478 REVIEWS — REPORT 0>~ VICTORIA BRIDGE. 



which influenced his decision on that occasion have heen in any 

 degree weakened by the successful use of the Niagara Bridge. 



Whatever opinions may be entertained on that point, there can be 

 only one in relation to the superior fitness of the " tubular" plan 

 for the Victoria Bridge, as compared with the suspension principle, 

 after reading the subjoined portion of Mr. Stephenson's report : 



" Having given you my views with re-pect to the coraparaiive merits of the dif- 

 ferent kinds of roadway, consiiting of " beams "th;it may be adopted in the Victoria 

 bridge, I now proceed to draw your attention to the adaptation of the " suspension " 

 principle, similar to that of the bridge which Ins been completed within thelast few 

 months by Mr. Roebling, over the Niagara River, near the great " Falls." 



You are aware that during my last visit to Canada I examined this remarkable 

 work, and made myself acquainted with its general details, since then Mr. Roebling 

 has kinJIy forwarded to me a copy of his last report, dated May 1S55, in which all 

 the important facts connected with the structure, as well as the results which have 

 been produced since its opening for the passage of railway trains, are carefully and 

 clearly set foith. 



No one can study the statements contained in that report without admiring the 

 great skill which ha3 been displayed throughout in the design ; neither can any one 



pension principle may be applied ; but until it is made rigid, I have my doubts about it." 

 Jn answer to the finest ion, "Do you think the present Menai Bridge could be so altered 

 and improved and strengthened as to be made able to support a Railroad ':" Mr. Stephenson 

 replied, " I think it might ; but it would leave it merely a Suspension Bridge, which I do 

 not like." — M ' Committee mi Railway E 



In his history of the design of the Britannia Bridge, alluding to the difficult position in 

 which he was placed by the requirements of the Admiralty, lie says: "In this position of 

 a'fairs I felt the necessity of reconsidering the question whether it was not possible to 

 stiffen the platform of a suspension bridge so effectually as to make it available for the 

 -o of railway trains at high velocities." » * * * "Amongst a variety of devices 

 for the accomplishment of this object, the most feasible appeared to lie the combination of 

 the suspension chain with deep trellis turning, forming vertical sides traversed by the sus- 

 pension rods from the chains, with cross bearing frames top and bottom to retain the 

 in the prop'-r position, thus forming a roadway surmounted on all sides by strongly ti u 

 framework." 



"A structure of this kind would no doubt be exceedingly stiff vertically, and has indeed 

 been applied and successfully employed in America on a large canal aqueduct, and is 

 clearly described in the ' Mechanics' Magazine ' for 1846." 



"The application, however, of this principle to an aqueduct is perhaps one of the most 

 favourable possible, for there the weight is constant and uniformly distributed, and ail the 

 strains consequently fixed both in amount and direction: two important conditions in 

 wooden trussing constructed of numerous parts. In a large railway bridge it is evident so 

 far from these conditions obtaining under any circumstances, they are ever varying to a 

 very large extent ; but when connected with a chain which tends to alter its curvature by 

 every variation in the position of any superincumbent weight, the direction and amount 

 of the complicated strains throughout the framing become incalculable, so far as all practi- 

 cable purposes are concerned." * * * • * " It was reverting to this bridge" (a small 

 wrought iron box girder) " that led me to apply wrought iron with a view to obtaining a 

 stiff platform to a suspension bridge, and the first form of its application was simply to 

 carry out 11k- principle described in the wooden suspended structure last spoken of, insti- 

 tuting for the vertical wooden trellis turning and the top and bottom cross beams, wrought 

 iron plates riveted together with angle iron. The form which the iron now assumed was 

 consequently a high wrought iron rectangular tube, so large that railway trains might pass 

 through it, with suspension cliains on each sids." 



