BEVIEWS — EEPOET ON TICTOEIA BRIDGE. 477 



ering the design of such a bridge as that to be erected for the Grand Trunk Rail- 

 way of Canada. 



Independently of the comparative weights and cost, which I believe have been 

 fairly placed before you, the comparative merits as regards efficiency have yet to 

 be alluded to. 



You may be aware that at the present time, theorists are quite at variance with 

 each other, as to the action of a load in straining a beam in the various points of 

 its depth, and the fact is not known, that all the received formulae for calculating 

 the strength of a beam subjected to a transverse load require remodelling ; therefore, 

 at present it is far beyond the power of the designers of trellis or triangular bridges, 

 to say with precision what the laws are which govern the strains and resistances, in the 

 sides of beams, or even of simple solid beams, yet one thing is certain, which is, 

 that the sides of all these trellis or " Warren " bridges are useless, except for the 

 purpose of connecting the top and bottom and keeping them in their proper posi- 

 tion ; ihey depend upon their connection with the top and bottom webs, for their 

 own support, and since they could not sustain their shape, but collapsed imme- 

 diately they were disc onnected from these top ai d bottom members, it is evident 

 that they add to the strain upon them ; and consequently to that extent reduce 

 the ultimate strength of the beams. 



In the case of the Newark Dyke Bridge, when tested to a strain of 6f tons to the 

 inch, its deflection was 7 inches in the middle, and when tested with its calculated 

 load of one ton per foot run, the deflection was 4| inches The deflection of the 

 Victoria tubes by calculation will not be more with the load of one ton per foot, 

 than 1-6 inch ; and we have sufficient proof of the correctness of this calculation in 

 existing examples. That of the Boyne bridge with a uniform load cf 530 tons, was 

 1-9 inch with the spans shortened in effect as described. 



Much misapprehension has existed in reference to Mr. Stephen- 

 son's estimate of the fitness of bridges built on the suspension 

 principles for railway traffic, and opinions have been attributed to 

 him quite adverse to their safety or practicability for railway pur- 

 poses. The present success of the bridge over the Niagara River 

 is pointed to as a refutation of his supposed opinions, and as evi- 

 dence that a cheaper structure on similar principles might have been 

 adopted for the Victoria Bridge. 



"We doubt whether Mr. Stephenson ever entertained opinions such 

 as we have alluded to. He certainly did not express any doubt of 

 their practicability, either in his evidence before the Committee of 

 the House of Commons in relation to the Britannia Bridge, nor in 

 his published history of the design for that work. On the contrary, 

 he at one time contemplated using the Menai Bridge for the Bail- 

 way, and was deterred from so doing by considerations apart from 

 those of safety,* and we do not believe that any of the reasons 



* "I thought also that that spaa (860 toet) could only !>•■ ex eeded by the adoption of the 

 Chain Bridge, which I do not approve of for the passage Of locomotive engines * * * 

 "I have thought of adopting another plan in connection with suspension which would 

 render the platform quite rigid ; and if the platform be quite rigid, then 1 think the sus- 



