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length of radius. A circumferentor is reckoned a good instrument for this purpose.

3. And though it be not absolutely necessary to mease ure any distance, because a stationary line being laid down from any scale, all the other lines will be proportional to it; yet it is better to measure some of the lines to ascertain the distances of places in miles, and to know how many geometrical miles there are in any length ; and thence to make a scale to measuțe any distance in miles. In meas, uring any distance, it will not be exact enough to go along the high roads, which scarcely ever lie in a right line between the stations, or can with ease and accuracy be reo duced to one. But the 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 obstacles. Only in case of water, woods, towns, rocks, banks, &c. where one cannot pass, such parts of the line must be measured by the methods of inaccessible distances į and beside, allow; ing for ascents and descents, when they occur. A good compass, that shews the bearing of the two 'stations, will always direct you to go straight, when you do not see the two stations ; and in the progress, if you can go straight, offsets may be taken to any remarkable places, and the ing tersection of the stationary line with all roads, rivers, &c. notel,

4. From all the stations, and in the whole progress, be very particular in observing sea coasts, rivers' mouths, towns, castles, houses, churches, windmills, watermills, trees, rocks, sands, roads, bridges, fords, ferries, woods, hills, mountains, rills, brooks, parks, beacons, sluices, flood gates, locks, &c. and in general all things, that are remarkable.

5. After you have done with the first and main station lines, which command the whole county, take inner stations at some places already determined, which will di

; vide the whole into several partitions ; and from these sta

tions determine the places of as many of the remaining towns as you can. And if any remain in that part, take more stations at some places already determined, from which you can determine the rest. And thus go through all the parts of the county, taking station after station, till all, įhat is wanted, be determined. And in general the station distances must always pass through such remarkable points, as have been determined before by the former, stations,

PROBLEM XIII,

To

survey a town or city.

This may be done with any of the instruments for tak, ing angles, but best with the plane table, where every mi. nute part is drawn while in sight. It is convenient also to have a chain 50 feet long, divided into 50 links, and an offset staff ļo feet long.

Begin at the meeting of two or more of the principal streets, through which you can have the longest prospects, to get the longest station lines. There having fixed the instrument, draw lines of direction along those strcets, using two men as marks, or poles set in wooden pedestals, or perhaps some remarkable places in the houses at the farther ends, as windows, doors, corners, &c. Measure these lines with the chain, taking offsets with the staff at all corners of streets, bendings or windings, and to all remarkable things, as churches, markets, halls, colleges, eminent houses, &c. Then remove the instrument to anoth. er station along one of these lines ; and there repeat the same process. And so on, till the whole be finished.

Thus, Thus, fix the instrument at A, and draw lines in the direction of all the streets meeting there ; and measure

[graphic]

: AB, noting the street on the left at m. At the second station B, draw the directions of the streets meeting there ; measure from B to C, noting the places of the streets at n and o, as you pass by them. At the third station C take the direction of all the streets meeting there, and measure CD ; at D do the same, and measure DE, note ing the place of the cross streets at P. And in this manner go through all the principal streets. This done, proceed to the smaller and intermediate streets ; and lastly to the lanes, alleys, courts, yards, and every part, that if may be thought proper to represent in the plan.

PLANNING AND COMPUTING.

PROBLEM

I.

To plan.

If the survey have been taken with a plane table, you have a rough plan of it already on the paper, which covered the table. But if the survey have been made with

any

a

any other instrument, a plan of it is to be drawn from the measures, that were taken in the survey, and first of all a rough plan on paper.

To do this, you must have a set of proper instruments for laying down both lines and angles ; as scales of various sizes, the more of them and the more accurate, the better ; scales of chords, protractors, perpendicular and parallel rules, &c. Diagonal scales are best for lines, because they extend to three figures, or chains and links, which are hundredth parts of chains. But in using the diagonal scale, a pair of compasses must be employed to take off the lengths of the principal lines very accurately. But a scale with a thin divided edge is much readier for laying down the perpendicular offsets to crooked hedges, and for marking the places of those offsets upon the station line ; which is done at only one applicatiou of the edge of the scale to that line, and then pricking off all at once the distances along it. Angles are to be laid down either with a good scale of chords, which is perhaps the most accurate way; or with a large protractor, which is much readier when

many angles are to blaid down at one point, as they are pricked off all at once round the edge of the protractor.

In general, all lines and angles must be laid down on the plan in the same order, in which they were measured in the field, and in which they are written in the field book; the angles for the position of lines being first, then the lengths of the lines, with the places of the offsets, and then the lengths of the offsets themselves, all with dry or obscure lines ; then a black line, drawn through the extremities of all the offsets, will be the hedge or bounding line of the field, &c. After the principal bounds and lines

. are laid down, and made to fit or close properly, proceed next to the smaller objects, till you have entered every thing, that ought to appear in the plan, as houses, brooks, trees, hills, gates, stiles, roads, lanes, mills, bridges, woodlands, &c.

The

.

The north side of a map or plan is commonly placed uppermost, and a meridian drawn on some part, with the compass or flower-de-luce pointing northward. Also in a vacant part, a scale of equal parts or chains is drawn, and the title of the map in conspicuous characters, and embellished with a compartment Hills are shadowed, to be distinguished in the map. Colour the hedges with different colours ; represent hilly grounds by broken hills and val. leys ; you may draw single dotted lines før foot paths, and double ones for horse or carriage roads. Write the name of each field and remarkable place within it, and, if

you choose, its content in acres, roods and perches.

In a very large estate, or à countý, dräw vërtical and horizontal lines through the map, denoting the spaces between them by letters, placed at the top, bottom and sides, for readily finding any field, or other object, mentioned in a table.

In mapping counties and estates, that have uneven grounds of hills and valleys, reduce all oblique lines, measured up and down hills, to horizontal straight lines, if that was not done in the field before they were entered in the field book, by making a proper allowance. For which purpose there is a small table, engraven on some of the instruments for surveying.

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An acre of land is equal to ten square chains; that is, ten chains in length and one chain in breadth.

Or, it is 220 X 22, or 4840 square yards. Or, it is 40X4, or 160

squarc

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