434 A Resultant System for the [Oct. 



120 per square foot, was put on, the deflection was 13J inches in the 

 centre. This load was allowed to remain on 3 days : it was subse- 

 quently unloaded and re-loaded several times with nearly the same 

 results ; and after the lapse of 1 7 days from the period of its first being 

 loaded, when all the weight was taken out of the baskets except 24 

 1ft s., which is proportional to the weight of the suspended platform of 

 the real bridge without the traffic weight, the longitudinal beam sprang 

 up to within f ths of an inch of the horizontal line on which it was first 

 constructed. 



Thus was this very extended curve, formed of such exceeding slen- 

 der material, not any of which could be proved before it was put toge- 

 ther, found equal, proportionally, to the greatest amount of the traffic 

 load that could on any extraordinary occasion come on the bridge, with- 

 out derangement of any of its parts : the combination appeared as stiff 

 under the load as could reasonably be expected with such slender wires, 

 and fully bore out the results detailed in experiment No. 1, and the 

 mathematical demonstration of the powers of the bridge, as set forth 

 in the specification of the Agra bridge. 



Subsequent to the above detailed loading, I continued adding weight 

 to the baskets, and correcting the masts as well as the power of the 

 tackle enabled me to do, till the weight in each baskest amounted to 

 81 lbs., when the longitudinal beam was torn asunder at the distance 

 of 25 feet from the centre, and the whole immediately buckled up. 



The breaking weight was therefore 174 ibs. per square foot of plat- 

 form, or a tension of 1 5 tons per square inch of that slight material, 

 the weldings of which were with difficulty made, and the strength of 

 which there was no means of proving. 



I cannot imagine any further proof to be necessary of the efficacy of 

 such a system as has been proposed, manifestly having for its object the 

 avoidance of the defects of both the uniform and extreme oblique 

 system, combining the strength and solidity of the former with the 

 rigidity, economy, and more scientific construction of the latter. 



In this construction, admitting the action of tension in every direc- 

 tion, and where the rods and bars are drawn in the direction of their 

 length, the full amount of tension that can possibly affect every part of 

 the structure can be accurately ascertained, and thus certain data are 

 afforded from which to proportion the sectional areas of every part of 

 the bridge. 



