best method, particularly in regular open fields lying together; and even when you are ufing the plain table, it is often of advantage to meafure fuch large open parts with the chain only, and from those measures lay them down upon the table.

The perambulator is ufed for meafuring roads, and other great diftances on level ground, and by the fides of rivers. It has a wheel of 84 feet, or half a pole, in circumference, upon which the machine turns; and the distance measured is pointed out by an index, which is moved round by clock work.

Levels, with telescopic or other fights, are used to find the level between place and place, or how much one place is higher or lower than another.

An offset-ftaff is a very ufeful and neceffary inftrument, for measuring the offsets and other fhort diftances. It is 10 links in length, being divided and marked at each of the 10 links.

Ten small arrows, or rods of iron or wood, are used to mark the end of every chain length, in measuring lines. And fometimes pickets, or ftaves with flags, are fet up as marks or objects of direction.

Various fcales are also used in protracting and meafuring on the plan or paper; fuch as plane fcales, line of chords, protractor, compaffes, reducing fcales, parallel and perpendicular rulers, &c. Of plane fcales, there should be several fizes, as a chain in 1 inch, a chain in of an inch, a chain in an inch, &c. And of thefe, the best for use, are thofe that are laid on the very edges of the ivory fcale, to prick off distances by, without compaffes.

In furveying with the plain table, a field-book is not ufed, as every thing is drawn on the table immediately

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when

when it is measured. But in furveying with the theodolite, or any other inftrument, fome fort of a fieldbook must be used, to write down in it a register or account of all that is done and occurs relative to the furvey in hand.

This book every one contrives and rules as he thinks fitteft for himself. The following is a fpecimen of a form very generally used. It is ruled into 3 columns: the middle, or principal column, is for the stations, angles, bearings, distances measured, &c; and those on the right and left are for the offsets on the right and left, which are fet against their correfponding distances in the middle column; as alfo for fuch remarks as may occur, and be proper to note in drawing the plan, &c.

Here I 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 crofs hedge. On the right, at o, 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 fo on for the other stations.

Draw a line under the work, at the end of every station line, to prevent confufion.

Form