used for ashlar work, and an inferior quality of stone for rubblework, with bricks.

The mortar used up to a short distance above the standard tide level, was made from stone lime, and above that, of lime made from sea-shells; cement was also used in several parts.

The modes of constructing these various works are given in minute detail; many of them, differing materially from the English method of construction, possess great interest; particularly those which relate to the embankments and the fascine work.

A description is then given of the Canal of Oegstgeest, which is a prolongation of the Canal of Katwyk, for the purpose of bringing into the latter, the waters from the Lake of Haarlem ; as well as a means of carrying off the waters of a portion of Rhynland, during and after the drainage of the lake.

In consequence of the establishment of this canal, the Canal of Katwyk required to be enlarged, which was done to the extent of rendering it 52 metres (56.86 yards) wide, with an average depth of 2.20 metres (2·40 yards) below the standard level. The bridges were also enlarged, and it is now contemplated to add two openings to the inner lock, those of the sea locks being already of sufficient capacity.

Having described the works in detail, the author enters into some general remarks upon the effect produced by the canal, one of the principal being its beneficial use in determining the possibility of draining the Lake of Haarlem. Thirty-five years of experience have demonstrated that this canal is the surest remedy for the peculiar position of the district of Rhynland, with regard to drainage; the constant action of the North Sea has made no impression upon the simple but solid masonry of the sea locks; in fact, the Canal of Katwyk appears to be one of the most remarkable hydraulic works ever constructed for the protection of Holland.

The author concludes the Paper by stating, that although he could with difficulty spare the time from his professional labours on the Amsterdam railway, of which he is the engineer, he was induced to undertake the labour of drawing up this memoir, by the subject being one of those proposed by the Institution of Civil Engineers, in the list of Telford and Walker Premiums for 1842, and by the desire of doing justice to the memory of his father, whose early decease alone prevented his name from becoming as extensively known as his talents deserved.

The Paper is illustrated by nine comprehensive drawings and charts, with some lithographic views; a portrait of Mr. Conrad, Sen., and the medal which was struck on the occasion of the first opening of the sluices.

"On the Construction of the Bridges on the Bolton and Preston Railway."-By A. J. Adie.

This Paper, which was written at the request of General Pasley, and by him communicated to the Institution, contains a description of the bridges over the Cowlin Brook, the Lancaster Canal, and the Chorley Road, which alone possesses any peculiarities of construction; and they formed the types upon which the other bridges were built.

In Colonel Sir F. Smith's report upon the Cowlin Brook bridge, he advised great attention being paid to the bridge on account of its "unusual slightness, and the badness of the ground upon which it was founded." The author states, that the latter circumstance induced him to design the present proportions of the work, as he wished to reduce the weight of the piers as much as possible; he therefore ventured to deviate from the original design given by Mr. Rastrick. The result has justified his anticipations, as "after the most careful inspection not a single crack nor a splintered stone can be detected."

The ground where this bridge was to be placed, was found to be a rotten and compressible mixture of moss, decayed wood, and sand, with a few large stones; a foundation was made for each pier, by driving in piles, 20 feet long by 12 inches square ; upon these were placed the footing courses of Limberick stone, 8 inches thick; the piers were built hollow, so that the utmost weight placed upon each superficial foot should not exceed 5 tons, which the author states to be a light load for ashlar work :— "In Edinburgh there are old rubble walls, 34 inches thick and above 100 feet high, which in addition to all their proportion of eight floors, and a roof, have 64 tons on each superficial foot of the bottom courses; and there is a brick chimney in Bolton, the bottom courses of which support 8 tons on the superficial foot."

The bridge consists of eight arches, each of 30 feet span; the arch stones are 18 inches thick, of hard sandstone from the Whittle hills, except seven courses at the crown, which are from a better quarry at Ackrington, near Blackburn.

The author then mentions, as a precedent for such dimensions, some arches constructed, under Mr. Jardine's direction, on the Edinburgh and Dalkeith Railway; they were of Craigleith stone, semi-elliptical in form, of 24 feet span, with a rise of 4 feet, or th of the span; the stones for these arches were 12 inches deep at the springing, and 9 inches deep at the crown; the abutments of one of them are founded on platforms of timber, without piles, resting upon soft plastic blue clay; they have been standing for upwards of ten years, and exhibit no signs of failure. Another arch is also mentioned, constructed by the same engineer, over the South Esk, near Dalkeith, the span of which is 55 feet, and the versed sine 12 feet; the key-stone is 18 inches deep, and the springers 21 inches in depth.

The author objects to placing a mass of earth upon the haunches of the arch, as, from the tremour caused by the passing of the railway trains, the earth has always a tendency to be wedged in between the side walls and to force them out; he therefore left voids above arch stones, allowing only sufficient weight of masonry upon the haunches, and thus securing the rapid hardening of the mortar; for this latter reason also the walls of rubblework never much exceed 3 feet in thickness, and they have been much stronger in consequence.

The railway is carried over this viaduct on longitudinal bearers, 13 inches deep by 6 inches thick, laid on planks 3 inches thick; the bearers and planks are not fixed together with a view to diminish the vibration of the passing trains; this method of laying is stated to be very effective in this respect.

The Lancaster Canal Bridge was originally intended to have been a direct span of 60 feet, constructed of iron, but the directors subsequently decided on building a skewed stone arch, of 25 feet span on the right angle. The arch is semi-elliptical on the square, with a transverse axis of 41 feet 2 inches, and a semiconjugate axis of 8 feet 9 inches; the arch stones are 2 feet 3 inches on the square at the springing, and 1 foot 6 inches at the key-stone; the bed joints intersect at right angles all the lines of sections of the intrados, made by vertical planes, parallel to the elevation; and it is that property that causes the chamfer lines of the beds of the stones to diverge from the springing to the crown. These lines of the curved joints are easily laid down on the sheeting of the centres, from a full-sized development, and by lines drawn at different heights, parallel to the springing of

the arch. The lines of the radiating bed joints are always perpendicular to the tangent of an ellipse of the same form as the elevation of the bridge, the moulds used to form this, being applied in the plane of the elevation. The twist on the length of the beds of the courses was taken from full-sized skeleton moulds of the form of the oblique ellipse or elevation. The five courses, running parallel to the abutments, are all of the same form, and have the same amount of twist on the beds of each stone, except the end stones of the courses, which are varied in length to suit the general breaking of the joints of the courses resting together. The centre part of the arch is plain square work.

This mechanical method of finding the lines, and the twist of the radiating beds for an elliptical skewed arch, is destitute of the scientific accuracy of the mode by which Mr. Buck calculates his spiral lines for oblique bridges, of which the section at right angles to the abutment, is an arc of a circle; but the workmen had no difficulty in putting it in practice, and the author states that he would have had more trouble in constructing trussed centres for a flatter curve of a circular arc, and at the same time keeping the towing path of the canal open. He states that he has not met with any description of an arch executed in this manner, but he considers it the only true principle. Every very thin section, parallel to the elevation, is a proper elliptical arch, and there is a very great saving of stone, from the smallness of the twist on the curved beds, as compared to the common method of working them.

The Chorley Road Bridge is a compound of the common and skewed arches, which the author finds convenient and economical. He has execnted several upon this plan; they are as perfect as the best common arches, and free from skirting of the soffits of the stones. The section of this bridge, at right angles, shows a rise of 5 feet, with a span of 25 feet. The springers, at this part, are 15 inches deep, and the key-stone is 13 inches deep; on the oblique section, or the elevation, the span is 37 feet 9 inches, and the rise 5 feet; the springers are 24 inches deep, and the key-stone is 17 inches deep.

The straight part of the arch is formed with courses, about 10 inches on the soffit, and these are turned round in curved lines, which are portions of circles, the straight parts of the courses being then tangents; and they cut the lines of the elevations at right angles, so that there is no more tendency of the arch to

sink at the elevation than would be the case with any elliptical segment of similar dimensions worked in the ordinary way. The part of the acute angle of the arch is formed with courses which converge from the elevation to the abutments, on account of being arcs cutting the elevations at right angles, and then becoming nearly tangential at the springing. The curves, for these courses, were transferred from the development to the sheeting, in the same way as those for the Lancaster Canal Bridge, and the twist of the beds was taken off full-sized sections of the arch, made in the directions of the converging lines of the extremities; so that at each of these places the beds were worked as if for part of a true elliptical arch; and the beds, between the points thus formed, were worked off with curved rules found from the development. After the masons got into the way of working this kind of arch, they, of their own accord, preferred it to the complete skewed arch. In brick-work, built in this way, it would be very easy to skew the ends of a long archway, by having the bricks moulded to the curvature of the key-course, as, with a very little alteration, they would fit any part of the concentric courses, and a few tapered bricks would facilitate the filling up of the fan-shaped part of the haunch of the acute angle. The communication was illustrated by several detailed drawings, and a model of the bridge, with schedules of the prices and cost of the works.

"On some peculiar Changes in the Internal Structure of Iron, independent of, and subsequent to, the several processes of its manufacture."-By Charles Hood, F.R.A.S., &c.

The singular and important changes in the structure of iron, which it is the object of this Paper to explain, are those which arise in the conversion of the quality of iron, known by the name of "red short iron," which is tough and fibrous, into the brittle and highly crystallized quality, known by the name of "cold short iron." This change the author considers has never been attributed (as it ought to be) to the operation of any definite and ascertained law, but has generally, when observed, been supposed to arise from some accidental cause, and been considered as an isolated fact.

The fracture of railway axles, by which some of the most lamentable accidents have occurred, arises from this molecular VOL. XXII. 2 K