OFFSETTING.

The

2140 70

2130

2720

130

2050

2000

1940

112

1710 403

11

chainage at which these offsets are taken, and their lengths, being all carefully noted. The annexed figure will best explain the nature of offsets, how, where, and for what purpose they are taken, and also how they are afterwards laid down on paper. This figure is a short extract from the field-book, in which you read from the bottom upwards towards the top. extract commences at 1000 links, or 10 chains, showing that the whole number of arrows has changed hands once; at 1060 an offset is taken; it is taken at 1060, because that is the link at which a line at right angles to the chain will intersect the corner of the two fences; the length of this offset measures 92 links, and is entered as such; 1130 again is the chainage from which a perpendicular to the chain will fall on the corner of a house; the same at 1235; at 1525 a similar offset is taken to the corner of a fence; a square has been drawn round this chainage, to show that it has been marked

1600 120

1625 120

70

1470

1437

130

1382

130

as a "station;" that is, a point from or to which another line hereafter will be measured; the same at 1940, from which an offset is taken not only to a bend in the fence, but also to another fence, which there runs into it; at 2000 another change of arrows; at 2050 there is an offset to a junction of fences; at 2120 the chain cuts the brow of a ditch, and at 2130 the quick; the figures 70, 45, and 80 in the buildings note their widths. In taking the boundaries of fields which are surrounded by hedge and ditch, it is the edge of the ditch which is the true boundary, and to which therefore the offsets are to be taken, or an allowance for the width of the ditch should be made in the field-book; six links is often given as the width of the ditch. Taking the offsets to the bends and irregularities of a fence is a very simple matter, but taking offsets to the junctions of fences requires some care, because it is the intersection of the edges of the ditches which has to be noted, and it requires some caution in finding on the chain the exact point from which a perpendicular will

fall on the intersection of the edges of the ditch. By neglecting to pay due attention to this, a boundary between two fields may be placed some eight or ten links wrong; in a working, or "permanent" survey, as it is called, this should be carefully attended to.

As regards the lengths of offsets, that is, the greatest distance from a chain line to which offsets may be taken; where merely the bends in a fence have to be determined, a length of offset of two or three chains may very well be taken without further precaution than fixing the perpendicular by the eye, and measuring its length; supposing, for instance, that in chaining through a field, a fence running by the side of it is at about from one to three chains from the chain line; this distance is not at all too great for the correct fixing of the position of the offsets to the bends in the fence; and the lengths of such offsets may be very accurately measured. But where the chain line cuts a fence obliquely, and there is another fence running into it, which is more or less parallel to the chain line, a little more caution is requisite to fix correctly the boundaries; the annexed cut will explain our

meaning to the young practitioner; let A B be the chain line; it is required to fix the point of intersection of the ditches at C, which is about two chains off; instead of fixing the position of C merely by a right-angled offset, it will be found better to measure from A to C, and then laying out another chain, measure from d to C, and note these dimensions in the fieldbook, marking in the dotted lines to explain how this has been done. It will be found that there is no loss of time in doing this, that the point is more accurately fixed, and consequently more accurately laid down on paper by means of arcs from A and d with the lengths A C and d C intersecting at C, the point required. The same observations will hold good as regards the fixing of the positions by offsetting of the corners of buildings; let it be understood that we are now speaking of surveys to be plotted or laid down on paper to a scale of from six to three chains to the inch; where, however, in consequence of the great number of irregularities or bends in a fence, it would be necessary to take a correspondingly great number of offsets of an average of two chains length, it will be found much shorter and more correct to lay a couple of perpendiculars towards the fence and join them by a line parallel or thereabouts to the fence, and so close that the offsets will only be about half a chain long, or even less, as shown in the annexed figure; where A B is the main chain

TAPE AND OFFSET STAFF.

13

line, dc and e f the two short perpendiculars, and c f the line from which offsets to the fence are to be taken; a little observation will show that this will be the shortest method of proceeding in such a case, and in every way

better and more correct than the number of long offsets which would have to be taken from the main line.

C

B

There are two instruments in use for measuring offsets; the tape, and the offset. staff; the first requires no description, and in using it, we have only to note the spot to which we are going to offset, and to find the link on the chain from which the perpendicular is to be measured; this is ascertained by the eye, and very correctly after a little practice. The principal objections are, that it requires two persons to attend to it, that even with care it very quickly frays out, and that in dirty weather, more particularly if much required, it soon gets so dirty as to become quite illegible; it is more desirable to use amongst buildings than in the field. The surveyor, however, should always have one in his pocket. The offset staff which is generally used by surveyors is the tenth of a chain in length, equal therefore to 10 links, or 6 feet 7 inches nearly. It may be of hickory, ash, or red pine, requiring to be made of tough springy stuff, as it has a good deal of rough usage to go through; in the centre it should be about one inch and a quarter, or one inch and a half in diameter, round, and slightly tapering towards the ends, which should be about three-quarters of an inch in diameter; one end should be armed with an obtuse pointed iron ferrule, with a steel point for sticking in the ground; at the other end should be another ferrule not pointed, with a strong hook fastened to the side, and wide enough to receive the brass handle of the chain; with this hook the offset staff is extremely useful for dragging the chain through a hedge; the links may be marked upon the offset staff by drawing rings round it with a red-hot wire; the centre may be marked with a V, and the other numbers read off by the eye. It is used in the following manner; having noted the spot to which the offset is to be taken, stand sideways along the chain with the rod in your right hand and between your legs, and pointing to the spot to which you are going to offset; you will soon see, after a little practice, when it is at right angles to the chain, which will give you the chainage to enter in your field-book; this done, lay the rod pointing to the spot you

are offsetting to, and keeping this point in your eye, turn your rod round end for end over and over again along the ground, until you reach the other end of your offset, counting the length as you go along, each length of the rod being 10 links; if you are at all active you will, after a time, do this at a running pace, but of course for accuracy the staff must come flat to the ground each time it is turned over. We may now conclude this portion of our subject with the following hint; that it is unnecessary to offset to fences or other objects one or two chains off, if these have to be picked up upon other chain lines to be set out hereafter.

If the reader has had no experience whatever in surveying, and is anxious to learn, we would now advise him to take a chain, arrows, and an offset staff, go to some quiet place in the fields, hire some youth to drag his chain, lay out a line of some half-mile in length-taking a tree, for instance, as a distant object, being careful that there are hedges along the side of the line to offset to-and then and there put the advice above given into practice; measure this line half-a-dozen times over, taking the offsets every time, and compare the results. With a little care in practising all this he will, in two or three days, be able to chain and take offsets. Writing off the chainage will perhaps puzzle him a little at first, but he will quickly overcome this; for instance, suppose his first offset comes upon the first half chain, then it will read 50 in the field-book, being 50 links; let another come upon 6 chains and 47 links, when he has 6 arrows in his hand, and the chainage will read 647; after the first change, let the cutting of a fence come at 3 chains and 83 links, then it will read 1383; if this had been after the seventh change, then it would have read 7383; again, suppose it to be at 67 links beyond the tenth change of arrows, then it would read 10067; or 5 chains and 79 links after the twentieth change, then it would read 20579, and so on; hence the necessity of carefully entering each time a change of arrows occurs, as it denotes that 1000 links, or 10 chains, have been expended; if this be neglected, you are very likely to make a 10 chains' mistake. Also with regard to the finger-marks on the chain, remember that 3 or 4 fingers on one side of the round 50 mark in the centre, read 30 and 40 links, but on the other side of the round 50 mark, they read 60 and 70, being respectively 10 and 20 links beyond the 50, and 30 and 40 short of the 100. This must not appear fastidious, for such mistakes do occur even to practised surveyors from oversight and occasional hurry.

We will now say a few words upon the subject of "stations." In making a survey, a line is chained from end to end to ascertain the measure of the total length, the distances at which

boundaries are apart, as also the different lengths at which offsets are taken to objects near the line, and more or less parallel to it; and if a survey is only to be four or five chains wide, the whole of it may, in many cases, be obtained upon that one chain line; but instead of this, it is seldom less than twenty chains wide for engineering purposes, except amongst buildings, and often as broad as long. Hence the necessity of other lines to pick up the features over the breadth of country under survey, and all these lines must be connected and tied together. The points at which they start out of, into, or through each other, or where they begin, and where they end, are called "stations." They are marked as such in the field-book, for reference during the survey, and when the work is being laid down on the paper; and they are also marked on the ground in order that they may be found when wanted. In the field-book this is very easily done by drawing a line above and below the figures denoting the chainage at which the station is made. On the ground it is sometimes more troublesome. In grass lands it is easy to cut a triangular mark, or a crow's-foot, just large enough to catch the eye, when revisiting the spot to pick up such station; but in a good deal of arable land such a mark would soon be lost sight of; in such cases, the best thing to be done is to drive in a picket, cut out of a hedge, of which the chainmen should have a few in their pockets, or in bags slung over their backs; one of these can be driven into the ground at the spot required with the bill-hook, which they have also to carry about with them. When, however, a station of this kind comes anywhere near a hedge which the chain line is intersecting, we often prefer marking the quick in it, as a false station, and chain back or forwards from it, when the station is required at a future time; we are then certain that our mark will not be lost or destroyed.

When, however, circumstances are such that the station can be conveniently marked it should always be done, taking first due care to look about you to see how a line running through it, right and left if necessary, will lay to pick up the work that will be by the side of it. In doing this, keep your eyes also open to any opportunity there may be of laying your station so that you may be able to take any natural object for the line to be chained upon instead of having to send forward to stick up a pole. It can never be too carefully or constantly kept in mind, that by attending to all these things much valuable time is often saved. If your fences, &c., lay so that you are likely to have two or three lines in different directions from about the same place, endeavour to place your station so that it may answer for all. Avoid putting a station upon odd links, but put it at a ten, or at