OF THE IMPROVED CIRCUMFERENTOR, WITH MR, GALE'S METHOD OF USING IT; A METHOD THAT IS APPLICABLE WITH EQUAL ADVANTAGE TO THE THEODOLITE, &c.

For the sake of perspicuity, it will be necessary to give again the example before used in page 211, and that not only because it will exhibit more clearly the advantages of Mr. Gale's method, but because we shall have occasion to refer to it when we come to his improved method of plotting; and further, because I have thought this mode so advantageous, and the tables so conducive to accuracy and expedition, that I have caused occasionally the traversing quad, rant to be engraved in smaller figures under the usual one of the limb of the theodolite.

Set the circumferentor up at B, fig. 1, plate 18, take the course and bearing of B C, and measure the length thereof, and so proceed with the sides CD, DE, EF, F G, G A, all the way round to the place of beginning, noting the several courses or bearings, and the lengths of the several sides in a field book, which let us suppose to be as follow:

N. B. By north 7° west, is meant seven degrees to the westward, or left hand of the north, as shewn by the needle; by north 55° 15′ cast, fifty-five degrees

* See page 212 of this work for a fuller account of this method..

fifteen minutes to the eastward, or right hand of the north, as shewn by the needle.

In like manner, by south 62° 30′ cast, is meant sixty-two degrees and thirty minutes to the eastward, or left-hand of the south; and by south 40° west, forty degrees to the westward, or right hand of the south.

The 21 chains, 18 chains 20 links, &c. are the lengths or distances of the respective sides, as measured by the chain.

To survey a field, or tract of land, having irregular boundaries.

When the boundaries of a survey have crooks and bends in them, it is by no means necessary to take a new course for every small bend; the best and most usual way, is to proceed in a straight line from one principal corner to another, and when you are opposite to any bend in the boundary, to measure the rectangular distance, termed the offset, from the straight line to the bend, noting the same in the field book, together with the distance on the straight line from whence such offsets were made. The offsets, as already observed, are generally measured with an offset staff.

For the purpose of noting these offsets, it is necessary that the field book should be ruled into FIVE COLUMNS. The middle column to contain the courses and distances; the adjoining columns on the right and left hand to contain the measure of the offsets, made to the right or left hand respectively; and the outside columns on the right and left hand, to contain remarks made on the right and left hand respectively, such as the names of the adjoining fields, or the bearing of any remarkable object, &c.

Example. Let fig. 3, plate 18, represent a field to be surveyed, whose boundaries are crooked.

Set up the instrument at or near any convenient corner, as at 1, and take the course, and bearing, as before directed, north 7° west, note this down in the

middle column of the field book, and measure with the chain as before directed, till you come opposite to the first bend, so that the bend be at right angles to the station line; note the distance thus measured, 3 chains 60 links, in the middle column, and measure the offset from thence to the bend 40 links, noting the same in the adjoining left hand column, because the boundary is on the left hand of the station line, and note in the outside column, the name or owner of the adjoining field, proceeding in the same manner all round the field, noting the courses, distances, offsets, and remarks, as in the following

To survey a tract of land, consisting of any number of fields lying together.

1. Take the outside boundaries of the whole tract as before directed, noting in your field book where the particular fields intersect the outside boundaries; and then take the internal boundaries of the several fields from the place where they so butt on the outside bounds.

Let fig. 4, plate 18, represent a tract of land to be surveyed, consisting of three fields.

First, begin at any convenient corner, as at A, and proceed taking the courses, distances, offsets, and remarks, as in the following field book.