SECT. II. OF MEASURING LAND; OR SURVEYING. Before I proceed to the practice of surveying, it is necessary to mention the inftruments used in meafuring land. 1. Of the Chain. The chain, called Gunter's chain, confifts of 100 equal links, each link being 22 of a yard, or 66% of a foot, that is 7.92 inches long; and the whole chain is 4 poles or 22 yards in length. An acre of land is equal to 10 fquare chains. An acre is divided into 4 equal parts, called roods, and each rood into 40 parts, called perches or poles. The length of lines measured with the chain is fet down in links, as integers, every chain being 100 links in length; therefore, when the content of a piece of land is found in fquare links, cut off 5 of the figures on the right hand for decimals, and the reft will be acres: thofe decimals are then multiplied by 4, to bring them into roods, and the decimals of the product multiplied by 40, for perches, as in the following example: EXAMPLE. What is the area of a rectangular piece of ground, the length of which is 1300 links, and the breadth 240? 1300 52000 2600 3.12000 •48000 40 Anfwer 19.20000 3 Acres, o Roods, 19 Perches. 2. Of the Plain Table. This inftrument confifts of a plain rectangular board of any convenient fize, fixed to a stand of three legs, by means of a ball and focket, by which the table is inclined in any direction: it has also a frame of wood to fit round its edges, which can be taken off, for the purpose of fixing a sheet of paper on the table. One fide of the frame is divided into feveral equal parts, for the purpofe of drawing lines across the paper, and the other fide of the frame is divided into 360 degrees from a centre in the middle of the table, for the purpose of taking angles, &c. There is alfo a needle and a compass on one fide of the table, to point out the directions, and fix the table in the fame pofition with regard to the points of the compafs at every remove. There is an index alfo, which is a brass two-foot scale, with two open fights, one at each end: these fights, and one edge of the scale, are in the fame plane, and that edge is called the fiducial edge of the index. In ufing this table, a fheet of paper is to be wetted and fpread fmooth, with the frame of the table preffed down clofe, to keep the paper fteady, which is to remain till it is dry, that it may stretch itself smooth: upon this paper the plan is to be drawn. In taking a furvey of any place, a point is to be made on the paper to denote that spot where the table is fixed, which is called the ftation; then in that point fix a pin, or one foot of the compaffes, and to it apply the fiducial edge of the index, moving the other part of the index about, till through the fights you perceive one angle of the field you furvey, or fome other remarkable object; and from the ftation point draw a line along the fiducial edge of the index. Then turn the index about upon the ftation point as a centre, till you perceive another angle, or fome other object, and draw a line from the station point along the edge of the index, as before: continue to do the fame, till you have drawn lines from the ftation, station, to represent the bearings of as many angles or objects as may be neceffary, and no more; then measure from the ftation where the table is fixed to every object which you have viewed, and lay the measures down upon their refpective lines on the paper. If it be required, as it fometimes is, to take a furvey from more than one station; remove the table, and by the help of the compass fix the table in the same pofition as before, and mark another point on the paper, for this second station point; and from thence draw lines to as many objects as may be neceffary, tharking the distance from the ftation as before. In ufing the plain table, choose fuch a point for your sta tion as fhall have an object both before and behind the station point, if it be poffible: and in moving the table from one station to another, it will be neceffary to prove that it be straight in the line towards the object, and also that the distance be rightly laid down on the paper. To know whether the table be set straight in the line, move the table about till through the fights of the index you can perceive either the fore or back object; then go round the table, and look through the fights at the other end of the index, to fee if the other object can be perceived; if it can, the table is in the line, but if not, the table must be fhifted according to your judgment. To know if the table be in the right part of the line, that is, if the diftance has been rightly measured, fix the table in the fame pofition as at firft, and lay the index along the station line; then turn the table about, till the fore and back objects appear through the fights, and the needle will point to the fame degree as at firft; then lay the index over the station point, and any other point on the paper reprefenting an object which is feen from the station, and if the fame object appears ftraight through the fights, the ftation may be de pended upon as right, but if not, the distance must be examined and corrected till the said object can be feep. of Of Shifting the Paper on the plain Table. When the paper is full written, and it is neceffary to continue the plan upon another fheet, draw a line through the farthest point of the last station line, then take the sheet off the table, and fix another fheet on, drawing a line upon it in the most convenient part for the rest of the work: then fold the old fheet back, close by the line drawn upon it; apply the edge to the line on the new sheet of paper, and as they lie in that pofition continue the last station line upon the new sheet, and also the rest of the measures, beginning at where the old fheet left off; and fo on from one sheet to another. When the work is done, the sheets are to be fastened together into one piece, and the lines in each sheet to be accurately joined together. It must here be noted, that the faid joining lines upon the old and new sheets must have the fame inclination with regard to the points of the compass. 3. Of the Theodolite. This is a brafs circular ring divided into 360 degrees, with an index, with open fights, or a telescope moveable upon the centre; also a compass to point out the bearings, &c. The whole is fixed by the centre upon a stand. When this inftrument is used, a field-book is neceffary, to note down all measures, angles, &c. to be remembered when the plan is drawn.. In ufing this instrument, any station may be taken as is judged moft convenient, but it is best to take a station from which most objects can be feen; and it is neceffary at every new station to fix the Theodolite in the fame pofition by means of viewing the fore and back objects, and the compass, as in ufing the plain table; registering in the fieldbook the number of degrees cut off by the index in viewing each object. The The best method of ufing this inftrument is to draw a large circle, quarter it, and mark upon it the number of degrees cut by the index, in viewing each object; then by a parallel ruler draw from ftation to ftation, lines parallel to the lines drawn from the centre to the respective points of the circumference. 4. Of the Crofs. This inftrument is only two pair of fights, fet at right angles to each other upon a ftaff with a fharp point to stick in the ground. The cross is very useful to measure small and crooked pieces of ground. The method of meafuring them is this: measure a base or chief line in the longest direction of the piece, from corner to corner, and, while measuring it, find the places where perpendicular lines fhould fall upon this line, from the feveral corners and bends in the piece, with the cross, by fixing it upon fuch parts of the line that through one pair of the fights both ends of the line may be seen, and through the other pair of fights the correfponding angle or angles may be seen, and then measure the length, &c. There are alfo feveral other inftruments used in surveying; as the Circumferentor, which resembles the Theodolite both in shape and ufe; the Semicircle, ufed for taking angles, &c.; and the Perambulator, for measuring roads and other great distances, on level ground; it has a wheel of 8 feet in circumference, upon which the machine turns, and the distance measured is pointed out by an index moved round by clock-work. Levels are inftruments with telescopes or other fights, used to find levels, or how much one place is higher than another. The offset-ftaff is ten links in length, and useful for meafuring the offsets and other fhort distances. There |