But some skilful Surveyors now make use of a different method for the field book; namely, beginning at the bottom of the page they write upward, sketching a neat boundary on each hand as they pass along. An example of this method will be given under the Problem, which requires the survey of a large estate.

In smaller surveys and measurements, a good way of setting down the work is to draw, by the eye, on a piece of paper a figure resembling that, which is to be measured; and to write the dimensions, as they are found, against the corresponding parts of the figure. And this method may be practised to a considerable extent, even in the larger surveys.

PRACTICE OF SURVEYING.

THIS part contains the several operations proper to be performed in the field, or the modes of measuring with all the instruments, and in all situations.

PROBLEM I.

To measure a line or distance.

To measure a line on the ground with the chain; being provided with a chain and ten small arrows, or rods, that one may be stuck into the ground, as a mark, at the end of every chain, two persons carry the chain, one at each end of it, and all the ten arrows are taken by one of them, who is to go foremost, and is called the leader; the other being called the follower, for distinction.

A

A picket, or station staff, being set up in the direction of the line to be measured, if no mark appear in that di rection; they measure in a straight line toward it, the leader fixing in the ground an arrow at the end of every chain, and the follower always taking it up, till all the ten arrows are used, and in the hands of the follower. They are then all returned to the leader, to be used again. And thus the arrows are changed from one to the other, at every ten chains' length, till the whole line is finished; then the number of changes of the arrows shews the number of tens, to which the follower adds the arrows he holds in his hand, and the number of links of another chain from him to the mark or end of the line. So, if there be three changes of the arrows, the follower hold six, and the end of the line cut off 45 links more, the whole length of the line is 3645 links.

When the line is on a declivity, ascending or descend ing, at every chain's length apply a small pocket level, or King's quadrant, to the chain, that it may shew how many links the slope is longer than the corresponding level line, and correct the length.

i. With the Plane Table.

The table being covered with a paper, and fixed on its stand ; plant it at the station A, and fix a fine pin, or a point of the compasses, in a proper part of the paper, to represent the point A. Close by the side of this pin lay the fiducial edge of the index, and turn it about, still touching the pin, till one object B can be seen through the sights; then by the fiducial edge of the index draw a line. In the same manner draw another line in the direction of the other object C, and it is done.

2. With the Theodolite, &c.

Direct the fixed sights along one of the lines, as AB, by turning the instrument about till you see the mark B through the sights; and there screw the instrument fast. Then turn the moveable index about till, through its sights, you see the other mark C. Then the degrees cut by the index, upon the graduated limb or ring of the instrument, shews the quantity of the angle.

3. With the Magnetic Needle and Compass.

Turn the instrument, or compass, so, that the north end of the needle point to the flow er-de-luce. Then direct the sights to one mark, as B, and note the degrees cut by the needle. Next direct the sights to the other mark C, and note the degrees cut by the needle. Then their sum, or difference, as the case is, will give the quantity of the angle BAC.

4. By Measurement with the Chain, &c.

Measure one chain's length, or any other distance, in both directions, as to b and c. Then measure the distance be, and it is done.-This is easily transferred to paper, by making

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OL. II.

DD

making a triangle Abc with these three lengths, and then measuring the angle A by a line of chords, or the graduated arc of an instrument.

Ahiklmm being a crooked hedge, or river, &c. from A measure in a straight direction along the side of it to B. And, in measuring along this line AB, observe when you are directly opposite to any bends or corners of the hedge, as at c, d, e, &c. and thence measure the perpendicular offsets cb, di, &c. with the offset staff, if they are not very long, otherwise with the chain itself; and the work is done. And the register, or field book, may be as follows: