carriages shall not be capable of disturbing them; in which latter case, the joinings of the rails to the chairs must be such, that the action of the carriages has not the power of deranging the continuity of the rail. To carry the former of these modes into practice, and to preserve the continuity of the rail with ease and freedom, the stone should be capable of moving round, or assuming any degree of inclination, to the line of the road that might occur in practice, without straining either the pin, or distorting the ends of the rails. To effect this, if the pin be made the centre of motion, the under side of the rail should be a portion of the circumference of a circle, formed from the pin as a centre; the base of the chair, could then be either the apex of a curve, or a circular cavity corresponding with the exterior semicircular surface of the rail; the stone might then be depressed on either side, without straining the pin or deranging the joints. Or, we might otherwise make, the bearance of the rail upon the chair or pedestal, the centre of motion; in such case, the pinhole should be a circular slit or opening, formed from the bearing upon the chair as a centre; the pin being made exactly to fit this cavity in a perpendicular direction, would prevent the rails from starting upwards out of their proper position, and the semicircular slit would allow it to turn longitudinally; when the stone became depressed towards one side or the other, the chair could then move round, without injuring the pin or deranging the joints of the rails. The form of chair, Fig. 4, nearly partakes of these properties, without a pin, if the bearance of the rail upon the chair, had been upon a point instead of a flat surface,-for the chair could then move upon such point, without affecting the joinings of the rails, but in that case, the ends of the rails should form an over-lap; or, if the rails rested upon the top of the

chair, and the top was of a circular form, described from the middle of the chair as a centre, the bearance of the rail on the middle of the chair, being the apex of a curve, the same effect would take place.

Innumerable forms of joinings might be devised, every one of which might, in some degree, effect the purpose intended; the essential consideration being, to secure a continued and permanent parallelism in the rails, under every derangement that may take place of the supports on which they rest.

It is not enough that the bearing be such, that the rails are all in the same plane, when the blocks on which they rest are in good order, or in their proper position, parallel with the line of the road; the parallelism of the rails should be preserved, when, by the yielding of the ground, or from any other cause, the blocks are displaced from their proper position, and are made to form a considerable angle with the line of the road. It would not have been necessary to have been thus diffuse on this point, had we not found that several even of the most modern forms of chairs were evidently formed contrary to this principle, many with a view of causing the mode of joining to keep the support or stone in its proper position, rather than allowing it to adapt itself to the unavoidable yielding of the ground on which it rests; but the least consideration will evince the futility of this, especially when the yielding of the ground causes the stone to rest entirely on one side: it will at once be seen, that when the carriages come upon the rails, something must yield and give way, by the great strain thrown upon the fastening, from the oblique action of the weight; but as we shall again have to revert to this subject, when treating on the formation of railways, we shall not enlarge on it further in this place.

§ 4.-Malleable Iron Rails.-Edge Rail.

We have previously stated, that malleable iron rails are now exclusively used on all public lines of railways; it will, therefore, be of great importance, to give a sketch of the successive improvements, made in that description of rails, down to the present period.

At the first introduction of malleable iron rails, they were simply a rectangular, or flat bar of iron, from one to two inches square; or of that breadth, and three inches deep,-the length various. Being very narrow they cut the wheels much, especially, as at that time casehardening the wheels of the carriages was not invented; and when the bearing surface was made broader, the weight and expense became greater than cast iron; and hence for some years they were very little used.

To remedy these defects, and at the same time to secure sufficient strength, Mr. Birkinshaw, of Bedlington Iron Works, in October 1820, obtained a patent for an improved mode of rolling railway bars. This patent consisted of a mode, of manufacturing or rolling, bars of iron, into a similar shape to that of the most improved form of cast-iron rail. A, B, C, Fig. 7, Plate II., represents this kind of rail; a, being an elevation, в, a plan, and c, a section; the form of this, it will be seen, does not differ materially from that of the most improved plan of the cast-iron rail. These rails are formed by passing bars of iron, when red hot between two rollers, one of which has a groove in its periphery corresponding with the intended shape of the rail; and being fixed on a false centre, the under side of the rail is rolled as nearly as possible into the outline of a true ellipse; and indeed expert workmen, by cutting out the groove correctly, can form it perfectly true. This mode of rolling bars or rails, giving them not only an elliptical figure on the

under side, but likewise producing a lateral swell, as at 1, 2, is very ingenious; and has led to the extension of the use of wrought iron, in many cases where the simple form of rolling it heretofore rendered it inapplicable. The elliptical form thus produced, was considered at the time it was accomplished, to be a very great improvement in this description of rail, and to remedy that defect in its shape, as compared with the cast iron, which existed when it could only be manufactured in the form of rectangular bars.

These rails are generally rolled into lengths of fifteen feet, subdivided into bearing lengths of three feet each; eighteen feet lengths were recommended by the patentee, but experience has shewn that the former are the most practicable.

The joinings of the ends of these rails, were at first square at the ends, similar to the old cast-iron rails; but they are now formed with a half-lap, as shewn in в, Fig. 7, and thus they now possess all the properties of the improved cast-iron rails.

A, B, Fig. 8, shews an elevation and plan, of the rail originally laid down by Mr. Stephenson upon the Liverpool and Manchester railway. These rails were in lengths of fifteen feet, subdivided into bearing lengths three feet apart, and weighed thirty-five pounds per yard, and were made with square joints. c and d are sections of the same rail, the former through the middle of the three feet lengths, and D, near the joint of bearing in the chair. On the one side, c, of the rail c, the lateral swell was continued throughout the whole length of the rail, but on the other side, d, it was made to terminate before reaching the point of bearing, and thus forming sections, as shewn in the figures. E, being a section through a b, or at the joint, shews the mode of joining the rails to the chair or pedestal; on one side of the

chair a cavity is cast, corresponding to the lateral projection on the rail; on the other side of the chair a similar cavity, d, is cast, for the purpose of receiving an iron key; when the rail is laid into the chair, the key is driven longitudinally into the cavity d, and being wedge-shaped; it presses against the side of the rail, forces the projection c, into the cavity on the opposite side, and effectually prevents the rail from rising upwards out of the chair.

Figure E, likewise shews the mode of fastening the chair to the block, k k is the block of stone, two feet square and twelve inches deep; two large holes, two inches diameter, are drilled into the block, and wooden plugs, represented by n n, are driven into these holes ; the wooden plugs are bored with a three-eighth inch auger, and iron pins, o o, half an inch diameter, are driven into the plugs, which secure the chair to the block.

A B, Fig. 9, represents the rail laid down upon the Garnkirk railway, near Glasgow; which, it will be seen, is nearly the same section as that of the Liverpool and Manchester railway; the keying, and mode of fastening the chair to the block, being likewise similar, as well as the plan of wedging the rail to the chair.

A B, Fig. 10, Plate II. is another form of rail, which has been made the subject of a patent by Mr. Losh. In the preceding figures, the under side of the rail, within the chair, and likewise that part of the chair whereon the rail rests, are parallel with the top of the rail; and although, when the key is driven against the side of the rail, if the parts are well fitted, it prevents the rail from rising upwards, yet the key has no tendency to tighten the rail down into the chair, especially when the projecting part of the rail does not fit tight into the longitudinal cavity of the chair. In Mr. Losh's plan, the key, being slightly tapered vertically, or of a