naval experience that the coating of bees-wax, with which the naval gun is always covered, is never melted by the most rapid firing under a tropical sun.

It is therefore very doubtful if this cause, the difference of temperature between the internal and external surfaces, produces the serious effects attributed to it.

As this objection is founded on theoretical considerations, it can only be satisfactorily sustained or refuted by the actual test of a trial gun of not less than 10 inches caliber, if a rifle, or 15 inches, if a smooth bore.

We are, very respectfully, your obedient servants,

H. K. DAVENPORT,

Captain United States Navy. WILLIAM N. JEFFERS, Captain United States Navy.

Commodore A. LUDLOW CASE,

Chief of Bureau of Ordnance.

OBJECTIONS ANSWERED-GENERAL DESCRIPTION AND ARGUMENT IN FAVOR OF THE IMPROVEMENT.

The bursting force is of two kinds, namely, explosive or projectile force and the expansive force of heat; the former ceases when the shot leaves the gun, while the latter is increased by every shot fired from the gun. If the gun is composed of wrought iron or steel, the force of this internal-heat expansion must be sustained by the strength of the wall alone. The nature of wrought iron or steel precludes the idea of its accommodating this expansion by the compressibility of the walls, for there is little or none of it in such metal. Hence the experience of the Ordnance Department, "that hitherto no steel gun has been made to certainly sustain large charges." If the walls are thick, certainly not.

And I may add the same of wrought iron. In practice, its use in such guns has shown only a small improvement; instance the "Peacemaker" on board the steamship Princeton. If the gun is fired rapidly with large charges of powder and heavy conical shot, the heat from such discharges must increase the radius and longitude of the bore. If the gun be a heavy one, with thick walls, its thickness must prove a point of weakness, because the gun will remain unexpanded on the outside, but will be expanded on the inside. If there is much porosity in the metal-and there will be some if it is made of cast iron-as the heat expands, the inside metal will compress, or the porous quality will be forced together if the firing be continued long enough to force this spongy quality into a solid mass, when, if this increasing cause be continued, the gun must soon become so strained that a rupture will ensue. And we infer that this is one reason why many artillerists say that in practice "a thick wall in a large gun is a point of weakness;" that it is not a positive insurance against the bursting force, and more especially is this the case if the metal of which the gun is composed is wrought iron or steel."

The unequal expansion of heat operating on a mass of metal that has been unequally or unevenly cooled, must have a very great influence in the destruction of many valuable guns of large caliber. This force is unquestionably unmanageable in an ordinarily constructed large gun, and is destruction to it unless some avenue is provided for its harmless escape. We present our perforated re-enforce as a rational remedy for this defect. Nearly all scientific men admit the correctness of the "heat theory," but so far as we know it has had no satisfactory test. We propose to make this, but before we proceed to do so on our own account, we ask the Government to do it, for if anybody is to be benefited by it it will be our Government.

If a large gun with thick walls be made of cast iron upon the Rodman plan, the surface of the bore will doubtless be contracted and show less porosity, but as it has not been perfectly steeled it will, by use, in a short time resume its former porosity; at all events, the wall of such a gun will be, to a certain extent, compressible, much more so indeed than that of a steel or a wrought-iron one.

The practical result is apparent, that the wall of such a gun will compress under strain to a very great extent, and in many instances will accommodate this internal expansion. But if the expansion is greater than the compressibility of the metal a rupture will ensue and a failure will be the result. Hence the great fatality attending steel guns. We think this must be plain to any constructor of ordinary experience. If the gun be made of cast iron on the Dahlgren plan, its power of endurance will be greater, but even in this regard they are limited, for the reasons before stated. It must be remembered that I am speaking of heavy guns, with thick walls, using large charges and solid conical shot, and to be fired rapidly, as occasion and emergency may require.

In connection with the foregoing it is desirable to know why guns of ordinary caliber and thickness of wall are safe and durable, while nearly all rifles larger than 30

pounders are utterly unsafe when fired rapidly with large charges and elongated shot. Why may not the thick walls of a 10-inch gun be made strong enough to stand the pressure of a proportional charge as well as the thinner walls of an ordinary field-piece! And why has the massing of various metals in divers methods about the chamber left the strongest walls more liable to explode than thinner and weaker ones? The uniform pressure of exploding gunpowder is measurable and so is the strength of metal. Captain Andrew Noble, F. R. S., in his researches upon the explosive force of gunpowder, says, upon the subject of the tension of powder-gases, that they were "generally registered extravagantly high." "Experiments had shown the pressure of R. L. G. powder to be about 32 tons to the square inch. The pressure indicated by the L. G. powder was 37 tons on the square inch."

The following are the practical conclusions deduced from the investigations :

First. The maximum of pressure of fired gunpowder is not much above 40 tons to the square inch.

Quare: If 40 tons to the square inch is the maximum of pressure of fired gunpowder, what breaks the steel guns? It cannot be caused by the projectile force alone. Does it not look like the unequal expansion of heat has something to do with it?

Second. In large guns, owing to the "violent oscillations produced by the ignition of a large mass of powder, the pressure of the gas is liable to be locally exalted even above its normal tension in a perfectly closed vessel; and this intensification of pressure endangers the gun, without adding to its useful effect."

Third. Where large charges are made, quick-burning powder increases the strains upon the gun without augmenting the velocity of the shot.

Fourth. The position of the vent or firing-point exercises an important influence on the intensity of wave-action, and in further enlarging the dimensions of heavy guns we must look to improved powder and improved methods of firing the charge, so as to avoid as much as possible throwing the ignited gases into violent oscillation.

Fifth. That in all cases it is desirable to have the charge as short as possible, so as to reduce the run of the gas to the shortest limit. Hence increase of the diameter of the gun, by shortening the charge, tends to save the gun from abnormal strains.

By referring to the cut of our muzzle-loader you will notice that the igniting-tube, or vent, is central, the powder is ignited at the base of the shot, the gas overcoming its inertia, the powder burning backward, thus obviating that violent oscillation, giving the shot an accelerating motion.

By this arrangement the combustion of the powder is slightly prolonged; at least the full forces of all the gases is not put into such a state of violent oscillation as would be the case if ignited at the bottom of the powder-bed or at a side vent. We thus avoid the danger of abrasion and deterioration.

Should the breech-block or screw-plug, through which the vent is made, become deteriorated from long use by rapid and continuous firing, it can be removed and a new one substituted. By this arrangement we lengthen the lives of our heavy guns beyond the time of allotment by the regulations.

It will be observed, from the printed description of our proposed gun, that the re-enforce is to be cast with eight rows of perforations disposed in equilateral triangles; these apertures are to be formed by cores set in the mold or flask; in this mauner we multiply the cooling surface, the requisite tensile strength is obtained with less danger of flaws and neutralizing strains.

You will please notice in the small exemplifying model that the walls of the re-enforce are to be of great thickness; whatever amount of metal which may be necessary to take out of it to form these apertures is to be added to the thickness of the wall.

By examining the model and the cuts you observe that there is about as much metal resting against the core or barrel (and sustaining it) as there is on the outside of the gun.

In constructing a 20-inch gun on this plan, the wall of the bore or barrel would be five inches thick, or one-fourth the diameter of the bore; five inches will then be the diameter of the apex of the conical apertures. (See cut Figs. 3 and 4.)

But to make sure of giving ample strength to our first experimental gun, we will reduce the diameter of the apex to about two and a half inches.

Referring to cut Fig. 3, and taking the point equidistant on the inside of the core, (which will give the angle of truncation,) we will have about the same amount of metal, or strength of wall, at every point in the re-enforce from the cascable to a point beyond the trunnions, as is shown in the cut. The trunnions are cored and cast hollow, but the amount of metal taken out to form the aperture is supplied to their size. By this arrangement the heat cannot remain any length of time at that point, but will be radiated away. Solid trunnions have a tendency to act as a compass, holding the outside of the gun at that point against an expanded inside; hence the perforation. The core or barrel is to be constructed of the strongest metal, to be tested by hydraulic pressure. The iron re-enforce, having been trued out, is slightly expanded by heat. When the barrel is placed inside of it, the re-enforce shrinks firmly on the core and becomes an interval support to it.