The following plate represents a survey, with the fieldbook from which it was drawn; and, as all the measurements are laid down on the plan with great care, it is hoped that the study of it will sufficiently illustrate the principle of this kind of surveying, as also show that, when the ground is tolerably level, a survey so conducted, if not of too great extent, need not yield in point of accuracy to any other known method. The field-book entries are in accordance with the instructions already given; the principal of which are, that you begin at the bottom of the page and write upwards, and that the fences and boundaries of rivers, roads, &c., be drawn in the field-book opposite the respective distances, at angles or otherwise, roughly representing the inclinations which they present to the lines measured. METHOD OF CONDUCTING A SURVEY. After a careful examination of the ground, the points marked A and B are found to be eligible stations to form the extremities of the base line, as they are not only visible from each other, but staves set up at D and C can also be seen from them both: marks are then set up so as to define a straight line running between A and B, and the measurement is begun at A.* Measurements on the line, A B. Starting from the point, A (see plan), the first entry in the field-book will be, at the bottom," From A." The chaining is then 'carried on in the direction of B. At 820 links, a point, a, appears likely to be useful as a secondary station; a peg is therefore driven at that place and an * Surveyors now use ranging rods of 8 or 9 feet long, and painted white, for ranging lines. entry made, as seen in the field-book; encircling it, in order to distinguish it from other points, and putting a letter (a) opposite. At 882 links we come to a fence, and are careful to give a slight slant to the short line drawn on each side of the number in the field-book, showing nearly the angle at which it is crossed by the chain. At 1115 we reach a point that will serve us when we come to trace, by means of off-sets, the Mitcham road, as well as to mark a point for a tie or proof-line for the triangle, A B C; a peg is, therefore, driven at that point, the number encircled, and the letter (b) placed. At 1222 and 1252, respectively, we cross the boundaries of the road; and at 1483 drive a peg for Oc, to facilitate the putting in of an irregular fence running towards E. (Points are thus often fixed, and noted in the field-book, upon the chance of their turning to account when running secondary lines.) The measurement of the line, A B, is found to be 2326 links. Write B in the right-hand column, and draw two lines across the centre column to show that the measurement of the base line is complete. Thus the middle column always contains the stations from, and the right column those to, which measurements are made; as in the fieldbook before us we see A at the bottom, and O a, b, c, and B on the right. Measurements on the line, B C. The next measurement is from B towards C; the distance measured is 1010 links, crossing a fence at 658, and a boundary of a road at 971 links. Measurements on the line, C A. From C it is 39 links to the fence on the left, an entry is therefore made of 39, opposite an O in the chain column; |