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 colours 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 colours 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 colour. 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 exceeding good one, having telescopic sights, and a good

length