( 72 ) [Jan., 



NOTICES OF SCIENTIFIC WORKS. 



WKOUGHT-IKON BBIDGES AND KOOFS * 



Of all materials used in construction in these days of progress, 

 there is none which plays so important a part in engineering and 

 architectural art as iron. This material has become the only 

 resource of the engineer for carrying out those large designs and 

 projects which thirty years ago would have been considered chime- 

 rical. The attempt to cross the Menai and Conway Straits with 

 bridges formed of wrought-iron plates was treated by mathematicians 

 and engineers as they would have regarded a chapter in the ' Arabian 

 Nights ; ' and more than one eminent mathematician pronounced 

 the attempt — however ingenious the combinations might be in the 

 shape of iron plates — as a wild and fabulous scheme. It was only 

 those connected with the preliminary experiments — which led to 

 the form and principle of construction — who could form a correct 

 idea of the project and establish with certainty the principle on 

 which those important structures were founded. 



It must be admitted that the position of the load and the form 

 of its distribution were not attended to with the same mathematical 

 accuracy as at the present day ; but the general dimensions, extent 

 of span, and weight of load were carefully considered, in order to 

 resist every possible strain and to render the structures secure. All 

 this was done in the face of detractors, and the doubts and fears of 

 men of science, and the results are the completion of the Britannia 

 and Conway Tubular Bridges, as they now exist, as firm and secure 

 as the first day they were opened for public traffic. It is true 

 that tubular bridges, such as the Britannia and Conway, are of 

 a more expensive type than those subsequently introduced; but 

 although extended practice and the progress of science may have 

 suggested improvements, it cannot be disputed that all subsequent 

 constructions of this kind are founded on the same principles as 

 those to which we may safely refer as the pioneers of all their 

 successors. "We have a much greater variety in the forms of 

 wrought-iron bridges now than when first introduced; but the 

 principle, so clearly exemplified in the Britannia and Conway 

 Tubular Bridges, is identical with more recent constructions in 

 the balance of the two resisting forces of tension and compression, 

 as exhibited in the upper and lower sides or flanges of those 

 important structures. 



* ' Wrought-iron Bridges and Roofs : ' Lectures delivered at the Royal Engineer 

 Establishment, Chatham. By W. Cawthorne Unwin, B.Sc. Associate Inst C.E. 

 E. & F. N. Spon. 



