126 SECTIONAL ADDRESSES 
According to his own account of the meeting, several members were. 
critical, but he convinced them in a way which suggests that members 
of ‘ Section G’ of those days were easily satisfied. He wrote: ‘ The above 
paper excited a discussion in which several members opposed my plan. 
I produced a drawing of a bridge, copied from the Saturday Magazine, 
March 1834, at Wandipore, which clearly proved that the principle in the 
construction of bridges I now advocate was acknowledged 195 years ago ; 
whereupon my plan received the unanimous approbation of the Mechanical 
Section.’ 
Dredge made good use of all the praise and influential support he 
received. In proof of his principle and claims he published elaborate 
calculations, and it is remarkable that his principle and calculations appear 
to have been approved by several who were considered to be experts and 
whose opinions carried weight. The Surveyor, Engineer and Architect 
denounced criticism as a striking example of professional prejudice, 
congratulated Mr. Dredge on his two bridges in Regent’s Park and 
announced that three additional bridges had been ordered by the 
Commissioners of Woods. At least twenty-seven bridges were built, 
including five in Regent’s Park, London, four in Wiltshire, and a number 
in India. 
The failures began in India. A bridge of 200-ft. span collapsed before 
it was completed, and another one failed to carry its proof load and 
collapsed also. A paper published in 1849, in which the failure of these 
bridges is referred to, states that seven bridges in India had had to be 
remodelled by engineers there on an ‘improved principle.’ The 
description of the alterations suggests little improvement on Dredge’s 
design. 
The disastrous source of weakness in Dredge’s bridges was, of course, 
the timber roadway platform. With no appreciable strength in the 
chains at the centre, the stiffness of the platform was all-important. 
In India, that part had failed by buckling, and sooner or later all the 
bridges must have suffered badly. Dredge seemed unable to appreciate 
the weakness, for in his book published in 1851, he argues that platforms 
always have ample margins of strength, and that in ‘ large structures 
the platform may be lighter in consequence of the horizontal strain 
being more efficient to prevent undulation than the heavy trussing and 
cross-planking which are used in the old system for the purpose.’ 
I have not been able to follow the later history of these bridges, but 
I believe that no single example exists. 
Several suspension-bridges, built before any of Dredge’s, are still in 
use. In all these the chains are of uniform strength throughout, and the 
whole weight of the bridge is suspended from them. 
The flexibility of these bridges under heavy moving loads is a source 
of trouble, and of wear and tear of the platforms. Nevertheless, when 
the chains are pulled by the loads into a line of equilibrium, so long as 
the anchorages are secure and the towers are sound, the stability depends 
solely on the tensile strength of the chain, and under these conditions almost 
all suspension bridges have a substantial margin of strength or stability. 
