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use of an undulating railway like that suggested by the | than the horizontal distances, in order that, by being made author of this theory. But, desirable as a perfect level or disproportionately steep, they may be more readily recognised uniform slope may be, it rarely happens that either can be attained for any great distance without involving such a deviation from the natural surface of the ground as would be very inconvenient. The engineer therefore so adjusts his inclinations or gradients as to make the nearest practicable approach to a level, avoiding if possible any loss of power from undulations of surface, by making all the inclinations on one side of the summit, or highest point to be passed over, rise towards it, and all on the opposite side descend from it. In order to the due adjustment of the gradients, a section or profile of the line of country is prepared, in which the elevations and depressions are drawn to a much larger scale Fig. 12

by the eye. Fig. 12 is a section of an imaginary line, resembling, except in its small size, those prepared for parliamentary inspection. The horizontal line at the bottom is given as a datum for measuring the elevations from, and is made to have reference to some fixed point near one of the termini. This section may be supposed to represent the line of a railway between a seaport town at A, and an inland town at F: the undulating line representing the natural surface of the ground; the straight lines from point to point, the intended surface of the railroad; and the vertical lines marking the changes of inclination. Owing to the intervening high ground, a uniform slope from A to

h

F is impracticable, but a line with very moderate inclina- | tions is obtained by tunnelling through the ridge at i, excavating the minor elevations, and filling up the hollows. If a road were made on the natural surface of the ground, a carriage passing along it would, after mounting to the elevation g, have to descend to h, and immediately remount to the top of i, thereby having twice to ascend an elevation equal to the difference between g and h, involving a considerable waste of power, which would be caused more or less by every undulation passed. But in a road constructed on the level of the proposed railway, not only would part of the elevation of i be avoided by the tunnel, but that which remains would have to be ascended but once, as every part between A and d, the suminit of the road, rises towards it, though in different degrees; and in like manner the whole distance between d and e inclines downward, while the remaining part, from e to F, is perfectly level.

Owing to the short interval which has elapsed since the commencement of railway operations on a large scale, many theoretical points respecting them yet remain unsettled. Even the amount of retarding effect caused by passing over a given elevation is calculated variously by different engineers. On an ordinary road the resistance arising from | friction and irregularity of surface is so great that the effect of gravity is scarcely perceptible on a moderate inclination; but on a railway the friction and road-resistance are reduced to so small an amount, that gravity, which remains the same, becomes a material part of the total resistance, even where the inclination of the road is so slight as to be almost imperceptible to the eye. A theory held by many engineers is, that an elevation of twenty feet requires an exertion of power equal to that on a mile of level railway; so that the same power which would move a given load over one mile of railway rising 1 in 264, or twenty feet in the whole, would move the same load over two miles of level road. The practical importance of this question is very great, because a correct understanding of it is essential to show how far it may be advisable to deviate from a direct course in order to avoid a given elevation. Supposing, for instance, that a railway is required between two points twenty miles apart, and that a straight course may be obtained by passing over an elevation of 100 feet, it may be preferable to increase the length to twenty-four miles, if by so doing a level can be obtained; because the elevation of 100 feet will require as great an expenditure of power as five miles of horizontal railway.

Another question on which there exists much difference of opinion, is the degree of steepness that may be allowed in any of the inclined planes without injuriously affecting the working expenses. It is often necessary to conduct a railway over a considerable elevation, but engineers differ as to the best arrangement of the unavoidable inclinations. Some prefer distributing the rise and fall as equally as possible throughout the whole line, while others consider it best to concentrate them in a few steep planes, in ascending which additional power is used, and making the rest of the line comparatively level. The Liverpool and Manchester railway may be cited as an instance of the latter mode, the main line having no gradient exceeding 1 in 849, with the exception of two inclined planes of about a mile and a half each, inclining 1 in 89 and 1 in 96, near Rainhill; at which it is usual to assist the trains by an additional locomotive engine. The

Great Western railway also, in a length of 117 miles, has no steeper gradient than six feet six inches per mile, or about 1 in 812; but has two inclined planes of 1 in 100 for a length of one and a half and two and a half miles respectively. The London and Birmingham railway is an example of the former system, its ordinary gradient being 1 in 330, or sixteen feet per mile, which is nowhere exceeded except on the extension from Camden Town to Euston Square which was intended for working by stationary engines. The characteristic or ordinary gradient on the Southampton, Brighton, South-Eastern, and many other lines, is 1 in 264, or twenty feet per mile.

A certain degree of similarity in the gradients is essentia to the economical working of a railway by inanimate power which cannot be so conveniently urged as that of horses to a temporary exertion to overcome a short but steep ascent. If therefore any inclination occur so steep that the ordinary power cannot ascend it by a reduction of speed, it must either be surmounted by the aid of auxiliary power, or the engine must run over other parts of the road with less than a maximum load, and consequently at unnecessary expense. So long as this inconvenience is avoided, it is the opinion of some scientific men that the degree of inclination is of little consequence on a railway with an equal traffic in both directions, because the assistance of gravity in the descent being set against the additional resistance in ascending, brings the total amount of power required in traversing the line in both directions to nearly the same as would be needed were the road a perfect level.

Some highly interesting experiments have been recently made on this and other points of railway economy, under the superintendence of Dr. Lardner, of which the following seems to indicate that this compensating effect takes place on inclinations of much greater steepness than has been generally supposed. Great caution is necessary in forming calculations on such a subject from single experiments, however carefully conducted, but the results are certainly such as to justify serious inquiry. In July, 1839, the Hecla engine, with twelve carriages, making a gross weight, including the engine, of eighty tons, was run from Liverpool to Birmingham and back in the same day; by which means the same train, under as nearly as possible the same circumstances, had to ascend and descend every plane on the line, a length of about ninety-five miles. The time of passing each quarter-mile was carefully observed, so as to obtain the speed on every portion of the road. The following table, extracted from the seventh edition of Lardner on the Steam Engine, gives the result of observations on gradients varying from level to 1 in 177, or nearly thirty feet per mile:

[blocks in formation]

1111

330

400

532

590

25.26 26.87 27.35 27.37 29.03

650

Level

From this table it appears that although the plane of I

in 177 diminished the speed from near thirty-one miles per hour, the velocity on a level, to little more than twenty-two miles, in the ascent, the deficiency was fully compensated by the increased rapidity in the descent. The trifling difference in the mean speed on the different gradients may probably be attributed to accidental circumstances, but, small as it is, it is rather in favour of the steepest inclinations than otherwise. The result fairly indicates a most remarkable and valuable fact, namely, that a line of railway with gradients of from twenty to thirty feet per mile may be worked in both directions by the same expenditure of power as a dead level; and this fact, if substantiated by more extended experiment, proves that many millions may be saved in the execution of future railways by being content with steeper inclinations than have hitherto been admitted by most engineers to be adviseable. The whole of the compensating effect here produced is not to be attributed to the agency of gravity and momentum; a part, and perhaps a very considerable part of it, being due to the diminished resistance of the air to the passing of the train on ascents, owing to its reduced velocity. The nature and extent of atmospheric resistance to railway trains is a point on which so little is known, and opinions are so conflicting, that the extent of its influence in the experiment alluded to cannot be stated with certainty, but it is probably considerable, as the result is very different from that which might by calculation have been expected from the mere effect of gravity and friction. The resistance of the air being almost imperceptible in the case of common roads, owing to the great friction and moderate velocity, has frequently been considered too trifling to become an element in calculations on railway transit, and hence arises much of the error that has hitherto prevailed respecting inclined planes. For further information on this subject see RESISTANCE.

Dr. Lardner thinks that his experiments indicate the gradient by which the gross resistance is doubled to be nearer 1 in 95 than 1 in 300, which he, in common with many others, had formerly considered the limit, though 1 in 264 has been mentioned above as being a more moderate and perhaps more usual calculation.

Curves on a main line of railway being, in consequence of the peculiar construction of the carriages and the speed at which they travel, very objectionable, a judicious engineer so adjusts his line as to avoid them when possible, and to make those which are inevitable of as large a radius as circumstances will admit. Curves of less than a mile radius are considered unadviseable for places where great velocity is required, although many of only half a mile radius are in use, the rails being so laid as to counteract the danger that might arise from the centrifugal force of trains passing over them, as explained hereafter. At stations and depôts, where the trains always move slowly, the radii may be much shorter without inconvenience.

trict the whole of its length, is entirely on a viaduct, and that from London to Black wall, a similar line, principally so. Railways, being usually constructed on as low a level as possible, frequently intersect the course of rivers and canals, rendering numerous and expensive bridges necessary. Where the course of the streams thus crossed is sinuous, expense may sometimes be reduced by making a new channel for the river, such a cut often being the means of avoiding the erection of two bridges, as in the instance of the Manchester and Leeds railway in the valley of the Calder. Obtaining an Act of Parliament.-Railways being in this country constructed by associations of private individuals, with a view to their own pecuniary advantage, as well as to public convenience, it is necessary that, on the one hand, legislative restrictions should be imposed, to protect the interests of those who may, directly or indirectly, be affected by the formation of the railway; and, on the other, that the promoters of the scheme should be invested with considerable powers, to enable them to carry it into effect. Lands, buildings, rivers, canals, roads, &c. have to be intersected and otherwise interfered with; and while justice requires that no unnecessary injury should be inflicted on their owners, or the parties using them, and that every unavoidable interference should be amply paid for, it is also necessary to prevent a plan likely to be of great public benefit from being defeated by objections arising from prejudice or private interest.

Owing to the number of crude and ill-judged speculations of 1835, 6, and 7, which proved the necessity of imposing various restrictions on the facility of obtaining parliamentary powers, new standing orders were introduced with a hope of more effectually insuring the public against being misled by over-sanguine projectors. An opinion is entertained by many, that these regulations are now too stringent; and the very limited number of new undertakings sanctioned by parliament since they came into operation, though partly to be accounted for by other circumstances, leaves some reason to question whether, in the attempt to restrain improper speculation, legitimate enterprise has not been injuriously shackled.

Under the existing standing orders of parliament respecting railway bills, it is required that plans and sections of a proposed line, on a scale of four inches to a mile, shall be deposited with the clerks of the peace for the several counties through which it is proposed to carry the railway, on or before the first day of March, and in the Private Bill Office, &c., on or before the first day of April in the year preceding that in which an application is made to parliament for an Act. The plans are accompanied by a book of reference, showing the owner, lessee, and occupier of every house or piece of land liable to be passed through or otherwise interfered with. The sections indicate not only the length and inclination of each gradient, but also the It is essential to the public safety that a railway should actual elevation of numerous points above the base not be allowed to cross any much frequented road on the line used as a datum, and the elevation and proposed same level. When the Liverpool and Manchester line was mode of crossing every stream or road intersected by the projected, as the rate of travelling was not expected to ex- railway. Portions of these plans and books are also deposited for ceed ten miles per hour, no danger was anticipated from reference with the clerks of parishes through which the line such intersections, which are called surface-crossings; and runs, if in England, or if in Scotland or Ireland, with other accordingly several were allowed; but their inconvenience specified officers; and notice is given of the intention and danger have caused some of them to be altered, the road to apply for an act of parliament, both publicly by Lonbeing conducted under or over the railway by means of a don and county newspapers, and privately by notices to bridge. In recent railway Acts it is enacted that no turnpike- owners and occupiers of property affected. The former of road or highway shall be crossed on the same level; a rule these notices being given in February and March, a to which exceptions are very rarely allowed; and if they are, whole year is allowed for interested parties to congates must be erected to enclose the railway, and attendants sider the scheme and make preparations for advocating stationed to open them when necessary for the passage of ve- or opposing it in parliament. Before 1837, notices given hicles across it. These gates should be so hung as to com- and plans deposited in the month of November before pletely close the railway when the road is open, and vice versa. the meeting of parliament, were considered sufficient In a few instances two railways have been allowed to inter- The shorter period was far more favourable to railway sect each other on the same level, but this highly dangerous companies than the present, because the surveys are frearrangement is now very rarely permitted. Where a single quently made in the autumn, immediately after the road is crossed, it may not be necessary to regard it much in removal of the crops, and the plans might then be preselecting the level for the railway, as such road may be made pared in time for obtaining an Act in the ensuing year; to slope gradually to the requisite level for passing under or or, if a company were defeated in parliament one session, over it; but in approaching towns, where many communi- they might amend their line to obviate the objections brought cations are interfered with, it is essential that the railway against it, and be prepared for the next session. Now, a line level be made higher or lower than the ordinary surface, in surveyed in the autumn of 1840, must have the plans deorder to avoid them. At Liverpool this is effected by tun- posited in 1841, and the application must be made to parlianels under the town; at the London end of the Birmingham ment in 1842, so that it could scarcely be commenced till 1843: railway by an open cutting; and at Manchester, Birming- and a company failing in one session, must wait till the next ham, and many other places, by an embankment or viaduct. but one, or proceed with plans deposited before a parliamenThe Greenwich railway, extending over a metropolitan dis-tary opposition had shown what objections would be brought

forward, or how they might be obviated. Owing to the long time between the plans being deposited and the Act being applied for, it frequently happens that they are deposited before a company is formed, with the intention of using them, if circumstances are favourable as the time approaches. The number thus provisionally deposited may be supposed from the fact that plans of thirty-six new lines were deposited for the session of 1840, none of which were brought forward. If the company intend to proceed with their project, the shareholders are required by the standing orders to subscribe to a contract, binding themselves, their heirs, executors, &c. to pay up the whole amount of the shares they take, when called upon to do so. This subscription contract must be signed between the time of making an application for an Act and the close of the session next preceding. They must also, according to the orders of the Commons, deposit a sum of ten per cent. on the proposed capital, in government securities. If the preliminaries have been duly attended to, a bill is brought in for incorporating the company and investing it with the necessary powers. After being read a second time, it is examined in a committee, which, if the bill be opposed, is composed of those members who represent the districts affected by the measure, and of a quorum, generally not less than three, of selected members having no interest in the question either personally or for their constituents. The committee report on the length, gradients, curves, and other peculiarities of the line; on the estimated outlay, and its apparent sufficiency; the traffic expected; the sufficiency or insufficiency of the existing means of communication for agricultural, commercial, manufacturing, or other purposes; and the probability of remuneration to the shareholders. They also receive lists of the owners, lessees, and occupiers of the land, &c. that may be required, showing whether they are assenting, dissenting, or neutral parties to the bill; and examine the list of shareholders, to guard against the introduction of irresponsible persons. Petitions presented respecting the bill are referred to the committee, who frequently insert clauses for the special protection of the petitioners. If there be any competing line of railway existing, in progress, or in contemplation; or if any parties oppose the bill on the ground of the line being unnecessary or injurious; a very expensive and tedious examination of witnesses is the result. Counsel are engaged on both sides, and evidence is heard sometimes on almost every point to be embraced in the report. The expense attending these contests is a strong argument against the existing system, which is considered defective also in many other points. After leaving the committee, the progress of a railway bill seldom excites much interest or attention. Unopposed bills are for the future to be rereferred only to the chairman of ways and means, and the two members in charge of the bill.

The preamble of a railway Act recites that it is expedient to construct the railway therein described, and that certain persons, whose names are given, are willing and desirous to make it at their own costs and charges. The Act forms them into a corporate body, invested with powers to take and make compensation for the necessary property, and to eonstruct the railway. As the surveys are often made hastily and under great disadvantages, a deviation from the line laid down in the plan to the extent of a hundred yards is allowed for the sake of improving the line, such deviation being limited to ten yards in towns, and not being allowed to extend into any lands not included in the plan and book of reference. Powers are also given for altering, to a very limited extent, the levels and gradients defined on the parliamentary section. The company is allowed to raise a certain sum, sufficient to cover the estimated expense, in shares among themselves; and also, if necessary, to borrow a further sum, not exceeding one-third of their capital, as soon as one-half of it is paid up. Such additional sums may be raised in new shares, at the option of the company. Clauses are inserted to protect the rights of individuals, to specify the dimensions of road, canal, and river bridges, and the slope to be given to roads where they are altered. A board of directors, selected from the principal shareholders, and generally from twelve to twenty-four in number, is ap pointed to conduct the affairs of the company, to make calls for the capital as required, &c.; and provisions are inserted for a change in this body by a certain number being balloted out periodically, and the vacancies filled up by the proprietors at their annual or half-yearly meetings. Powers are given to the company to take certain specified tolls, to

carry passengers and goods, and for many other purposes. To provide for the possible abandonment of the scheme, it is stipulated that the compulsory powers for taking land shall cease after the lapse of two or three years, and that, if the works are not completed within a period of, in most instances, seven years, or, having been completed, are not used for three years, the land shall revert to the owners of adjoining property.

Owing to the numerous subjects embraced, a railway Act frequently fills from one to two hundred folio pages. It has been suggested that much expense and trouble might be saved by the passing of a General Railway Act, embracing those points common to all, so that an ordinary Act need contain only what is peculiar to the individual line. In many cases Amendment Acts are required by a railway company to enable them to raise additional money, or to execute extensions or alterations of the original line; but these do not require any detailed notice. As instances of the expense attendant on the present mode of obtaining railway Acts, when opposed, it may be stated that the London and Birmingham Railway Company spent more than 72,000l. in procuring theirs, and the Great Western upwards of 88,000l. The London and Brighton is perhaps the most expensive contest of the kind that has taken place, four or five companies having engaged in it for two successive sessions. When in committee, the expense of counsel and witnesses in the latter case is stated to have amounted to 10007. daily, for about fifty days.

The act of parliament being obtained, the land required for the railway is definitely set out and purchased. Power is usually given to take a width of twenty-two yards, ex clusive of what is necessary for the sloping sides of cuttings and embankments, but this width is seldom required When moderate compensation is demanded for the land taken and the injury caused by the severance of estates, the removal of buildings, and other circumstances, the company have no need to put the compulsory powers in force. But where, as too often has been the case, exorbitant claims are made, recourse is had to a jury. In most cases where this alternative has been resorted to, the sum awarded has been much under that claimed,-frequently less than a quarter, and in one recent case only about a fiftieth part of it. The item of land is one of the causes of that excess of cost over estimates which has been so severely animadverted on, and another is the expense of extra bridges claimed by landowners as communications between severed lands, the trifling utility of which is indicated by the circumstance that, after extorting an agreement to build them, persons have often accepted one-half of their cost, in lieu of having them erected.

Formation of the Road.-Under this head is included the execution of those works necessary for the construction of a road (independent of the rails and finishing works), of the required level and width. These works consist of tunneling, excavation, embankment, and masonry for bridges, viaducts, and other erections. They are commonly divided into convenient portions, and let to contractors under agreement to complete them at a stipulated price and within a specified time. It is usual to commence those works which take the longest time first, that the capital expended on others may not lie idle till they are completed.

Tunnels are, in general, the most formidable works, and the time and expense of forming them can be least accurately calculated, because unforeseen circumstances often arise to retard their progress. Trials of the nature of the ground are made by boring, but these may indicate favourable strata, while, as in the well-known instance of the Kilsby tunnel, difficulties may exist requiring great energy and skill, and an enormous outlay to overcome. Being objectionable also on other accounts, tunnels are avoided as much as possible in the more recently designed railways. For the mode of constructing them, see TUNNEL.

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Cuttings or excavations of great depth and extent are of frequent occurrence where the railway passes through high ground, but not at such a depth from the surface as to require a tunnel. The depth of cuttings is frequently from fifty to seventy feet and occasionally even greater. One very extensive excavation through the Cowran Hills, on the Newcastle and Carlisle railway, is as much as a hundred feet deep. The degree of slope necessary in the sides of cuttings varies greatly in different soils. Rock will stand when nearly vertical; chalk varies from nearly vertical to a slope of one horizontal to one vertical, or an angle of 45';

gravel stands usually at ore and a half to one; London | cious drainage may do much in such cases, and the inserclay from one to one to three to one, having in some in- tion of a frame-work of timber to bind the earth together stances stood at the former and slipped at the latter slope. and thereby check the unequal settlement of the embankSome materials are insecure at even a greater slope; blue ment, has been tried with apparent success by Mr. Braithsoapy shale having, according to Lecount, slipped at an in-waite on the Eastern Counties railway. To prevent carelination of four horizontal to one perpendicular. The un- riages which escape from the rails falling over the sides of expected slipping of the slopes sometimes occasions much an embankment, mounds of earth are sometimes raised trouble and expense. A case lately occurred in the north of along them. The embankments raised across Chat Moss England in which a cutting to be formed in the side of a hill on the line of the Liverpool and Manchester_railway, was estimated to require the removal of about 50,000 cubic and similar places have excited much interest. The diffiyards of earth. It turned out, however, that the soft earth culties arising from the yielding nature of the material are was held up by a seam of shale, which was no sooner cut greatly obviated by drainage, as, when dry, the moss itself through than a mass of earth slipped down into the line of becomes a fit substance for embanking, and stands well at the railway, of such magnitude as to require the removal a slope of less than 45°. The railway is sustained on part of about 500,000 cubic yards. The great cutting at of Chat Moss by a platform of timber and hurdles, covered Blisworth, on the London and Birmingham railway, affords with earth and broken stone, and floating, as it were, on the an example of a convenient and economical method of pass- spongy substratum. A peculiar kind of embankment reing through earth in which strata of rock occur. The quired in hilly districts and along coasts consists of a road railway is at a depth of fifty or sixty feet, the upper portion on the side of a steep elevation, one side being supported by a of which is rock, and the lower consists of a less solid ma- sustaining or revêtement wall. An important work of this terial. Instead of making an excavation of the slope kind is being executed along the face of part of the Dover required by the lower strata, which would have ren- Cliffs, for the South-Eastern railway, in which the revêtedered the removal of the superincumbent rock indispensible, ment wall is exposed to the sea. Similar constructions the sides were made nearly vertical, and the rock was sup- have been introduced on the Dublin and Kingstown railported by an under-setting of masonry. The great breadth way, where there is also a remarkable embankment across of ground occupied by the slopes of cuttings, is a serious ob- the strand at Blackrock, that, at high-water, has the appearjection when they are in the vicinity of towns or pass through ance of a mole stretching into the sea, which is allowed to valuable property, in which cases the sides may be made pass through it by culverts. On the Preston and Wyre nearly vertical, and supported by retaining walls, so curved railway is an extensive embankment in a similar situation, as to enable them to sustain the pressure of the earth. but, when completed, it is intended to exclude the sea. The extension of the Birmingham railway to the Euston Though yet unfinished, carrriages are enabled to pass along station affords a very bold and handsome example of this by the rails being temporarily supported on piling. On the kind of work. In designing the works of a railway, the Stockton and Hartlepool line a sea-embankment of clay has amount of excavation and embankment should be balanced been recently completed, the side being puddled and formed as nearly as possible, so as to avoid the necessity of deposit- into such a curve as to bear the dashing of the waves withing earth from cuttings in spoil-banks, or having to purchase out injury. Retaining walls are occasionally used to additional land to supply material for the embankments. diminish the space occupied by embankments, as before Attention to this point will sometimes decide which is most mentioned in the case of cuttings. The Dublin and Kingsexpedient, a short tunnel or an open cutting. town railway commences in this manner, arches being introduced at the intersection of streets and roads.

The earth-works on most of the great lines of railway in England are very extensive, in many cases averaging from 100,000 to 150,000 cubic yards per mile. On the London and Birmingham line alone the quantity of earth and stone removed was about 16,000,000 cubic yards, which, if formed into a belt three feet wide and one high, would more than encompass the earth at the equator! When completed, it is adviseable to sow the slopes of cuttings and embankments with grass-seed, as their appearance is thereby improved, while the roots give cohesion to the surface, and render it less likely to be affected by weather.

Embankments are the artificial ridges of earth formed to support the railway on a higher level than the natural surface of the ground. Their dimensions are often fully commensurate with those of cuttings, from which their materials are mostly procured. In the ordinary mode of proceeding, an embankment is formed simultaneously with a catting, the earth-waggons proceeding filled from the excavation along a temporary railway to the embankment, where they are tipped up to discharge their contents. A heavy embankment often forms the key, as it were, to the time of completing a railway. Tunnelling and excavation may be proceeded with at many different points, but an embankment, under ordinary circumstances, can be carried on The amount of masonry and brickwork required in the only at the ends, and the number of men employed there is various erections of a railway is very great. The lining of restricted by the limited space. Time is occasionally saved tunnels, where the ground penetrated is of such a nature as by the erection of a temporary wooden stage at the end of to require support, forms a peculiar kind of work. Arching the embankment, affording the means of tipping a greater of almost every kind is more or less required in viaducts, number of waggons at one time than can be done without bridges, culverts, and drains; and simpler work in the it. Where the excavations do not afford sufficient material, retaining walls, station buildings, and other necessary erecembankments are partially formed of earth dug from tions. Viaducts of great magnitude are often executed for trenches along their sides, and thrown up into the centre. the purpose of crossing valleys at an elevation greater than This is called side-cutting, and, being an expensive pro- could be conveniently obtained by embankment, and also ceeding, should be resorted to as little as possible. An im- for entering or passing through towns. They are usually of portant element in the cost of embankments is the length stone or brick, but sometimes of wood or iron. [VIADUCT] of the lead, or distance to be traversed by the earth-wag- Bridges are required occasionally for crossing rivers, and gons between the points of filling and emptying. The sides very frequently at the intersection of roads, and as commuof embankments, like those of cuttings, require a consider-nications between severed property. From a statement by able slope, especially when the material is of an unfavour- Lecount, in the Encyclopædia Britannica,' it appears that, able nature. The earth should be deposited in layers of taking the mean of nearly a hundred railways, the number two or three feet thick, slightly concave on the upper sur- of bridges averages about two and a quarter per mile. Besides face, and, if time permit, it is well to allow one layer to settle ordinary arches of brick and stone, bridges consisting of before another is spread over it. The subsidence of newly- cast-iron girders laid from one abutment to the other, and made embankments is a source of great expense, and some- supporting a platform of flag-stones, iron plates, or planks of times of danger. It is usual to lay the rails in such a man-wood, are very common. When the railway itself passes ner as to diminish the risk of accident from this cause, and over such a bridge, six ribs are used, the distances of which to travel slowly over parts where a tendency to slip is obser- are so adjusted that four of them sustain the rails and the vable, especially in wet weather, yet casualties will some- other two the parapets, leaving nothing necessary between times occur until these great earthworks are thoroughly con- the ribs or girders, except a flooring of iron plates. By this solidated by time. Allowance should be made for sub-arrangement great strength is ensured, and the depth or sidence by making the embankments rather higher than they are intended to be finally. Great difficulties are experienced in embanking across marshy or boggy soils, which frequently sink under the weight of the earth deposited, the ground bulging up at the sides in consequence. Judi

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thickness of the bridge is reduced to a minimum, no ballast or road material being necessary. Wooden bridges of similar character are occasionally used.

A remarkable circumstance in the appearance of railway works is the frequent occurrence of skew-bridges. They aro

introduced when the railway intersects any existing com- | tions, the effect of which is to increase the resistance. munication at an oblique angle. Such arches were built It has been thought that these undulations were of little before the introduction of railways called them into general consequence, the gain in descending being a counterbalance use, but as, in an ordinary road or a canal, a deviation from to the retardation of the ascent; but Professor Barlow, in the straight line is of little consequence, it was seldom reporting on experiments made by him in 1835, for the Lonthought necessary to apply them, and was customary to build don and Birmingham Railway Company, expresses an the arch of the ordinary form, on the square, and accommo- opinion that 'the advantage of the descent is, owing to the date the direction of the road or canal to it by curved ap- velocity and the shortness of the inclined plane, scarcely proaches. But as on a railway straightness is of great im-appreciable, and that the result of the deflection will be portance, it frequently becomes necessary, in crossing other equivalent to the carriage being carried up a plane of half roads, to adopt a skew-bridge, in which the communications the whole length, the other half being horizontal.' over and under the bridge form unequal angles with each other. For an account of the construction of these ingenious works, see SKEW-BRIDGE.

When the various works described are completed, with the requisite drains and fences (which are highly important), the road is ready for receiving those finishing works which entitle it to the distinctive name of railroad. The level of the earth-works, when completed, is called the formation level, and is usually about two feet below the intended surface of the rails. The width of this surface is about thirty feet, exclusive of the drains and fences, and it is made a few inches higher in the middle than at the sides, in order to throw off water.

Ballasting and Laying the Permanent Way.-In order to obtain a firm dry foundation for the blocks or sleepers to which the permanent rails (so called to distinguish them from the slight temporary tracks laid down during the progress of the work), are fastened, a layer or stratum of broken stone, technically called ballast, is spread over the road for a thickness of a foot or more, varying according to the construction adopted and other circumstances. After the rails are laid down, similar materials are used to fill in the spaces between the blocks and sleepers. The broken stone should be so small that any piece would pass through a ring two inches and a half diameter. Other substances are occasionally used, especially for the upper part of the ballast, as gravel, river-sand, and burnt clay. In some situations, with good ballast, no surface drains are necessary; but drains consisting of a brick channel along the middle of the line, with small cross drains at intervals towards each side alternately, are often required.

The great variety of opinions as to the best form and manner of fixing the rails, renders it impossible, in the limited space which can here be devoted to the subject, to do more than select a few examples of the plans principally used. The most important question involved in these differences is that of the intermediate or continuous support of the rails. The most common method of fixing them is to fit them into iron chairs, which are spiked down to blocks of stone imbedded in the ballasting. This plan, although it appears by experiment to afford the firmest foundation, has several disadvantages. The points of support, being isolated from one another, are liable to be deranged by any subsidence in the ground, as well as by the constant vibration consequent upon the rapid passage of heavy trains, and the small but irresistibly powerful action of temperature in causing the expansion and contraction of the rails.

The former of these inconveniences is in some degree obviated by substituting cross sleepers of wood (like those described as being used in the early railways), for the stone blocks upon such parts of the line as are likely to sink. The two rails being, in this case, attached to the same sleeper, are not liable to be thrown out of gauge, or, in other words, to lose their parallelism, although the unequal sinking of the sleeper may cause one rail to become lower than the other. This application of wooden supports has been in most cases considered a temporary one, it being intended to lay stone blocks in their stead so soon as the ground became sufficiently firm; but as it appears from experience, both in this country and in America (where, owing to the abundance of timber and the high price of labour, wood has been much more extensively applied to railways than in this country), that the motion of carriages on those parts of a line supported by wood is smoother and quieter than on others, some engineers consider that the plan of construction upon cross-sleepers is preferable to that upon stone blocks.

These and some other considerations have led to the adoption of a continuous support to the rail, which has been effected in several different ways, and with various success. Intermediate supports, being the most extensively employed, will be first noticed, and stone blocks, according to general opinion, claim the precedence among them.

The blocks used upon recently constructed railways are about two feet square and one thick, though much smaller ones were considered sufficient before the use of locomotive engines became general. They are roughly squared, but have so much of the surface as is to receive the chair accurately flattened. The chairs are usually fastened down by two or three iron spikes, to receive which holes are made in the stone, and filled with wooden plugs. The plugs should always be bored to receive the spike, and driven tight into the stone, though they are sometimes put in loose and split by driving the spike. Spikes or pins of well dried oak have been used instead of iron spikes for securing the chairs, and have been found very durable, but are not generally approved for lines worked at great speed. The introduction of a piece of felt between the chair and the block is useful in deadening concussion. As it is highly important that stone blocks should be well bedded, it is usual to cause them to form a solid foundation for themselves by repeatedly falling from a small elevation on to the spot where they are to rest, sand or very fine gravel being thrown under them between the times of falling. For this purpose a portable machine with an elastic wooden lever about twenty feet long is used, the block, to which the chair has been previously attached, being suspended from the short end, and a man stationed at the opposite end to raise and drop it. When the stone has made a firm bed, and has dropped in the right position, which is determined by levels and sights, it is detached from the lever and surrounded by ballasting, care being taken not to disturb it at all. It is evident that this careful bedding would be thrown away on an embankment, or any part where the newness of the ground would render subsidence probable. Fig. 13 is a ground-plan illustrating the use of stone blocks and wooden sleepers. a, a, represent blocks laid square with the road Fig. 13.

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and b, b the same laid diagonally, a position now generally preferred, being convenient in repairing the road when a block sinks, because workmen can get at every side for the purpose of ramming ballast under it. Blocks of Scotch asphalte have been tried in lieu of stone, but with what success the writer is not aware. A few were laid down on the Southampton railway, and the chairs were spiked down without boring the block. Other similar substances have been suggested in order to diminish expense. It has also been proposed to use cast-iron bed-plates instead of blocks, by which several important advantages were anticipated, but no such plan appears to have been brought extensively into use. In the Dublin and Kingstown railway an attempt was made to ensure increased solidity by introducing throughgoing stone blocks, which were formed of granite, six feet long, two wide and one thick, and stretched across the track. These were placed fifteen feet apart, ordi

In both of these modes of supporting the rail, it is sustained only at intervals of three or four feet, the interven-nary single blocks being used between them, at intervals of ing portion acting as a bridge, which, though very rigid, yields in a slight degree when carriages, and particularly the heavy locomotive engines, pass over it. The surface of the rail is thus converted into a series of minute undula

three feet. Owing perhaps to the difficulty of bedding such large blocks, the plan did not answer, the motion over them being harsh and unpleasant, and the vibration such as to break many of the long blocks. In some cases, particularly

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