PARISH SURVEYING. Now, having shewn how to survey a small portion of land with the chain, and also to plot it and calculate its area, we shall next proceed to lay before the reader the method at present practised on the Parish Survey of England, under the Tithe Commissioners appointed for that purpose. Captain Dawson, in his report to the Commissioners, says, "It is necessary to determine the area of the whole parish by some means, which make the correctness of that area independent of the result obtained by summing up the contents of each encloser, minute errors in many of which would escape observation, if not checked by comparison with the correctly ascertained whole. It is essential, in fact, to arrive at the total area of the parish by direct admeasurement of the space included within its external boundary; and the simplest and cheapest means by which a survey and plan may be made for effecting this object appear me to be as follows: "1st. To measure two straight lines through the entire length and breadth of the parish. "2nd. To connect the ends of these lines by means of other lines; and "3rd. From these connecting lines (by measured triangles and offsets) to determine the entire parish. boundary. "The true area of the parish may then be obtained by calculation from the measured distances, and by the admeasurement of the included space upon the plan." Part of these instructions, as far as the author could learn, have never been strictly acted upon. If two lines could be drawn through the greatest length and breadth of the parish, and their extremities connected, as recommended by Captain Dawson, the contents of the encloser may be found, no doubt, much more expeditiously and cheaply than by any other plan that could have been proposed for the purpose; but in real practice, there is scarcely a parish in England or Wales so open, that the four extremities of these intersecting lines can be visible from any one extreme point, a condition supposed to exist in every parish, to render the plan practicable. The plan generally practised is the following, viz. : You travel over the parish, examining it minutely, with a view to ascertain the direction of its greatest length, and having satisfied yourself upon this point, chain a base line from one extremity, as nearly as you can guess, in that direction, placing marks or false stations, as they are called, at the end of every five or ten chains, and taking special care to make the necessary correction in chaining over hilly ground. In chaining the base or any other long line, you will most likely be interrupted by private houses, public buildings, gentlemen's gardens, lakes, or other obstructions, which would make it impossible to chain accurately in a straight line; in that case the use of the theodolite, or some other angular instrument, is indispensable. When you meet with such obstructions, measure, with great care, an angle of 60°, either to the right or left of your direct line, and measure out, with the chain, any length so as to get clear of the object that obstructed your direct course, then take another angle of 60° with your present course, and measure the same distance as the last line. If this be done with great exactness and care, you will have arrived at the exact spot that your first direct course would have brought you to, had you met with no obstruction. This process is simply measuring two sides and angles of an equilateral triangle, the third side being the distance, through the obstruction, from the last point arrived at to that from which you first diverted from your original course. Having arrived at this last point in your original course, measure the supplementary angle of 120° from the last measured side of the equilateral triangle, and it will direct you in the required course. In order to verify the measurement, the bearing of the line should be ascertained before and after having passed the obstruction, and if they were found to disagree, the work should be repeated. To measure inaccessible distances with the chain and cross-staff only. When you meet with the obstruction, leave the chain stretched in the direction of your line, and measure, by means of the cross-staff, a line at right angles to the chain, so as to get clear of the obstruction; at the end of this line measure another line at right angles to itself, so as to clear the other side of the obstacle, and at right angles to this last line, measure a third of the same length as the first which deviated from the original course, and you will come on a point in the original line; to proceed from which point in the proper course, you erect a perpendicular, by means of the cross-staff, to the last measured line; the length of the line, parallel to the original one, will give the distance across the obstruction. Having measured the base line, construct triangles on it to the right and to the left, taking care to have them as nearly equilateral as the nature of the ground will admit. On the sides remote from the base line, construct other triangles, measuring the sides of each triangle, and noting them down in your fieldbook; and so proceed till the entire parish be triangulated. It is best to begin to fill in the triangles after having laid out two or three, lest the stations should be lost; but to guard against such an occurrence, great care should be taken to mark them well, by driving a short piece of wood, pointed at one end, fast in the station, and cutting a circle round it. It would also be advisable to make a note of some surrounding objects, as landmarks, by which the position or locality of the station may be easily discovered. Before you begin to fill in your triangles, run proof lines from the vertex of every triangle, if possible, to close on the base; but should intervening obstacles render it difficult to run these proof lines from the vertex, measure them from side to side of the triangle, having them as long as the ground will admit. Having measured the sides of the triangles and proof lines, numerous tye lines are to be measured, from which offsets are to be taken to the several objects, ditches, fences, &c. in each triangle. With regard to the direction of these tye lines, circumstances alone can direct. From these secondary lines, other tye lines might be measured if occasion required it. All these may be measured in any direction, without regard to the false stations erected during the measurement of the base or primary tye-lines; because having driven stakes at intervals of five or ten chains, the distance from any one of them to the point at which a line crosses “can be measured as correctly as if that spot had been fixed on for a station, when these principal lines" were measured. These primary and secondary tye lines will answer as good proofs of the accuracy of the chainage. In measuring offsets, none should be longer than one chain. If the boundary of the parish be very crooked, the extreme triangles must necessarily be small, so as to mark the extreme boundary by offsets not longer than one chain. In measuring the sides of triangles, mark accurately where these lines meet with any hedge, ditch, river, lake, &c., and where any remarkable object is placed, omitting nothing that ought to be represented on the map of the parish. It would be well to set marks at the intersections of all the hedges with the station lines, that you may know where to measure from, when you require to measure all the fields. The place where you run upon or cross a chain line may be easily ascertained by setting up poles at two of the nearest stations on that line, the crossing will be at the point in a direct line with these poles. The persons at the poles will set you right, by directing you |