268 Iron and Steel in the Construction of Ships and Bridges. 



The owner of an iron ship is seriously interested in its preser- 

 vation j the shareholder in a railway company ought to be 

 anxious that the bridges on his line should last as long as pos- 

 sible, since the cost of their repair or renewal must be effected 

 with money which otherwise would be his. The traveller, 

 whether by sea or railway, is also deeply concerned, as there is 

 the question of his safety. The general public is concerned, since 

 it is impossible to proceed in any direction without passing under 

 one or more railway bridges ; and this, if they are allowed to 

 corrode as rapidly for the future as at present, cannot but be 

 attended with peril. 



Iron and steel as materials for ship and bridge building 

 possess advantages which will render their use for these pur- 

 poses still more general than it is. We never can return to 

 the materials they have supplanted. It behoves us, therefore, 

 to make every effort to lessen or remove the inconveniences by 

 which their use is at present accompanied. Science, if it 

 does not now, will certainly hereafter supply us with the 

 means for effecting this. But future safety, and a large saving 

 in the time to come, must not be sacrificed, to a trifling advan- 

 tage in the present. The precautions that are taken must be 

 wise and not specious ones. It is not unusual, for example, to 

 contract for iron- work by weight, in the hope of securing the 

 required amount of strength ; but this important object is not 

 to be attained in such a way. For the strength of iron and 

 steel depends not only on their massiveness, but their quality ; 

 and the contractor may exactly fulfil his bargain as to weight, 

 while at the same time he supplies what is vitiated by 

 dangerous weakness. 



