through the ports, and so arranged that the guns brace each other, and that the inertia of the entire structure is made available to resist recoil. It shows, also, the means adopted to facilitate the working and repairs on the guns and turret.

Figure 39 is a side elevation of two spherical guns, mounted according to this portion of my invention. The guns may be, in all respects, like that shown in Figures 5 and 6, or may be differently constructed, as may be preferred.

Figure 40 is a section across the turret, on the line SS, in Figure 39, with certain parts removed. Figure 41 is a horizontal section, on the line TT, in figure 39, with certain parts removed.

A2 42 represent the guns The trunnions H, are mounted in bearings G, in the inside of the turret M, and the spherical form of the guns allows each to be rotated to any extent desired, without uncovering the port. Each gun moves inward to a small extent, before rotating it, the bearings G being adapted to allow such motion, and to induce it, by the gravity of the gun, so soon as the parts which prevent such motion are removed.

FF1, are substantial cheeks, or movable braces, standing so that one is partly embraced and sustained by the other, and I is a stout wedge, adapted to operate between these cheeks, and, by their aid, to brace the guns outward very rigidly. I force outward both guns, so that they apply themselves firmly to the interior of the turret, before firing either. When the gun, represented on the right hand side of the figure, is fired, its tendency to recoil is resisted, first, by its own inertia; second, by the inertia of the cheeks FF1, and wedge I; third, by the inertia of the gun, on the left hand side of the figure; fourth, by the inertia of the entire turret M; and, finally, by the elasticity of masses of rubber K and K1, which are introduced in the manner represented.

On the scale represented, the guns are fourteen inches caliber, and weigh each fifty-one tons; and on any scale which may be assumed, each gun weighs about one hundred times as much as the charge which is fired therefrom. The recoil of such guns, thus braced and provided, will not be so great as to occasion serious inconvenience. L, L, represent rollers which support the turret M, and its attachments, and allow it to turn freely. M', represents the circular track, or stout ring, on which the rollers L, L, traverse. N, N, are holding-down bolts, which pass through the rubber K, and are adapted to allow much lateral movement. P, is a hollow cylinder of iron, provided at the bottom with large doorways P1, to allow the ingress and exit of the men, and with gearing Q, and a capstan R, by which it is rotated. This cylinder is connected with the turret M, through the aid of strong pins or projections V, which stand in suitable jaws v, on the inside of the turret at its base, and compel the turret to turn therewith, while at the same time, allowing for slight imperfections in the adjustment of the parts, by the liberty of the projections V, to move vertically in the jaws v. W, is an endless screw, adapted to be rotated by the winch w, near the bottom of the structure. It stands near the rear face of one of the spherical guns A2, and a like screw, not represented, stands near the opposite gun. X, X, are two nuts which are carried on the same screw W, and which are moved simultaneously, up or down, according as W is turned in one direction or the other. Y, Y2, are wire ropes which are wound each partially around the gun, fitting tightly in a groove in a piece Z, bolted on the gun for the purpose. The rope Y, is attached to the nut X, and the rope Y1, to the nut X1, and both ropes are firmly secured to the gun. These ropes and nuts incline the gun in either direction, and to any extent which may be desired, by simply turning the screw W'in the proper direction by the crank w.

I provide strong heavy beams M2, M2, across the base of the turret M, in the directions represented. These sustain the weight of the bracing parts, and resist that portion of the recoil which is directed downward, when the guns are fired at high elevations.

The iron covering 1, which is applied upon the masonry 2, around the base of the turret M, is very strong, and is held down by bolts not represented. A heavy flange m, extends outward from the base of the turret M, and stands under the inner edge of the iron covering 1. This guards the turret from being overturned by any chance, or by any severe recoil of its guns.

The blower 3, is operated vigorously by the crank 4, during an action, and by drawing in air through the pipe 5, induces a plus pressure in the entire structure. This pressure induces an upward flow of air through the cylinder P P, and turret M, the air finally escaping through apertures in the top of the turret.

There is an intermediate floor 6, in the cylinder P, and a ladder for mov-' ing up and down therein, may be arranged in any obvious manner.

Sight holes JJ, are provided as represented, which may be furnished with mirrors, and other approved appliances, if preferred.

Figure 42 is a plain view, showing one of the rollers L, on which the turret M, turns, and the rings L1, L2, which connect the rollers, and compel them to maintain uniform distances, each from the other.

When it becomes necessary, from any cause, to take out or replace one of the rollers L, I have provided means of doing so, without lifting the turret M. Figure 43, is a side view of one part of the circular track M1, where this is accomplished. A slight shaft, or guide spindle 7, is inserted through each roller L, and the outer end is provided with a T-shaped part 71, which is bolted to the outer ring L2, as represented.

To take out a roller, I turn the turret until the defective roller comes to the position shown in dotted outline, in Figure 43. I then remove all the bolts which hold the several parts 1, to the outer ring L2, and raise or lower L2 out of the way. I then remove the nut which holds the defective roller to the inner ring L1, remove the guide spindle l, and the defective roller is then free, except that it is still supporting its share of the turret, and consequently cannot be drawn out, being prevented by the flange on its inner end, as also by the friction due to the great load resting on it.

I next remove the small portion M3, from the circular track M1, it being made in a piece separate from the other parts, to allow its removal for this purpose. I then turn the turret until the defective roller is brought over the place where this piece M3 stood, as shown by the dark lines. The previous removal of the piece M3, now allows the defective roller to be readily withdrawn, because it readily falls down by gravity out of contact with the turret M, leaving all of the weight to be supported by the remaining rollers; and the space made by the removal of M3, is sufficiently wide and deep to allow the roller to be removed and a new one substituted; after which a reversal of the process, above described, makes all again complete. Figure 43a shows a front elevation of spindle l, showing slight projections 12, which hold 1 in horizontal position, 12 being removed.

There must, of course, be a suitable passage, at the point required, through the masonry, to allow access to the place in the circular track, where this operation is performed.

The fort above described was designed for New York harbor, to be erected in the center of the river at the Narrows, and for other like places. [AM. INS.]

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The number placed in one channel can be as great as desired, but the size of the fort, or the number of guns for each fort, should not be increased. The foundation may be on a rock bottom or on piling. The stone work could not be injured by an assault, for it is practicable to cover its small exposed surface with plating that would resist any shot. The piles driven about it would be a sufficient harbor breakwater, and the loose rock deposited about its base would insure safety against an assault by rams. The men and magazines are placed below, so as to be protected, and the turret may be of any required thickness. There is no opening through which the smallest projectile could enter, and no men in the turret to be injured if there were. The guns are absolutely safe from bursting, and of a size to throw a projectile that would crush any ship that can be floated into a harbor. I offer it as an impregnable fort with irresistible guns. It can be constructed in less time and at less cost than any equally efficient means of defence.

The hour for adjournment having arrived, Mr. Wiard proposed to continue his remarks at the next meeting.

Mr. Edward Cooper asked leave to interpose an explanation of his position on the rupture of heavy guns; claiming that he, rather than Mr. Wiard, was entitled to the credit of the discovery, and inviting the attention of the authorities to the fact that heat rather than strain was the cause of the rupture of large guns.

Mr. Wiard briefly explained his theory, averring his belief that he was the earlier discoverer, and related some of his experience and failures in making steel 50-pounders. He used the same form of gun with this material as Captain Dahlgren has used successfully with cast iron. They .worked well on firing a great number of times slowly, but on firing fast, while the exterior was cold, and in cold weather, all soon burst. He believed it due to the heat on the inside expanding, the middle remained small as at first. Two burst on the ninth round each. Steel differs from cast iron in this respect. The Rodman system of casting iron around a cool core is, however, more like a steel gun.

Mr. Cooper asked if guns at the battle of Malvern Hills were fired by their heat alone.

Mr. Wiard did not believe this ever had occurred.

Mr. Clinton Rosevelt presented a theory of his own in regard to the explosion of guns: he averred that the rupture began on the inside, and could not, therefore, be produced by heat.

Mr. Wiard maintained his previous opinion, and thought it was proved by the fact that the modern tapering (Dahlgren) gun is hot on the outside, first at the muzzle where it is thin, and that the heat comes to the surface at other points in lines directly proportional to its increased thickness of metal.

Mr. Wiard exhibited diagrams of a cross section of a cylinder, to answer the objections of Mr. Rosevelt. The fracture begins on the inside. This would seem to prove that guns burst by pressure rather than by expansion of the inner metal-as if the inner metal were expanded by the communication of heat before the outer metal gave way—a strain of compression resisted by the strength of the outer metal would rest upon the

inner metal of the gun that would prevent fracture; and, undoubtedly, if it ever occurred to an ordnance officer to inquire whether the communication of heat to the inner metal of guns was the cause of their failure, the beginning of fracture on the inside would appear to him an argument against the theory. This I consider a critical point, but one

C

directly favoring my theory. It repuires a most familiar knowledge of the effects of heat, and a careful recollection of time and place of all the phenomena, to comprehend and explain this part of the subject. The accompanying diagram exhibits a cross section of a gun at the point of greatest pressure, and, consequently, highest temperature; the surface of the bore is supposed in this example, to be continuously exposed to the high temperature evolved from the combustion of powder when its expansive force is resisted by the inertia of a heavy projectile, or, as if a fire were constantly burning

within the gun. The space between the curved lines represents the place and

quantity of heat thus communicated to the metal, showing the greatest expansion immediately at the surface of the bore.

To represent a reduction of temperature by lines converging towards each other I know is unusual, but as no conventional lines have been adopted to represent intensity of heat by their direction, and as I have confidence my meaning will be understood, I have chosen to use them in this manner.

We are to recollect that, in the most rapid firing, the surface of the bore is exposed to this high temperature only about one hundredth part of the time, while during the other ninety-nine hundredths the heat of the surface of the bore is radiating away. If the diagram represented a gun. of six inches diameter of bore and eight inches thickness of metal about the bore, the range to which the heat would penetrate the metal at the first discharge would be about four inches; for heat enters metal with a velocity depending on the difference in temperature of the source from which it flows and the metal into which it is flowing. The heat is communicated to the small surface of the bore, while it is radiated from the large outside surface of the gun; from this cause, if from no other, the temperature would be much higher within the mass than on the outside.

The penetration from the first discharge being four inches, it might be supposed that the range of the heat from the next discharge would be greater; but heat having been communicated by the first discharge, the range of the second is less, from the reduced difference of temperature. Although, of course, the heat flows onward, its motion is very slow. If, then, the penetration be four inches, at the distance of four inches from the surface of the bore the temperature will be comparatively low, but little higher than that of the metal at four and a half inches from the surface of the bore. The heat, therefore, is conducted from the point of four to that of four and a half inches slowly; more slowly from that of four and a half to five, and with a continually reduced and very slow rate of motion to the outside.

As the heat is communicated from one inner stratum to the stratum surrounding it, for each inch of the increasing distance it travels, the mass of which the temperature has to be raised is greater in circumference also;