"That a vertical measure, from the datum line to the line of railway, shall be marked in feet and inches, at every change of inclination, and that the rate of inclination between each such change shall also be marked," &c. (See the Plate GH.) "That the height of the railway over or under the surface of every turnpike road, navigable river, canal, or railway, or junction with a railway, shall be marked in figures at each crossing thereof; and if there shall be no such crossing in every half mile, then the height over or under the surface of the ground shall be marked once in that

space; and if any alteration in the present level or rate of inclination of any turn-pike road, carriage road, or railway, be intended, then the same shall be stated on the said section," &c. (See TT Plate) "That where tunnelling, as a substitute for open cutting, or arching as a substitute for solid embankment, be intended, the same shall be marked both on the plan and section." (See YY on Plate.) "That it shall not be lawful for the said company to deviate from the levels of the said railway, as referred to the common datum line described on the section so approved of by Parliament, and as marked on the same, to any extent exceeding in any place five feet, or in passing through towns, two feet, without the consent of the owners," &c. "And that no increase in the inclination or gradients of the said railway, as denoted by the said section, shall be made in any place, to an extent exceeding the rate of three feet per mile," &c. It is also enacted, "That it shall not be lawful to diminish the radius of any curve, as described on the plan deposited with the Clerk of the Peace, or principal Sheriff-clerk, unless such radius

such case,

exceed one mile; nor to diminish it in any so that it shall become less than one mile, nor to diminish any greater radius by more than a quarter of a mile, unless when it exceeds two miles, or by more than half a mile, unless when it exceeds three miles on the said plan." On the plan should be exhibited the height of the several embankments, and the depth of the several cuttings respectively. (See the dotted lines on the Plan.) This is called Sectio-Planography.

By consulting the Acts of Parliament relating to the construction of rail-roads, canals, &c. all the information required on such subjects may be learned, by which the engineer will be enabled to comply with the provisions of the "standing orders."

The removal and disposition of the cuttings, to form embankments, so as to produce the greatest economy in labour and expense, is a question of great difficulty, and one demanding a knowledge of analytic science of no ordinary character.

In removing the volume of an excavation to form an embankment, the principle applied in all cases is, "that to make the transportation a minimum between the points from which the earth is taken, and that where it is deposited, the lines passed over by the centres of gravity of all the particles must neither cross each other in a horizontal, nor in a vertical direction."

In forming the excavations, particular care must be taken to form the slopes according to the particular nature of the soil. In cutting through a rock which does not crumble on being exposed to the action of the atmosphere, the sun, or any other natural agent,

Let us take a line 100 miles long, 15 yards wide, and averaging in depth of cutting and height of embankment, 8 yards.

First, 5.455×100=545.5 acres for roadway, ditching, and fencing; and 8x 1.454545 x 100=1163.636 acres required for the slopes, at 2 to 1; which added to 545.5, gives 1709.136 acres for the roadway, ditching, fencing, and slopes. In crossing a ravine, it would be necessary to calculate whether or not a viaduct would be cheaper than an embankment; if the making of a viaduct be found cheaper, it is to be preferred to an embankment.

Breadth between rails.-Before the Great Western Railway, the distance between the rails varied from four feet and a half to six feet. Mr. Brunel has made the distance between the rails 7 feet, or 7 feet 2 inches from centre to centre of rail, and the Irish railway commissioners recommend 6 feet 2 inches; some of the Scotch railway engineers have made the distance between the rails 5 feet. The breadth then may be said to vary from 4 to 7 feet. On a broad railway the velocity may be increased without any danger. On a narrow railway, the danger increases with the velocity. In forming embankments, it is sometimes (but very seldom) more economical to procure the materials from some neighbouring locality, than to bring them a considerable distance from the cuttings in the line. In this case the redundant contents, termed spoil bank, of the excavations, are to be disposed of in the cheapest way that the circumstances of the case will permit. In equalizing the excavations and embankments, for the purpose of finding the surface of the

rails, the extremities of the line may be a little elevated, and so may the approaches to the principal stations also; as the trains can more easily start from such elevations, and arrive with more security. When a small portion of the excavation or embankment is made, temporary rails should be laid down, for the purpose of facilitating the removal of all the materials from one place to another.

When it becomes necessary that two lines of railway should cross each other on the same level, the point of intersection should, if possible, be on an embankment, but never in deep cutting. When the crossing occurs on an elevated point, no obstacle can impede the sight of the conductors of the trains; but when two roads cross each other, or a curve occurs, in deep cutting, much danger may be apprehended.

Tunnels. When a hill, town, river, canal, or other obstacle presents itself, so as to make it necessary to form an under-ground passage, the work is generally tedious and expensive, and often attended with extreme difficulty. Tunnels are very common, as a means of conducting canals as well as roads under elevated ground. Among the works of this kind may be mentioned, the canal tunnel under Staindedge, between Manchester and Huddersfield, the length of which is upwards of three miles, and is 660 feet below the surface; the railway tunnel under Liverpool; and the road tunnel under the Thames, which will soon be completed. This, by far the most stupendous work of the kind ever attempted, cannot fail to transmit to the latest posterity, the name of Brunel. This great national undertaking is thirty-eight feet in width, and