Improvement in the Construction of Bridges, $e. 23 
safety of the arches, piers, &c., is sufficient to save either the 
bridge or the piers, in the event of the destruction of one of the 
arches, or of one of the piers. A case in point, tested the truth 
of thin statement, at Pittsburg, in 1832. <A high freshet, in the 
Ohio, forced away one pier of one of the long bridges at that 
place, by which two arches were destroyed; and “although the 
bridge was intended to be secured with tie- -string pieces, effectu- 
ally, at or near the foot of each arch, yet such was the effect 
when, by the absence of two arches, the whole connteracting 
pressure of the arches was destroyed, that the patentee found, by 
careful examination, soon after the destruction of the two arches, 
that all the other arches were giving way and settling, nearly or 
quite across this wide river. The giving way of these ties, on 
Which the road-way was placed; was so great as to require prompt 
and ample additional ‘support, by props and otherwise, to keep 
some of the arches from falling ; and even then, they settled so 
as to push nearly all the piers from their true pomitiel in a hori- 
zontal direction, so as to produce cracks and violence, which was 
plainly seen ; but was greatest in those piers nearest to the part 
broken avis These piers were not very high, and yet were 
large in proportion, and of hewn stone on the exterior. The re- 
maining parts were much injured ; and, by great care and good 
fortune, were saved from a general destruction. This, then, is a 
Very strong proof, that such mode or intention to secure the 
arches agaist so formidable an evil,-is not generally done so as 
to render them safe, in case of such an accident. That all 
bridges should be safe in this respect, especially long ones, is of 
So great importance, as not to admit, with prudeuce, of any possi- 
ble doubt or question on the subject. 
3d. The arched bridge requires great weight of timber; most 
of which, large enough to be subjected to the dry-rot. 
Ath. The feet of the arches generally stand against the abut- 
ments and piers, at a point much lower than the floor of the 
bridge. By this means, they are exposed to rains in windy 
Weather, aud to dampness from the piers; so much so, as to 
cause their decay in twenty or twenty-five years. ‘This was the 
ease with the bridge at Trenton, over the Deleware ; the feet of 
the arches were renewed, at very great expense, about 1832; and 
from the great exposure to the weather, of this bridge, aiiine the 
floor, it will probably require rebuilding, in the upper parts, within 
