288 Mr Stevenson’s Description of Bridges of Suspension . 
eomplish the transit of goods and passengers over a river, or 
e ,r en an arm of the sea, in a manner which, but a few years 
since, would have been considered as wholly impracticable. 
Bridges of Cast-iron.— During the late war, when the 
prices of timber and iron, of foreign production, had become 
extravagantly high, every means was resorted to for the in- 
troduction of iron of British manufacture into works of almost 
every description. Among these, its application to bridges of 
cast-iron soon became conspicuous. The first bridge of this 
metal appears to have been erected in the year 1779) over the 
Severn, near the iron-works of Colebrook Dale in Shropshire. 
It consisted of one massive arch of 100 feet. Soon after this 
bold attempt, a number of cast-iron bridges were erected in 
various parts of the United Kingdom ; the most considerable of 
which, was that upon the river Wear at Sunderland, which 
measures 9.8 6 feet in the span ; and more lately, we have 
the bridge of Southwark over the Thames, the design of Mr 
Bennie, the middle arch of which is no less than 240 feet in 
the span. Propositions have even been made for extending 
arches of cast-iron to upwards of 500 feet. These stupendous 
works in cast-iron, which are unquestionably the invention of 
British artists, have their limits, however, both in regard to 
extent, and also as works of a very expensive nature. Other 
means were therefore still wanting, to enable the engineer, in 
many situations, to substitute a continuous roadway for a dan- 
gerous and troublesome ferry. This has been effected with 
wonderful simplicity and economy, by the application of the 
catenarian curve, the properties of which have hitherto been 
regarded, by mathematicians, only as a matter of curious en- 
quiry; but now, by the use of malleable iron-chains, in the 
form of an inverted arch, this curve is applicable to bridges of 
suspension, substituted for arches of the usual form. 
Winch Chain-bridge.— The earliest bridges of suspension 
of which we have any account, are those of China, said to be of 
great extent; Major Rennell also describes a bridge of this kind 
over the Sampoo in Hindostan, of about 600 feet in length. 
But the first chain-bridge in our own country, is believed to have 
been that of Winch Bridge over the river Tees, forming a com- 
munication between the counties of Durham and York. This 
