78 ANNUAL OF SCIENTIFIC DISCOVERY. 



attached to the sides of the ship. Great difference of opinion con- 

 tinues to exist on this subject ; some are for entirely dispensing with 

 wood ; probably the greater number contend for a wood backing. I 

 confess myself in the minority on this question ; and, judging from 

 the experiments, I am inclined to believe from past experience that 

 wood combined with iron is inferior to iron and iron in its power of 

 resistance to shot ; and I am fully persuaded that ultimately the iron 

 armor-plates must bo firmly attached to the side, technically called the 

 skin, of the ship. It must, moreover, form part of the ship itself, and 

 be so arranged and jointed as to give secm-ity and stability to the 

 structure. It must, however, be admitted that plates on wood back- 

 ing have certain advantages in softening the blow, but this is only 

 at the expense of the plate, which is much more deflected and driven 

 into the wood, which, from its compressibility, presents a feeble sup- 

 port to the force of impact. Again, with wood intervening between 

 the ship and the iron plates it is impossible to unite them with long 

 bolts so as to impart additional strength to her ; on the contrary, they 

 han^ as a dead weight on her sides, with a constant tendency to tear 

 her in pieces. Now, with iron on iron, we arrive at very different and 

 superior results. In the latter, the armor-plates, if properly applied, 

 will constitute the strength and safety of the structure ; and, not- 

 withstanding the increased vibration arising from the force of impact 

 of heavy shot, we are more secure in the invulnerability of the plates, 

 and the superior resistance which they present to the attack of the 

 enemy's guns. In these remarks, I must not, however, attempt to 

 defend iron constructions where they are not defensible, and I am 

 bound to state that in constructions exclusively of iron there is a 

 source of danger which it is only fair to notice, and that is, that the 

 result of two or more heavy shot, or a well-concentrated fire, might 

 not only penetrate the plates, but break the ribs of the ship. This 

 occurred in experimenting on a target of iron of my own construction, 

 where a salvo of six guns concentrated four on one spot, not more than 

 fourteen inches in diameter, went through the plates, and carried away 

 a part of the frame behind. The same effect might have taken place 

 with any other target ; and certainly nine inches of wood are of little 

 value when assailed by a powerful battery of heavy ordnance and a 

 well-concentrated fire. 



MANUFACTURE OF ARMOR-PLATES. 



From a paper recently contributed to the Institution of Mechani- 

 cal Engineers, Birmingham, Eng., by Mr. John Brown, of Sheffield, 

 and published in the London Mechanics' Magazine, we make the fol- 

 lowing extracts respecting the process by which iron plates for the 

 armor of ships are fabricated in Great Britain : 



Two methods of producing large masses of wrought iron have 

 been in use ; the first by the process of building up under the steam- 

 hammer, and the second by building up under the rolls. Under the 

 steam-hammer, the plate is produced by welding together lumps or 

 masses of scrap iron, each mass of scrap being added and welded 

 to the end of the plate, until it reaches the required length. Plates 

 made in this way have been seriously objected to on account of their 

 brittleness ; and it is reasonable to suppose that this mode of manu- 



