1848.] Construction of Iron Tension Bridges. 429 



Results of a series of experiments instituted for the purpose of testing 

 the newly proposed Resultant Taper Chain principles. 



PI. XXIV. Fig. 1, is illustrative of the first experiment, which was 

 intended to test the theory of a system based on the " resolution of 

 forces," as explanatory of the proposed construction of the Agra bridge. 



The idea of compression in the horizontal line having, from actual 

 proof, been deemed untenable in bridges of any ordinary span, the 

 opposite power of tension has been admitted as the third in the series 

 to produce an equilibrium jointly with those of gravity, and the tension 

 in the oblique direction from chain to platform, thus : (See Fig. 18). 

 The oblique and horizontal force in a series bearing theoretically a 

 certain proportion to each other with reference to the obliquity of the 

 former, the weights at each point being uniform ; this experiment was 

 instituted to prove practically how far that theory was correct. 



It was also intended to illustrate practically the theory relative to the 

 position and power of the chains, the links of which are calculated to 

 be true resultants from the two forces immediately below them in the 

 chain, viz. the link and oblique rod attached to the lower extremity of 

 that resultant. 



Fig. 1, shows the experiment which was to prove whether, indi- 

 vidually or collectively, the several sets (three forces applied to any 

 point to produce equilibrium) of forces which may be applied to any 

 single rod, link, or the entire series of rods and links, will be propor- 

 tionate to the different strains, which are those calculated as due to the 

 parts of a bridge of 100 feet span, 16 feet wide, constructed on the 

 above principle. 



The experiment was on full scale as regards heights and distances, 

 but formed of material ^th of the strength of the real bridge, the 

 uniform weights at the points of junction of the oblique rods with the 

 platform being in the same proportion, allowing 120 lbs. per square 

 foot. 



The point of suspension is 2 feet from the centre of the standard, 

 making the half span of the chain 48 feet. 



The power of the centre link, by actual construction, was made equal 

 to ^th that of the upper link, or whole amount of tension which would 

 be due to a uniform chain, and the angle of the central oblique rod de- 

 termined to be 30°., the deflection being JLtfh. 



3 l 2 



