the time of the action of the force and heat is longer for each discharge; consequently less rapid firing bursts the gun.

104. The 30-pounder that endured four thousand six hundred rounds was a small gun, and was heated more nearly uniform throughout because of the thinness of the walls, and because of the long intervals between the rounds, which was fifteen minutes.

105. Built-up guns, like the Armstrong or Whitworth guns, although capable of enduring heavy charges, fail with rapid firing.

106. Guns forged solid, like the two guns on the United States steamer Princeton, and the Ericsson thirteen-inch gun burst because it is impossible to attain uniformity of fabrication, and because of the unequal expansion. The Ames gun, although somewhat more uniform, cannot be absolutely so, and will either burst or enlarge in the bore.

107. No absolutely safe gun has ever yet been made; yet, undoubtedly, we can have such guns, if we first learn the cause of failures. The Naval Board, appointed by the Ordnance bureau, report that they are unable to decide why they burst. This conclusion was to be expected, as they were neither practical mechanics nor inventors. The business of designing guns has usually been confined to such persons, and the facts upon which to found correct theories, upon which to base invention, have also always been kept a profound secret. It has been light literally hid under a bushel.

108. The subject deserves and should receive the immediate attention of Congress, for our dignity, unity, and power as a nation depend upon it.

109. I have shown that no large gun ever made could be pronounced a good one until it was burst or cut open. Yet I believe that it is possible to so construct a gun that not a single trial shot need be fired for the purpose of demonstrating its good qualities.

110. When I proposed to show that the heat evolved from the burning powder in a gun was the principal agent in bursting, I found ordnance officers opposed the theory, on the ground that but little heat was communicated to guns. This was said to me by Major Wade, by Captain Rodman, and indirectly by several others occupying high positions. Major Wade, however, afterward told me he recollected having seen copper melted by the heat of powder, at a time when a few kegs of powder exploded in a powder mill. Captain Rodman, in a part of his book before quoted, speaks of higher temperature exhibited when larger masses of powder are burned in a 11-inch gun than in a 7-inch, as accounting for three times more force in the larger gun than in the smaller; and Captain Dahlgren, in his report to the Secretary of the Navy for 1862, says a gun was so heated by firing that it was afterward 'eighteen hours in cooling.

111. In the report of Brigadier General E. W. Crofton, Royal Artillery, from headquarters Tein Tsin, China, 9th September, 1860, we are informed that on the 21st August preceding, at the capture of the Peiho forts, "the vent pieces, after about twenty-five rounds, became so hot that they had to be changed, and at the end of the firing (85 rounds) both vent pieces were so hot as to be inconvenient in handling." "No clogging or other hindrences in loading took place, except from the excessive heating of the vent piece. And Major Hay reports to the same office, 6th September, 1860, referring to another battery: "The vent pieces become so hot that it it is difficult for a man to hold them; some non-conductor of heat round the neck appears to be necessary."

112. Now I have never claimed that heating a gun would burst it, or that cooling it would burst it; but that heating or cooling one part of the gun to a certain extent, while the rest of the gun was at the opposite state of temperature, would burst it, and the extent of this unequal expansion necessary to burst the gun must be greater than the elasticity and ductility of the metal of the gun provides for

113. Professor F. A. P. Barnard, attached to the coast surveys, in a letter, says, "Speaking of my theory and the pressure of powder, I do not think that your theory needs the support of that consideration pushed to the extent to which it is apparently carried in your pamphlet, while there is no strength whatever which can be possibly given to a cast-iron gun which the immense force arising from inequal expansion by heat may not be sufficient to overcome." 114. Of wrought-iron guns that at present are most conspicuous is that of Mr. Ames. He claims three qualities for his guns. First, that it is made of a superior, strong, and tough, or ductile iron, the Salisbury; secondly, that it is homogeneous; and thirdly, that it has fibre transverse around it, in the direction best disposed to resist the pressure of the powder. It is made by welding disks or cross sections together by end blows of the steam hammer. Guns were made in this manner as long ago as the year 1716, by M. Villons, of Porte de Marle, France, but they failed, and the process was abandoned. With regard to the iron it is not as good as the iron used by Armstrong for his large guns; the quality of toughness or ductility is the one sought for by English gunmakers, and undoubtedly obtained. But the Armstrong 110-pounder will endure but about forty rounds before it has to be repaired if fired rapidly, from the distension caused by unequal heating, although the same gun will stand very heavy charges without injury, if fired at long intervals so that the heat becomes uniformly distributed.

115. The Salisbury iron used by Ames cannot compare with Krupp's steel for ductility, a cylinder of which four inches in length and two in diameter was pressed down cold in a hydraulic press to a lozenge of half of its original length, without cracking in the slightest degree. Its tensile strength is much greater than the Salisbury iron, yet guns made of this fine Krupp's steel burst when fired rapidly, but do not explode from excessive charges of powder.

116. In large masses of wrought-iron, as in cast-iron, the strongest metal does not make the strongest gun, as seen from the quotation already made from Rodman's work, pages 137 and 138. The reason being from want of uniformity in cooling; one part of the mass is straining either to compress or rupture another part. And the more dense the metal the more severe the strain.

117. În support of this theory, I will give another extract from "Holley's Ordnance and Armor," where he quotes Mallet, page 355. "If it were possible that a cylindrical mass of heated forged iron could be examined while cooling so as to bring it into evidence, there can be no doubt that the following would be the phenomena resulting from the conjoint reactions of its originally soft condition and uniformly high temperature, its external cooling, contraction, and assumption of rigidity, and the final cooling contraction, and rigidity of the internal portions; the external surface would rupture in several places, parallel to the axis, and directed to the centre in the first instance. These fissures would afterwards all close, and the opposite and abutting surfaces would press against each other, like the voussiors of a circular arch. The internal diameter fissure or fissures would then be rent, the external form of the mass would change from a circle to an oval, the minor axis being in the plane of the internal rent, and the whole mass would at length assume stable equilibrium with respects to molecular forces. The change to the oval would probably be accompanied with a reopening of some of the external fissures, situated towards the end of the major axis of the oval sections.

118. Fibre in wrought-iron is only possible, or is only attainable by extending a block or bloom to from ten to sixty times its original length, under pressure as between rolls. If a bloom four inches by four inches, and twelve inches long were heated to a welding heat, and by the rolling process drawn out into a half-inch square bar, it would be near sixty feet in length, and would exhibit well defined fibre. If sufficient quantity of such bars were provided, cut into

lengths of five feet each, and, after being polished on the surface to remove all oxide, made into a pile eighteen inches square, being five feet long, for which it would require 1,296 bars, held together with a strong band shrunk on each end; upon raising the temperature of the pile to a welding heat, in a most careful manner, it would be found firmly united throughout, without a defective weld, without either hammering or pressure, but upon breaking the block so made in two, it will be found to have no fibre, but a central star shaped-fissure.

119. A new crystalization having taken place, under a law not well understood, regulated by the size of the mass and the outside form, fibre could be re-established in this metal only by rolling it out again to fifty or sixty times its original length. Fibre could not be established under the hammer without extending its length at least twice as much as with rolls.

120. As this is an experiment I have conducted many times, I speak of the facts with confidence. I have now twelve wrought-iron guns made in this manner, from bars a half-inch square, each block having been extended under the hammer, continuing the square form (i. e. without rounding the block, the central fissures are usually attributed erroneously to rounding the block,) to twice its length in the large pile, yet there is no fibre; in fact, the crystalization closely resembles the crystalization in other masses of the same material, made up in the ordinary manner by welding the original blooms, from which the small bars were made and massed together.

121. The only advantage got by this laborious process is in being assured of more perfect homogeneity, there being no extensive planes of weakness. I have also noticed very little difference in the transverse or longitudinal tensile strength, except at the centre, subjected to the cooling strains that promote fissures, which can be partially avoided by extremely slow cooling, but by leaving the whole mass porous.

122. Having thus shown the fallacy of adhering to the present received systems, and the difficulties attending the fabrication of large wrought-iron guns, I will now show how I have endeavored, as a first effort, upon an entire new system, to make a gun not liable to failure from any of the foregoing causes, and will give the description as found in Holley's Work on Ordnance, page 327.

123. Mr. Wiard's Plan. Mr. Norman Wiard, whose ingenious and important speculations on the bursting of guns by the heat of firing have been referred to in the foregoing chapter, has received a large order for heavy cannon, based upon the endurance of either one of two test guns. The engravings illustrate the general features of his plan, but not the exact proportions; these are the subject of extended experiments and calculations not yet perfected.

The gun is said to have the same diameter and length of bore as the navy 15-inch gun, and about nine inches greater external diameter, and is to weigh 43,000 pounds. The interior parts may be cooled uniformly by water passing through the cores between the ribs, and in the bore, upon Captain Rodman's plan. The exterior part or reinforce being thicker than the other parts, will cool last after casting, and is by this means intended to compress the barrel with such force as to bring all parts of the metal into equal strain at the instant of firing, according to Professor Barlow's formula. The ribs are curved in both directions, from front to rear, and from the inner barrel to the outer hoop or reinforce, so that they can spring enough to allow the inner barrel to expand both longitudinally, and the intention is, radially, by the heat of firing, without straining the structure. The ribs also yield, during the process of casting, under unequal contraction, due either to unequal cooling, or to chemical difference in the metal. They are proposed to be stiff enough to resist the pressure of the powder, and sufficiently flexible to bend under the greater force of expansion, a force limited

only by the ultimate strength of the metal. The elasticity of the whole structure would be greater than that of guns without ribs.

125. This gun will undoubtedly cool without serious initial rupturing strains. The whole practice in founding, especially in founding car-wheels, (which a cross-section of the gun resembles,) warrants this conclusion. A plain disk wheel, not annealed, can only be stretched or compressed, and so broken or greatly strained in cooling, and therefore goes to pieces under service. A gun, when so corrugated as to bend in cooling at some thin part intended to be bent, instead of breaking or being severely strained at some part that cannot be bent, endures more hard service than would be ordinarily expected of cast iron.

126. For the foregoing reasons, the strongest iron may be employed. It has already been shown that a pure, high iron, of great tenacity, shrinks too much to make a safe casting by other plans. But car-wheels are cast as sound from the highest and strongest iron as from a weaker iron, because ample provision is made for it to change its figure more or less, as required, without strain.

127. Upon the proper tension and strength of the reinforce as modified by its large diameter, the heat of firing, and the elasticity of the parts within it, depends, after all, the chief strength of the gun.

128. Comparing the reinforce with an equal thickness of metal on the exterior of Captain Rodman's gun, the former is cooled on all sides to prevent, as far as possible, unequal shrinkage, and is carried in two directions to prevent unequal and injurious strain due to what unequal shrinkage there may be. The latter is cooled (in practice) only from the inside, so that its exterior surface is strained and weakened. It appears, then, that the former would be in a better condition to stand the tension, in which case too the tension can be the better regulated.

129. The official report already quoted (376) is evidence that the outer part of the Rodman gun is drawn into compression by the subsequent shrinkage of the intermediate metal. It cannot be put into the desired tension except by cooling the gun exclusively from within; and this can only be done by keeping the mould at a temperature 2700°-a process so difficult that it has not been realized in practice. But there is nothing to draw the corresponding part of the Wiard gun-the reinforce-into compression. All the parts enclosed by it have already cooled and set.

130. In other words, the part that cools last regulates the strain of the rest. The interior and the exterior parts of the walls of the Rodman gun cool independently, and without any great strain; then the intermediate metal cools and puts strains into them which are just opposite to those required. But the reinforce of the Wiard gun cools last, and if it shrinks most, must compress the inner tube, and be itself drawn into tension-the required condition.