THE CROSS-STAFF.

The Cross-Staff is an instrument used in the field by surveyors, to erect perpendiculars, and may very easily be made in the following

manner.

Procure a piece of board about 6 inches square, either of sycamore, box, or mahogany.

Draw the two diagonals; and at their extremities fix four small studs or pins, which will serve as sights to direct to any object or angle.

Or, instead of studs or pins, you may saw two fine grooves at rightangles, about a quarter of an inch deep, in

the board.

This being fixed upon a staff, of a convenient length for use, pointed with iron at the bottom to enter the ground readily, the instrument is called a cross-staff.

Suppose a b c d, to represent a cross, and the grove a c to be directed to an object at m; then will the groove b d point to another at n.

Reverse the direction of the grooves, so that b d may be in the direction of m; then, if a c be in the direction of n, the instrument is correct.

NOTE 1.

m

- The cross must be fixed upon the staff by a screw, in such a manner that it may be easily turned without moving the staff.

2. The cross may be made of a circular piece of board; you must then draw two diameters crossing each other at right-angles. The fourth part of a square, or of a circle, will answer the purpose equally well.

3. Great care ought to be taken in making this instrument, as its accuracy depends on the sights, or grooves, being at right-angles with each other.

THE OFFSET-STAFF.

The Offset-Staff is an instrument used to measure short distances; and may be in length, 10, 12, or 15 links. It would be advisable to number the links from each end, on opposite sides, with the figures, 1, 2, 3, &c. as the staff, thus marked, will be more convenient for use. NOTE. As the Cross-Staff is sometimes thought incommodious, a small pocketcross may be so contrived as to be readily fixed, upon occasion, to the Offset-staff. This may be most expeditiously accomplished by means of a hole made through the cross, admitting the top of the staff, to the eighth link, counting from the bottom or piked end; at which place there must be attached a small shoulder, upon which the cross will rest.

THE COMPASS.

The Compass is an instrument used by surveyors, to point out the range or direction of lines; and also to shew the bearings of objects. The circumference of the card of the compass contains 360°, and is divided into thirty-two equal parts, called Points, each containing

11° 15'.

Of these, the four principal (namely, East, West, North, and

South) are called Cardinal Points; from which the names of the

others are derived.

To the under-side of the card, and in the direction of its north and south lines, is attached a magnetic bar of hardened steel, called the Needle, by which the north-point is directed toward the northern part of the horizon; and the other points, consequently, to their corresponding ones in the heavens.

The card and needle are suspended on an upright pin, called the Supporter, which is fixed in the bottom of a brass, or wooden box; and the whole is covered with a plate of glass to prevent the action of the wind upon the card.

Although the compass is divided into thirty-two points, yet surveyors reduce them to eight, namely, the four cardinal, or chief points; and the four midway between them; viz. the north-east, north-west, south-east, and south-west, which may be expressed by their initial letters, as E., W., N., S.; N. E., N. W., S. E., S. W. NOTE 1. A small pocket-compass may be procured for about five shillings, which will answer the purpose of a surveyor; but for the sake of those who may not possess such an instrument, the following methods of finding a meridian line, &c. are given. When a surveyor enters a field, let him call that side, which is next the sun rising, east; then will the opposite side be west; and, in measuring from the east to the west, he will have the north on his right-hand, and the south on his left. If his direction should lie between any two of the above points, as for example, between the north and the west, he may call the range of the line north-west, &c. This method will suffice, when a correct plan is not required. A true meridian, or north and south line, may be found by observing which line or fence points accurately toward the sun at noon, he being then upon the meridian, or full south. Lines, at right-angles to this meridian line, are east and west.

2. The north point of the compass does not point exactly to the north-point of the horizon; but inclines, in some places toward the east, and in others toward the west; and this inclination is called the variation of the compass. In most parts of England, the variation is, at this time, more than 24° westerly; so that the true range of any line, or the bearing of any object, will be above two points more toward the east than what is indicated by the compass.

This wonderful phenomenon has perplexed our greatest philosophers; neither Halley, nor the immortal Newton, having been able satisfactorily to account for it.

3. Some compasses have the cards attached to the bottom of the boxes, and the needles only are suspended upon pins. When this is the case, place the compass in such a manner that the north-point of the needle may rest about 24° to the west of the north-point of the card; and you will thus make an allowance for the variation; for in this situation of the compass, all the points on the card will be in their true positions.

4. It is necessary sometimes to get the needle of the compass retouched with the magnet, in order that it may traverse properly; as the power of the magnet on the needle has a tendency, in lapse of time, to decrease.

THE FIELD-BOOK.

Scarcely any two surveyors set down their field-notes exactly in the same manner. The method, however, now generally adopted, and which is certainly preferable to all others, is to begin at the bottom of the page and write upward.

Each page of the book must be divided into three columns. In

the middle column must be set down the distances on the chain-line at which any mark, offset, or other observation is made; and in the right and left-hand columns respectively, those marks, offsets, and observations must be entered.

The crossings of fences, rivers, &c. may be denoted by lines drawn across the middle column, or part of the right and left-hand columns, opposite the distances on the chain-line, at which they are crossed; and the corners of fields, and other remarkable turns in the fences, to which offsets are taken, may be denoted by lines joining or lying in the same relation to the middle column, as the fences, &c. do to the chain-line.

Thus a tolerably accurate representation of the fences, &c. may be sketched in the field, which will very much assist the surveyor in drawing the plan.

With respect to the characters used to denote stations, the letters of the alphabet will do very well, in small surveys; but in those of a larger extent, numeral figures must be used, and the sign + (plus) placed before each figure; thus, + 1, or + 2, which may be read, station first, or cross first; station one, or cross one, &c. Upon the plan they are generally represented by this (O) mark.

Most surveyors take the exact range of the first line, and enter it in their field-book; and from it the range of any other may be easily determined. This method I shall adopt in the following work.

The expression, R off B, or L off B, &c. denotes that you are to turn to the right or left-hand, and measure from B, &c.

NOTE 1. - Many surveyors not only begin at the bottom of the field-book, but also at its right-hand side, and write toward the left, which method I generally follow myself.

2. It is useful for a beginner to draw a rough sketch of the field, or estate which he is about to measure; and upon it, to note the stations in the same manner

as they are put down in taking the survey. This will materially assist his memory in planning.

3. The field-book, for practical use, should be made convenient for the pocket, and interleaved with blotting-paper.

4. The field-notes should always be set down with ink, which may be carried in a bottle suspended from a button of your waistcoat. Double fountain-bottles, such as are used by excise officers, are the best.

DIRECTIONS AND CAUTIONS TO YOUNG SURVEYORS WHEN IN THE FIELD, &c.

In addition to the instruments already described, you must provide ten arrows, each about a foot in length, made of strong wire, and pointed at the bottom. These should be bent in a circular form at

the top, for the convenience of holding them, and a piece of red cloth should be attached to each, that they may be more conspicuous among long grass, &c.

Poles, likewise, generally called Ranging-poles, or Station-staves, will be wanted as marks, or objects of direction, each about ten feet in length, piked with iron at the bottom; and having a red or white flag at the top, that they may be better seen at a distance. Thus equipped, and having entered the field or estate which you are about to survey, first, make yourself acquainted with its form; and then consider in what manner you must run your lines, according to the directions hereafter given in Parts Third, Fourth, and Fifth after which you must proceed in the following manner.

Let your assistant or chain-leader take nine arrows in his left-hand, and one end of the chain with one arrow in his right; then, advancing toward the place directed, at the end of the chain, let him put down the arrow which he holds in his right-hand. This the follower must take up with his chain-hand, when he comes to it; the leader, at the same time, putting down another at the other end of the chain. In this manner he must proceed until he has put down his tenth arrow; then, advancing a chain farther, he must set his foot upon the end of the chain, and call out, "change." The surveyor, or chain follower, must then come up to him, if he have no offsets to take, and carefully count to him the arrows; and one being put down at the end of the chain, proceed as before, until the whole line be measured.

Each change ought to be entered in the field-book, or a mistake of 10 chains may happen, when the line is very long. The chainfollower ought to be careful that the leader always puts down his arrow perpendicularly, and in a right-line with the object of direction; otherwise the line will be made longer than it is in reality. The follower may direct the leader by the motion of his left-hand; moving it to the right or left, as circumstances require, and always placing his eye and chain-hand directly over the arrow which is stuck in the ground. The leader likewise, as soon as he has put down his arrow, ought to fix his eye upon the object of direction, and go directly toward it. This he may easily effect by finding a tree or a bush beyond the station to which he is going, and in a straight line with it and himself.

In hilly ground, if the follower lose sight of the mark toward which he is going, he must stand over his arrow; and the leader must move to the right or left, till he sees the follower in a direct line between himself and the mark from which they last departed.

The surveyor ought to put down at each station a small stake, called a station-stake, with the number of the station upon it; so that