than seven years, and the difficulties which the engineer has had to meet and surmount may be judged from the fact that the basin itself is cut through a stratum of peat, and another of quicksand, through which percolated a spring which afforded some eight hundred gallons of water per minute. The whole of these strata were dug through to the depth in some places of 125 feet, and the sub-springing waters were conducted through various channels towards the river. The alters, or steps, on each side of the dock, which are twenty-four in number, extend from the top to the bottom of the basin, which, viewed from its upper end, presents the appearance of an inverted parabola, and the whole of which is formed of hewn granite masonry; every stone being joggled to its neighbour by pieces of Bangor slate, so that no part of the work can sink in, or get out of place; or, if it should, then, that all parts of it would sink equally, without disturbing their respective bearings and proportions to each other.

The masonry, which is eighteen inches in depth, is laid upon concrete seven feet thick, The dock itself is executed from the plans of Mr. Walker, by Messrs. Grissell and Peto, and is calculated to have cost some eighty thousand pounds, exclusive of the steam-engine.—

Times.

RAISING SUNKEN VESSELS.

SIR T. DEANE has explained to the British Association the method adopted by his brother, Mr. C. A. Deane, to raise the Innisfaile steamvessel, of five hundred tons, which was sunk by striking against an anchor in the Cork river, a few years ago. The ordinary methods of raising sunken ships having proved ineffectual, a coffer-dam was made round the vessel in the middle of the river, and pumped dry by means of eight or nine chain-pumps. The leak was ascertained by digging under the ship, and a cow-hide was nailed over it to keep it watertight. The coffer-dam was removed as quickly as possible, when the Innisfaile again floated by her own buoyancy; and the steam having been got up, she was taken to Passage to undergo the necessary repairs. The whole cost was £400, and the work was done in the course of four tides.

CONCLUSION OF OPERATIONS ON THE WRECK OF THE ROYAL GEORGE. ON November the 4th, the divers worked for the last time in searching for guns, to which their efforts had been exclusively devoted for more than six weeks, in consequence of the whole of the woodwork of this celebrated wreck having previously been removed. When the Royal George went down, in 1782, there were one hundred guns on board, viz. twenty-eight iron 52-pounders, sixteen iron 12-pounders, twenty-eight brass 24-pounders, and twenty-eight brass 12-pounders. Of the above, six iron 12-pounders, and nine brass 12-pounders, were removed in the course of the same year by means of the diving-bell; after which, nothing was done till the year 1834, when Mr. C. A. Deane first brought the diving-helmet and dress (which was a very old idea, suggested in various books for nearly three centuries back,) to such a state of perfection as to render it available for the most important

and practical purposes, to which it never had been applied until he showed the example.

In the years 1834, 1835, and 1836, Mr. Deane recovered seven iron 32-pounders, eighteen brass 24-pounders, and three brass 12pounders, twenty-eight in all; for these he received salvage from the Board of Ordnance, after which the remaining guns being buried in mud, or under the timbers of the upper parts of the wreck, eluded his efforts, as nothing but gunpowder could render them accessible. In 1839, when Major-General Pasley, then Colonel of the Royal Engineers, commenced his operations, he recovered twelve guns, eleven more in 1840, and six in 1841; but, in 1842, he only recovered one iron 12-pounder, because he then directed that the divers, who had got down to the floor-timbers and keel, should not lose time by searching for guns, but should confine their efforts to the removal of the woodwork of the hull; and he pursued the same system in the summer of 1843, until the whole of the keel and bottomplanking were got up; after which the half-anchor creeper drawn transversely, and a frigate's anchor longitudinally across the original position of the hull, proved that no more woodwork remained; he then directed that guns only should be sought for, in consequence of which no less than thirteen have been recovered this season. Hence, forty-two guns in all have been recovered by the divers employed under MajorGeneral Pasley, which, with fifteen recovered in 1782, and twentynine recovered by Mr. Deane, as before mentioned, amount to a total of eighty-six, leaving fourteen guns still at the bottom; of which number six are iron 12-pounders, one is a brass 24-pounder, and six are brass 12-pounders. The quantity of iron ballast in the hold of the Royal George when she sunk was 126 tons 12 cwt., generally in pigs of seven to the ton, of which more than 119 tons have been sent up by the military divers, and delivered into Portsmouth dockyard; so that the quantity now remaining at the bottom is less than seven tons, being only forty-seven pigs, which, having been scattered about by the constant creeping, and by the numerous explosions, cannot obstruct the anchorage. In respect to the fourteen guns still remaining, all buried about four feet under the mud, and of which only one is a heavy gun, should a ship's anchor hereafter get hold of one of them, which is possible, though very unlikely, it will, on being weighed, raise the gun up to the surface of the mud, or a little above it, after which it will release it; and, if the spot be marked by a small buoy to guide a diver down to the gun, he may sling it with ease; whilst from its form it can in the meantime have done no injury, either to the ship's anchor or cable. The quantity of gunpowder fired this season amounted to 19,193 pounds, that is, to nearly 214 barrels.

Mr. Purdo, the principal master-attendant of Portsmouth dockyard, having examined the spot, by dragging a frigate's anchor repeatedly over it, and meeting no obstruction, reported to Rear-Admiral Hyde Parker, that the ground where the wreck of the Royal George ormerly lay was now clear, and quite as fit for the use of Her Majesty's

ships as any other part of the anchorage at Spithead ; which report, in corroboration of Major-General Pasley's opinion, having been communicated officially to the Admiralty, their lordships have ordered the wreck buoy to be removed from the spot, as being no longer necessary. In the sailing instructions annexed to the tide tables, annually published by order of the Admiralty, it will be seen that there were six or seven fathoms of water only over the wreck of the Royal George, the hull of which, then nearly perfect, stood 33 feet higher than the general level of the anchoring ground.

Though the demolition and removal of this celebrated wreck commenced in 1839, yet only two months of that year, and six months of each of the four succeeding years, that is, twenty-six months, or little more than two years, were employed in actual labour; and this object might have been accomplished much sooner, perhaps in half the time, if Major-General Pasley, who directed, and the officers and men who executed this important undertaking, had possessed on commencing it the experience that they afterwards acquired in the course of their operations, to which there was no parallel in the history of mankind; but to which Mr. Deane's introduction of the diving-helmet, and the improvements in the voltaic battery, especially that made by Professor Daniell, undoubtedly paved the way. In the course of these operations, however, Mr. Siebe's improved diving-apparatus was used exclusively after the first year or two, as being safer and more convenient than Deane's original pattern; and, latterly, plate batteries of zinc and iron were used instead of Daniell's constant battery, having been found more convenient for firing gunpowder, though not considered better for other purposes.-Abridged from the Times.

COFFER-DAM AT WESTMINSTER BRIDGE.

FOR some years past it has been known that the foundation of Westminster Bridge has suffered seriously, and, in fact, has become undermined to a considerable extent by the wash of the river. The consequence of this has been a settlement of the various piers, attended with an extensive alteration of the original level of the arches and road-way; whilst, from the soft nature of the stone, such parts of the piers as are exposed to the action of the atmosphere by the alternate rising and falling of the tide, have become much injured.

Mr. Walker, the eminent engineer, upon examining the foundation of the bridge, discovered that the edges of the caissons on which the piers of the arches were originally built, and which extended a short distance beyond the superincumbent masonry, had become undermined; and although those parts on which the piers rested, were solid and in good condition, (though, in some cases, sunk below their original level), yet that their projecting ends were forced upward; whilst the wash of the tide was hourly working under their edges, and thus rendering the foundation insecure.

To remedy this evil, Mr. Walker commenced by forming an extensive Coffer-Dam, by driving down two rows of piling into the clay below the gravelly bed of the river; and having done this, the whole

of the gravel and clay between the inner and outer faces of the CofferDam was excavated to a considerable depth below the level of the caissons. This excavation was then filled up with puddling, thus excluding the possibility of any leakage, either through or under the piling; and by which means was obtained a certainty of carrying on the works, not merely secure from occasional interruption by water, but in perfect dryness at all times. The Coffer-Dam being thus made secure, the whole of the water, gravel, sand, and soil, between the inner face of the Coffer-Dam and the foundation of the piers, was removed to a level of 3 feet below that of the caissons themselves, which were left perfectly dry. To restore the foundation, Mr. Walker surrounded all the piers at a distance of 6 feet from the stone-work facing with a series of piles of green beech, 15 feet long; their lower ends being driven many feet into the clay, and their upper extremities cut off flush at & level with the edge of the foundation. This range of piling had bolted on to it walling-pieces at the distance of every 2 or 3 feet; the bolts extending through the piling, and being made fast to the bed of the caisson itself. The space between the inner piling and the caisson was then filled up within a short distance of the top with concrete, on which is laid squared masonry paving 18 inches in thickness, accurately fitted. The piers of the bridge themselves, on the southern side, were carried out or extended some 12 feet beyond the face of the original pier, and were based on platforms of wood, resting at distances of 3 feet on bearing-piles. The whole of the masonry is executed with Bramley Fall stone, cemented with pozzolano. The new stone facings of the piers average 2 feet in thickness, i. e. the headers are 2 feet 6 inches thick, and the stretchers 1 foot 6 inches; and they have dove-tailed joints.

It will thus be seen that the outer edges of the caissons on which the piers rest were completely surrounded and defended from the underwash of the water; whilst the foundations were extended and rendered completely solid--first, by the beech piling, which, being at all times covered with water, and never exposed to alternation of wet and dry, may be supposed to be almost imperishable; and secondly, by the intervening concrete and stone covering.

The under surfaces of the piers and arches were completely repaired, and, where necessary, faced with fresh stone-work; and all injured or unsound arch-stones are replaced by new ones. In the first place, the diameter and form of the stone to be replaced having been determined by accurate measurement, three pieces of stone were prepared, which, when placed together, exactly corresponded with the size of that to be displaced; the injured arch-stone was then cut out, and a large piece, corresponding exactly with the lower portion of that removed-i. e. having its inner surface larger than its exposed surfacewas next laid in its place, but having upon its lower surface a projection or joggle fitting into a cavity in the lower stone on which it rests. The two upper portions, which are nearly perfect cubes, were then placed upon the top of the new stone, and were thus fastened to it: corresponding holes were made on the surface of the upper and lower

stones; in the hole of the upper one was fixed a sort of slate bolt, kept from falling out by a string, and which preserved the end of it level with the surface of the stone in which it was eventually to enter. Upon this latter being put into its proper place, with the hole on its lower surface containing the bolt brought right over the corresponding hole in the lower stone, the string was cut, the bolt let fall with its lower end into the under stone, and part of its upper end in the upper stone, thus accurately connecting the two. Such was the state of the works at the close of April last.

Messrs. Walker and Burgess then thought it prudent to take the opinion of two other eminent engineers, Messrs. Cubitt and Rendell ; we understand their opinion also to have been that the sinking of the piers of the bridge was caused by the great load upon the clay foundation, there being no piles under the bridge, and the ground on the Surrey side being of a loose nature.

In autumn last, the carriage-way of the bridge was stopped, the state and situation of that part of the bridge by which the alarm had been caused, rendering this step necessary. The following was the state of the works at the close of the year :-The pier called the "seventeenfeet east pier" has been repaired and widened. Its pressure on the bed of the river was found to be at the rate of five tons and a half to a square foot; the timbers of the original caisson, which were very much decayed, had been on the edges of the stonework of the pier forced out of their horizontal position, and bent and broken upward by the enormous weight. The engineers, amongst other means to remedy this defect, enclosed the whole of the lower portion of the pier with sheet piling, driven seven feet into the clay of the bed of the river, and made water-tight by the closeness of the piles one to the other. Between the piles and the pier, stonework, closely cemented, was introduced, and the work was submitted to the judgment of those who were considered competent to form an opinion, and who gave an opinion that the means adopted were the best that were available. Nevertheless, the pier began or continued to sink, and danger was apprehended for the fate of the arch which it supported. The plan adopted to prevent such a catastrophe, and which it is hoped will prove effectual, was this-the pavement of the bridge was taken up, and the immense mass of Kentish rag-stone, cement, &c. composing a concrete, and weighing upon the pier 2,400 tons, was removed from the spandril of the arch. Since this has been done, the pier has remained firm, and the settling at the foundation appears to have ceased. The concrete has since been removed from the spandrils of all the arches; and, in the place of a solid mass, brick arches have been substituted between the spandrils, by which nearly a third of the weight of the bridge will be removed, and the consequent pressure of the piers on the clay-bed of the river relieved. The enormous weight of the balustrades and the heavy recesses will be removed, by which a further reduction of weight will be obtained, and the future projected ornamental alterations facilitated*.-Times. * For Reports of the previous Repairs of Westminster Bridge, see FearBook of Facts, 1839, p. 43; 1840, p. 93; 1842, p. 59.