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better than those which are pointed at each end, because the surveyor cannot mistake by counting to a wrong end; which error may be frequently committed, in using a two-pointed needle.
Two-pointed needles have sometimes a ring, but more usually a cross towards the north end : and the south end is generally bearded towards its extremity, and sometimes not, but its arm is a naked right line from the cap at the centre.
Having taken the degrees or bearing of the first stationary line AB, let the line be measured, and the length thereof in chains and links be inserted in the third column of your field-book, under the title of distances, opposite to station No. 1.
It is customary, and even necessary, to cause a sod to be dug up at each station, or place where you fix the instrument: to the end, that if any error should arise in the field-book, it may be the more readily adjusted and corrected, by trying over the former bearings and stationary distances.
Having done with your first station, set the instrument over the hole or spot where your object stood, as at B, for your second station, and send him forward to the next angle of the field, as at €; and having placed the instrument in an horizontal direction, with the sights, directed to the object at C, and the north of the 'box next your eye, count your degrees to the south end of the needle, which register in your field-book, in the second column opposite to station No. 2; then measure the stationary distance BC, which insert în the third column, and thus proceed from angle to angle; sending your object before you, till you
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 pointwhere 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 objeet 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 sáme. 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 husiness of three, for one of those who chain, may be your object; but in fore-sights, you must have an object before you, besides two chainmen.
It was said before, that a surveyor should have a persori 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 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 fron B he 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 there to 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 contained in the given angle.