oiled, under the same circumstances, the number was 290; and, when still more copiously oiled, the number was reduced to 244.

The result of all these experiments is, therefore, that no increase of resistance, above that on cast-iron, takes place upon wrought-iron rails; and that the resistance is a minimum, when the rails are quite dry, and free from any extraneous matter.

CHAPTER IV.

ON THE FORMATION AND CONSTRUCTION OF
RAILWAYS.

§ 1.-Formation of the Line of Railway.

In the early stage of the construction of railways, little

or no care seems to have been taken, to level the surface of the ground, so as to form the best line of road between the two extremities. Horses being then exclusively used, casual undulations were levelled down, but the general line of railway does not appear to have been laid out, with a view of obtaining the best gradients for the road which the country afforded. The only principle acted upon seems to have been, that the line should be so formed, as that a horse should take down a certain determinate load. If, therefore, any particularly steep place existed, where that load could not be overcome, it was levelled down to such an extent, as to enable the horse to take the load fixed upon; and that was laid down as the guide, by which the other parts of the line were laid out; it being deemed sufficient, if a horse could take, upon the other parts of the line, the same load which it could do upon the steeper or more inclined portions. When mechanical power was applied, a different system was required;-it then became necessary to lay out the line of railway, suitable for the different kinds of motive power, intended to be used upon it, consistently with the facilities which the nature of the country afforded.

It is not our intention, however, in this chapter, to enter upon the consideration of the principles of laying out a line of railway, between any two places, with reference to the motive power intended to be used upon it. We shall reserve that consideration, until we have ascertained the capabilities of each description of motive power; by which we may be enabled, to elicit some general principles for our guidance, in determining that very important question. We shall, therefore, in this place, pass over the consideration of the proper levels, or gradients, to be observed in forming a line of railway between two points or places, and confine ourselves to a detail of the mode of forming the railway, supposing the line and gradients previously determined upon; which detail will comprise the execution of the earthwork, laying down the rails, and accomplishing the various other descriptions of work, requisite to form a complete railway.

§ 2.-Earthwork. Excavating and Embanking.

Let A, B, C, Fig. 1, Plate V., represent a section or the outline of the country, over which the railway is to pass, and a, b, c, d, e, the level, at which the railway is to be formed. All those parts of the section which are above the line a, b, c, d, e, to the extent of the width required for the railway, will, therefore, require to be cut through, excavated, or levelled down; and those portions which are below that line, will require to be embanked or levelled up. The portions A and c, will, therefore, have to be cut down, and the portion в, raised up or embanked. The portions of railway, a b, and c d, of the section, are, consequently, called excavations, or cuttings; and the portions bc, de, embankments, or embanking. Where, therefore, a trifling variation in

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the general inclination of the line, or of the gradients, is not of great importance, it is very advisable, that the line should be so laid out, that the quantity of earth obtained from the excavations or cuttings should be equal to, but not exceed, the quantity required for filling up, or forming the embankments; or, that the quantity of earth, or material, required for the making embankments, should not be greater than what is to be obtained from the excavations or cuttings. If this is not the case, it then becomes necessary, if the embankment does not require the whole of the earth obtained from the cuttings, to lay the surplus earth upon the land or ground adjoining the line of railway, where it is not required, which is called laying it to spoil; or, where there is an excess of embanking, or deficiency of excavation, to make a cutting out of other land, (called side-cutting,") for the express purpose of filling up the embankment; in both of which cases the expense of the formation of the road, is increased to the extent of what is required for the accomplishment of these superfluous operations. There is, however, an exception to this, in cuttings or embankments of great lengths. Cases may occur, where the distance between the cutting and embankment is such, that the expense of conveying the earth, from one part of the line to another, is greater than the increased expense of making an express excavation, alongside the line of railway, or near the embankment, for the purpose of forming the embankment; and of depositing the earth from the cutting, which ought to have formed the embankment, upon waste ground alongside such cutting, or of depositing it to spoil. These are, however, cases to be judged of by the engineer of the work, and are entirely questions of comparative expense, between the one mode and the

§ 3.-Width of the Railway at the Formation Level.

Fig. 2. is a cross section of an excavation or cutting, and Fig. 3. a cross section of an embankment; a b, being the original surface of the ground, and g h the formation level, or extreme depth of the excavation; the formation level, being the foundation whereon the superstructure of the railway is to be raised. The first question, therefore, to determine is, the width at the formation level, as by this the whole of the operations are guided; and this depends upon two considerations, first, the width between the rails; and, next, the width between the two lines, if the railway is intended to be a double line.

§ 4.-Width between the Rails.

The first public railway, of any extent, which was executed, was the Stockton and Darlington railway, the engineer being Mr. George Stephenson. The width, between the rails, of that railway, was made four feet eight inches and a half, taking the Killingworth colliery railway as a standard. The Liverpool and Manchester railway, also constructed by Mr. Stephenson, was formed of the same width; and it was then made a standing order of the legislature, that, in all public lines of railway, the width, between the rails, should be four feet eight inches and a half; and in some railway bills, the breadth of the rails, or outside width, was, also, stipulated; that of the Newcastle and Carlisle railway, in 1829, being required, by the act, to be five feet and one inch, between the outside edges of the rails. The London and Birmingham; Grand Junction, and other railways, connected with these; are all constructed of the width of four feet eight inches and a half. In 1836, this standing order was suspended, and there is