BRIDGES. 
raised foot- way on each side 7 feet. The 
upper surface of the bridge is a portion of 
a very large circle, which forms an elegant 
figure, and admits of convenient: passage 
over it. On each pier there is a recess or 
balcony, with two Ionic columns and pilas- 
ters, which stand on a circular projection 
of the pier above high-water mark. The 
bridge is rounded off at each extremity to 
the right and left, in the form of a quadrant 
ot a circle, rendering the access commo- 
dious and agreeable. This edifice must be 
regarded as a fine specimen of Mr. Mylne’s 
ingenuity and judgment, though the me- 
thod of construction has never been made 
public. 
Wooden bridges now demand our atten- 
tion. The simplest ease of these edifices 
n J n which the road way is laid over 
beams placed horizontally, and supported 
at each end by piers or posts. This me- 
thod, however, is deficient in strength and 
width of opening : it is, therefore, neces- 
sary, in all works of any magnitude, to ap- 
ply the principles of trussing, as used in 
roofs and arches. Wooden bridges of this 
kind are stiff frames of carpentry, in which, 
by a proper disposition, beams are put so 
as to stand in place of solid bodies, as large 
as the spaces which the beams enclose ; 
and thu,?, two or three, or more, of these 
are set in a butment with each other, like 
mighty arch stones. At Schaffhausen, in 
Switzerland, where the Rhine flows with 
great rapidity, several stone bridges had 
been destroyed, when, in 1754, Gruben- 
hamm offered to throw a wooden bridge of 
a single arch across the river, which is 
nearly 390 feet wide. The magistrates, 
however, required that it should consist of 
two arches, and that he should, for that 
purpose, employ the middle pier of the 
last stone bridge, which would divide the 
new one into two unequal arches of 172 
and 1 93 feet span. The carpenter did so ; 
but contrived to leave it a matter of doubt, 
whether the bridge is at all supported by 
the middle pier. It was erected on a plan 
nearly similar to the Wittengen bridge, at 
the expense of about 8,0007. sterling. 0 Tra- 
vellers inform us, that it shook if a man 
passed over it ; yet waggons, heavily laden, 
also went over it without danger. This 
curious bridge was burnt by the French 
when they evacuated Schaffhausen, in April 
1799. 1 ’ 
Iron bridges are the exclusive invention 
of British artists. The first that has been 
erected on a large scale is that over the 
river Severn, at Coalbrook Dale, in Shrop- 
shire. This bridge is composed of five ribs, 
and each rib of three concentric arcs, con- 
nected together by radiating pieces. The 
interior arc forms a complete semicircle, 
but the o fliers extend only to the cills un- 
der the road-way. These arcs pass through 
an upright frame of iron, at each end, 
which serves as a guide ; and the small space 
in the haunches between the frames and the 
outer arc is filled in with a ring of about 
seven feet diameter. Upon the top of the 
ribs are laid cast iron plates, which sustain 
the road-way. The arch of this bridge is 
100 feet 6 inches in span ; the interior ring 
is cast in two pieces, each piece being about 
‘ 0 feet in length. It was constructed in 
the year 1779, by Mr. Abraham Darby, 
non-master at Coalbrook Dale, and must 
be considered as a very bold effort in the 
first instance of adopting a new material. 
The total weight of the metal is 3781 
tons. ~ 1 
The second iron bridge, of which the par- 
ticulars have come to our knowledge, was 
that designed by Mr. Thomas Paine, au- 
thor of many political works. It was con- 
structed by Messrs. Walkers, at Rother- 
ham, and was brought to London, and set 
np in a bowling-green at Paddington, where 
it was exhibited for some time. After 
which it was intended to have been sent to 
America ; but Mr. Paine not being able to 
defray the expense, the manufacturers took 
it back, and the malleable iron was after- 
wards worked up in the construction of the 
bridge at Wearmouth. 
The third iron bridge of importance 
erected in Great Britain was that over the 
river Wear, at Bishop Wearmouth, near 
Sunderland, the chief projector of which 
was Rowland Burdon, Esq. M. P. This 
bridge consists of a single arch, whose span 
is 236 feet ; and as the springing stones at 
each side project two feet, the whole open- 
ing is 240 feet. The arcli is a segment of a 
circle, of about 444 feet diameter, its 
versed sine is 34 feet, and the whole height 
from low water about 100 feet, admitting 
vessels of from two to three hundred tons 
burthen to pass under, without striking 
their masts. A series of one hundred and 
five blocks form a rib, and six of these ribs 
compose the breadth of the bridge. The 
spandrils, or the spaces between the arch 
and the road way, are tilled up by cast iron 
circles, which touch the outer circumfer- 
ence of the arch, and at the same time sup- 
port the road-way, thus gradually diminish- 
