1848.] Construction of Iron Tension Bridges. 431 



To prove the proportions due to the chain links in connection with 

 the rest of the parts, the oblique rods were severally disengaged from 

 the pulleys, and attached to the chain as follows. The rod (a B ) was 

 first attached to the centre link (b 6 ), the outer end of which was fixed 

 to a chain passing over a pulley, and to which was appended weight x 6 . 

 The lower end of the link (b*) was likewise attached to the junction of 

 *he two rods, and its upper end to a chain passing over a pulley with 

 weight x 4 appended, the intermediate pulley and weight x 6 being remov- 

 ed. In this position was remarked the amount of the weights required 

 to produce equilibrium, and what proportion x 4 , which denoted the 

 tension on link b 4 , bore to the numbers mathematically calculated : the 

 result of the whole is shown in the table, and the annexed Sketch, the 

 position of the rods at this period: (See Fig. 19) (b 4 ), being a 

 true resultant of b 5 and a 5 . Each other link (b 3 , b 2 , &c.) was then 

 added in succession, the weights (x*, x 5 , &c.) being withdrawn in turn, 

 and that attached to the link under investigation being increased as 

 the experiment approached the upper link (b), when the weight Z de- 

 noted the total tension on the upper link. 



Thus was shown the separate tension on the oblique rods, the hori- 

 zontal tension on longiti*6inal beam, and the tension on each link of the 

 chain : the results, as compared with theory, are noted in the table, and 

 are satisfactorily approximate to each other. 



It was stated in the report of the Committee on the Bailee Khal 

 bridge, and referred to in the ninth paragraph of my statement on the 

 resultant system, before alluded to, that the power of the longitudinal 

 beam at the centre, added to the power of the centre link should, toge- 

 ther, be nearly equal to the power of the upper link, so that whatever 

 power was taken from the chains in the centre, should be compensated 

 for in the longitudinal beam. Now the result of the experiment entire- 

 ly coincides with that opinion, and confirms the view taken of this part 

 of the construction. The total corrected amount of weight Z was 

 1086 fts., and the sum of weights x 6 and Y, or 572+519=1091 lbs. 



Experiment the second, Fig. 2, was proposed by Colonel Forbes, on 

 Mr. Dredge's extreme oblique principle, with the sole exception that 

 the central portion of the roadway beam formed the horizontal connec- 

 tion between the first slanting links on each side of the centre, thus, 

 in the Fig. 2, as before, c, c 1 , c 2 , &c, denote the platform, b, b 1 , b 8 , the 



