correct idea of the manner of executing a finished plan; neither do I consider very great skill in the art as imperative on officers in general. All that is really wanted for use in the field may be scratched with a pen. A person seeking to acquire a thorough knowledge of military plandrawing, must either procure plans to copy, or obtain instruction in the art beyond what a book can furnish; I therefore hold it useless to swell my pages with elaborate details on the subject.

Plans are copied in various ways. The best is by tracing at a glass frame or window; for which purpose the paper intended to receive the copy is pinned to the original. When mounted on pasteboard, or other opaque substance, some other mode must be resorted to, as that of dividing the original plan into compartments or squares, by ruling lines upon it lighly with a pencil; similar squares are then formed on the paper, and the copying becomes easy. This latter method is employed for increasing or diminishing the size of the copy, as compared with the original. By using what is called tracing paper, through which the details of a plan are visible, a copy is speedily and very correctly made; and afterwards, if necessary, a tracing may be made from it upon thick paper at a window. There are also other methods, but the above are sufficient.

Plate XV. contains the conventional signs in plan-drawing which are generally employed: instead of multiplying these to an inconvenient extent, it is better to make memoranda on the plans. For instance, signs are sometimes used to denote whether a ford or a marsh be passable for troops; and even to notice whether practicable for infantry, as well as guns and cavalry; but, in my opinion, it is better to write, in language that cannot be mistaken, what description of ford it may be.

SECTION XII.

GENERAL REMARKS ON SURVEYING, PLAN-DRAWING, AND SKETCHING.

MILITARY TOPOGRAPHY, notwithstanding the boasted improvements made in it abroad, together with some attempts to advance the art amongst ourselves, is, so far as I may pretend to give an opinion, nearly where it stood thirty or forty years ago. And the same remark holds good with respect to surveying generally: this, however, is by no means suprising; surveying, in all its branches, being an exceedingly simple process, requiring, it is true, for great trigonometrical operations that the surveyors should be men of science, in order that certain measurements may be made with the utmost possible accuracy; yet the principles of surveying are easy of acquirement, and their application, under ordinary circumstances, requires little beyond good instruments, and great exactness in the use of them. Few persons can rise from a study of the Account of the Trigonometrical Survey of the United Kingdom, without entertaining an impression that geometrical and trigonometrical operations, as applied to measurement on the earth's surface, have been carried very nearly to perfection.

So far, then, as horizontal measurements are required, whether for the purpose of mapping countries, or of determining the length of an arc of a meridian, it does not seem that any thing remains to be desired.

Again, the height and exact slopes of hills, as also the depression of valleys, to suit the purposes of the military or civil engineer, can be obtained with the utmost accuracy, by means of levelling and trigonometrical operations. So that in every accessible part of a country, the most perfect knowledge of its surface, whether flat or mountainous, may be obtained: and, having plans and sections accurately drawn to a scale, we can at any time measure distances upon paper. But although we can measure horizontal distances over every part of a map or plan, yet vertical measurements, as those of heights and depths-shown on paper by sections-can only be made upon the precise lines along which such sections have been carefully taken; and if other vertical measurements are wanted, our ground plans can avail us nothing: we must proceed to the ground, and ascertain them by actual operations.

Herein lies the imperfection of plans; and the attention of scientific men has long been directed towards the discovery of a method of drawing ground plans, from which sectional measurements may be made. Hitherto their efforts have been attended only with partial success; that is to say, by means of very great accuracy in taking measurements over the surface of a hill-similar indeed to what would be requisite for sections-a knowledge of its form being obtained, symbols are used to designate a certain degree of perpendicular elevation, together with the angle at which the hill slopes at each gradation. Thus, in France, military engineers run a succession of horizontal lines round their hills at every ten mètres of difference of level, by which they obtain two sides with their included angle of a right-angled triangle, namely, the perpendicular height of ten mètres, and the base of the slope, for that distance of perpendicular height, with the included right angle; from which data the value of the slopes at every gradation can be obtained.

In some of the continental countries a system of shading is used according to a scale; different degrees of shade representing the angles at which a hill slopes. This is the principle of Major Lehman's method, and prevails to a certain extent among the Germans.

A few years ago, the late Sir J. C. Smyth, of the Royal Engineers, published a little work, to recommend a modification of the normal system, as set forth by Colonel Van Gorkum, of the Netherlands' army, for adoption in our service. But I very much doubt whether any of these systems can be rendered available for general topographical purposes.

The system of tracing contour lines, upon a plan of any portion of ground, as introduced by the French officers of engineers, is now gaining ground amongst those in the British service, and is practised in the trigonometrical survey under the direction of Colonel Colby: "these lines being traced at short, known, and generally equal vertical distances over the ground, afford ample data for the construction of sections in any required directions, and even for a model of the features of the ground."* The method of tracing such contour lines will be found under the head of Levelling: the process is necessarily slow; but there can be no question, that a plan of any portion of ground may thereby be obtained with almost mathematical accuracy. A moment's consideration will, however, convince any one that it is wholly unsuited to the ordinary purposes of the topographical draftsman, who has often a considerable extent of country to sketch in a very short time; and for objects, moreover, which do not require the ground to be delineated with extreme precision.

Most assuredly it is a great desideratum, to be able, by the inspection of a map or plan, to determine the elevation of the hills; and the person who may discover a truly prac