PROBLEM XII.

To survey a county, or large tract of land.

1. Choose two, three, or four eminent places for stations; such as the tops of high hills or mountains, towers, or church steeples, which may be seen from one another, and from which most of the towns, and other places of note, may also be seen; and so as to be as far distant from one another as possible. On these places raise beacons, or long poles with flags of different colors flying at them, which may be visible from all the other stations.

2. At all the places, which you would set down in the map, plant long poles with flags of several colors on them, to distinguish the places from one another; fixing them on the tops of church steeples, or the tops of houses, or in the centres of less towns. These marks being set up at a convenient number of places, and being such as may be seen from both stations; go to one of these stations, and with an instrument to take angles,standing at that station take all the angles between the other station and each of these marks. Then go to the other station, and take all the angles between the first station and each of the former marks, setting them down with the others, each against the corresponding one of the same calor. You may also, if you can, take the angles at some third station, which may serve to prove the work, if the three lines intersect in the point, where any mark stands. The marks must stand till the observations are finished at both stations; and then they must be taken down, and set up at new places. And the same operations must be performed, at both stations, for these new places; and the like for others. The instrument for taking angles must be an exceedingly good one, having telescopic

A circumferentor is

sights and a good length of radius. reckoned a good instrument for this purpose.

3. And though it be not absolutely necessary to measure 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 measure any distance in miles. In measuring 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 reduced 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; and beside, allowing for ascents and descents, when they occur. A good compass, that shows 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 intersection of the stationary line with all roads, rivers, &c. noted.

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 divide the whole into several partitions; and from these stations determine the pla

ces 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, that is wanted, be determined. And in general the station distances must always pass through such remarkable points, as have been determimed before by the former stations.

PROBLEM XIII.

To survey a town or city.

This may be done with any of the instruments for taking angles, but best with the plane table, where every minute 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 10 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 streets, 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 another station along one of these lines; and there repeat the same process. And so on, till the whole be finished.

Thus, fix the instrument at A, and draw lines in the direction of all the streets meeting there; and measure 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 directions of all the streets meeting there, and measure CD; at D do the same, 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 smaller and intermediate streets; and lastly to the lanes, alleys, courts, yards, and every part, that it 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 other in

strument, 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 pa per.

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 offects upon the station line; which is done at only one application 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 be laid down at one point, as they are pricked off all at once round the edge of the protractor.

In general, all the 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 were 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.