AS TO CROSSING FENCES.

143

This should be shown in the field-book by a

line from E to B. sketch in the margin.

Foot Paths and Cart Tracks.-Foot-paths should always be shown by a single dotted line, cart-tracks by a double dotted line; but in taking the latter it is customary to ascertain the average width, the offsets of which are always taken and booked to the centre thereof unless for very exceptional reasons to the contrary.

Gates. In picking up a gate in a fence it is necessary to fix the position of one of the posts accurately by means of a triangle and then to ascertain the width of the gate; it is not absolutely necessary to take both posts.

How to mark Hedge and Ditch. It will be seen in the course of this survey that the fences are shown by a strong line, which indicates that it is a hedge; the little T's indicate the position of the hedge. In the case of Plate I. it will be seen that the northern and a greater part of the eastern fences are shown by dotted lines, with crossed dashes; this indicates that it is a post-and-rail fence, and where the line is firm it is evident that it is an ordinary hedge. The north-western fence E H J is a double line, from which it is to be understood that it is a wall.

Avoid crossing Fences as much as possible. On a large survey it frequently happens that many of the lines cut through a large number of fences, but it is very desirable to minimise this as much as possible, and it not unfrequently happens that, if one stands on an eminence at the commencement of (say) line 1, it is possible to command a long stretch of country to the termination of that line, passing, it may be, through ten or twelve fields. It is wise, therefore, for the surveyor, having determined upon his stations at the commencement and termination of this line, to dispatch his assistant with laths or other means of marking, with instructions that, in front of every fence through which the line passes, he is there to leave some distinguishing mark according to directions given by means of signalling right or left, as the case may be. This should be done at every fence, for it is not at all an uncommon thing, in the process of chaining such a line, especially in a valley, that it is not only found impossible to command a view of the end of the line, but the hedges themselves may obscure the view also. But another reason in favour of marking the exact point of intersection is, that the chain-men can see the exact place through which the chain should pass, for which purpose the offset staff has a hook arrangement (as illustrated at Figs. 1 and 2, Chap. I.) to facilitate getting it through.

Be careful not to cut Fences unnecessarily. — There are many parts of England, especially in Leicestershire, where the

hedges are not only very thick but exceedingly high; and in a survey for a railway which I made some years ago of about twenty miles in length, with the snow on the ground, my patience and that of my assistants was very severely taxed by the constant necessity of passing through such fences; and here I would repeat the warning I have given elsewhere, that the surveyor must exer cise very great judgment as to how he passes through such fences. I have seen most wanton damage done to a fine, handsome, fully-grown hedge by thoughtless and often wilful cutting of huge gaps. No good surveyor would descend to such a questionable practice, and it is to obviate such expedients that I recommend the line to be accurately ranged out before proceeding to chain. Here again my theory of becoming intimately acquainted beforehand with all the characteristics of the property holds good, as, unless the surveyor has walked completely round the boundaries and made mental note of the position and form of the various fences and other circumstances, he must not be surprised if after the expenditure of some hours' work he is brought face to face with the fact that the line, which he thought would be clear of a fence running parallel therewith, at an unexpected point project right into the line, involving a fresh line being set out and all the previous work thrown away.

Don't cut down a Tree to save moving a Line.-Again, by a reconnoitre such as I have recommended, the necessity of cutting down trees (which intercept the line) is avoided. I speak somewhat feelingly on this subject, as in one case the reckless carelessness of one of my assistants-in cutting down a valuable oak-tree in my absence—not only involved me in heavy pecuniary loss. and other unpleasantness, but very nearly was the means of throwing an important project out of Parliament.

In conclusion, it only remains for me to say that when a surveyor goes on a property-no matter whether at the instance of the owner or occupier, or whether he is really a trespasser-there are certain courtesies which devolve upon him, which, if neglected, may involve him in unpleasantness if not in more serious results. If it be necessary to pass through a gate, it is equally desirable that you should close it after you; the same remark applies to doors. If curiosity prompts individuals to interrogate you as to what you are doing, a little tact may evade the necessity of your divulging your business, and protect you from the mortification of afterwards finding out that a discourteous answer was given to a person who not only had a right to know what you were doing, but who had the power to make things very unpleasant.

Clear up the Ground after you. After having completed the survey, before leaving the ground insist upon the chain-men re

moving all pegs and laths, which are often considered not worth carrying away, and pieces of paper that may have been used in the operations. In fact, leave the ground as nearly as possible in the state in which you found it.

Cautions.—It is not only not desirable to throw stones at dogs on the property, but the time occupied in so doing may be devoted to better purposes without the risk of giving offence to those to whom they belong! In putting pegs in the ground, especially in meadow land, care should be observed that they project very slightly above the surface, as otherwise serious injury is often done to cattle and horses grazing thereon.

The chain should be tested every morning before commencing operations.

If a station has been made by driving a peg into the ground, is necessary to remove the peg if a rod is to remain there for the purpose of chaining to, as it should be exactly in the same position as the peg.

L

CHAPTER VI.

THEODOLITE SURVEYING.

Ir seems hardly necessary to say, that all important surveys are now executed with the theodolite or other instrument for obtaining the angles which a line or lines make with another.

In Chapters II. and V. I have endeavoured to show how surveying may be accomplished with the chain only, but in the present I propose to demonstrate how any large or complicated survey can only be accurately and expeditiously done by means of the theodolite.

Check-lines obviated.—In the first place we have seen that in the simple case of a four-sided figure, whose sides may have been carefully chained, it is impossible to plot the same except by diagonal or other check-lines-the only means of testing the accuracy of the work—whereas with a theodolite all check-lines are not only obviated, but in the field the accuracy of the relative positions of the four stations is made absolute by the addition of the four angles together, the sum of which should give 360 deg.

Accurately mark Station.-In commencing a theodolite survey, it is necessary to establish the chief stations in the first case, and at these points to drive stout pegs well into the ground, and into the centre of these should be driven nails to mark the exact point of intersection of the lines, which is absolutely necessary.

When to take Angles.—It is a matter entirely of choice whether the angles be taken at the commencement of the survey or not; but it will be found most convenient to take them altogether (and possibly it is preferable to do so the last thing), as it is not desirable to keep the instrument knocking about in the field, as accidents, often of a serious nature, easily happen.

The necessary Number of Angles.-I have been frequently asked by my pupils how many angles are necessary to be taken in a survey, and the syllabus of the Surveyors' Institution examination leads up to this question; so that I deem it advisable at this stage to consider the matter in detail.

In trigonometry, it is proved that to solve a triangle two angles and one side, or two sides and one angle, must be given to prove the other sides.