REVIEWS — REPORT ON VICTORIA BRIDGE. 473 



dependent upon the number of pier?, which is again regulated by the spans be- 

 tween them. 



The width of the openings in bridges is frequently influenced, and sometimes 

 absolutely governed, by peculiarities of site. In the present case, however, the 

 spans, with the exception of the middle one, are decided by a comparison with 

 the cost of the piers ; for it is evident that so soon as the increased expense in 

 the roadway, by enlarging the spans, balances the economy produced by lessening 

 the number of piers, any further increase of span would be wasteful. 



Calculations, based upon this principle of reasoning, coupled to some extent 

 with considerations based upon the advantages to be derived from having all the 

 tubes as nearly alike as possible, have proved that the spaus which have been 

 adopted in the present design for all the side openings, viz : 242 feet, have pro- 

 duced the greatest economy. The centre span has been made 330 feet, not only 

 for the purpose of giving every possible facility for the navigation, but because 

 that span is very nearly the width of the centre and principal deep channel of 

 the stream. 



The correctness of the result of these calculations obviously depends upon the 

 assumption that the roadway is not more costly than absolutely necessary ; for if 

 the comparison be made with a roadway estimated to cost less than the tubular 

 one in the design, then the most economical span for the side openings would 

 have come larger than 242 feet, and the amount of masonry might have been 

 reduced below what is now intended. In considering the quantity of masonry iu 

 the design, you must, therefore, take it for granted for the moment that the 

 tubular roadway is the cheapest and best that could be adopted, and leave the 

 proof of this fact to the sequel of these remarks." 



The Ice Breakers are next considered, and the value of the plans 

 adopted as compared with the unwieldy " islands " of timber and 

 stone at first proposed, as well as the comparative economy of the 

 masonry, is made sufficiently apparent : 



" It may perhaps appear to some in examining the design, that a saving might 

 be effected in the masonry, by abandoning the inclined planes which are added 

 to the up-side of eich pier, for the purpose of arresting the ice, and termed 'Ice 

 breakers.' 



In European rivers, and I believe in those of America als o, these ' Ice-breaker's 

 are usually placed a little way in advance of, or rather above, the piers of the 

 bridges, with a view of saving them from injury by the ice shelving up above the 

 level of (frequently on to) the roadway. 



In the case of the Victoria Bridge, the level of the roadway is fir above that to 

 which the ice ever reaches; and as the ordinary plan of " Ice-breakers" com- 

 posed of timber and s'one would be much larger in bulk, though of a rougher 

 character, than those which are now added to the pier--, I have reason to believe 

 that they would be equally costly, besides requiring constant annual reparation ; 

 it was therefore decided to make them a part of the structure itself, as is now 

 being done." 



The comparison which Mr. Stephenson draws (relative to econo- 

 my) between the "Boiler Plate Girder " as adopted for the Victoria 



