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O in @ After a rough plan has been completed, the contents of all the fields, &c., must next be found, by the methods already given in Chaps. II. and III. The scale to which the plan referred to is drawn, is 10 chains to one inch; it being drawn to this scale to accommodate it to the size of a page of this work, but for the purpose of finding the contents with accuracy, the scale to which the rough plan is drawn, should not be less than three or four chains to one inch, otherwise the several parts of the plan cannot be measured with accuracy. The fine plan may next be made to any required scale that may be thought most convenient. Fine plans are of various scales, from 5 to 20 chains to an inch, according to the size of the estate, parish,
or manor, or to the desire of the proprietor or proprietors. The fine plan is reduced from the rough one by the pantagraph, or by any of the other methods already given, and is accompanied by a book of reference, containing the names and contents of the several fields and other enclosures, the names of the occupiers, and whatever other particulars, concerning the estate, parish, or manor, that may be required. If the estate be a small one, the reference may be put on one side of the plan. The name of the estate, &c., is usually inscribed with large ornamental letters in a vacant corner of the plan, with the scale to which the plan is drawn.
From what has been already explained with reference to the method of laying down plans, keeping the field book, &c., the student will now have no difficulty in conducting such extensive surveys of parishes, estates, manors, as are referred to at the end of Chap. III., whatever be their varieties of shape; since all surveys made with the chain only, are continued systems of triangulation, or the prolongations of all or some of the sides of the fundamental triangles being made the bases of the fur. ther extensions, as may be seen at pages 60, 61, where the
lines for the surveys of the parishes of Woolbedding and Lodsworth are given.
Before quitting this subject, it will be proper to remark, that when two, three, or four surveyors are employed in the survey of a large estate, parish, or manor, it is advisable to divide it into four parts by two large base or main lines crossing one another, at any convenient angle, as near the centre of the work as can be judged by roughly examining it. The main lines must next be tied, as near their extremities as convenient, by four other main lines; which, when laid down, will constitute a proof of the basis of the survey, and will form four large triangles, each surveyor surveying one of these large triangles or spaces cut off by the two first lines. The work, in this case, will be as well connected as if it had been done by one surveyor. The system of fundamental lines in such a survey will nearly resemble that proposed by the Tithe Commissioners for their
surveys for first class maps of parishes, for the purpose of the commutation of tithes. This system of lines has been already referred to at p. 59, Chap. III.
EXTENSIVE SURVEYS OF VARIOUS KINDS, EITHER WITH OR
WITHOUT THE THEODOLITE. PREVIOUS to undertaking any extensive projects in engineering, as railways, canals, harbours, the improvement of the navigation of rivers, &c., the district or country through which the railway, canal, &c., is proposed to be formed, must first be surveyed, and an accurate map made thereof, to exhibit the surface required to be occupied by it, and show how far and in what manner the different properties passed over, or near it, may be damaged, if not wholly required by the undertaking, by its cuttings, embankments, &c., if a railway, canal, or harbour; also, by the severance of estates, removal of buildings, diversion of roads, brooks, and watercourses, by the drainage of wells, ponds and watering places, or by filling them up.
When the intended engineering project is laid down on a map of this kind, and, if a railway or canal, the vertical section thereof accompanying it (see Plate III. at the end of the book), the damage done by it may be readily determined, and the diversion of road, watercourses, &c., contrived in the most convenient manner; in order that the several parties affected may be satisfied.
The survey given at the end of Chapter III, viz., that of the Parish of Lodsworth, is adapted to railway surveying, on account of its long and narrow form; and by tieing other base lines to A B, in that survey, it may be continued to any extent required. But previous to making surveys of this kind, the line of 1 he proposed railway, as far as it can be determined by trial levels, (see Levelling, Part II., Chap. I.) must be roughly delineated, on such a map of the part of the country or district through which it is proposed to pass, as can be procured; (if the railway be in England or Ireland, Ordnance maps are the best for the purpose) with which the superintendent of the survey must be provided that he may know what part or parts of the country is required to be surveyed for the intended project, and in what direction the main lines ought to be taken, which direction must be as near the proposed line of railway as the obstructions arising from woods, rivers, &c., will admit.
Surveys, containing all the required details for this purpose, may be obtained from the first class parish maps, made under the direction of the Tithe Commissioners. These maps may be generally considered as specimens of accuracy, with the exception of a few that were surreptitiously manufactured by disingenuous surveyors; (see pape 61) but as it was optional to the parish authorities whether they would have first or second class maps, they more commonly choose the latter, on account of the expense being less. The great mass of those second class maps, being partly made or compiled from old and incorrect maps, and partly surveyed by unskilful surveyors, are little better than mere sketches of the parishes of which they are put forth as the maps; so much is this the case, that in making surveys for railways, the author, in running a line of little more than a mile in length, has found them to deviate upwards of ten chains from their true position, while fields shewn by the reference to contain about equal contents, were, as shewn by the map, one more than double another in size. These maps are, therefore, utterly worthless for the work in question, for which nothing less than the most accurate surveys are requisite.
When, therefore, a new survey is required to be made, range the first base line, fixing station flags therein at the most convenient points, also other station flags, to the right and left of the main line, in the direction of fences, roads, rivers, &c., except where there are natural marks that will answer the same purpose as the flags. The measurement of the base line,
and the filling up of the survey on the right and left may then proceed, in the same manner, as already shewn in the narrow part of the Lodsworth survey just referred to. When the first base or main line begins to leave the direction of the proposed line of railway, a second main line must then be set out, from a station 10 or 15 chains short of the extremity of the first main line, that the two main lines may thus be effectually tied to each other; after which the survey may be continued along any number of main lines. Sometimes obstructions prevent the effectual tieing together of the main lines, in this case the theodolite must be used, as shall be shewn liereafter. The width of the survey should be
A R from 5 to 20 or 30 chains ; the greater widths being where it has not yet been settled where the line of railway shall pass, or where there are therein, or some other engineering difficulty.
The annexed figure represents a survey of this kind; in which the thick, curved line RW, is the projected railway; A B the first base line, which at B begins to leave the direction of the line of the railway. At OC in the first main line another main line CD is set out, crossing and recrossing the railway. The line C D is connected with A B by the tie
E line BE. In the same manner
B the next main line may be connected with CD, and the survey conducted thus to any extent or in any direction. The filling up of the chief parts of the survey is shewn by the dotted lines on both
W sides of the main lines.
:D ENGINEERING AND OTHER SURVEYS BY THE THEODOLITE.
The use of the theodolite is either preferable, or absolutely necessary, both in engineering and other surveys; the chief cages of which are the following: