Polytechnic Association Proceedings. 827 



The method of covering the chains with white instead of any 

 other color, as was Finley's practice, is first mentioned in the 

 description of the Hammersmith bridge in England. The same 

 Hammersmith bridge, as seen in the year 1854. was stifiened hori- 

 zontally by cast iron beams, suitable chords and diagonals, and the 

 vertical movements were prevented by strong railings. This was 

 perfectly sufficient for common traffic, and the Hammersmith bridge 

 was celebrated for its good proportions and strength. 



Many bridges of this time suffered by gales of wind; many of 

 Brown's structures, and generally those near the sea, and more 

 especially those constructed with stays, were destroyed entirely; 

 others badly damaged. Telford's Menai bridge, for instance, was 

 extensively injured, and the engineers fell into the great mistake 

 of preventing the undulations and motions, caused by wind, by 

 increasing the dead weight of the bridge itself. The floor of the 

 Menai bridge has a weight of ninety-seven pounds per superficial 

 square foot. But the evils of this system soon produced a change 

 in the opinions of the engineers, and it was the engineer Rendel, 

 to whom was confided the repair of the suspension bridge at Mon- 

 trose, who was induced to apply a good method of stiffening the 

 floor of suspension bridges. Though undoubtedly Finley and 

 Templeman are to be regarded as the first constructors of stifiened 

 suspension bridges, as wo well know, and as Rendel's method is 

 merely one of its applications, yet the ideas in that time were 

 disturbed to such a degree, that he is to be regarded as the true 

 reformator of suspension bridges, and as the man who again brought 

 to clear understanding the idea of longitudinal beams and trusses 

 reaching from one end of the bridge to the other. Rendel also 

 condemned more decidedly the use of stays, and proved by fact 

 the truth of his judgment. 



This bridge of Montrose was built in the year 1825, by Samuel 

 Brown, its span being four hundred and thirty-two feet, deflection 

 of cables equal to forty-two feet, and width of floor twenty-six feet. 

 In the year 1838 the platform was destroyed by a heavy gale, and 

 in the year 1840 the chains gave way with a load of seven hundred 

 men on the floor, whereby a considerable loss of life was caused. 



Rendel, in his report, says: 



" In the anxiety to obtain a light roadway, mathematicians, and 

 even practical engineers, had overlooked the fact that when lightness 

 induced flexibility, and consequently motion, the force of momentum 

 was brought into action, and its amount defied calculation. 



