proper direction to permit the expansion of the inner metal without any undue strain upon the reinforce, as shown in the two sections above. Captain Rodman's book, page 297, exhibits the impossibility of casting a solid projectile, cavities Fig 20

being formed in the centre of the mass, due to the shrinkage of the inner metal after the outer shell had frozen, so as to prevent any supply of metal to the centre thereafter; and this is related as the cause which led to the hollow mode of casting. These cavities do not occur of necessity in the centre of a casting, but of necessity in the centre mass at equal distances from the cooling surfaces if subjected to an equal rate of cooling; and they are to be found near the centre of the mass in the Rodman gun as well as in any other. Their presence Fig 21

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cannot be detected at any of the surfaces of the casting. If they were generally distributed between the inner metal of the gun and the reinforce, a sufficient elasticity be'ween these parts of the gun might be had, and

a similar result arrived at to that obtained by the drilling of the holes, proposed by me, as shown by diagram. Fig. 19.

79. The 15-inch guns can be shown to be inefficient, for they only give a velocity of 750 feet per second; or they are unreliable (perhaps both) for they will burst as often as the accidental porosity above spoken of is not evenly distributed between the inner metal and the reinforce. And who can say when these condition are all fulfilled, except by a practice inaugurated by the man "who had the goose that laid the golden eggs," viz., BY CUTTING OPEN. By that practice, THE GUN THAT WE KNOW TO HAVE BEEN A GOOD GUN IS NO

LONGER A GUN.

80. It is perhaps pertinent to this subject to consider that the gasses of gunpowder always have the same weight as the powder from which they have been evolved. A musket barrel is burst at the muzzle if the shot is carelessly inserted and not put down against the powder, by the momentum, it is supposed, or vis viva of the gasses, that, having weight and velocity, are projected against the bullet.

When a long rifled cannon is fired at a high elevation, the gun recoils backward on a plane, representing the deck of a ship, different from the plan of the bore. All bodies in motion resist a change of direction, in the proportion of 1-90th of their whole momentum, for a change of direction of 1°. If one ivory ball of a pair, suspended to the ceiling by threads is projected against the other at rest, striking it at right angles 90°, the one in motion comes to a state of rest, communicating ts whole momentum to the one before at rest. If the one at rest should be struck at angle of 45°, the ball in motion would have its direction changed 45° and it would give one-half its momentum to the other. Each would be projected the same distance. So, also, if the angle with which they came in contact was one degree, 1-90th of the momentum would be given to the ball at rest. The whole sum of the momentum of a shot projected from a rifled cannon, is very great. At the muzzle of the gun, the resistance to a change of direction is sufficient to overcome the preponderance of the gun. If the bore was crooked, the shot would not be much diverted, but the gun would be moved to conform to the direction of the shot, and many have noticed, when firing guns Mis. Doc. 47- 2

on the ship-carriages, at high elevations, that the breech of the gun was raised, and came down again with a considerable blow on the quoin or elevating screw. If the chase of the gun is light, the muzzle will sometimes be broken

off, instead of overcoming the inertia of the gun, or lifting the breech suddenly, against the resistance of the preponderance.

82. This result would occur with more certainty if the whole interior metal of the gun were heated and expanded laterally and longitudinally, straining the gun to the extreme verge of its strength to resist. This example is inserted as one of the peculiarities of living force, as exhibited in gunnery, viz: resistance to changes of direction by bodies in motion, and to account for the failure of many of the Dahlgren and Parrott guns, from the breaking off of their muzzles, as has frequently happened since the war began.

83. In 1855 I made a heavy pile-hammer in Chicago, for a contractor on the Illinois and Michigan canal, which was removed from the mould in the foundry too early, and placed on a paving of brick on the deck of a canal boat for transportation to Joliette. It was so hot when put on board that it set fire to the deck about two hours after, while en route. In dashing water under it upon the deck, some was thrown' upon the hot iron, cooling parts in advance; at a later time when the heat left the interior, it burst in two parts, and each piece was thrown to the bow or stern, and passing down through the bottom, sunk the canal boat. The report was heard two miles.

84. One of Blakely's first guns, as exhibited in the following diagram, failed by the longitudinal extension of the inner tube, and the bands between the trunnion ring and the cascabel. The gun was strengthened longitudinally by four bolts, reaching from the trunnion ring to a cascabel piece against the breech of the gun.

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85. Captain Blakely says of this accident: "At this round the four bolts gave way—the four united being equal to a solid bar the size of the bore. The rest of the gun was uninjured. I had this gun re-made with four bolts of the best charcoal iron, but they, too, broke without injury to the tubular part."-Paper read by Captain Blakely before the United Service Institution, England; vol. III, Journal.

86. There is no way to account for this except by the extension of the length of that part of the gun sustained by the bolts, by heat; if the pressure of the powder had broken the bolts, the whole breech would have been shot away. It is satisfactory to us in this manner to learn that in England they do not know the cause of the failure of guns; we may thus now far excel them, if we utilize the knowledge we have.

87. The inner tube of the Whitworth gun shown in General Gilmore's report increased in length one inch, (shown marked a b on the cut,) by the heat communicated to it, and closed the vent. If the bands had been fastened by screw threads, as recommended by Prof. Treadwell, and by General Gilmore, the bands would have parted transversely as d' the bolts of the Blakely gun.

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There are two views of this gun in General Gilmore's book, a slight mark on the reinforce would lead us to suppose the reinforce had been cracked transversely. It is strange that the other view should be one of the opposite side of the gun, and that nothing should be said of the crack.

88. A three hundred pounder Armstrong gun, in which the breech piece was inserted by screw threads within the principal reinforce band abutting against the inner tube of steel, was burst by the lengthwise expansion of the inner tube, pushing out the whole breech, breaking the reinforce band transversely, (cut on left side.) Compare this example with the Whitworth gun shown in General Gilmore's report and with those Parrott's that have failed at the breech, (see cut to right,) and see the analogy.

89. When a Parrott gun is strained radially as well as longitudinally forward and under the band by the heating inside, the reaction of the forces having a tendency to push out the breech also tend to push outward and forward the slab of the cast-iron reinforce that leaves the gun forward of the band or wroughtiron hoop, and in this effort the pressure of the powder assists; hence the forward reinforce fractures, and when the band also breaks, the cause is obvious.

300 pouuder Armstrong gun, breech pushed out by extension of inner tube. Par., 88.

Parrott gnn breech fcrced out by same cause.

90. An Armstrong gun, a banded tube, failed by the breaking of the outside band. If the pressure of the powder had broken it. the parts would have been thrown off with projectile force.

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81. Here we have five guns, exhibiting the effect of the expansion of the inner metal of guns by heat of the powder to the extent of rupturing them, and the most astute of our ordnance officers will find it difficult to account for the result in any other manner.

92. In the conclusion of this part of the subject, I repeat here what I have before said in the Intelligencer, to exhibit the danger of relying on the faulty guns we have now in service.

94. The Dahlgren gun is a shell gun, and is the most beautiful gun in any service in the world, but it is believed that more effective guns are now required for attack on iron-clad ships. The first Monitor was armed with guns of this class; and great reliance was placed on them in case that certain wrought iron solid projectiles, prepared for them, were to be used in any encounter with the Merrimac; but it is understood that the inventor forbade the use of the latter, even with the fifteen pound charge of powder. Lest his directions should not be obeyed, it is said that he caused them to be taken off the Monitor, while she was at anchor in Hampton Roads, and certain other hollow shots, covered with bronze, substituted. Shells broke against the sides of the Merrimac, inflicting no injury. Hence the Merrimac continued to be the terror to our army and navy for a long critical time. But for this we might have captured Richmond sooner than we did Yorktown; and who can conceive or estimate the cost of life or money that has resulted?

95. Other eleven-inch shells have been projected against iron sides without effect. We must have better guns than these to meet the requirements of modern naval warfare.

96. Next we have the Rodman fifteen-inch gun, cast hollow, and cooled from the interior, the object attained by which is to freeze the metal from its liquid state immediately surrounding the bore first. As the heat is nearly all withdrawn from the cast block through the surface of the bore, successive strata of the iron freeze and contract upon the stratum within it, having the effect to contract or squeeze it into smaller dimensions, both longitudinally and radially. In this manner the state of "initial tension" is attained in the gun, which makes it capable of resisting a greater pressure from within, having a tendency to rupture the wall or enlarge the bore of the gun; the necessity for which tension has been beautifully described and illustrated by Professor Treadwell, of Harvard, and by Captain Blakely, R. A., England. Although the longitudinal tension might be considered advantageous in assisting to resist the lengthwise pressure of the powder against the bottom of the bore or chamber of the gun, there is another rupturing force to be provided for, viz: the unequal heating when it is fired; for then this force has the tendency that cannot be resisted by any amount of strength in the gun to increase both the longitudinal and radial