146 Mr Bucli an aii's Report on the Bridge of Suspension 
building, presents new resources in this, as in every other branch 
of practical mechanics, into which it has been introduced. A 
cast-iron arch, or arches, however, would still require interme- 
diate piers similar to those already described, and the roadway 
to be elevated at least SO feet above the present level, and would 
form altogether a work of greater magnitude and expence than 
what I have reason to think the Commissioners would be in- 
clined to undertake. For this reason, and not having been re- 
quired to do so, I have not entered into any particulars as to 
the most proper design of this kind, nor into any estimate of the 
expence; but have turned my attention chiefly to the only other 
construction which remains to be considered, and to which we 
are thus led, not from the novelty of the scheme, or even from 
choice, but rather from the peculiar circumstances of the case, 
to which this construction alone seems adapted, namely, the 
Pendent Bridge of malleable iron; that sort of hanging or in- 
verted arch, where, instead of founding the piers or abutments 
as low as possible, and carrying the arch and the roadway which 
rests on it to a great height above them, two or more support- 
ing pillars are raised on high, one at each end of the bridge; 
the arch, or iron-chain- work, is suspended from the top of these 
pillars, and hangs down between them, so that in the central 
part it is on a level with their base ; and, lastly, the roadway, 
hanging from this main chain, and running everywhere on a 
level, is kept as low as the surface of the water will permit. On 
the fullest consideration, I am of opinion that this construction 
is the most advisable to be erected in lieu of the present bridge 
of wood : and I am the more induced to propose it, being con- 
vinced that the present state of the arts, and it may be added also 
of science, will enable us to raise a structure of this nature, su- 
perior in point of strength, stability, and accommodation, to any 
thing of the kind which has yet been erected. 
The general construction of such bridges will be seen by the 
annexed drawing, Plate V. ; but, as their nature is not generally 
understood, I may remark, that the suspended arch is, in most re- 
spects, the reverse of the common arch. The common arch, it 
is well known, is only sustained in consequence of the nice ba- 
lance and adjustment of its several parts. But the materials of 
the arch and its road- way lying above the abutments from which 
