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different colours flying at them; so as to be visible from all the other stations.

2. At all the places, which you would fet down in the map, plant long poles with flags at them of feveral colours, to diftinguish the places from one another; fixing them upon the tops of church fteeples, or the tops of houses, or in the centres of leffer towns.

But you need not have these marks at many places at once, as fuppofe half a score at a time. For when the angles have been taken, at the two ftations, to all thefe places, the marks may be moved to new ones; and fo fucceffively to all the places you want. These marks then being fet up at a convenient number of places, and fuch as may be feen from both ftations; go to one of thefe ftations, and with an inftrument to take angles, standing at that station, take all the angles between the other station, and each of these marks, obferving which is blue, which red, &c, and which hand they lie on; and fet all down with their colours. Then go to the other station, and take all the angles between the first station, and each of the foriner marks, and fet them down with the others, each against his fellow with the fame colour. You may, if you can, alfo take the angles at fome third station, which may ferve to prove the work, if the three lines interfect in that point, where any mark ftands. The marks must ftand till the obfervations are finished at both stations; and then they must be taken down, and fet up at fresh places. And the fame operations must be performed, at both stations, for these fresh places; and the like for others. Your inftrument for taking angles must be an exceeding good one, made on purpose with telescopic fights; and of three, four, or five feet radius. A circumferentor is reckoned a good inftrument for this purpose.

3. And though it is not abfolutely neceffary to measure any distance, because any stationary line being

laid down from any fcale, all the other lines will be proportional to it; yet it is better to measure fome of the lines to afcertain the distances of places in miles; and to know how many geometrical miles there are in. any length; and from thence to make a scale to meafure any distance in miles. In measuring any distance, it will not be exact enough to go along the high roads; by reason of their turnings and windings, and hardly ever lying in a right line between the stations, which muft caufe infinite reductions, and create endless trouble to make it a right line; for which reafon it can never be exact. But a better way is to measure in a right line with a chain, between station and station, over hills and dales or level fields, and all obftacles. Only in cafe of water, woods, towns, rocks, banks, &c, where onecannot pafs, fuch parts of the line must be measured by the methods of inacceffible diftances; and befides, allowing for afcents and descents, when we meet with them. And a good compafs that fhews the bearing of the two ftations, will always direct you to go ftraight, when you do not fee the two ftations; and in your progrefs, if you can go ftraight, you may take offsets to any remarkable places, likewife note the interfection of your stationary line with all roads, rivers, &c.

4. And from all your ftations, and in your whole progrefs, be very particular in obferving fea coafts, river mouths, towns, caftles, houfes, churches, windmills, watermills, trees, rocks, fands, roads, bridges, fords, ferries, woods, hills, mountains, rills, brooks, parks, beacons, fluices, floodgates, locks, &c; and in general all things that are remarkable.

5. After you have done with your first and main ftation lines, which command the whole county; you muft then take inner ftations, at fome places already determined; which will divide the whole into feveral partitions: and from these stations you must determine

the places of as many of the remaining towns as you can. And if any remain in that part, you must take more ftations, at fome places already determined; from which you may determine the reft. And thus we must go through all the parts of the county, taking station after station, till we have determined all we want. And in general the ftation distances must always pafs through fuch remarkable points as have been determined before, by the former stations.

6. Laftly, the pofition of the ftation line you meafure, or the point of the compafs it lies on, muft be determined by aftronomical obfervation. Hang up a thread and plummet in the fun, over fome part of the station line, and obferve when the fhadow runs along that line, and at that moment take the fun's altitude; then having his declination, and the latitude, the azimuth will be found by spherical trigonometry. And the azimuth is the angle the station line makes with the meridian; and therefore a meridian may easily be drawn through the map. Or a meridian may be drawn through it by hanging up two threads in a line with the pole ftar, when he is juft north, which may be known from aftronomical tables. Or thus; obferve the star Alioth, or that in the rump of the great bear, being that next the fquare; or elfe Caffiopeia's hip; I fay, obferve by a line and plummet when either of thefe ftars and the pole ftar come into a perpendicular; and at that time they are due north. Therefore two perpendicular lines being fixed at that moment, towards these two stars, will give the position of the meridian.

PROBLEM XIII.

To Survey a Town or City.

This may be done with any of the inftruments for taking angles, but beft of all with the plain table, where

It

where every minute part is drawn while in fight. is proper also to have a chain of 50 feet long, divided into 50 links, and an offset-ftaff of 10 feet long.

Begin at the meeting of two or more of the principal streets, through which you can have the longest profpects, to get the longeft ftation lines. There having fixed the inftrument, draw lines of direction along those streets, ufing two men as marks, or poles fet in wooden pedestals, or perhaps some remarkable places in the houses at the further ends, as windows, doors, corners, &c. Measure thefe lines with the chain, taking offsets with the ftaff, at all corners of ftreets, bendings, or windings, and to all remarkable things, as churches, markets, halls, colleges, eminent houfes, &c. Then remove the inftrument to another ftation along one of thefe lines; and there repeat the fame process as before. And fo on till the whole is finished.

m

Θ

Thus, fix the inftrument at A, and draw lines in the direction of all the streets meeting there; and meafure AB, noting the ftreet on the left at m. At the fecond ftation B, draw the directions of the streets meeting there; meafure from в to c, noting the places of the streets at n and o as you pafs by them. At the 3d ftation c take the direction of all the streets

meeting

meeting there, and measure CD. At D do the fame, and measure DE, noting the place of the cross streets at p. And in this manner go through all the principal streets. This done, proceed to the fmaller and intermediate streets; and lastly to the lanes, alleys, courts, yards, and every part that it may be thought proper to represent.

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CHAPTER III.

Of Planning, Cafting-up, and Dividing.

PROBLEM I.

To Lay down the Plan of any Survey.

F the furvey was taken with a plain table, you have a rough plan of it already on the paper which covered the table. But if the furvey was with any other inftrument, a plan of it is to be drawn from the measures that were taken in the furvey, and first of all a rough plan upon paper.

To do this, you must have a set of proper inftruments, for laying down both lines and angles, &c; as fcales of various fizes, the more of them, and the more accurate, the better; fcales of chords, protractors, perpendicular and parallel rulers, &c. Diagonal fcales are beft for the lines, because they extend to three figures, or chains and links, which are hundredth parts of chains. But in ufing the diagonal fcale, a pair of compaffes must be employed to take off the lengths of the principal lines very accurately. But a fcale with a thin edge divided, is much readier for laying down the perpendicular offsets to crooked hedges, and for marking the places of thofe offsets upon the station line; which is done at only one application of the edge of

the

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