476 REVIEWS— REPORT ON VICTORIA BRIDGE. 



ted, namely, over the river Aire at Ferry Bridge. Although the similarity is not 

 so great with this as with the Victoria tube, yet I believe it is sufficiently so to form 

 another proof that the advantage is in favor of the solid side. 

 As before : 



NEWARK-DYKE BRIDGE. 



Span, 240 feet, 6 inches ; weight, 292 tons. 



FERRY BRIDGE. 



Span, 225 feet; weight 235 tons. 

 The difference between thfse weights is more than sufficient to compensate for the 

 difference of ?pan; besides which, in the Ferry bridge, made according to my de- 

 signs and instructions, I was lavish in the thickness of the side-plates, and the bear- 

 ings which are included in the above weight were stiffened by massive pillars of 

 cast iron. 



For a further example, let me compare the BDyne Trellis bridge (held by some 

 to be the most economical) with the present Victoria tubes. 



The Boyne Bridge has three spans, the centre one being 26 1 feet, and the height 

 is 22i feet. It is constructed for a double line of way, and is 24 feet wide. The 

 total load, including the beam itself, the rolling load at two tons per foot, and plat- 

 form rails, &c, amount to 980 tons, uniformly distributed. 



The bridge is constructed upon the principle of " continuous beams," a term which 

 signifies that it is not allowed to take a natural defection due to its span ; but being 

 tied over the piers to the other girders, the effective central span is shortened to 

 174 feet; in fact, this principle changes the three spans into five spans. Now the 

 effective area given for compression in this centre span is 1131- inches, which gives 

 a strain for the 174 feet span of nearly 6 tons to the inch in comparison. 



The Victoria tubes are so dissimilar in fjrm and circumstances, to the Boyne 

 bridge, that it is a troublesome matter to reduce the two to a comparative state. 

 However, the Victoria tubes are know.i to be 275 tons in weight — 242 feet in span, 

 and of 19 feet average depth, the strain not being more than 4 tons per inch for 

 compression, with a uniform loai of 514 tons, which includes its own weight, sleep- 

 ers and rails and a rolling load of one ton per foot. 



The Victoria Bridge has not been designed upon the principle of continuous 

 beams for practical reasons, including the circumstance of the steep gradient, on 

 each side of the centre span, and the great disturbance which would be caused by 

 the accumulated expulsion and contraction, of such a continuous system of iron- 

 work, in a climate where the extremes of temperature are so widely apart ; other- 

 wise the principle alluded to, was first developed ia tubular beams, namely in the 

 Britannia bridge. 



But since we are only now discussing the merits of the sides, let the Boyne 

 bridge be supposed to have sufficient area in its top to resist 4 tons per inch, ('the 

 proper practical strainj and let the spans be not continuous; it will be found by cal- 

 culation that the area required at top will be 364 inches, instead of 113^ inches 

 and the weight of the span would be found by calculation to come out little short 

 of 600 tons; whereas it is now 386 tons; and if we suppose the Victoria tube to 

 carry a double line of way and 24 feet wide with a depth of 22-J- feet, even if we 

 double the size in quantity, the whole amount of weight will be certainly very little 

 more than 500 tons for 242 feet span. 



It will be necessary to conclude my remarks, with some further observations rela- 

 tive to the comparisons under our notice, which are of vital importance in consid- 



