"To execute a survey of this kind, supposing the line to have been previously chosen, the surveyor must set up his compass at one extremity of the work, and take the beating of some distant object situated in the direction of the intended line of railway or road; having done which, and entered it in his field book, he must commence chaining in that direction, taking offiets to the fences of the fields, and every remarkable object within a short distance to the right and left of the line; he must also note the point at which his chain crosses the various fences, and at the same time and place set up his compass to observe the bearing of such fences, or, in other words, the angle their (Erection makes with the meridian ; this angle is at once given by the compass, and furnishes data for laying down their position with regard to the mainline which crosses them, but does not determine their respective lengths ; the surveyor must therefore measure along the side of each fence, both to the right and loft of the point at which he crosses it, till he comes to their extremity, or the points where such fence meets the other, or side fences of the field; these now become known or fixed points, from whence the bearing of every fence which diverges from this may be taken, giving the means of laying down their several directions on the general plan.
" If the surveyor should require to represent the boundaries of the fields which are still more 'remote from his main line, he must similarly measure the lengths and curves of the fences he has previously taken the bearings of ; and then again the bearings, &c. of others, UM be possesses sufficient data for his purpose ; but he will occa'uonally find it more convenient to measure secondary or side lines branching from the main line which, by crossing a number of fences, give so many fixed points to take bearings from, as to reduce his labour materially, both in the field, and afterwards in the work.
" Having proceeded onward with the inessurement of his first main line, as far as may be convenient for his purpose, and also completed the measurements branching therefrom, the surveyor must again set up his compass at the point where he wishes to change the direction of his course, or commence a second main line • when having taken the bearing of some natural conspicuous object in the required direction, he must proceed to measure such second line, and all.its subsidiary dimensions, in the same manner as before, completing as much as possible all the minor measurements depending on each main line before he commences a new one.
" Such is the general method of procedure ; but as every thing depends upon the experience and tact of the surveyor, it is impossible to give more than a general description ; particular rules for surveying are useless, as new cases, and sometimes difficult ones, are hourly occurring, which the experience of the surveyor alone will enable him to overcome, and suggest at the time a method, which no book, in all probability, could inform him of.
" The protraction of a survey is the most easily performed by having a protractor laid down on the plot itself, from which the angles can be transferred by a parallel ruler to any part of the work." In making the necessary calculations for the quantities of earthwork, &c., we would earnestly recommend the use of the tables formed for that purpose by Mr. Macneill. Though the calculations are not intrinsically difficult, yet they unavoidably contain a great number of figures ; Mr. Macneill's tables so simplify the operation, as to render errors of consequence scarcely probable, and at the same time are founded on such•scientific principles, as to elicit, with certainty, the most correct results.
The hne of road being fixed, and marked out, we now come to the consideration of the.principles of road-making, and the just application of them in the selection and disposal of materials. The first principles of any branch of science, are gene rally clear and comprehensive, and confidently appealed to by the advocates of most opposite opinions in justification of their peculiar dogmas. But while all admit
the essentiality (so to speak) of correct principles, how various and contradic tory are their plans of carrying these principles into effect Road-making pre sents no exception to this general rule. It is admitted by all, that a road should combine the qualities of hardness, smoothness, and strength, or sub stance. To obtain these requisites, it would to us appear unnecessary that great care should be taken to prepare the bottoming, or foundation, on which the surface materials are to rest; but on this point there exists much difference of opinion ; and as it is of great importance, we shall briefly state the argu ments of each party, as given in their respective publications. Mr. Mac Adam, in his Ilemarks on the present System of Road-making, maintains that the elas ticity of the sub-soil is rather a benefit than an injury, in contradiction to the opinion of Telford and other eminent engineers, that on a substratum of a spongy nature, as bog-land, or morasses, it is absolutely imperative to render the foundation firm. The following evidence was given by Mr. Mac Adam before a Committee of the House of Commons, in the year 1819: " What depth of solid materials would you think it right to put upon a road in order to repair it properly 1—I should think that ten inches of well consoli dated materials are equal to carry any thing. That is, provided the substratum is sound?—No; I should not care whether the substratum was soft or hard ; I should rather prefer a soft one to a hard one. You don't mean you would prefer a bog ?—If it was not such a bog as would not allow a man to walk over, I should prefer it. What advantage is derived from the substrata not being per fectly solid think, when a road is placed upon a hard substance, such as a rock, the road wears much sooner than when placed on a soft substance. But must not the draught of a carrriage be much greater on a road which has a very soft foundation, than over one which is of a rocky foundation think the difference would be very little indeed, because the yield of a good road on a soft foundation, is nJt perceptible. Would a carriage run so true' upon a road, the foundation of which was soft, as upon one of which the foundation was hard 1—If the road be very good, and very well made, it will be so solid, and so hard, as to make no difference. The road in Somersetshire, between Bridgewater and Cross, is mostly over a morass, which is so extremely soft, that when you ride in a carriage along the road, you see the water tremble in the ditches on each side ; and after there has been a slight frost, the vibration of the water from the carriage on the road will be so great as to break the young ice.— That road is partly in the Bristol district. I think there are about seven miles of it; and at the end of those seven miles, we come directly on the limestone rock. I think we have about five or six miles of this rocky road Immediately succeeding the morass; and being curious to know what the wear was, I had a very exact account kept, and the difference is as five to seven in the expendi ture of the materials on the soft and hard." It would exceed our limits to give more of this gentleman's evidence in detail, we must content ourselves with the substance of the remainder, viz. that no intermediate material is to be put between the broken stone and the bog ; that no stone is to exceed six ounces' weight ; that a foundation of bog does not sink ; and that there is the same thickness of material on bog as on firm ground. In absolute contradic tion to the doctrines of Mr. M'Adam, we now quote a Terri of Mr. W. A, Froths, assistant engineer to Mr. Telford, under whose immediate superin tendence all the works on the Holyhead Road in North Wales were executed.