ee 
478 
and vertically by caft-iron braces, formed 
with dovetails and forelocks ; -the ribs are 
covered with caft-iron plates, and the 
railing to the fides is of iron, the total 
Weight of iron is:378 ton and a half; the 
project's being carried into execution, was 
chiefly owing to the genius and exertions 
of Mr. John Wilkinfon and Mr. Abra- 
ham Darley, iron-mafters, whofe {cientific 
knowledge and extenfive practice in all 
that regards the manufacture of iron have 
long been known to the public. The 
bridge was builc by Mr. Abraham Dar- 
ley, and the iron-work was caft at Coal- 
brooke-Dale, in the year1779. It was.a 
bold effort; for in the firft inftance, in 
adopting a new material they exceeded 
the fpan of the centre arch of Black friars- 
bridge, which had been confidered as a 
great exertion with ftone. 
The iron-work of this bridge has fully 
jultified the idea of making ufe of that 
metal ; for it is at this time as perfect as 
when it was firft put up, except the crack- 
ing of fome of the fmall pieces, owing to 
the giving way of the abutments of ftone, 
which-it is to beregetted were not made 
fufficiently ftrong to oppofe the great mafs 
of alluvial earth, of which the very high 
and fteep adjoining banks are compoied ; 
for if thofe abutments had been fortunate- 
ly built on the coal-meafures, no fuch flip 
could have taken place. 
The fecond iron-bridge was built over 
the famé river, about two miles above the 
former one, at a place called Buildwas. It 
was ereéted at the expence of the county 
of Salop, agreeably to a plan and under 
the diregtion of Mr. Thelford, who is em- 
ployed as furveyor of the public works of 
that county ; it was alfo caft at Coal- 
brooke. Dale, in 1795 and ‘1796. Ti con- 
fifts of one arch of 130 feet in the fpan, and 
rifes fromthe fpringing to the foffit of the 
arch 27 feet; in this bridge, as it was ne- 
ceflary to keep the roadway as low as 
poffible, the principle’ of ° the Schaff- 
haufen-bridge is in fome degree adopted, 
for the outfide ribs are made to go up as 
high as the tops of the railing ; they are 
conneéted with the ribs that bear the co- 
vering plaies, by means of picces of iron 
dovetail’d in the form. of king-pofts. 
The plates which form the covering over 
the lower-ribs, are caft with deep flanches, 
are laid clofe to each other, and form an 
arch of themfelves, fo that altogether the 
bridge is compaét and firm ; the weight of 
iron, is 173 tons, 18 and.a half hundred 
weight. Some fmaller bridges, and an aque- 
duct at Longden (the firft made of iron 
_ for anavigable canal), have allo been made 
Improvements in the Port of London. 
[July 7, 
uitier Mr. Thelford’s dire&tion, in Shrop- 
fltire. ; | 
The next bridge, on a large ‘cale, which 
was made of iron, was that over the River 
Wear, at Monk-Wearmouth, in the courrs 
ty of Durham: the bridge is 236 feet in’ 
the fpan, and the arch rifes only 34 feet ; 
it is compofed of very fhort caft-iron 
frames, which are conneéted together by 
bars of wrought-iron, and hollow tubes 
with flanches and {crews ; the ribs are co- 
vered with timber planking. The weight of. 
cait-iron ufed in this bridge is’ 205 tons, 
hammered-iron 55 tons; this bridge was 
built under the direétion and chiefly at 
the expence of Rowland Burden, Efq. It 
was caft at the manufactory of Mefirs. 
Walker’s, -of Rotheram, in Yorkfhire, and 
does much honour to the projector, and te 
the iron-mafters. 
Tt was a confiderable ftep in the prac- 
tice of bridge building, being nearly double 
the {pan q@f the arch of Buildwas, and con- 
fiderably more than double that/of the 
centre-arch of Blackfriar’s Bridge. This 
will pethaps appear rafh to thofe who have 
not had an opportunity of confidering the 
qualities of iron, or who have not careful- 
ly compared its ftrength with the ftrength 
of the materials formerly ufed in confirué- 
ing bridges. In great works, it is proper 
we fhould proceed with caution; but the 
very principle of improvement muft be 
wholly abandoned, if the demonftrations 
of fcience and the evidence of praétical 
knowledge are to be difregarded. To 
thofe who will take the trouble of come 
paring the {pecific gravity and the ftrength 
of cait-iron with thofe of flone, it will 
not appear extraordinary, that by ufing— 
that metal the practice of bridge~building 
may be changed, and the openings of arch= 
ways made to extend far beyond what has. 
hitherto been attempted. The advantages 
to be derived from this pra&tices are ob- 
vious, and become of great national impor- 
tance in every country where the free na-. 
vigation of rivers is intimately conneéted 
with its profperity. _ ! 
We have been led into the confideration 
of this fubjeét by the information we have 
received refp¢éting the plans for re- 
building London Bridge. Underftanding 
that there was a plan for conftruéting a 
bridge over the Thames, of a Single arch 
of caft-ircn, we have made particular en- 
quiries, and have authority to fay, that 
the following is a correct ftatement of the. 
hiftory, principles, and pian of the defign. 
The manufaétures, trade, and commerce 
of Great Britain having increafed to-an ex- 
tent unparallgled in the hiftory of nations, 
ipa aAgreat 
