REESE TIBRARY UNIVERSITY PRACTICAL SURVEYING. CHAPTER I. INTRODUCTION. "SURVEYING is the art of ascertaining, by measurement, the shape and size of any portion of the earth's surface, and representing the same, on a reduced scale, in a conventional manner, so as to bring the whole under the eye at once." Subjects necessary to be known.-Such being the concise description of the science of surveying by an ancient writer, I am induced to inaugurate these pages with it. In the " Encyclopædia Britannica" it is argued that, "considered as a branch of practical Mathematics, Surveying depends for its principle on Geometry and Trigonometry; and further, "it may be proper to mention the previous knowledge which a surveyor ought to possess, and to notice the instruments which he is to employ in his operations. As a surveyor has perpetual occasion for calculation, it is necessary that he be familiar with the first four rules of Arithmetic, and the rule of Proportion, both in Whole Numbers and in Fractions, especially Decimals, with the nature of Logarithms and the use of Logarithmic Tables, and with at least Algebraic Notation. As it is his business to investigate and measure lines and angles, and to describe them on paper, he should be well acquainted with the elements of Geometry and Trigonometry, and with the application of these principles to the mensuration of Heights, Distances, and Surfaces. In particular, he should be familiar with the best practical methods of solving the ordinary geometric problems, and should be expert in drawing lines and describing figures. He should be acquainted with the principles and practice of Levelling; he should know something of the principles of Optics and Magnetism, and should possess at least a smattering of the arts of Drawing and Painting." The foregoing remarks, from so eminent an authority, represent B more forcibly than any words of mine could the range of subjects which demands the attention of the student, and it will be my endeavour in the following pages to give them practical effect. It is necessary, however, that I should traverse to some extent familiar ground, which I shall avoid where practicable; but I wish to make this work as complete as possible, and would therefore claim the indulgence of the reader if I seem inclined to be too elementary. Standards of Measure. In this country we are accustomed to what is known as the duodecimal system of measuring, whereof the foot of twelve inches is the basis. I do not propose to question the wisdom of continuing this standard in the face of the almost universal adoption of the metric system upon the Continent, and indeed nearly all over the globe; but I am bound to confess that the latter method, apart from its universality, offers greater facilities both in practical and theoretical application. Chains. For surveying purposes in England we have two kinds of chains, viz. the 100-feet and Gunter's. These chains, made of stout iron or steel wire, are composed each of 100 links ; in the former case each link being equal to one foot in length, and in the latter 7.92 in., or 1-100th part of 66 feet, being the length of the link. It will be manifest that the 100-feet chain has many great advantages, the chief being that it is so easily understood; and it is further argued that its increased length over Gunter is more conducive to accuracy in its use in the field. Advantages of 100-feet Chains. For large plans of estates especially those destined for building operations, where every inch is of consequence, or for works of construction, the 100-feet chain will prove to be invaluable. But in the operations of surveying proper, for many potent reasons, pending the complete revolution in our system of mensuration, I must admit my preference for Gunter's chain. Gunter's, or 66-feet Chain. This instrument, if I may so call it, was invented about two hundred and fifty years ago by the Rev. Edmund Gunter, an eminent professor of astronomy at Gresham College (A.D. 1620). It is also called a four-pole chain. It is 66 ft. long (or four poles of 16 ft.*), composed of 100 links of strong iron or steel wire, each link being 7.92 in. or 1-100th part of 66 ft. At every 10 links is fastened a brass tablet of different *Poles, sometimes called perches or rods, in different parts of the kingdom, were formerly (by custom) of various lengths; as, of 15 ft. or 5 yds., 7 yds., 8 yds., &c. All these are now obsolete, and the statute acre (35th year of the reign of Edward I.), consisting of 160 square perches (of 272 square feet each), is general throughout England. CHAIN AND ARROWS. shapes to denote its value in tens, whilst at each end is a con veniently constructed brass handle. Divisions of Gunter's Chain.-The first 10 links is distinguished by a tablet like this ; the 20 thus, &; the 30 thus, 40 30 the 40 thus and 50 links or the centre of the chain (33 ft.) by a circular tablet thus 50 so that from each end of the chain are tablets of similar shape and position, and the number of links is counted therefrom. But it is necessary to explain that, having reached the centre of the chain, or 50 links from one end, in pro ceeding to the other extremity, what represents 40 links from that end is really 60 from the commencement, and similarly 30 is 70, 20 is 80, and 10 is 90, whilst the handle represents 100 links. The following sketch may serve to illustrate this. 1 Chain of Poles or 66 Feet or 100 Links of 7-92 inches each. So that the 1st, 2nd, 3rd, 4th, and 5th labels represent 10, 20, 30, 40, and 50 links respectively from either end. A very little practice enables one to acquire a perfect facility in reading the chain. Décamètre Chain. The décamètre chain is similar in construction to the Gunter, being divided into 100 links. Each 10 links equal a metre, or 3.2809 ft., so that a décamètre chain is 32.809 ft., or nearly the length of half of our Gunter. Arrows. Accompanying each chain are 10 arrows, or skewers, about 9 in. long, pointed at one end and having a ring at the other for greater facility in carrying. These arrows are made of stout wire, and are used to mark upon the ground the end of each chain. The reason why ten is the number adopted is that ten chains (66 ft.) equal one furlong, and eight furlongs or eighty chains equal one mile. Again, an acre of land is ten square chains. Offset Staff.-Besides the chain, the surveyor should be provided with a small staff or rod (called an offset staff), 6 ft. 7.20 in. long, divided into 10 parts or links. This staff should be made of well-seasoned wood, painted white, with black rings to distinguish the links; it should have an iron spike at one end and at the * It is usual to tie a piece of red cloth or tape round the handle of the arrows, so that they may be the more easily distinguishable when stuck in the midst of grass or plants, &c. other a stout open ring (as sketch, Figs. 1 and 2) for forcing or drawing the chain through a hedge. 33-feet Tape. It is also advisable that the surveyor should carry in his pocket a small tape, say 33 ft. long, to be used only under circumstances when absolutely necessary. These tapes are divided into Figs. 1 and 2.- pointed so as Red 50 links, similar to the chain. Poles. In order to mark out upon the ground any lines necessary for surveying purposes, poles from 10 to 20 ft. long, according to circumstances, must be provided. They should be 2 or 3 in. thick at the bottom, and taper to about 1 in. at the top. They should be shod with an iron shoe, to easily penetrate the ground. These poles should be made of well-seasoned deal, free from knots, and perfectly straight. Although it is an unquestionable advantage to have them painted (white, or alternate white and red, or black and white, according to fancy), yet it is not a matter of very much consequence, unless they are intended to be used again upon another survey, in which case the paint is a protection. Ironshoe White White I prefer to surmount these poles with a flag about 18 in. by 14 in. square, of red and white bunting, and it will be found extremely useful, especially for long distances, if a piece of white canvas is fastened by tapes half way-up the rod (see Fig. 3). These poles are chiefly used for stations at the end of long lines. In some cases even these will not be long enough, when of course arrangements must be made according to circumstances, as will be hereafter explained. Fig. 3.-Station Ranging Rods. No surveyor should be provided with less than about a dozen (or more if necessary) ranging rods, equally very straight and well seasoned to ensure against warping. They should be 6 ft. 7.20 in. long, with iron shoes at the bottom, and tapering from 11⁄2 in. to §ths of an in. in diameter,* and should be divided into ten equal parts (one link each), and painted alternately black and white, or black, white, and red, or red and white, and I have known them to be painted blue and white (this of course is entirely a matter of fancy). Red and white flags should be fastened at the top and white flags tied half-way down. * I have a strong preference for my rods to be octagonal in section in preference to circular, as I think the arris of the former is of great assistance in ranging out lines. |