55 
On Bridges of Suspension. 
necessarily introduced the powerful proving machine. A know- 
ledge of the strength of bolts and bar iron of large dimensions, 
was thereby obtained, which formerly was deduced from trivial 
experiments, leading to most erroneous calculation ; and as the 
importance of this new branch of naval equipment developed it- 
self, the principal iron manufacturers of England vied with each 
other in its improvement ; and British iron is now brought to a 
state of perfection, that will, for general purposes, entirely su- 
persede the use of foreign. There is also a uniformity in the 
strength of the improved British iron, beyond that of any other 
country ; so that by adopting straight bolts or bars, united end 
to end in the direction of their length, by coupling plates and 
pins of proportionate strength, instead of chains, we have an in- 
crease of strength with less weight ; the risk of bad workman- 
ship is almost entirely obviated ; and the subsequent proof to 
which every part of the work is subjected, reduces the calcula- 
tion of its strength to a certainty.” 
These observations state distinctly the extent rvf Captain 
Brown’s claims in this great work of improvement. On convers- 
ing with this active and ingenious officer, on the subject of the 
bridges of suspension observed in South America, and other 
countries, he said, that the only one which has the road on the 
same plane with the banks, is that here described by Captain Hall; 
all the others which he had heard of, having the road erected over 
the chains, and partaking of the curve, which, with a flexure neces- 
sary for the security of the bridge, rendered the passage very 
inconvenient : Further, that his observations were written before 
Captain Hall could have seen the bridge over the river Maypo 
in Chili, and with which he now, for the first time, became ac- 
quainted. He claims whatever merit may be due to the mode 
of construction, which is entirely new, and for which he obtained 
a patent seven years ago. The model of this original plan is 
erected in Captain Brown’s premises at Mill Wall, on the river 
Thames, near to London, and is, as above stated, 105 feet span, 
and strong enough to carry loaded carriages. In 1819 he erect- 
ed a bridge on the same plan over the river Leader, at Carolside 
in Berwickshire ; and he is now constructing the iron-work of the 
bridge over the Thames at Hammersmith, with scarcely any va- 
riation, at least none that he considers as a deviation unconnected 
with the necessary arrangements of a bridge on a larger scale. 
