447. Perhaps it may be thought that the structures we have been lately
considering are not those which are most universally used, and that the
bridges which are generally referred to as monuments of engineering
skill are of quite a different construction. Every one is familiar
with the arch, and most of us have seen suspension bridges and the
celebrated Menai tube. We must therefore allude further to some of
these structures, and this we propose to do in the present lecture.
It will only be possible to take a very slight survey of an extensive
subject to which elaborate treatises have been devoted.
We shall first give a brief account of the use of iron in the arts of
construction. We shall then explain simply the principle of the tubular
bridge, and also of the suspension bridge. The more complex forms are
beyond our scope.