These field memoranda show that at the end of fourteen chains, on the first line, the second line begins, making an angle with the first of 97° 32'. This angle was measured with the sextant held over the station B, by bringing the picket at the first station A, and that at the end of the next line C, into apparent contact, as seen in the instrument. At C, on the second line, the angle measured between the back station B and the fore station D, is = 78° 38'. At D the angle, measured in a similar manner between C and the first station A, now made the fore-mark, is = 93° 2'. At A the lines cross, and here the angle between the last line and the first, that is, between the stations D and B, being measured and found = 90° 56', affords a proof on the angles; the sum of which, in a quadrilateral figure, should be = 360°. (See page 44.) 97° 32' 78 38 93 2 90 56 The sum of these four angles is = 360 8 being 8' more than the truth. Let 2', therefore, be subtracted from each of the angles, by way of making an equal distribution of the error. All the observed angles, in this instance, are inward angles, having been measured from the back station of one line to the fore station, or fore-mark of the next. It is, however, frequently more convenient to measure an external angle, viz. from the fore-mark of the line which has just been measured (instead of the back station), to the fore station of the succeeding line. The supplement of the angle observed then becomes the internal angle. From the foregoing data, the plan of these two fields, laid down to a scale of six chains to an inch, together with the lines of construction, will be shown in the following figure: The contents of these fields, computed either by the methods which have already been explained, or by that which will be found at page 241., are as follows, viz. A. R. P. SURVEY OF AN ESTATE. FOR the sake of illustrating the foregoing principles we will show how they may be applied to the measur ing of the estate represented in the frontispiece. In the former editions of this work directions are given by the author for dividing this estate into three por tions, surveying each separately with the theodolite, and afterwards drawing a connected plan of the whole. For the reasons that have been already explained, it will be much better to construct a triangle or trapezium with the chain only, so as to include within it as much of the estate as possible, and in order to do so, it will be proper to proceed as follows: - Having walked over the ground, and observed that its general outline is that of a trapezium, whose longer diagonal is somewhere in the direction AF, begin by selecting the most conspicuous object you can find that may serve as a fore-mark for setting out such a line, taking care to avoid the Plantation No. 20., and the Nursery, No. 27., which, in this instance, is effected by passing between them. Let the directions which have already been given for preserving a straight course, be carefully attended to. Make some good mark on the ground at the first station A, and cut a notch on the gate leading into the field, No. 18., called Little Sandpits. Let other marks be made as stations either on or near all the fences which you cross, carefully observing that all these points are exactly in the line. Having proceeded as far as F, which lies rather beyond the limits of the estate, and made a station in the last fence by a cut on the stump of a tree, (as marked in the field-book), begin to look out for a second line in a direction nearly parallel to your eastern boundary This being a road, let such an object be chosen as will enable you to set out the line EG, which lies within the fences of the road for the greater part of its length, and is therefore most conveniently adapted for measuring it. If no suitable object present itself exactly in the required direction, your choice of a fore-mark being confined by the road within narrow limits, send forward an assistant with a staff, and direct him by signals to fix it up at any point G where it may best suit your purpose. Having ranged out the line EG, and left such stations as may be necessary, |