56 ANNUAL OF SCIENTIFIC DISCOVERY. 



ever, some may assert, that if the requisite machinery existed in this 

 country for giving the same proportionate tenacity and tensile strength 

 to heavy single plates, as good results would be produced. This se- 

 quence, although a natural one, is not, it seems by experience, a cor- 

 rect one. A combination of thin plates is said to be more effective in 

 resisting the impact of a heavy shot than a single plate of the same 

 thickness, by reason of their elasticity or reaction after the instant of 

 percussion. All experience goes to prove this assertion ; where heavy 

 plates have been shattered to fragments, the thin ones have been dis- 

 placed and bent, but not destroyed, and the injuries to them rarely ex- 

 tend through a whole section of armor. The heavy plates, when 

 smashed, require much time and expense for their renewal, and are at 

 best a poor substitute for thinner coats in many layers. 



Recent improvements have rendered the thin plates still more ef- 

 fectual. The gunboat Essex, after her misadventure at Fort Henry, on 

 the Cumberland river, was taken to St. Louis and there re-clad on the 

 forward casemate with iron plates only one inch thick ; under these 

 were placed India-rubber sheets one inch thick, the whole being in- 

 clined at an angle of 45 upon a wooden backing of oak 16 inches 

 through. Thus defended, the ship went into service. 



" In the action between this gunboat, commanded (at that time) by 

 Commodore W. D. Porter, and the batteries at Vicksburg, Port Hud- 

 son, and other points on the lower Mississippi River, the forward caser 

 mates were struck repeatedly by solid shots, varying from 32 to 128 

 pounds, some of which were fired from rilled guns at short range. None 

 of those shots penetrated the forward casemate, but some of the larger 

 ones indented the armor plates, started the wood-work, and broke in 

 pieces, showing that the force of the shot was entirely spent. The 

 after-casemates, covered with iron of the same thickness, and made by 

 the same manufacturers, but without india-rubber, were penetrated in 

 several places by shots fired from the same batteries and similar guns ; 

 in all, over 125 shots struck this vessel at about the same range, proving 

 that this thickness of iron affords no protection when placed immedi- 

 ately upon a solid timber support." Scientific American. 



Corrugated Armor Plates. - - The following is an abstract of a paper on 

 the above subject, read to the British Association, 1863, by Mr. George 

 Bedford. The principle of protecting ships by thick plates of iron against 

 projectiles of steel or homogeneous iron, hardened and tempered, would 

 appear to be erroneous, for the following reasons, namely, that iron 

 plates must always be softer than the projectile, while the latter has an 

 almost unlimited advantage in the force which can be o-iven to it by 



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strengthening guns so as to bear very large charges, and thus gain in- 

 crease of velocity with increased weight of shot. Still more is this the 

 case if flat-headed projectiles, hardened and tempered as the Whit worth 

 shell and shot, are to be provided against. The method which I pro- 

 pose is founded upon two principles of strength, - - cohesive strength and 

 mechanical strength. The plates being made of steel, hardened and 

 tempered as nearly as possible up to the cohesive strength of the Whit- 

 worth shot and shell, are of two kinds, --one thick and corrugated, the 

 other thinner and plain. The steel corrugated plates, which "are three 

 inches thick, are placed upon the thinner plates of one inch, also tem- 

 pered, arid bolted through the skin of the ship to the ribs in the iron 



