Chai*. VIII.

BRITAIN.

473

I; J J j J I

BRIDGE OVER THE OUSE, SECTIONS AND I'I.aN.

Bridges in Ireland. — Queens Bridge , Dublin , over the Liftey, was finished in the year1768, under the superintendence of Colonel Vallency ; it consists of three arches, that inthe middle spans 46 feet, and each of the others 35 feet; the piers are 7 feet in thickness,and the breadth between the parapets is 35 feet.

Essex Bridge. , in 1753, was commenced after a design of Mr. George Semple ; it con-sists of five arches, one 58 feet span, three of 45 feet, and one of 37 feet; the thickness ofthe piers on each side of the centre arch is 6 feet, the breadth between the parapets 48 feet:a very interesting account of the building of this bridge was published by the architect in1780.

Previous to the work being commenced, the above ingenious architect directed hisattention to the nature of the foundations of the old bridge, and found that where thepiers were built upon a bed of sharp gravel, the lime had so penetrated that the wholesurface seemed petrified or converted into stone ; he then enters fully into the nature ofthe construction of walls, called by the Italians Beimpiuta , or cofferwork, and recommendsthat no stone used among the stuffing should in weight exceed 1 pound; but he moreparticularly dwells upon the nature and properties of lime, mortar, and grout, detailsmany experiments that he had made, and informs us that he had heard a Scotch masonaffirm, that in 100 years good mortar would become as hard as stone. In these descrip-tions we have the author’s opinion upon the manner adopted in building the walls ofchurches and castles. “ After the masons had laid the outside courses with large stoneslaid on the flat in swimming beds of mortar, they hearted their walls with their spawls andsmallest stones; and as they laid them in, they poured in plenty of boiling grout, or hotlime, liquid among them, so as to incorporate them together, as if it were with melted lead,whereby the heat of it exhausted the moisture of the outside mortar, and united mostfirmly both it and the stones, and filled every pore, and so set that it grew hard imme-diately ; and this method was taught to our ancient masons by the lloinish clergy thatcame to plant Christianity in these countries; and this mortar,” he affirms, “so runtogether, was harder to break than the stones that were imbedded it.” There are manyvery sensible and useful remarks contained in his curious work, which relate to a varietyof subjects connected with constructions in water, and which would interest the civilengineer.

Sarah's Bridge was built by Mr. Stevens, in 1792; it consists of one arch, 110 feet span,with a rise of 22 feet; the breadth between the railing is 37 feet

Carlisle Bridge consists of three arches, the middle 50 feet span, the others 40 feet each ;the thickness of the piers 10 feet, and the breadth between the parapets 63 feet.

H'ellesleg Bridge. i, at Limerick, erected after the designs of Alexander Nimmo , consists offive segmental arches, each 70 feet span, with a versed sine of 8 feet 6 inches; the piers areeach 10 feet in thickness, and the soffite of the arch, measured from one face to the other, is43 feet.

This bridge bears considerable resemblance to some of those constructed by Perronet,