Note 52 — CHAPTER THE SECOND

These date from about the year 1816, when Galashiels Bridge was constructed. It was only 112 ft. in length. But in 1819 Telford designed the Menai Bridge, in which the span of the catenary is 570 ft. and the dip 43 ft. The success of this work gave rise to much imitation, and in several places very great projects were carried through with success. At Pesth, for instance, the span was 666 ft., and at Fribourg 870 ft. But engineers, having no imagination and but little prudence, went too far, so they had to retreat from their cocksureness. Soon it became evident that a long suspended bridge of metal suffered much from the lateral oscillation caused by wind, and that its flexibility made it unfit for railway traffic. “The platform rose up as a wave in front of any rapidly advancing load, and the masses in motion produced stresses much greater than those which could result from the same weights when at rest. Moreover, the kinetic effect of the oscillations produced by bodies of men marching, or even by impulses due to wind, may give rise to strains which cannot be foreseen, and which have actually caused the failure of some suspension bridges. On the 16th of April, 1850, a suspension bridge at Angers gave way when 487 soldiers were passing, and of these 226 were killed by the accident.”—Professor Fleeming Jenkin.