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architect was Mr. William Mylne , who agreed with theown-council of Edinburgh to finish the work for £10,140,n d to uphold it for ten years. It was also to be finishedefore Martinmas , 1769; but on the 8th of August thatyear, when the work was nearly completed, the vaults andme walls on the south fell down. This misfortune wasc ®^, 10tle d by the foundation having been laid upon thebbish of the houses which had long before been built one north side of the High-street; and which had beenrown out into the hollow to the northward; of this rub-ls n there was a depth of no less than eight feet between the^undation of the bridge and the solid earth. Besides thish r t enc y ' n the foundation, an immense load of earth, whichth a |T e . en over the vaults and arches, in order to raise'bridge to a proper level, had, no doubt, contributed to« . ce the catastrophe above-mentioned. The bridge was

paired by pulling down some parts of the side walls, andrebuilding them; strengthening them in othersthe 1 C ^ la ' n bars; removing the quantity of earth laid uponTh VaU ^ s ’ an d supplying its place with hollow arches, &c.butt W k°le was supported at the south end by very strongjj a ress es and counterforts on each side; but on the north itfr 3 0t rty a single support. The whole length of the bridge,K ri'gh-street, in the Old Town, to Princes-street, in theat ,'l' v Town, is 1,125 feet; the total length of the piers and72 f 63 ’ 13 feet- The width of the three great arches, isea , eat each; of the piers 13^ feet; and of the small arches,tc ® feet. The height of the great arches, from the basebrido' to P °f the parapet, is 68 feet; the breadth of theb ° e > within the wall over the arches, is 40 feet; and the'rith ^ eac b ent l> nO feet. The South Bridge is in a linetbe ti- '^ ort b Bridge, so as to make but one street, crossingttyg ’Sb-street almost at right angles. It consists of twenty-Viz tr C ^ es °f different sizes ; but only one of them is visible,i n ' e large one over the Cow-gate ; and even this is smalll ban Q P r f nson w itli those of the North Bridge, being no moreDl i n at ® Peet wide, and 31 feet high. On the south, it ter-Inft„ 6S a ^ tbe University on one hand, and the Royal^mary on the other.

tvliictf a< l ue( tuct bridge at Glasgow , over the river Kelvin,is t [ le con ducts the great canal from the Forth to the Clyde,betw Wor k °f that great engineer, Mr. Smeaton . Its lengthW hic r t b e abutments, or land-piers, is 245 feet; the arches,15 f e . ar ? Pour i n number, are each 50 feet in span, risingth e th ” ln pbes, from 15^ feet above the looting of the piers;riusivg 66 ,. P ' ers are each 15 feet thick, and 54 feet high, ex-tbe C a i tPe f°°tlng. The extrados is a straight surface forPnixici f ' bbis bridge is constructed upon true mechanicalbtoX e :> and the parapet is recessed opposite to the archesland-pT" t0 res ' st the pressure of the water in the canal. TheWardly PS 016 ‘ dso Ingeniously contrived to be concave out-Theb - 83 t0 s P read ou t at the base,and i 7 -.? dge at Perth was erected between the year 1766Patronao- ’ accor< llng to a plan by Smeaton , under thearches ° P ^le late Earl of Kinnoul. It consists of ten589| f e ° ae °f which is a land arch. The clear water-way istriog-wall’ f* 1 ® exte nt of all the arches, 730f feet; and theDOga f ep . S * , feet '• so that the total length of the bridge is12s. 3 (j ' f be expense of building amounted to £26,446

brido- e ' anc : Was defrayed by public subscription. Blenheimfeet In nsists °f three arches, the chief of which is 1014One 0 f J 6 s P an ‘

Over the 1 Tx'a- S * ex ^ raord ' nar ybridgesin Great Britain, ; s thatby the W l i near Plantrissent, in Glamorganshire , calledTdwards 6 °* 1 ^ >ont ~2/~ t y--Pridd. It is the work of William1746” f 11 Uneducat ed mason of the country, who engaged,’ 0 erect a new bridge at this place, which for

elegance of design, and neatness of execution, surpasses any I ithing of the kind throughout the Principality. The descriptionand history of the progress of this bridge, we shall borrow | jfrom Mr. Malkin’s Tour in South Wales: “ It consisted of j !three arches, elegantly light in their construction. The hewn jstones were excellently well dressed and closely jointed. It !was admired by all who saw it. But this river runs through !a very deep vale, that is more than usually woody, and jcrowded about with mountains. It is also to be considered, !that many other rivers, of no mean capacity, as the Crue, the |Bargoed Taff, and the Cunno, besides almost numberless ibrooks, that run through long, deep, and well-wooded vales jor glens, fall into the Taff, in its progress. The descents iinto these vales from the mountains being in general very ; Isteep, the waters, in long and heavy rains, collect into these j :rivers with great rapidity and force, raising floods, that intheir description would appear absolutely incredible to theinhabitants of open and flat countries, where the rivers are |neither so precipitate in their courses, nor have hills on each ■ ;side to swell them with their torrents. Such a flood unfor- ! ,tunately occurred soon after the completion of this under- j 'taking, which tore up the largest trees by the roots, and | ;carried them down the river to the bridge, where the arches j ;were not sufficiently wide to admit of their passage: here 1therefore they were detained. Brush-wood, weeds, hay, istraw, and whatever lay in the way of the flood, came down, ;and collected about the branches of the trees, that stuck fastin the arches, and choked the free current of the water. In | jconsequence of this obstruction, a thick and strong dam was ] jformed, and the aggregate of so many collected streams I ■being unable to get any farther, the waters rose to a pro- jdigious height, and by the force of their pressure carried the | :bridge entirely away! Edwards had given security for the istability of his bridge during the space of seven years; ithad stood only about two years and a half; of course he wasobliged to erect another, and he proceeded on his duty withall possible speed. The second bridge was of one arch, forthe purpose of admitting freely under it whatever incum-brances the floods might bring clown. The span or chord of Ithis arch was 140 feet; its altitude 35 feet; the segmentof a circle, whose diameter was 170 feet. The arch wasfinished, but the parapets were not yet erected, when suchwas the pressure of the unavoidably ponderous work over thehaunches, that it sprang in the middle, and the key-stoneswere forced out ! This was a severe blow to a man, whohad hitherto met witli nothing but misfortune in an enterprisewhich was to establish or ruin him in his profession. WilliamEdwards, however, possessed a courage which did not easilyforsake him; he engaged in it a third time, and by means ofcylindrical holes through the haunches, so reduced theirweight, that there was no longer any danger to be appre-hended. The second bridge fell in 1751 ; the third, which :has stood ever since, was completed in 1755.” The breadth j ,of this bridge is about 11 feet in the widest part; but in jorder to strengthen it horizontally, it is contracted towards j ,the centre by seven off-sets, so that the road-way is there :one foot nine inches narrower than at the extremities. It jconsists of a single arch, 140 feet in width, forming the seg- j jment of a circle of 175 feet; its height is 35 feet. This > iarch is between 40 and 50 feet wider than that of the cele- j ,brated Rialto, at Venice , and its additional altitude only in !proportion. In each haunch are three cylindrical openings I Irunning quite through, from side to side, like circular win- •dows : the diameter of the lowest is nine feet; of the middle jone, six feet; and of the uppermost, three feet. j

Besides the bridges already mentioned, there are otherneat and elegant structures in various parts of Great I

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