1848.] Construction of Iron Tension Bridges. 433 



rods and beam, heights and distances, being to a full scale, whilst the 

 sectional area of the iron was y^th part of reality. The sections of 

 the whole of the parts are given, and proof calculations that each was 

 correctly proportional to the full sections of the actual bridge. The 

 standards were formed of spars, firmly supported by struts in front* 

 and stayed back with ropes and chains, the latter having tackle on them 

 to correct the perpendicularity of the masts, should they yield to the 

 load. 



The horizontal beam was upheld by forty-four rods from the chain 

 and six direct from each standard ; the chain double, tapering in the 

 centre to a power equal to Ith the upper link. 



The angle of the centre oblique rod 25°, and that of the one next 

 the standard 38° ; so that there was only a difference of 13° between 

 the two extremes, divided amongst twenty-eight points, or a difference 

 of tension between the extremes in the proportion of 263 to 1'62. 



The deflection of the chain was equal to J^th the span. 



The section of the longitudinal beam at the centre, added to the 

 section of the centre links, was equal to the sectional area of the upper 

 links of the chain. 



The whole of the experiment being, as before said, T ^th part of 

 reality, is a model of the curve, which was designed for the Agra bridge, 

 and the result of this experiment will go far to prove the correctness of 

 the theory advanced. 



The calculations show the proportional load for the experiment to be 

 1352 ibs., at the rate of 120 lbs. per square foot of platform, to be 

 uniformly distributed over 56 points. This was done by slinging a 

 basket at each point, and gradually loading them up to the amount of 

 57 lbs. each. 



"When loaded with 24 lbs. in each basket, or 51 lbs. per square foot 

 (exclusive of weight of experiment), the deflection in the centre, after 

 the masts were made upright, was lf ;/ only in the centre. 



With an additional load of 16 lbs. per baskest, making in all 40 lbs., 

 or 84^ lbs. per square foot of platform, the deflection in the centre was 

 5\ inches, and midway between the centre and standards, on one side 

 1£", and on the other 1\", on account of the greater flexibility of one 

 mast than the other. When the full load of 5/ lbs. on each point, or 

 * Left out in drawing, to prevent confusion. 



