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of a town, or any part of a river or coaft furveyed, or any other inacceffible objects; by taking two stations, on two towers, or two hills, or fuch like.

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When the plain table is used; plant it at one station m, draw a line m n on it, along which lay the edge of the index, and turn the table about till the fights point directly to the other station; and there fcrew it faft. Then turn the fights round m fucceffively to all the objects ABC, &c, drawing a dry line by the edge of the index at each, as mA, mв, mc, &c. Then measure the distance to the other station, there plant the table, and lay that distance down on the station line from m to n. Next lay the index by the line nm, and turn the table about till the fights point to the other station m, and there fcrew it faft. Then direct the fights fucceffively to all the objects A, B, C, &c, as before, drawing lines each time, as në, në, nc, &c; and their interfection with the former lines will give the places of all the objects, or corners,

A, B, C, &c.

When the theodolite, or any other inftrument for taking angles, is ufed; proceed in the fame way, meafuring the ftation distance mn, planting the inftrument firft at one ftation, and then at another;

then

then placing the fixed fights in the direction mn, and directing the moveable fights to every object, noting the degrees cut off at each time. Then, thefe obfervations being planned, the interfections of the lines will give the objects as before.

When all the objects, to be furveyed, cannot be feen from two stations; then three ftations may be used, or four, or as many as is neceffary; measuring always the distance from one ftation to another; placing the inftrument in the fame pofition at every ftation, by means defcribed before; and from each station obferving or fetting every object that can be feen from it, by taking its direction or angular pofition, till every object be determined by the interfection of two or more lines of direction, the more the better. And thus may very extenfive furveys be taken, as of large commons, rivers, coafts, countries, hilly grounds, and fuch like.

PROBLEM XI.

To Survey a Large Estate.

If the eftate be very large, and contain a great number of fields, it cannot well be done by furveying all the fields fingly, and then putting them together; nor can it be done by taking all the angles and boundaries that inclose it. For in these cafes, any fmall errors will be fo multiplied, as to render it very much diftorted.

1. Walk over the eftate two or three times, in order to get a perfect idea of it, and till you can carry the map of it tolerably in your head. And to help your memory, draw an eye draught of it on paper, or at leaft, of the principal parts of it, to guide you.

2. Choose two or more eminent places in the eftate, for your ftations, from whence you can fee all the principal parts of it: and let thefe ftations be as far

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diftant

diftant from one another as poffible; as the fewer ftations you have to command the whole, the more exact your work will be: and they will be fitter for your purpose, if these ftation lines be in or near the boundaries of the ground, and efpecially if two lines or more proceed from one station.

3. Take what angles, between the stations, you think neceffary, and meafure the diftances from station to station, always in a right line: these things must be done, till you get as many angles and lines as are fufficient for determining all your points of ftation. And in measuring any of these station distances, mark accurately where thefe lines meet with any hedges, ditches, roads, lanes, paths, rivulets, &c, and where any remarkable object is placed, by measuring its diftance from the station line, and where a perpendicular from it cuts that line; and always mind, in any of thefe obfervations, that you be in a right line, which you will know by taking backfight and forefight, along your ftation line. And thus as you go along any main ftation line, take offsets to the ends of all hedges, and to any pond, houfe, mill, bridge, &c, omitting nothing that is remarkable. And all these things must be noted down; for these are your data, by which the places of fuch objects are to be determined upon your plan. And be fure to fet marks up at the interfections of all hedges with the station line, that you may know where to measure from, when you come to furvey thefe particular fields, which muft immediately be done, as foon as you have measured that ftation line, whilft they are fresh in memory. By this means all your ftation lines are to be measured, and the fituation of all places adjoining to them determined, which is the first grand point to be obtained. It will be proper for you to lay down your work upon paper every night, when you go home, that you may fee how you go on,

4. As to the inner parts of the eftate, they must be ́determined in like manner, by new station lines: for, after the main stations are determined, and every thing adjoining to them, then the estate must be subdivided into two or three parts by new ftation lines; taking inner stations at proper places, where you can have the beft view. Measure thefe ftation lines as you did the first, and all their interfections with hedges, and all offsets to fuch objects as appear. Then you may proceed to furvey the adjoining fields, by taking the angles that the fides make with the ftation line, at the interfections, and measuring the distances to each corner, from the interfections. For every station line will be a bafis to all the future operations; the situation of all parts being entirely dependant upon them; and therefore they fhould be taken as long as poffible; and it is best for them to run along fome of the hedges or boundaries of one or more fields, or to pafs through fome of their angles. All things being determined for thefe ftations, you must take more inner ftations, and continue to divide and fubdivide till at last you come to fingle fields; repeating the fame work for the inner ftations, as for the outer ones, till all be done and clofe the work as often as you can, and in as few lines as poffible. And that you may choose stations the moft conveniently, fo as to caufe the least labour, let the ftation lines run as far as you can along fome hedges, and through as many corners of the fields, and other remarkable points, as you can. And take notice how one field lies by another; that you may not mifplace them in the draught.

5. An eftate may be fo fituated, that the whole cannot be furveyed together; because one part of the eftate cannot be feen from another. In this cafe, you may divide it into three or four parts, and furvey the parts feparately, as if they were lands belonging to different perfons; and at last join them together.

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6. As it is neceffary to protaret or lay down your work as you proceed in it, you must have a fcale of a due length to do it by. To get fuch a scale, you must measure the whole length of the estate in chains; then you must confider how many inches long the map is to be; and from thefe you will know how many chains you must have in an inch; then make your fcale, or choose one already made, accordingly.

7. The trees in every hedge row must be placed in their proper fituation, which is foon done by the plain table; but may be done by the eye without an inftrument; and being thus taken by guess, in a rough draught, they will be exact enough, being only to look at; except it be fuch as are at any remarkable places, as at the ends of hedges, at ftiles, gates, &c, and these must be measured. But all this need not be done till the draught is finished. And obferve in all the hedges, what fide the gutter or ditch is on, and to whom the fences belong.

8. When you have long ftations, you ought to have a good inftrument to take angles with; and the plain, table may very properly be made ufe of, to take the feveral fmall internal parts, and fuch as cannot be taken from the main ftations, as it is a very quick and ready inftrument.

PROBLEM XII,

To Survey a County, or Large Tract of Land.

1. Choose two, three, or four eminent places for ftations; fuch as the tops of high hills or mountains, towers, or church fteeples, which may be feen from one another; and from which most of the towns, and other places of note, may alfo be feen. And let them be as far diftant from one another as poffible. Upon thefe places raife beacons, or long poles, with flags of

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