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return to the place where you began, and you will have the field-book complete ; observing always to signify the parties names who hold the contiguous lands, and the names of the town-lands, rivers, roads, swamps, lakes, &c. that bound the land you survey, as before ; and this is the manner of taking field-notes by what is called foresights.
But the generality of mearsmen frequently set themselves in disadvantageous places, so as often to occasion two or more stations to be made, where one may do, which creates much trouble and loss of time; we will therefore shew how this may be remedied, by taking back-sights, thus : let your object stand at the point where you
begin your survey, as at A; leaving him there, proceed to your next angle B, where fix your instrument so, that you may have the longest view possible towards C. Having set the instrument in an horizontal position, turn the south part of the box next your eye, and having cut your object at A, reckon the degrees to the south point of the needle, which will be the same as if they were taken from the object to the instrument, the direction of the index being the same. Let the degree be inserted in the fieldbook, and the stationary distance be measured and annexed thereto, in its proper column ; and thus proceed from station to station, leaving your object in the last point you left, till you return to the first station A
By this method your stations are laid out to the best advantage, and two men may do the business of three, for one of those who chain, may be
your object; but in fore-sights, you must have an ob. ject before you, besides two chainmen.
It was said before, that a surveyor should have a person with him to carry the hinder end of the chain, on whom he can depend: this person should be expert and ready at taking off-sets, as well as exact in giving a faithful return of the length of every stationary line. One who has such a person, and who uses back-sights, will be able to go over near double the ground he could at the same time, by taking fore-sights, because of overseeing the chaining; for should he take back-sights, he must be obliged, after taking his degree, to go back to the foregoing station, to oversee the chaining, and by this means to walk three times over every line, which is a labour not to be borne.
Or a back and a fore-sight may be taken at one station, thus; with the south of the box to your eye, observe from B the object A, and set down the degree in your field-book, cut by the south end of the needle. Again from B observe an object at C, with the north of the box to your eye, and set down the degree cut by the south point of the needle, so have you the bearings of the lines AB and BC; you may then set up your instrument at
D, from whence take a back-sight to C, and a foresight to E: thus the bearings may be taken quite round, and the stationary distances being annexed to them, will complete the field-book.
But in this last method, care must be taken to see that the sights have not the least cast on either side ; if they have, it will destroy all : and yet with the same sights you may take a survey by fore-sights, or by back-sights only, with as great truth as if the sights were ever so erect, provided the same cast continues without any alteration ; but, upon the whole, back-sights only will be found the readiest method.
If your needle be pointed at each end, in taking fore-sights, you may turn the north part of the box to your eye, and count your degrees to the south part of the needle, as before ; or you may turn the south of the box to your eye, and count your degrees to the north end of the needle.
But in back-sights you may turn the north of the box to your eye, and count your degrees to the north point of the needle; or you may turn the south of the box to your eye, and count your degrees to the south end of the needle.
The brass ring in the box is divided on the side into 360 degrees, thus; from the north to the east into 90, from the north to the west into 90, from the south to the east into 90, and from the south to the west into 90 degrees ; so the degrees are numbered from the north to the east or west, and from the south to the east or west.
The manner of using this part of the instrument is this; having directed your sights to the object, whether fore or back, as before, observe the two cardinal points of your compass, the point of the needle lies between, (the north, south, east and west being called the four cardinal points, and are graved on the bottom of the box) putting down those points, together by their initial letters, and thereto annexing the number of degrees, counting from the north or south, as before, thus; if the point of your needle lies between the north and east, north and west, south and east, or south and west points in the bottom of the box, then put down NE, NW, SE, or SW, annexing thereto the number of degrees cut by the needle on the side of the ring, counting from the north or south as before,
But if the needle point exactly to the north, south, east, or west, you are then to write down N, S, E, or W, without annexing any degree.
This is the manner of taking field notes, whereby the content of ground may be universally determined by calculation ; and they are said to be taken by the quartered compass, or by the four nineties.
To find the number of degrees contained in any given angle.
Set up your instrument at the angular point, and thence direct the sights along each leg of the angle, and note down their respective bearings, as before ; the difference of these bearings, if less than 180, will be the quantity of degrees contained in the given angle; but if more, take it from 360, and the remainder will be the degrees containod in the given angle.
THIS instrument is a circle, commonly of brass, of ten or twelve inches in diameter, whose limb is divided into 360 degrees, and those again are subdivided into smaller parts, as the magnitude of it will admit; sometimes by equal divisions, and sometimes by diagonals, drawn from one concentric circle of the limb to another.
In the middle is fixed a circumferentor, with a needle ; but this is of little or no use, except in finding a meridian line, or the proper situation of the land.
Over the brass circle is a pair of sights, fixed to a moveable index, which turns on the centre of the instrument, and upon which the circumferentor-box is placed.
This instrument will either give the angles of the field, or the bearing of every stationary distance line, from the meridian; as the circumferentor and quartered compass do.
To take the angles of the field.
PL. 6. fig. 6.
Lay the ends of your index to 360°, and 180°; turn the whole about with the 360 from you; direct