Improvement in the Construction of Bridges, ^c. 283 



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 this 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 akhough the 

 bridge was intended to be secured with tie-string pieces, eftectu- 

 ally, at or near the foot of each arch, yet such was the effect 

 when, by the absence of two arches, the whole counteracting 

 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 position, 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 away. 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 against 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 prudence, 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. 



4th. 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, and to dampness from the piers ; so much so, as to 

 cause their decay in twenty or twenty-five years. This was the 

 case 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, above the 

 floor, it will probably require rebuilding, in the upper parts, within 



