326 Transactions of the American Institute. 



These have to consist of long pieces of wood forming the frames, 

 and of wooden Andrew crosses put together at right angles. The 

 connections of the different pieces should be made by iron bolts, 

 piercing the frames or cords between the joints of the diagonals, 

 allowing any desired tension and great rigidity." 



Further, Seguin says: 



" The first quality of the floors or platforms of suspension bridges 

 is to have as much rigidity as possible, and to obtain it care is to 

 be taken to fasten together the different parts, so as to get a con- 

 tinuity preventing any separation. It is customary to attach the 

 suspension rods to cross bearers which are supporting the floor 

 itself, but it is possible as well to apply longitudinal pieces to 

 support the cross-bearers, and it seems to me to be far preferable 

 to establish in all cases longitudinal flooring before cross-bearers. 

 The longitudinal pieces had to be of the greatest possible dimen- 

 sions, their joints to be well connected to avert those horizontal 

 movements, which are consequences of the deficiency of continuity 

 in the floor. 



" The Americans had adopted one-seventh of the spans for deflec- 

 tions of cables. This disposition, being very favorable in reference 

 to solidity, is inconvenient in regard to deplacements, which become 

 always the less the more the deflection of cables is diminished. But 

 the Americans have neutralized that inconvenience by adding to the 

 floors great ma'Sses, and using strong railings to increase the rigidity." 



Concerning the said masses, Seguin meant evidently Finley's 

 longitudinal and continuous beams laid on the cross-bearers; the 

 weight and action of which reduced the side motions caused by 

 wind, and which had, besides this effect, the more direct object 

 which Seguin mentioned before, but did not understand fully. 

 Navier's influence on Seguin is evident already. 



The brothers Seguin introduced the method of boiling the wire 

 in oil, thus giving a good coating as a preventive of rust. But 

 they observed that the wire, after the process of boiling, lost a 

 portion of its strength, an observation which is confirmed by newer 

 and very minute experiences of reliable men.* Indeed, the tem- 

 perature of boiling linseed oil is at six hundred degrees Fahr., 

 which is the same temperature required to soften steel, at which 

 that dark-blue color, so characteristic of the tempering of steel, is 

 observable. 



* Experiments by Professor Karmarsoh and Engineer BriZi in Prnssia. 



