in the one Sight it will be loweft in the other, and fo of the small ones: Therefore the small Aperture in one is oppofite to the large one in the other; in the Middle of which laft, there is placed a Horsehair, or fine Silk Thread.

The Inftrument is then fixed on a Ball and Socket; by the Help of which and a Screw, you can readily fix it horizontally in any given Direction; the Socket being fixed on the Head of a three-legged Staff, whofe Legs when extended support the Inftru ment, whilft it is used.

How to take Field-Notes by the Circumferentor.

Plate VI. Fig. 6.

Let your Inftrument be fixed at any Angle as A, your firft Station; and let a Person stand at the next Angle B, or caufe a Staff, with a white Sheet to be fet there perpendicularly for an Object to take your View to: Then having placed your Inftrument horizontal (which is eafily done by turning the Box fo, that the Ends of the Needle may be equidiftant from its Bottom, and it traverses or plays freely) turn the Flower-de-Luce or North Part of the Box to your Eye, and looking through the fmall Aperture, turn the Index about, till you cut the Perfon or object in the next Angle B, with the Horfe hair or Thread of the oppofite Sight: The Degrees then cut by the South End of the Needle, will give the Number to be placed in the fecond Column of your Field-Book in a Line with Station, No. 1, and expreffes the Number of Degrees the ftationary Line is from the North, counting quite round with the Sun.

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Moft

Moft Needles are pointed at the South End, and have a small Ring at the North: Such Needles are 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 fometimes a Ring, but more ufually a Crofs towards the North End; and the South End is generally bearded towards its Extremity, and fometimes not, but its Arm is a naked right Line from the Cap at the Center.

Having taken the Degrees or Bearing of the firft ftationary Line AB, let the Line be meafured, and the Length thereof in Chains and Links be inferted in the third Column of your Field-Book, under the Title of Distances, oppofite to Station, No. 1.

It is cuftomary, and even neceffary, to cause a Sod to be dug up at each Station, or Place where you fix the Inftrument; to the end, that if any Error fhould arife in the Field-Book, it may be the more readily adjusted and corrected, by trying over the former Bearings and ftationary Diftances.

Having done with your first Station, fet the Inftrument over the Hole or Spot where your Object flood, as at B, for your fecond Station, and fend him forward to the next Angle of the Field, as at C; and having placed the Inftrument 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

fecond

fecond Column oppofite to Station, No. 2; then measure the stationary Distance BC, which infert in the third Column, and thus proceed from Angle to Angle, fending your Object before you, 'till you return to the Place where you began, and you will have the Field-Book compleat; obferving always to fignify the Parties Names who hold the contiguous Lands, and the Names of the TownLands, Rivers, Roads, Bogs, Loughs or Lakes, &c. that mear the Land you furvey, as before; and this is the Manner of taking Field Notes by what are called Fore-Sights.

But the Generality of Mearfmen frequently fet themselves in difadvantageous Places, fo as often to occafion two or more Stations to be made, where one may do, which creates much Trouble and Loss of Time: We will therefore fhew how this may be remedied, by taking of Back-Sights, thus: Let your Object ftand at the Point where you begin your Survey, as at A; leaving him there, proceed to your next Angle B, where fix your Inftrument fo, that you may have the longest View poffible towards C. Having fet the Inftrument in an horizontal Pofition, 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 fame as if they were taken from the Object to the Inftrument, the Direction of the Index being the fame. Let the Degree be inferted in the Field-Book, and the ftationary 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 firft Station A.

By

By this Method your Stations are laid out to the beft Advantage, and two Men may do the Bufinefs of three, for one of thofe who chain may be your Object; but in Fore-Sights, you must have an Object before you, befides two Chainmen.

It was faid before, that a Surveyor should have a Person with him to carry the hinder End of the Chain, on whom he can depend: This Perfon should be expert and ready at taking Off-fets, as well as exact in giving a faithful Return of the Length of every flationary Line. One who has fuch a Perfon, and who uses Back-Sights, will be able to go over near double the Ground he could at the fame Time, by taking Fore-Sights. But if a Surveyor has no fuch Perfon on whom he can with Safety depend, he must take Fore-Sights, because of overfeeing the Chaining; for fhould 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 Slavery not to be born.

Or a Back and a Fore-Sight may be taken at one Station, thus; with the South of the Box to your Eye, obferve from B the Object A, and fet down the Degree in your Field-Book, cut by the South End of the Needle. Again, from B obferve an Object at C, with the North of the Box to your Eye, and fet down the Degree cut by the South Point of the Needle, fo have you the Bearings of the Lines AB and BC, you may then fet up your Inftrument at D, from whence take a Back-Sight to C, and a Fore-Sight to E; thus the Bearings may be taken quite round, and the stationary Diftances being annexed to them, will compleat the Field-Book.

But

But in this laft Method, Care must be taken to fee that the Sights have not the leaft Caft on either Side; if they have, it will deftroy all: And yet with the fame Sights you may take a Survey. by Fore-Sights, or by Back-Sights only, with as great Truth as if the Sights were ever fo erect, provided the fame Caft continues without any Alteration: But upon the whole, Back-Sights only will be found the readieft 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 Brafs Ring in the Box is divided on the Side into 360 Degrees, thus; from the North to the Eaft into 90, from the North to the West into 90, from the South to the Eaft into 90, and from the South to the Weft into 90 Degrees; fo the Degrees are numbered from the North to the Eaft or Weft, and from the South to the Eaft or Weft.

The Manner of using this Part of the Inftrument 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