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80. It has been customary, since the first settlement of this country, to use the compass in all land surveys, so that the description of lands, in purchase and sale, and by which they are recognized in the courts, involves the length and bearing of each straight line of the boundary. The method, therefore, is, at present, a necessary one.
The errors to which the compass is liable are so numerous and so variable, even in the same instrument, that a change of practice is very desirable. Many surveyors, to insure a higher degree of accuracy, measure the angles of a field with the theodolite or transit, and then, having determined the bearing of one side with sufficient accuracy, calculate the others by a method to be shown in a subsequent article.
81. In surveys of large areas, the surveying party should consist of at least four persons-viz., a compass-man, a flagand two chain-men. In smaller areas, the work is generally performed by the surveyor and one assistant; the surveyor serving alternately as compass-man and hind-chainman, and the assistant as flag-man and fore-chainman.
82. The best method of recording the notes of the survey of any line, from which numerous offsets are measured, is to record the distances along the line in a central column of the left-hand page of the note-book, beginning the record at the bottom of the page, and reserving each right-hand page for a diagram of the survey, and such remarks as are necessary.
The advantage of beginning at the bottom of the page is this: that when standing on the line to be surveyed, and looking in the direction we propose to go, the column in the book lies before us just as the line does, and all measurements made to the right or left of the line are recorded at the right or left of the column. In surveys where many auxiliary notes are
taken, a diagram is an important aid to a ready interpretation of the other notes.
83. To explain the method, in full, of making a compass survey and recording the notes, we will take an example of a farm, in which, in addition to the usual survey of the boundary, such other measurements are made as to enable us to make a correct map of the whole.
Page 119, represents a farm to be surveyed, and page 118, the notes which are made, in the operations on the field.
Beginning with the corner marked A, the bearing of the line AB, is taken. In most cases, offsets from both A and B would be taken, in order that the survey may be clear of the fence, but such offsets are not recorded.
The record of the bearing of the first course is entered at the right of the column (page 118), while the letter designating the station, is placed to the left.
The symbol A, which signifies station, is placed in the column, between the letter and the bearing, for each angle of the farm.
In chaining the first course, the intersection of the line with any objects worthy of notice is recorded. The first record is of the road leading to the quarry. As it is an unimportant road, a single measurement of the distance on the course to its centre is sufficient to locate it. The distance is 4.30 chains.
At 11.30 and 12.35 the sides of the turnpike are intersected. The bearing of the road, at this point, is also carefully taken and recorded.
The intersections of the Garden fence and of the brook are also noted (17.40) and (18.10); and these, with the entire length
At B, the bearing of the northernmost chimney of the farmhouse is taken (N. 73° E.) Such bearings serve two purposes. They aid in the location of the objects observed, upon the map, and serve also, in case of errors, to aid in detecting their location.
In general, in surveying large or small areas, some prominent point or points, within the boundary, should be selected, and their bearings, from different angles, carefully noted.
The chimney of the farm-house and the oak-tree in the corner of the wheat-field, are thus employed in this survey.
At C, the corner of the field, is in the centre of the brook, and from this point to D, the brook is the boundary. A straight line is run between the stations, and offsets are measured to each bend of the brook.
It is necessary, in such a case, for the chain men to exercise unusual care in keeping in the line between the stations, otherwise the lengths of the offsets cannot be correctly measured.
At E, the bearing of the oak-tree is taken (N. 73° E.) On the course between E and F, a marsh is encountered, which the chainmen pass, by an offset course.
At F, another bearing is taken of the oak-tree (S. 444° E.)
At G, the bearing of the farm-house chimney is noted (S. 26° E.) At G and H the bearings of the division-fences are taken. On the course from H to I, the turnpike is again crossed: the intersection of both sides, together with the bearing, are carefully noted.
From I to K, the intersection and bearing of the fence between the potato and the wheat field, are recorded. The course from K to A closes the survey.
To locate the buildings about the farm-house, a few measurements would be necessary; but they may begin with the point already located by the bearings taken to the chimney nearest the north end of the house.