BKI I'Hi K. 



541 



against the abutments in the manner of avchstonc;;. 

 Mwrmigbujroo bars, of a length to t:mhr;i< e sundry 

 frames, were tlien fitted into tin- grooves. Hollow 

 >f cast-iron, four inches in diameter, fitted to 

 re.ich ! i. 'tween each two frames, across the soffit, 

 \vi-i.- introduced. Upon the ends of these pipes are 

 Haunches, in which there are holes, answerable to the 

 holes ii> the four inch pieces of tire frames, and also 

 to those of the wrought-iron bars. Through these 

 holes, wrought-iron bolts were introduced, which 

 brought all the before-mentioned parts together by 

 means of fore-locks. The frames do not meet at the 

 upright pieces, but on the three points of the four- 

 inch pieces only. On the ends of the hollow pipes, 

 there are small projecting pieces, which embrace the 

 upper and lower edges of th? frames opposite each 

 joining. These operations were repeated until the 

 \vhole of the frames were placed, and the arch key- 

 ed, forming six ribs between the abutments. Upon 

 the ribs perpendicular pillars are placed ; and be- 

 tween them are cast-iron circles, which come m con- 

 tact with the cxtrados, the upright pillars, and the 

 bearers of the roadway. The bearers and covering, 

 we suppose for cheapness, are made of timber. The 

 railing is cast-iron. The inclinations each way upon 

 the arch, probably to save weight, are inconvenient- 

 ly steep. 



From its great elevation, and lightness of con- 

 struction, this bridge is justly esteemed a bold effort 

 of art, and a magnificent feature in the country. The 

 wooden bridges in Switzerland, and that in America, 

 are of greater span j but, being placed near the sur- 

 face or the water, and from the difference of materi- 

 al, their parts being of larger dimensions, there can 

 be no comparison as to the fineness of effect. This 

 arch is incontrovertible evidence of what may be ac- 

 complished by means of cast-iron, since it answers so 

 well, charged, as it is, with, the following, we con- 

 ceive, material defects : 



1. The frames are much too short, thereby multi- 

 plying, very unnecessarily, the number of joinings in 

 the main ribs to 125x6=750 ; and, in the same ra- 

 tio, increasing the number of braces, ties, and bolts. 

 The pieces of the frames, being of unequal dimen- 

 sions, is also improper. 



2. The preservation of the due position of the 

 frames is made to depend too much upon wrought- 

 iron bars, and bolts, which should be, as mach as 

 possible, excluded from structures of this kind. 



3. The circles in the spandrels, placed as supports 

 for the roadway, we hare already stated, are im- 

 proper in a situation where they are not equally 

 pressed around. 



. We shall observe nothing respecting the timber 

 in the superstructure, because this is mere economy ; 

 if properly managed, any bad effects from the differ- 

 ence of expansion and contraction in the two male- 

 rials, may be easily avoided ; and the timber, not in- 

 terfering with the essential parts, it may, when ne- 

 cessary, be removed, with little interruption to the 

 intercourse over, and none to that under this noWe 

 arch. We cannot here resist drawing the attention 

 of our reader to the perfection of this double accom- 

 modation, in crossing this deep ravine with facilitv, 



Prj- 1 . 1 



vessels of '.AX) toes arc passing full rigged be 

 lo .v. 



:-t-iron bridge has lately been built over the At : 

 river Witham, at Huston, in Lincolnshire, from a dc- ,,, A , t 

 sign by Mr Rennie. The span is about H.> feet, tin xoV. 

 rise is about five feet six inches, the brcadt' 

 feet) and there are eight ribs, each rib is comp< 

 of eleven frames, three feet depth in the direction of 

 the raJius. At each joining there is a cast-iron grat- 

 ing across the arch, which connects the fr;;r 



the same principles as practised at P n^y- 



sylte aqueduct. Instead of three pieces in the direc- 

 tion of the cui-ve, as at Sunderland, here then: aic 

 only two, but they are seven inches by 4J. Thoe 

 are, in each iramc, connected in the direction of the 

 radius, by pieces four by three inches. Upon the 

 back of the ribs, pillars, four by three inches, are 

 placed perpendicularly to support the roadway. Tl 

 superstructure resembles that of the first iron bridge 

 at Coalbrookdale. The arch Ins. been kept \ 

 flat, to suit the tide below, and the streets ab 

 The rise being only about -,' r of the span, is another 

 proof of the facilities which may be acquired by 

 using cast-iron. The frames being mad.- about four 

 times the length of those at Sunderland, and being 

 connected with cast iron gratings instead uf wrought-' 

 iron, are essential improvements ; but from the 

 pieces in the frames, which are in the direction of the 

 radius, being only four by three inches, while the 

 main pieces, in the direction of the curve, are 7 by 

 4', a great proportion of the former are broken. This 

 is a defect ; and the pillars which support the road' 

 way, being perpendicular, do not correspond with 

 the radiated pieces of the frames. The ribs, in spring- 

 ing from the perpendicular face of the masonry of 

 the abutment, have also a crippled appearance. 



In improving the port of Bristol, Mr.Icssop found At P 

 it necessary to change the course of the river Avon, PLATE 

 and to make two cast-iron bridges over the new Xf IV. 

 channel. The span of tha iron-work of each arch is 

 100 feet ; the rise- 12 feet 6 inches, or ^ of the sp 

 the breadth is 30 feet ; and there arc six ribs ; each 

 rib is composed'of two pieces meeting in the mid 

 and they are connected crosswise by nine cast-i 

 ties, which are dovetailed, and wedged into the ribs ; 

 the cross sections of these ties are in this form "J . 

 The ribs stand upon abutment plates, winch are laid 

 in rhe direction of the radius. These plates are 

 32 feet in length, 2 feet 4 inches in breadth, and -r 

 inches in thickness; in each plate are five aoertnr 

 each .5 feet long and 20 inches in width. The i 

 are 2 feet 4 inches in depth in the direction of the 

 radius, and two inches in thickness, and -have each 

 80 apertures, one foot square, separated by L 

 three inches broad, excepting opposite the cross tie.-, 

 where the solid is 12 inches broad. Where the ribs, 

 meet in the middle, they have Haunches eight inches 

 broad and two thick', and they are connected by cat- 

 iron screw-bolts thiec inches diameter. Between thv 

 ribs and the bearers of the roadway, perpendiculd; 

 pillars, with cross sections of this form T, an 

 The bearers are of the same form. The whole is 

 vered with cast-iron plates, and there are railing; 

 cast iron. 



