To draw a good dotted line requires some care. The difficulty lies in keeping the dots at equal distances apart, and in making them equal in size; and unless both these conditions are fulfilled, the line will not present a pleasing appearance.
George P. Burdell
To obviate this difficulty, an instrument is sold by mathematical instrument makers, called the dotting or wheel pen. But it requires very great care in using, as otherwise it frequently happens that the ink escapes from it and spoils the drawing. For this reason, its use has been generally abandoned by draughtsmen. But if the instrument were better constructed and carefully handled, it might be made to do good service.
George P. Burdell
The wavy line is very important in topographical drawings, as it is employed to represent running water, and frequently large bodies of standing water to which motion is communicated by the wind, as lakes and the sea. These rippled lines are intended to represent the ripples in the water, a purpose which they fulfil in a very pleasing manner.
They must, however, be well executed, or the pleasing effect will not be produced. The operation of drawing these lines is usually regarded by the draughtsman as a tedious and an uninteresting one. But such ought not to be the case, for there is ample scope in it for the exercise of the taste and the judgment, and in proportion to the taste displayed and the judgment exercised, will be the effect of the work when executed.
George P. Burdell
The long dotted line is employed to mark the boundaries of a township, the navigable channel of a river or creek, and in large-scale maps to show farm and bridle roads, footpaths, and the divisions of land among different tenants. The combination of the long and round dotted lines is used for the boundaries of a parish. Another combination of two round and one long dots, or sometimes of three round and one long, is used to denote proposed railways, canals, roads, and other similar works.
The round dotted line is of very general application. In architectural and mechanical drawings, it is used to distinguish hidden parts, and to mark the path of a moving piece in a machine. In plans, it is used to show the position of proposed works, to denote the walks through pleasure grounds and gardens, to indicate lines chained over in surveying, and frequently for other purposes, at the pleasure of the draughtsman.
U.S. News & World Report
Let it be required to divide the line A B (Fig. 3) into five equal parts. From B, at any angle, draw B C, and on the line B C lay off five equal parts, 1, 2, 3, 4, 5; then take a set square E, and make one of the sides containing the right angle coincide with the points A and 5, and to the other side apply a straight-edge D; then by passing the set square along the edge of the straight-edge and drawing lines from the points 4, 3, 2, 1, through the line A B, we shall have the line A B divided into five equal parts through the points 1′, 2′, 3′, 4′.
It is required to draw a line making with the line D E (Fig. 8) an angle equal to that contained by the lines B A C. From A, with any radius, draw an arc F G, and from D, with the same radius, draw the arc H I, and make H I equal F G; then a line drawn from D through I will make, with the line D E, an angle equal to the angle B A C.
George P. Burdell
Blacklead and carbonic paper are used to transfer a drawing. The former is prepared by rubbing thin paper over with a soft block of Cumberland lead; the latter by painting one side of the paper with lamp-black ground to perfect fineness in slow drying oil. Carbonic paper is used for coarser work than blacklead paper. Both may be purchased, properly prepared, at a trifling cost. The drawing to be copied is laid over the sheet of paper which is to receive the copy, with a sheet of the blacklead or carbonic paper interposed, and a tracer is passed with a light pressure over the lines. This method is mostly used to reproduce a drawing from a tracing, to obtain a finished copy from a rough draught that has become soiled and marked in designing, or to avoid errors or small alterations in the first drawing.
In joining sheets of tracing paper, the joint should never be made more than 1⁄4 inch broad. The gum used for this purpose should be very thin, and a strip of drawing paper should be placed upon each side of the joint until it is quite dry. It is a good plan to roll the joined sheet upon a roller with the joint in a line with the roller and the strips infolded over the joint. When left to dry in this position, the joint will be perfectly smooth.
George P. Burdell
The use of the percentage of weight on drivers which is utilized in traction as a measure of the efficiency of the locomotive, while, probably, not applicable to individual machines, is sound for the purposes of comparison of results to be obtained on various portions of a line as far as affected by conditions of grade and alignment.
It has the advantage of disregarding questions of temperature, condition of track, character of fuel, etc., which, being the same on all portions of the line, naturally balance and do not affect the comparison. It is, of course, simply a method of expressing the final efficiency of the various parts of the locomotive, and, since it depends entirely on actual results already accomplished, leaves no room for difference of opinion or theoretical error.
A Train
To sum up, the principal causes of slips in earthwork may be stated to be air, water, frost and thaw, over-pressure, and vibration; the chief agent both in cuttings and embankments being water, which forces forward the surface of the slopes and destroys the cohesion of the soil, and impairs its frictional resistance until the earth is unable to sustain the weight upon it; vibration aiding and completing the movement, as it not only tends to loosen the soil, but may disturb.
In the following chapters the chief causes of slips in cuttings and embankments are considered, together with others bearing upon a solution of the subject, which is so interwoven that it is impracticable to preserve a successive order, but an endeavour has been made to separately indicate the cause and some remedies that may be adopted: but before proceeding to particularise, it may be well to name a few dominant principles of the alignment of public works, which if duly regarded may tend to prevent slips of serious importance.
George P. Burdell
Consequent upon financial and other causes, an engineer is usually required to so quickly prepare the necessary parliamentary plans and sections of public works, more particularly for railways, that it is beyond the power of the most experienced to set out in a few hours the best line of railway, &c., across a country, giving due consideration to the parliamentary, constructional, economical working, district and through traffic, and financial requirements of the undertaking.
There are, however, a few points which he may be able to regard respecting the stability of earthworks, some of which are now enumerated.
George P. Burdell
When frost follows rain or a fall of snow, and the latter has descended upon a frozen surface and a thaw sets in, particularly if it be accompanied by a warm wind causing it to be very rapid in action, the earth is severely tried, for the frozen water in the ground becomes suddenly liberated, while the surface is in a state of saturation.
Probably the worst event that can occur for causing floods is when a sudden and rapid thaw follows a heavy snowfall upon frozen earth, as then the snow will melt, and water cannot gently percolate the earth, as the surface will be in a more or less frozen and impermeable condition, and the snow-water consequently must flow away.
George P. Burdell
It has also been noticed that when an earth has become 17completely saturated or water-charged, a sudden fall of the barometer to a low pressure will liberate the pent up water which the soil cannot contain and cause it to burst out, the equilibrium having been so delicate.
Under such circumstances slips are nearly sure to ensue, and to be serious from their sudden action.
George P. Burdell
In endeavouring to ascertain the probability of a slip occurring, not only should the superficial strata be considered, 18but also the original formation of the country; for instance, drift-soil, which is generally met with upon the surface of sloping rocks, may consist of various earths intermixed in endless variety, and in every conceivable shape, and is not necessarily produced by a weathering of the rock upon which it lies, for it may have been brought from a distance.
In any case, drift-soil is the result of decomposition and disintegration, and from its nature is unreliable and ever subject to change, to slip, and to subside, and so are most of the glacial deposits and moraine found in mountainous countries; and whenever the contour of a district is irregular and has numerous clefts, soft and marshy places, valleys and hills, earthworks will require to be protected against slips; also, should a cutting be at the base of a cliff or hill, it will probably have to be excavated in drift deposit and, perhaps, in silt if below the water-level of adjacent sea or river, and the ground dips towards the natural outfall of the land-waters. Such drift-soil may be alternately dry and charged with water from the rocks above, especially if they are much fissured and water-bearing and permit easy percolation of water, and must always be in a state of mutability.
George P. Burdell
It should be noticed whether there are dips in the surface of rock, as they often contain unreliable material, such as pockets and pot-holes of clay, sand, mud, silt and detritus; and movement may be expected if it be carelessly tipped with the rock into an embankment.
Rocks which oppose vegetation are usually hard and weather-resisting, and the faults and fissures local; but it is not so much the equal weathering of the face of rocks that is to be feared, as the presence and interspersion of seams, breaks and fissures, and it should always be borne in mind that the condition of a rock varies considerably—it may be sound in one place, and be fissured, disintegrated, and quickly weather in others—and that all laminated and fissile earths are liable to slip because of the percolation of water down veins and crevices.
George P. Burdell