Polytechnic Association- Proceedings. 825 



suspension bridges, and after having examined the use of rollers 

 on the towers, he gives some hints about the effect of the same 

 forces on the platforms, which he supposes to Ije movable. His 

 own words in this respect are: 



"By applying continuous longitudinal pieces in the platform of 

 the bridge, it will be necessary to compound these pieces of parts 

 connected by joints, which leave a little freedom, so that the 

 adjoining parts can slip on the others, where the heat is length- 

 ening the same." 



But it is not to be understood that Navier meant to apply such 

 slipjoints to the cords of a truss, for in our climate such a truss 

 would not begin to work before it was bent to deflections equal to 

 about ^Q of the span. Hence, it follows that if such a truss with 

 slipjoints were applied to a suspension bridge, it would not work 

 at all, but merely act as a dead weight. 



In the same classical book, Navier describes the suspension canal- 

 bridge, built by Count Chabrol in the department of Puy-de-Dome, 

 m France, the length of which was six hundred and fifty feet, and 

 iiud he gives calculations and plans of a project of this kind. These 

 ideas and plans have been applied by constructing the Pennsylvania 

 canal-bridge for spans of one hundred and sixty feet. 



The first suspension bridge on the continent of Europe was built 

 in the year 1823 at Geneva, in Switzerland by Colonel Dufour. 

 It was a wire bridge. 



In the year 1824 the elder Seguin published the first edition 

 cf his work on wire bridges; a book important in many respects, 

 giving many new ideas and improvements. 



There the utility of the stiffness of the platform of suspension 

 bridges was not overlooked, as was done by Navier and the English 

 engineers. On the contrary, the meaning and the importance of stiff 

 railings as well as of longitudinal beams was fully appreciated. 



I must not omit to translate a portion of this work, throwing 

 light on the fact, that James Finley and Templeman are to be 

 regarded as inventors and improvers of suspension bridges with 

 stiffened floors, rejecting all later pretensions and claims of this kind. 



In the aforesaid book is to be found: 



"One of the greatest inconveniences of suspension bridges are 

 the vacillations arising from moving loads of any considerable 

 masses. To prevent these, there should be employed all possible 

 means affording rigidity; the very best of all existing of which I 

 know is the arrangement of strong trusses as parapets of the bridges. 



