Iron and Steel in the Construction of Ships and Bridges. 257 



IRON AND STEEL IN THE CONSTRUCTION OF 

 SHIPS AND BRIDGES : THEIR ADVANTAGES 

 AND DISADVANTAGES. 



BY PROEESSOE McGAULEY. 



A great revolution has taken place in two of the most important 

 branches of construction : the "wooden walls of Old England/' 

 which for ages were justly considered its impregnable bulwarks 

 at home, and the infallible means of asserting its superiority 

 abroad, have been discarded; stone and brick, which were 

 relied upon as affording a power of crossing rivers, since the 

 progress of civilization enabled mankind to be independent of 

 fords, inflated skins, and other such rude, inconvenient, and 

 unsafe appliances, are now almost equally fallen into disuse 

 for such purposes. The transition has been, in many respects, 

 so sudden, and iron and steel, which have supplanted wood in 

 the building of ships, and stone and bricks in the erection of 

 bridges, are so different in properties from the materials hitherto 

 employed — while, at the same time, so brief has been our 

 experience with regard to them — that we may be considered as, 

 in a great measure, working in the dark, as far as they are 

 concerned. This is a circumstance the more serious, as on 

 the proper construction of our ships depends even the safety 

 of our country, and on the proper construction of bridges the 

 security of our lives, when passing on or beneath them. 



It is certain, such are the inducements held out to the- 

 use of iron and steel, both for ships and bridges, that a return 

 to the materials formerly employed is out of the question. A 

 wooden ship would be exposed to almost certain destruction 

 by the projectiles employed in modern warfare. And such are 

 the spaces now, in so many cases, to be spanned in bridge- 

 building, that the erection of the structures indispensable to 

 our present system of engineering would be, not only very 

 expensive, but often impossible, with either stone or brick. 

 The widest stone arch in existence, that over the Dee, near 

 Chester, is only 200 feet in span ; the main spans of the 

 Menai tubular bridge are each 460 feet wide. 



That iron should be so generally used for almost every 

 purpose, is but the natural consequence of its abundance, its 

 cheapness, and its great strength. Comparing the cost of its 

 production at present with what it was in former times, it is 

 evident that it could not be employed, until now, on the pre- 

 sent enormous scale of consumption. Many circumstances 

 contributed to limit its use, until a recent period. From the 

 method adopted in smelting, it could be obtained only to an 

 vol. x. — NO. iv. s 



