NAVY, UNITED STATES. 



C19 



the usual cast-iron guns, is especially due to 

 the increased charge 35 to 60 pounds, or more, 

 of powder of which their greater tenacity and 

 strength admit. So far as smooth-bore guns 

 admit of heavier charges than rifled, the former 

 have also the advantage in this respect; but 

 there are important differences in the behavior 

 during flight of the two kinds of projectiles, that 

 must also be considered. At short ranges, say, 

 under 400-600 yards, the round shot of the 

 smooth-bore gun still moves with somewhat 

 nearly its initial velocity ; but this it is rapidly 

 losing, owing to the greater resistance it en- 

 counters from the air ; and a little farther on 

 it is outstripped by the rifled projectile, which 

 at long ranges is thus the more effective. Ad- 

 miral Dahlgren says, "The rifle shot has great- 

 er penetration than the round, but much less 

 concussive power. ... If, in battering an iron- 

 clad, penetration only shall be the paramount 

 consideration, and other effects merely incident- 

 al, the rifle cannon must be selected. But if 

 the concussion and shattering of the plate and 

 its backing be preferred, with such penetration 

 as might be consequent thereon, then the heavy, 

 swift, round projectile will supply the blow 

 best adapted to such work. So long as the 

 present mode of plating continues, there can be 

 little doubt that it will be most effectively at- 

 tacked by cracking and bending the iron, start- 

 ing the bolts, stripping off the armor, and break- 

 ing away large portions of the wooden structure 

 within." In respect to the form of the ends 

 of shot, Prof. Fairbairn's experiments appear 

 to prove that the penetrative power and effect 

 of round-ended is twice as great as that of 

 flat-ended projectiles. 



The material of the shot has also an import- 

 ant bearing upon the nature of its effects. In 

 striking armor or other rigid obstacle, hard- 

 ened steel shot undergo less compression than 

 any others, and their great tenacity renders 

 them but little liable to fracture ; hence, the 

 work of which they are capable is, in higher 

 degree than with other sorts, expended upon 

 the opposing body. For round-ended shot, 

 Prof. Fairbairn has found by experiments in 

 punching plates, that when these are of steel, 

 the dynamic resistance or work of which they 

 are capable is more than three times that of 

 like shot of cast iron. He concludes (in a pa- 

 per read before the Brit. Assoc., 1862,) that 

 the conditions apparently desirable in projec- 

 tiles, in order that the greatest amount of work 

 may be expended upon the armor plate, are : 1. 

 Very high statical resistance to rupture by com- 

 pression. In this respect, wrought iron and 

 steel are both superior to cast iron. The stat- 

 ical resistance of steel is more than 3 times, 

 and that of wrought iron more than twice, that 

 of cast iron. Lead is inferior to all the other 

 materials named. 2. Resistance to change of 

 form under great pressure. In this, also, hard- 

 ened steel is superior to wrought iron, and 

 cast iron inferior to both these. Finally, the 

 shot which would effect the greatest damage to 



a plate would be one of adamant, incapable of 

 change of form. Such a shot would yield tip 

 the whole of its tin vira to the plate. And ex- 

 periments prove that the projectiles that ap- 

 proach nearest to this condition are the most 

 effective. The much greater cost of steel shot 

 has hitherto stood in the way of their adop- 

 tion ; but M. Bessemer appears to have assured 

 Fairbairn that he could produce steel shot at lit- 

 tle more than the cost of those of cast iron. Dahl- 

 gren asserts that the actual damaging effect of 

 cast-iron is greater than that of wrought-iron 

 shot, in that, while the latter is merely flatten- 

 ed or crushed by impact, and tends then to 

 lodge in the plating, the former, though it 

 breaks, is more apt to pass completely through, 

 making a larger hole, and badly cracking the 

 plate. 



In this country, guns for throwing very 

 heavy shot 450-4V6 Ibs. solid are in success- 

 ful use ; and one at least for throwing a 1000- 

 Ib. ball is already constructed and in readiness. 

 But the most recent change in the direction of 

 efficiency of shot, appears to be in the adoption 

 of the plan, which had already come into favor 

 in England, of larger charges of powder. The 

 maximum charge, up to this time, has been 35 

 Ibs. of powder. The Government, it is stated, has 

 now ordered cannon, preparations for fabricat- 

 ing which are already in progress, which will 

 bear the explosion of 60. and possibly of 70 Ibs. 

 of powder ; and it is believed that the 450-lb. 

 shot thrown with such a charge, will prove the 

 most destructive missile thus far ever employed. 

 Admiral Dahlgren, also, in his recent report, 

 states as the result of repeated and severe tests 

 of their capacity in this particular, that the 9- 

 inch and 11-inch cast-iron guns, until recently 

 the largest in use, bear continued firing with 

 charges much greater than those for which 

 they were intended; the 9-inch one half greater, 

 and the 11-inch with double the original weight 

 of powder. 



Resistance of Iron Plates. The law admitted 

 to hold generally true in respect to the resist- 

 ance of plates of any given kind of iron to 

 punching or fracture, is, that such resistance 

 is directly proportional to the sheared or frac- 

 tured area the total length and breadth of 

 metal, throughout which the cohesion of the 

 particles is overcome, and hence, that it is as 

 the depth and diameter of a hole cut in the 

 plate, or as the total length and depth of the 

 fracture produced in it. 



The question as to the relation the strength 

 and resistance of a single homogeneous plate 

 bear to its thickness, appears not yet to be de- 

 cided. Experiments early made at Manchester 

 appeared to show that the resistance varies 

 directly and simply as the thickness, so that a 

 plate twice as thick as another has only twice 

 its power of resisting impact. During the last 

 year, however, at Shoeburyness, a target of 5-8 

 inch boilerplates, with a 1^-inch plate in front. 

 the whole held together by alternate rivets and 

 screws 8 inches apart, and having a thickness 



