will then find, with due exercise of care and precision that he will acquire speed in proportion as he is diligent in practice.

Efforts have been made to supply the needs of architects, engineers, and surveyors in the following pages. Railway Surveying and Parliamentary work have been dealt with, in special chapters, as useful for engineering students. Architectural students must not, however, conclude that this book needs no place on their shelf. Part of architecture consists in the consideration of a site with a view to placing a building on the land, and in the case of a mansion to be built on a new estate, an architect who surveys the estate himself, will know much more about the ground, than an architect, who, without inspecting the site has employed a surveyor to do the survey for him. The laying out of an estate round a mansion, needs to be considered in relation to the mansion itself, as the centre of the whole.

Precautions in the handling of instruments are given, but the limits of space allow their actual use to be only briefly described. Once, however, the construction of an instrument is understood, and the general principles of its application become realised, a little out-door practice will contribute more towards efficiency, than several hours spent in reading written descriptions of field-work.

The Author is indebted to several well-known instrument makers, as well as to previously-published Student's Column articles in THE BUILDER, for the illustrations which accompany this work.

August, 1900.

A. T. W.

LAND SURVEYING AND LEVELLING.

CHAPTER I.

INTRODUCTION.

THE origin of Land Surveying has been disputed by historians, but it is generally supposed to have originated with the Egyptians, who were compelled by the annual inundation of the River Nile, removing or defacing the boundaries of different proprietors, to devise some method of ascertaining the position of their land-marks by measurement after the waters had subsided. From the banks of the Nile, it is said to have been introduced into Greece by Thales, who was born 640 B.C., after he had travelled in Egypt with a view to study mathematical science, and to him as well as to Euclid, Archimedes and others, we are indebted for many geometrical deductions which have proved of great value in improving the art of measuring land. So great was the value set by the ancient Romans upon a knowledge of the art, that they accounted no man capable of commanding a legion who was incapable of measuring a field.

The area of permanent pasture in Great Britain is becoming largely increased, and dependence upon wheat supplies from abroad is becoming more and more absolute, because wheat cannot be profitably grown here, and because the profits. of barley growing are so uncertain. Towns extend in all directions giving an increasing value to land, with the consequent necessity to ascertain accurately its dimensions and

content.

Compendiums of mensuration, together with trigonometrical expressions for the calculation of heights and

B

distances, form no small portion of existing treatises upon the subject; but a knowledge of the practical use of instruments is of primary importance, and in this study, it is essential to start upon true principles, otherwise it is difficult afterwards, to steer clear of error.

Professor Leslie, in his Geometry, writes: "In surveying hilly ground it is not the absolute surface that is measured, but the diminished quantity, which would result, had the whole been reduced to a horizontal plane, the distinction being founded on the obvious principle that since plants shoot up vertically, the vegetable produce of a swelling eminence can never exceed what would have grown from its levelled base. All the sloping or hypothenusal distances are, therefore, invariably reduced to their horizontal lengths, before the calculation is begun."

Thus we see the practice of professional surveyors supported by the experience of a leading mathematician of his day, and the same opinion is approved by all who have had to deal with the value of land, for it is evident that if a field be sold by the surface measurement, and if it be afterwards levelled by filling up the valleys with material from the hills, the owner would not have the same quantity of land as he had paid for, if the field be re-measured. The only thing that can be reasonably admitted is the work of the labourer, consisting wholly of lineal and superficial measurement, such as mowing, reaping, hedging, ditching, etc. Lastly, no more houses could be built upon sloping ground, than could be erected upon its base, if the site were levelled by the removal of the hill. Hence the purchaser of ground, situated on a hill, would be unjustly treated, if the area be calculated by hypothenusal dimensions.

In the field, a surveyor has, in the first place to consider what lines are necessary to be measured, not for the purpose of obtaining the area, but from which to measure the necessary offsets, in order to secure a correct outline plan of all the short indentations contained within the boundaries, and to accurately connect together the whole survey. The area can then be expeditiously calculated from the plan. It is a mistake to rush on to the ground in order to commence a survey before you have carefully examined the extent,