piston, by friction of their moving parts, and by resistance of the water, and by working their air-pumps; and the best and newest engines probably still less. It would, of course, be understood that he meant by 3 lbs. what is commonly called 11⁄2 lb. for moving the engine each way, or through each half stroke; but that is not a correct way of stating it: 14 lb. friction in coming in-doors, and 1 lb. friction and resistance of water, in going out-of-doors, would be more likely to be correct. With all that has been done in Cornwall, these matters still admit of further improvement. April 5, 1842. The PRESIDENT in the Chair. By D. P. Hewett, Grad. Inst. C. E. The Menai Strait is peculiarly fitted for a harbour of refuge for vsssels entering the Rivers Dee and Mersey from the north, and the increasing number of ships frequenting this navigation, as well as the insufficiency of its beaconage, rendered it desirable that the entrance should be distinctly marked; the Corporation of the Trinity House accordingly decided, in 1834, to effect this object by the construction of a Lighthouse, to be situated on a sunken rock about 200 yards from the Anglesey coast, on the west side of the entrance, which is divided by the Puffin Island into two channels, defined by a beacon and two buoys. The principal novelty in the construction of the Lighthouse, is the base, which, instead of diminishing, like the Eddystone, with a regular curve, recedes, by a series of rectangular offsets; the object of this form of structure is to break the force of an impinging wave, and prevent the whole effect of its shock being thrown upon the upper part of the building, as it is when guided up by the curved surface. The building, which was designed by Messrs. Walker and Burges, is a handsome circular tower, 75 feet high, 40 feet in diameter at the base, and 20 feet 6 inches diameter at the top, terminated by a castellated parapet, and entirely constructed of Anglesey marble. The base of the building is solid to the height of 22 feet 6 inches from the rock, diminishing at intervals of 2 feet 3 inches, by offsets of 9 inches each, up to 6 feet 9 inches above high-water mark, where its diameter is 22 feet. On that level is the entrance doorway, which is accessible by steps cut in the base stones. The interior contains six floors, forming rooms for the use of the light-keepers, stores, &c. Every precaution has been taken to render the exterior joints of the courses watertight; each stone is secured to that below it by a slate joggle, and two oak trenails, passing entirely through it, and entering 8 inches into the lower stone. On the upper bed of each course of stones is a projecting fillet, which fits into a corresponding groove in the under side of the course placed upon it, in order to prevent the water from being forced between the courses. The two upper courses project internally and externally, to form a gallery, which supports the parapet and the lantern, the foundation and the framing of which are of cast-iron. The wall diminishes gradually in thickness, from 6 feet 9 inches to 2 feet. The communication describes minutely the construction of the floors, the partitions, the stairs, the lanterns, &c., and the proportions of the materials for the mortar, which consisted of three measures of sand, one of ground lime, and one of Italian pozzuolana. The light is a stationary, red, dioptric light, of the first order, without mirrors. The burner consists of four concentric wicks, of which the largest is 3 inches diameter; its ordinary consumption of oil is one pint per hour. The various bearings are given from which the light is visible at sea. After deducting all expenses, the surplus revenue derived from the light dues, during the year 1840, is stated to have been £388. 13s. 3d. The Lighthouse is connected with the shore by a foot bridge, which consists of a platform, 2 feet 3 inches wide, supported upon a series of iron columns, placed 10 feet apart, secured into the rock and strengthened by stays. This slight construction has withstood the violence of the waves for three years. The paper notices the buildings which have been erected on the shore for the residence of the light-keepers, and then proceeds to describe the Beacon before alluded to, which points out a dangerous ledge of rocks on the opposite side of the channel. It consists of a cone of masonry, 20 feet in diameter at the base, and 37 feet high, surmounted by a staff and globe, rising 13 feet above the apex of the cone. The globe, which is 4 feet diameter, is formed of copper bands, and is 36 feet above highwater mark. The whole amount expended in these different constructions is stated to have been about £12,800. The communication was illustrated by a series of detailed drawings and a chart of the straits. April 12th, 1842. The PRESIDENT in the Chair. "Observations upon the Sections of Breakwaters, as heretofore constructed, with suggestions as to modifications of their forms." By Lieut.-Col. H. D. Jones, R. E., Assoc. Inst. C. E. This communication is the result of several years' observation of the effect of storms upon the sea faces of breakwaters and piers those principally alluded to, and of which drawings were exhibited, were Plymouth, Kingstown, Howth, Ardglass, and Dunmore; a section was also given of the sea wall of the Kingstown Railway, and of the mole of St. Jean de Luz. The mode of building with "Pierre perdue" appears to have been brought into notice about the time of Louis XV., when the cones at Cherbourg were sunk and filled with stones as a foundation for a wall; since then the general method of constructing sea defences, has been to throw down masses of stone, allowing them to form their own angle, subject to the effect of the sea in giving them a greater or less slope. In many instances, this rough foundation has been paved down to below the low-water mark with square blocks of stone, secured with much care, and above this, a wall is built of solid masonry, generally with a considerable slope on the sea face. The author contends, that the system of assimilating the sea face of breakwaters to the form of the shore at low water, is erroneous, because the sea shore is the line of least or non-resistance, not opposing, but yielding to the sea: he asserts that, as far as he can ascertain, no pier or breakwater, constructed with a sea slope, has been found to resist the effects of storms, without considerable repairs and expense being subsequently required. He then gives his observations upon the several sections, and states that the waves have the most violent effect at about half tide, hence the stones at that line are first disturbed, and then are carried down into the deep water. To parry this evil, nearly 200,000 tons of stone have been deposited on the foreshore of Kingstown Eastern Pier, yet more must still be added. Similar additions have been repeatedly made to Plymouth Breakwater, with no better effect. At Dunmore, iron chains have been fixed in the face of the walls, to secure them. At Howth, a slope of 3 to 1 has been found insufficient. At Ardglass, the pier head and lighthouse have been washed away. From these and numerous other examples, it is argued, that piers in exposed situations, with a considerable inclination of the sea face, do not resist the violence of the waves, whereas there are many instances of upright walls having resisted perfectly. As instances of this, Old Dunleary Pier is adduced as being nearly perpendicular, yet never having been injured during a long series of years, although quite as much exposed as the New Pier, now called Kingstown. Kilrush Pier, although not built of heavy materials, has resisted all the shocks of the heavy seas which break upon it from the Atlantic. From these considerations, Colonel Jones proposes upon the "Pierre perdue" to rise a perpendicular wall, from a little below the level of low-water spring-tides: this form, he contends, would resist the upward pressure of the sea upon the broad bases of the stones, and prevent their being removed. He argues that although the proposed walls would require to be built with squared stones, instead of "Pierre perdue," that the cost would not be greater than at present, as the area of the section of his proposed wall, if applied at Kingstown, would be only 4860 square feet, whereas the sectional area of the present pier is 10,085 square feet. The French appear to have partially adopted this form at the new works at Cherbourg; but he considers this mode of construction objectionable, inasmuch as it leaves in front of the outer face, that part of the breakwater which is most subjected to injury. An extensive series of drawings, containing the plans and sections of existing breakwaters and piers, showing the injury sustained from storms, accompanied the same. Colonel Jones explained, by the various sections of breakwaters shown in the drawings, the changes of form and the additions to their cubic contents, which had been made at different periods in consequence of the violent action of storms. The Plymouth Breakwater has had its form altered three times; each time the base has been extended and the sectional area increased. At the Howth Pier, the sections showed three distinct forms assumed by the mass of materials, in consequence of the varied action of the waves. The damage done is now so extensive, that the sea threatens to make a clear breach through the works. The sections of the Kingstown Pier showed the original form to have been a slope of 4 to 1 and 5 to 1, covered with heavy pitching, which had been repeatedly torn up; and some of the stones, weighing 10 tons, were carried considerable distances; an external mole of rough work, containing nearly 200,000 tons of stone, which had been deposited upon the fore-shore, was almost all washed away; while the toe of the work, beneath low-water mark, although at a greater angle than the other parts, remained undisturbed. At Dunmore Harbour, although the long glacis, with a slope of 5 to 1, is protected by pitching, composed of square stones of from 2 to 6 tons weight, and above 12,000l. has been expended, it has received very extensive damage. Many other cases of injury to sloped works, were mentioned, and it was stated, that from these examples, coupled with observations upon some ancient piers in Cornwall and other exposed situations, which, although built of rough materials and with a |