nearly vertical sea face, had resisted the action of heavy seas. The Shannon Commissioners had determined to try, at Kilrush, a sea wall with a very slight inclination, and, up to the present time, it had sustained no injury, although previously the sloped work had been destroyed.

Colonel Jones, being convinced of the superiority of this form, had devoted much time to observations of the action of the waves upon works of all kinds, as well as to the various modes of using the materials composing the sea walls; and he felt assured, that if the stones were of an average size, square-jointed, and well laid, even without cement, forming an almost vertical wall of moderate thickness, springing from a point as much below lowwater mark as could be conveniently attained, the work would be more durable. "Béton" (concrete) was now much used in France for the construction of sea defences; it was generally done by building caissons of ashlar, filling them in solid with "Béton," and then caulking all the ashlar joints with oakum ;—this kind of work was very durable.

In answer to a remark by General Pasley, Colonel Jones believed that the greatest injury was done by the receding waves, particulary if the joints of the work were not well closed.

Mr. Rennie took a hasty review of the moles and breakwaters mentioned by the early writers, as being thrown out for the purpose of forming harbours; Vitruvius particularly described, among other similar works, a mole constructed with a kind of concrete, composed of "pozzuolana."

Mr. Rennie contended that engineers were not in error in taking, as their guide, the natural inclination of the sea-shore, opposite the situation where the breakwater was intended to be placed. It would be found, in following the coast of England from the perpendicular primitive cliffs of Cornwall to the flat shingle beach of Norfolk, between which places is found almost every variety of geological formation, that the profile of the sea-shore differed according to the material of which it was composed, and the peculiar action of the sea upon it from local circumstances. It had been shown that the force of the waves acted more prejudicially

upon the point above low-water than below it; that the work would stand at a greater inclination at the latter point, indeed that it was rarely injured, even when all above it was carried away; that if the water was deep, the action of the waves would extend deeper: all these and many other points required to be considered in fixing upon the slope for any sea wall; and, therefore, he could not accord with Colonel Jones's views in adopting an arbitrary form for all situations, without considering the exigencies of peculiar localities. He had been particularly struck with the regularity of the slope assumed by the materials at the Kingstown pier after a storm: but in that and all similar positions, the inclination of the face varied with circumstances, and with the degree of violence of the action of the waves.

Among the many arguments against the proposed perpendicular form, might be mentioned the increased expense; for if built of squared stones, below low-water mark, the work must be done from a diving bell; and also that the form is objectionable for a pier, as the wave is thrown up in a mass, instead of expending its force in rolling over the long slope of the fore-shore.

Mr. Telford had abandoned vertical sea-walls on these and other accounts.

Mr. Vignoles agreed to a certain extent (but not fully) with the form proposed by Colonel Jones: he believed that although the construction might be rather more costly, it would be amply compensated for by the greater durability; and he saw no difficulty in doing the work; the proposed plan he understood to be, by commencing the foot of the wall only at such a depth below low-water, as should prevent the violent action of the waves upon it.

At Ardglass the upper portion only of the pier is destroyed; all that part below low-water remains perfectly sound: it is of ashlar of large dimensions, placed from a bell.

Mr. Gordon had seen sections of the works which were commenced for forming a breakwater at Madras: the materials reached at the highest point to within about ten feet of low-water, and amidst the violence of the surf of that coast, the work stood VOL. XXI. 2 N

undisturbed, at an angle of 45°: it was composed of "pierre perdue."

At Algiers the French engineers had used extensively masses of concrete, (blocs de béton,) but at first they were displaced and destroyed by the force of the seas; the cubic capacity of the masses had, however, been increased to the extent of 2 metres square by 3 metres long; they were floated out and allowed to drop into their places from slings; and now they succeeded perfectly. The upper part of the work is intended to be of concrete, cast in caissons; the section below low-water, is at an angle of 45°, and above it, like an ordinary quay wall, with a curved “batter.”

In allusion to the depth of the wave and the power of its action at Madras, Sir John Robison said that, during a violent storm, a quantity of pigs of lead had been cast ashore near the fort, and it was proved that they had come from a vessel which had been wrecked, at more than a mile from the shore, during the siege, by La Bourdonnaye.

The President observed, that at the Plymouth Breakwater, the largest blocks (some of them weighing from 6 to 8 tons) and the greatest number, have been washed from the sea face over into the Sound. The square stones, with which the fore-shore is paved, are placed with the utmost care, and little comparative injury has been done since that method has been adopted. Engineers now generally recommend a deep paving of squared stone, in bond courses, as the best mode of construction. In order to insure the stability of the lighthouse now erecting at the extremity of the Plymouth Breakwater, a foundation of squared stones has been carried up from the natural rock, and an inverted arch turned below the level of the top of the work; and, for its further security, a buttress is now thrown out upon the foot of the south slope, in order to prevent the stones from being carried

away.

It is evident, that if the materials are deposited at an inclination, any portion being displaced, is only carried down, to where, (although, strictly speaking, it may not be wanted,) it must, nevertheless, assist in consolidating the mass; and the vacant spaces

can easily be filled up. Under similar circumstances, a perpendicular wall would suffer more severely, and probably would have fallen entirely. He, therefore, considered that, in situations like that of the Plymouth Breakwater, which was exposed to a heavier sea than Cherbourg, a long slope for the sea face was essential. Still, there were situations where the form proposed by Colonel Jones would, no doubt, be available, and the members were much indebted to him for the suggestion, as also for the valuable observations shown in the sections accompanying the paper: he hoped that he would continue them, and that other members, who had equal opportunities, and less arduous duties to perform than the author, would give the Institution the benefit of their observations.

Mr. Macneill had seen at the mouth of the Helder, in North Holland, banks, nearly vertical, constructed of sea-weed and hazel-wood fascines, backed with clay: they were exposed to a very heavy sea, and yet stood extremely well,-there was considerable elasticity in them, for when a wave struck them, the vibration was felt at a distance along the bank. In other situations, on the coast of Holland, the sea-banks are long slopes of sand, at an inclination of 10 to 1, thatched with straw in many places, groins were built, to break the length of the wave, and to diminish its force; he had adopted similar groins, and found them to answer perfectly.

List of Patents

:

[To be continued.]

Granted for SCOTLAND, subsequent to October 22nd, 1842. To John Varley, of Colne, in the county of Lancaster, engineer, and Edmondson Varley, of the same place, cotton manufacturer, for certain improvements in steam-engines.-Sealed 26th October.

James Hyde, of Duckenfield, Cheshire, mechanic, and John Hyde, of the same place, cotton spinner and manufacturer, for a certain improvement or improvements in the machinery used for preparing cotton, wool, silk, flax, and similar fibrous materials for spinning.-Sealed 3rd November.

John Clay, of Cottingham, in the county of York, Gent., and Frederick Rosenborg, of Sculcoates, in the county of York, Gent., for improvements in arranging and setting-up types for printing.-Sealed 3rd November.

James Pilbrow, of Tottenham Green, in the county of Middlesex, engineer, for certain improvements in the application of steam, air, and other vapours and gaseous agents, to the production of motive power, and in the machinery by which the same is effected.-Sealed 7th November. Francis Roubiliac Conder, of Highgate, in the county of Middlesex, civil engineer, for improvements in the cutting and shaping of wood, and in the machinery for that purpose,-being a communication from abroad. Sealed 9th November. John Michell, of Birmingham, in the county of Warwick, steel pen manufacturer, for a certain improvement in the manufacture of metallic pens, and a certain improvement in the manufacture of pen-holders. Sealed 11th November.

Henry Clarke, of Drogheda, in the county of Louth, in the kingdom of Ireland, linen merchant, for improvements in machinery for lapping and folding all descriptions of fabrics, whether woven by hand or power. Sealed 17th November. John Spinks the Younger, of John-street, Bedford-row, in the county of Middlesex, Gent., for an improved apparatus for giving elasticity to certain parts of railway and other carriages, requiring the same,-being a communication from abroad.— Sealed 21st November.

New Patents

SEALED IN ENGLAN D.

1842.

To Matthew Gregson, of Toxteth Park, Liverpool, Esq., for improvements applicable to the sawing or cutting of veneers,— being a communication.-Sealed 2nd November-6 months for inrolment.