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



become so clieap as to be applicable to the ordinary purposes 

 for which iron is now used. 



Whatever the materials of which merchant vessels shall still 

 be constructed, we have scarcely a choice with regard to ships 

 of war. Our wooden walls belong to the past. We must 

 henceforward depend on our walls of iron. The rams and im- 

 proved projectiles at present in use would soon send the largest 

 vessel of timber to the bottom. The contest between projec- 

 tiles and armour is still undecided. It may, perhaps, be ad- 

 mitted that the projectiles already in use would, under favour- 

 able circumstances, penetrate any armour a ship could carry. 

 But in battle such circumstances can scarcely ever exist. A 

 projectile fired against a certain plate in a direction exactly 

 at right angles to it may penetrate it without difficulty, while 

 impinging at a less angle, it will glance off, after having done 

 little or no mischief. The chances are many to one that in 

 battle the angle of incidence will not be a right angle. There 

 is, therefore, no well-founded reason for hesitating about the 

 use of armour, and this can scarcely be applied with effect ex- 

 cept to an iron ship. 



Our only considerations at present are the comparative 

 strength and durability of timber and iron ships. We have 

 nothing to do with their form or armament, their sailing 

 power, or their capability of efficient ventilation ; though all of 

 these must be more or less modified by the use of iron in ship- 

 building. The superior strength of an iron ship is derived, 

 not only from the nature of the material, but from the forms 

 which may be given to it. The ponderous beams of the tim- 

 ber ship have been replaced by a much lighter, and at the same 

 time stronger combination of plates and angle iron, so arranged 

 as to afford the greatest amount of strength with the least 

 expenditure of material. The resistance to fracture in every 

 direction, afforded by a hollow iron beam or girder, consisting 

 of plates judiciously arranged so as to prevent a yielding in any 

 direction, is marvellous to those who have not studied the sub- 

 ject. Of all the forms which have been given to the ribs and 

 other portions of a ship requiring enormous strength, the cel- 

 lular is the most effective. It has the additional advantage of 

 affording spaces for the stowage of water, without its occupy- 

 ing any otherwise disposable room, a circumstance of great 

 importance on board a ship. 



There is, however, one objection to the use of iron in ship- 

 building, which lias often caused serious doubts as to the pro- 

 priety or even tho possibility of continuing to employ it for the 

 purpose. Iron is the most perishable of tho common metals, 

 not even excepting zinc, which, though more strongly electro- 

 negative, is more durable, being to a gri less extent 



