279. Remarks on the Third Method.

The third method should be employed whenever a map, more or less perfect, is to be made. The notes should be placed on a left-hand page of the field book, and the map on the right page, facing.

By referring to the notes and map illustrating this method, it will be observed that the survey began at A, the S. E. corner of the farm, at the middle of the turnpike, and that we commenced to record the notes at the bottom of the page..

This will keep the notes of the objects, at the right or left of each line run, in their natural position on the page, at the right or left of the parallel lines inclosing the distance from the station at the beginning of the line to the objects worthy of record encountered in running the line.

The character denotes station, at the left of which stands the letter marking its position on the map, and at the right the bearing of the next course.

A prominent object, such as the chimney of the house, a large tree standing in an open field, may be selected, and its bearings from the principal stations be taken. These bearings will serve as checks against errors in drawing the map, and may aid in finding the corners should they be lost. In the present example, a chestnut tree on the top of a hill, in the pasture at the left of the lane, is selected, and its bearing from A, B, and D given.

280. Surveying Creeks and Roads.

1. Creeks may be meandered as described under the head of Survey of the Public Lands.

2. They may also be surveyed by running straight lines connecting points on the bank, taking the bearings of these lines, the distances from the origin of these lines to the perpendicular offsets run from the lines to the bank of the river, and the length of the offsets, as exhibited in the following field notes. and plot.

2.84

1.50

2.24

.50

1.40

1.08

.40

B

The name of stations and the left-hand offsets are noted on the left of the parallels, the righthand offsets and bearings on the right, the distance from the station to the offsets, and the sign for station, between the parallels.

Station A A E

3. In surveying an existing winding road, keep in the road, run straight lines as far as possible, without running out of the road, note the bearing of these lines, the distances to the offsets at different points to the sides of the road, the lengths of these offsets, and make an accurate plot of the road.

B

4. To survey a new road, find the bearing of the middle line from the origin to the next angle or intersection with another road, measuring the distance

S. N. 24.

from the origin to the lines of farms, creeks, etc., which it intersects.

Set temporary stakes at the angles, and at convenient distances along the middle line, to guide in making the 'road, and plant monuments at a given distance and bearing from the angular points, so that they will not be disturbed in making or working the road. Take notes, and make a correct plot of the road.

281. Surveying Towns.

Commence at the intersection of principal streets, take their bearings, measure their lengths, noting the distances to the streets and alleys crossed, taking offsets to corners of streets and prominent objects, as public buildings, etc., till a prominent cross-street is reached, which survey in the same manner, changing the courses at such stations as will lead back to the original station.

Survey all the streets and alleys enclosed. Then survey an adjoining district, and so on, till the entire town or city has been surveyed.

Take notes, and make an accurate map of the town, on which locate not only the streets and alleys, but public buildings, parks, fountains, monuments, etc.

282. Reverse Bearing.

Let AB be a line run from A to B, AN and BS meridians, then will NAB be the bearing of AB, and SBA will be the reverse bearing.

Since the meridians AN and BS may be regarded as parallel, the bearing and reverse

bearing are equal. Thus, if the bearing of AB is N. 30° E., the reverse bearing is S. 30° W.

The bearing and reverse bearing agree in the value of the angle, and differ in both the letters which indicate the general direction of the line. In fact, the reverse bearing of a line is the bearing of the line if run in the opposite direction. Thus, SBA, the reverse bearing of the line AB, run from A to B, is the bearing of the line BA, run from B to A.

Of the letters used in bearings, we shall call N and S latitude letters, and E and W departure letters.

To guard against inaccurate observations, and the disturbance of the needle occasioned by local attraction, the reverse bearing should be taken at every station. If the bearing and reverse bearing agree in value, the bearing may be considered as correctly taken; if they differ materially, both should be taken again. If they still differ, the difference may be regarded as occasioned by local attraction.

To ascertain at which station the local attraction exists, place the instrument at a third station, at a considerable distance from each of the doubtful stations, and sight to each, then from these back to the third station. The local attraction may be considered to exist at the station where the bearing of the third station. disagrees with its bearing taken at the third station.

If the error occurred in the foresight, correct it before entering the bearing in the field notes, and note the amount of disturbance; if the error occurred in the backsight, the next foresight will be affected, and should be corrected before entered.