Читать книгу: «The Atlantic Monthly, Volume 11, No. 63, January, 1863», страница 11
Mr. Benjamin H. Ellicott, who was a true friend of Banneker, and collected from various sources all the facts concerning him, wrote in a letter as follows:—
"During the whole of his long life he lived respectably and much esteemed by all who became acquainted with him, but more especially by those who could fully appreciate his genius and the extent of his acquirements. Although his mode of life was regular and extremely retired,—living alone, having never married, cooking his own victuals and washing his own clothes, and scarcely ever being absent from home,—yet there was nothing misanthropic in his character; for a gentleman who knew him thus speaks of him: 'I recollect him well. He was a brave-looking, pleasant man, with something very noble in his appearance. His mind was evidently much engrossed in his calculations; but he was glad to receive the visits which we often paid him.' Another writes: 'When I was a boy I became very much interested in him, as his manners were those of a perfect gentleman: kind, generous, hospitable, humane, dignified, and pleasing, abounding in information on all the various subjects and incidents of the day, very modest and unassuming, and delighting in society at his own house. I have seen him frequently. His head was covered with a thick suit of white hair, which gave him a very dignified and venerable appearance. His dress was uniformly of superfine drab broadcloth, made in the old style of a plain coat, with straight collar and long waistcoat, and a broad-brimmed hat. His color was not jet-black, but decidedly negro. In size and personal appearance, the statue of Franklin at the library in Philadelphia, as seen from the street, is a perfect likeness of him. Go to his house when you would, either by day or night, there was constantly standing in the middle of the floor a large table covered with books and papers. As he was an eminent mathematician, he was constantly in correspondence with other mathematicians in this country, with whom there was an interchange of questions of difficult solution.'"
Banneker died in the year 1804, beloved and respected by all who knew him. Though no monument marks the spot where he was born and lived a true and high life and was buried, yet history must record that the most original scientific intellect which the South has yet produced was that of the pure African, Benjamin Banneker.
* * * * *
THE SLEEPING SENTINEL
When the great Theban, in his midnight tramp,
A sleeping guard beside the postern saw,
He slew him on the instant, that the camp
Might read in blood a soldier's swerveless law.
"Blame not your General!"—pointing to the slain,—
The wise, severe Epaminondas said,—
"I was not cruel, comrades, for 't is plain
I only left him, as I found him, dead!"
IRON-CLAD SHIPS AND HEAVY ORDNANCE
The new system of naval warfare which characterizes the age was proposed by John Stevens of Hoboken during the War of 1812, recommended by Paixhans in 1821, made the subject of official and private experiment here and in Europe during the last ten years especially, subjected to practical test at Kinburn in 1855, recognized then by France and England in the commencement of iron-clad fleets, first practised by the United States Government in the capture of Fort Henry, and at last established and inaugurated not only in fact, but in the principle and direction of progress, by the memorable action of the ninth of March, 1862, in the destruction of the wooden sailing-frigates Cumberland and Congress by the steam-ram Merrimack, and the final discomfiture of that powerful and heavily armed victor by the turreted, iron, two-gun Monitor.
The consideration of iron-clad vessels involves that of armor, ordnance, projectiles, and naval architecture.
ARMOR
Material. In 1861, the British iron-plate committee fired with 68-pounders at many varieties of iron, cast-steel and puddled-steel plates, and combinations of hard and soft metals. The steel was too brittle, and crumbled, and the targets were injured in proportion to their hardness. An obvious conclusion from all subsequent firing at thick iron plates was, that, to avoid cracking on the one hand, and punching on the other, wrought-iron armor should resemble copper more than steel, except that it should be elastic, although not necessarily of the highest tensile strength. Copper, however, proved much too soft. The experiments of Mr. E.A. Stevens of Hoboken, with thick plates, confirm this conclusion. But for laminated armor, (several thicknesses of thin plates,) harder and stronger iron offers greater resistance to shot, and steel crumbles less than when it is thicker. The value of hard surfaces on inclined armor will be alluded to.
Solid and Laminated Armor compared. Backing. European experimenters set out upon the principle that the resistance of plates is nearly as the square of their thickness,—for example, that two 2-inch plates are but half as strong as one 4-inch plate; and the English, at least, have never subjected it to more than one valuable test. During the last year, a 6-inch target, composed of 5/8-inch boiler-plates, with a 1-1/2-inch plate in front, and held together by alternate rivets and screws 8 inches apart, was completely punched; and a 10-inch target, similarly constructed, was greatly bulged and broken at the back by the 68-pounder (8 inch) smooth-bore especially, and the 100-pounder rifle at 200 yards,—guns that do not greatly injure the best solid 4-1/2-inch plates at the same range. On the contrary, a 124-pounder (10 inch) round-shot, having about the same penetrating power, as calculated by the ordinary rule, fired by Mr. Stevens in 1854, but slightly indented, and did not break at the back, a 6-5/8-inch target similarly composed. All the experiments of Mr. Stevens go to show the superiority of laminated armor. Within a few months, official American experiments have confirmed this theory, although the practice in the construction of ships is divided. The Roanoke's plates are solid; those of the Monitor class are laminated. Solid plates, generally 4-1/2 inches thick and backed by 18 inches of teak, are exclusively used in Europe. Now the resistance of plates to punching in a machine is directly as the sheared area, that is to say, as the depth and the diameter of the hole. But, the argument is, in this case, and in the case of laminated armor, the hole is cylindrical, while in the case of a thick armor-plate it is conical,—about the size of the shot, in front, and very much larger in the rear,—so that the sheared or fractured area is much greater. Again, forged plates, although made with innumerable welds from scrap which cannot be homogeneous, are, as compared with rolled plates made with few welds from equally good material, notoriously stronger, because the laminae composing the latter are not thoroughly welded to each other, and they are therefore a series of thin plates. On the whole, the facts are not complete enough to warrant a conclusion. It is probable that the heavy English machinery produces better-worked thick plates than have been tested in America, and that American iron, which is well worked in the thin plate used for laminated armor, is better than English iron; while the comparatively high velocities of shot used in England are more trying to thin plates, and the comparatively heavy shot in America prove most destructive to solid plates. So that there is as yet no common ground of comparison. The cost of laminated armor is less than half that of solid plates. Thin plates, breaking joints, and bolted to or through the backing, form a continuous girder and add vastly to the strength of a vessel, while solid blocks add no such strength, but are a source of strain and weakness. In the experiments mentioned, there was no wooden backing behind the armor. It is hardly possible,—in fact, it is nowhere urged,—that elastic wooden backing prevents injury to the armor in any considerable degree. Indeed, the English experiments of 1861 prove that a rigid backing of masonry—in other words, more armor—increases the endurance of the plates struck. Elastic backing, however, deadens the blow upon the structure behind it, and catches the iron splinters; it is, therefore, indispensable in ships.
Vertical and Inclined Armor. In England, in 1860, a target composed of 4-1/2-inch plates backed with wood and set at 38° from the horizon was injured about one-half as much by round 68-pounder shot as vertical plates of the same thickness would have been. In 1861, a 3-1/4 plate at 45° was more injured by elongated 100-pounder shot than a 4-1/2 vertical plate, both plates having the same backing and the weights of iron being equal for the same vertical height. When set at practicable angles, inclined armor does not glance flat-fronted projectiles. Its greater cost, and especially the waste of room it occasions in a ship, are practically considered in England to be fatal objections. The result of Mr. Stevens's experiments is, substantially, that a given thickness of iron, measured on the line of fire, offers about equal resistance to shot, whether it is vertical or inclined. Flat-fronted or punch shot will be glanced by armor set at about 12° from the horizon. A hard surface on the armor increases this effect; and to this end, experiments with Franklinite are in progress. The inconvenience of inclined armor, especially in sea-going vessels, although its weight is better situated than that of vertical armor, is likely to limit its use generally.
Fastening Armor. A series of thin plates not only strengthen the whole vessel, but fasten each other. All methods of giving continuity to thick plates, such as tonguing and grooving, besides being very costly, have proved too weak to stand shot, and are generally abandoned. The fastenings must therefore be stronger, as each plate depends solely on its own; and the resistance of plates must be decreased, either by more or larger bolt-holes. The working of the thick plates of the European vessels Warrior and La Gloire, in a sea-way, is an acknowledged defect. There are various practicable plans of fastening bolts to the backs of plates, and of holding plates between angle-irons, to avoid boring them through. It is believed that plates will ultimately be welded. Boiler-joints have been welded rapidly and uniformly by means of light furnaces moving along the joint, blowing a jet of flame upon it, and closely followed by hammers to close it up. The surfaces do not oxidize when enveloped in flame, and the weld is likely to be as strong as the solid plate. Large plates prove stronger than small plates of equally good material. English 4-1/2-inch armor-plates are generally 3-1/2 feet wide and to 24 feet long. American 4-1/2-inch plates are from 2 to 3 feet wide and rarely exceed 12 feet in length. Armor composed of light bars, like that of the Galena, is very defective, as each bar, deriving little strength from adjacent, offers only the resistance of its own small section. The cheapness of such armor, however, and the facility with which it can be attached, may compensate for the greater amount required, when weight is not objectionable. The 14-inch and 10-inch targets, constructed, without backing, on this principle, and tested in England in 1859 and 1860, were little damaged by 68-and 100-pounders.
The necessary thickness of armor is simply a question of powder, and will be further referred to under the heads of Ordnance and Naval Architecture.
ORDNANCE AND PROJECTILES
Condition of Greatest Effect. It is a well-settled rule, that the penetration projectiles is proportionate directly to their weight and diameter, and to the square of their velocity. For example, the 10-1/2-inch Armstrong 150-pound shot, thrown by 50 pounds of powder at 1,770 feet per second, has nearly twice the destructive effect upon striking, and four times as much upon passing its whole diameter through armor, as the 15-inch 425-pound shot driven by the same powder at 800 feet. The American theory is, that very heavy shot, at necessarily low velocities, with a given strain on the gun, will do more damage, by racking and straining the whole structure than lighter and faster shot which merely penetrate. This is not yet sufficiently tested. The late remarkable experiments in England—firing 130-and 150-pound Whitworth steel shells, holding 3 to 5 pounds of powder, from a 7-inch Armstrong gun, with 23 to 27 pounds of powder, through the Warrior target, and bursting them in and beyond the backing—certainly show that large calibres are not indispensable in fighting iron-clads. A destructive blow requires a heavy charge of powder; which brings us to
The Strain and Structure of Guns, and Cartridges. The problem is, 1st, to construct a gun which will stand the heaviest charge; 2d, to reduce the strain on the gun without reducing the velocity of the shot. It is probable that powder-gas, from the excessive suddenness of its generation, exerts a percussive as well as a statical pressure, thus requiring great elasticity and a certain degree of hardness in the gun-metal, as well as high tensile strength. Cast-iron and bronze are obviously inadequate. Solid wrought-iron forgings are not all that could be desired in respect of elasticity and hardness, but their chief defect is want of homogeneity, due to the crude process of puddling, and to their numerous and indispensable welds. Low cast-steel, besides being elastic, hard, tenacious, and homogeneous, has the crowning advantage of being produced in large masses without flaw or weld. Krupp, of Prussia, casts ingots of above 20 tons' weight, and has forged a cast-steel cannon of 9 inches bore. One of these ingots, in the Great Exhibition, measured 44 inches in diameter, and was uniform and fine-grained throughout. His great success is chiefly due to the use of manganesian iron, (which, however, is inferior to the Franklinite of New Jersey, because it contains no zinc,) and to skill in heating the metal, and to the use of heavy hammers. His heaviest hammer weighs 40 tons, falls 12 feet, and strikes a blow which does not draw the surface like a light hammer, but compresses the whole mass to the core. Krupp is now introducing the Bessemer process for producing ingots of any size at about the cost of wrought-iron. These and other makes of low-steel have endured extraordinary tests in the form of small guns and other structures subject to concussion and strain; and both the theory and all the evidence that we have promise its superiority for gun-metal. But another element of resistance is required in guns with thick walls. The explosion of the powder is so instantaneous that the exterior parts of the metal do not have time to act before the inner parts are strained beyond endurance. In order to bring all parts of a great mass of metal into simultaneous tension, Blakely and others have hooped an inner tube with rings having a successively higher initial tension. The inner tube is therefore under compression, and the outer ring under a considerable tension, when the gun is at rest, but all parts are strained simultaneously and alike when the gun is under pressure. The Parrott and Whitworth cannon are constructed on this principle, and there has been some practice in winding tubes with square steel wire to secure the most uniform gradation of tension at the least cost. There is some difficulty as yet in fastening the wire and giving the gun proper longitudinal strength. Mr. Wiard, of New York, makes an ingenious argument to show that large cannon burst from the expansion of the inner part of the gun by the heat of frequent successive explosions. In this he is sustained to some extent by Mr. Mallet, of Dublin. The greater the enlargement of the inner layer of metal, the less valuable is the above principle of initial tension. In fact, placing the inner part of the gun in initial tension and the outer part in compression would better resist the effect of internal heat. But Mr. Wiard believes that the longitudinal expansion of the inner stratum of the gun is the principal source of strain. A gun made of annular tubes meets this part of the difficulty; for, if the inner tube is excessively heated, it can elongate and slip a little within those surrounding it, without disturbing them. In fact, the inner tube of the Armstrong gun is sometimes turned within the others by the inertia of the rifled projectile. On the whole, then, hooping an inner steel tube with successively tighter steel rings, or, what is better, tubes, is the probable direction of improvement in heavy ordnance. An inner tube of iron, cast hollow on Rodman's plan, so as to avoid an inherent rupturing strain, and hooped with low-steel without welds, would be cheaper and very strong. An obvious conclusion is, that perfect elasticity in the metal would successfully meet all the foregoing causes of rupture.
In America, where guns made entirely of cast-iron, and undoubtedly the best in the world for horizontal shell-firing, are persisted in, though hardly adequate to the heavy charges demanded by iron-clad warfare, the necessity of decreasing the strain on the gun without greatly reducing the velocity of the shot has become imperative. It would be impossible even to recapitulate the conflicting arguments of the experts on this subject, within the limits of this paper. It does appear from recent experiments, however, that this result can be accomplished by compressing the powder, so that, we will suppose, it burns slowly and overcomes the inertia of the shot before the whole mass is ignited; and also by leaving an airspace around the cartridge, into which the gases probably expand while the inertia of the shot is being overcome, thus avoiding the excessive blow upon the walls of the gun during the first instant of the explosion. Whatever the cause may be, the result is of the highest importance, not only as to cast-iron guns, but as to all ordnance, and warrants the most earnest and thorough investigation. The principles of the Armstrong gun differ in some degree from all those mentioned, and will be better referred to under the head of Heavy Ordnance Described. The Armstrong gun is thus fabricated. A long bar of iron, say 3 by 4 inches in section, is wound into a close coil about 2 feet long and of the required diameter,—say 18 inches. This is set upon end at a welding heat under a steam-hammer and "upset" into a tube which is then recessed in a lathe on the ends so as to fit into other tubes. Two tubes set end to end are heated to welding, squeezed together by a heavy screw passing through them, and then hammered lightly on the outside without a mandrel. Other short tubes are similarly added. Five tubes of different lengths and diameters are turned and bored and shrunk over one another, without successively increasing tension, however, to form a gun. The breech-end of the second tube from the bore is forged solid so that its grain will run parallel with the bore and give the gun longitudinal strength. Both the wedge and the screw breech-loading apparatus are employed on guns of 7 inches bore (110-pounders) and under. It will thus be seen that the defects of large solid forgings are avoided; that the iron may be well worked before it is formed into a gun; and that its greatest strength is in the direction of the greatest strain; and on the other hand, that the gun is weak longitudinally and excessively costly, (the 7-inch gun costs $4,000, and tin 10-1/2-inch, $9,000,) and that the material, although strong and pretty trustworthy in the shape of bars, has insufficient elasticity and hardness. Still, it is a formidable gun, especially when relieved of the weak and complex breech-loading apparatus, and used with a better system of rifling and projectiles than Armstrong's. The 110-pounder Armstrong rifle has 99-1/2 inches length and 7 inches diameter of bore, 27 inches maximum diameter, and weighs 4-1/3 tons. The "300-pounder" smooth-bore has 11 feet length and 10-1/2 inches diameter of bore, 38 inches maximum diameter, and weighs 10-1/2 tons. The Mersey Iron-Works guns are of wrought-iron, and are forged solid like steamboat-shafts, or hollow by laying up staves into the form of a barrel and welding layers of curved plates upon them until the whole mass is united. But few of these guns have been fabricated. The most remarkable of them are, 1st, the Horsfall smooth-bore, of 13 inches bore, 44 inches maximum diameter, and 24 tons weight,—price, $12,500; 2d, the "Alfred" rifle, in the recent Exhibition, of 10 inches bore,—price, $5,000; 3d, the 12-inch smooth-bore in the Brooklyn Navy-Yard, which, though very light, has fired a double 224-pound shot with 45 pounds of powder: if properly hooped, it would make the most formidable gun in America. Blakely has constructed for Russia two 13-inch smooth-bore guns, 15 feet long and 47 inches maximum diameter, of cast-iron hooped with steel: price, $10,000 each. He has also fabricated many others of large calibre, on the principles before mentioned. The 15-inch Rodman smooth-bore cast-iron gun is of 48 inches maximum diameter, 15 feet 10 inches long, and weighs 25 tons. The cost of such guns is about $6,000. The Dahlgren 15-inch guns on the Monitors are about four feet shorter.
Results of Heavy Ordnance. The 10-1/2-inch Armstrong gun sent a round 150-pound shot, with 50 pounds of powder, through a 5-1/2-inch solid plate and its 9-inch teak backing and 5/8-inch iron lining, at 200 yards, and one out of four shots with the same charge through the Warrior target, namely, a 4-1/2-inch solid plate, 18-inch backing, and 5/8-inch lining. The Horsfall 13-inch gun sent a round 270-pound shot, with 74 pounds of powder, entirely through the Warrior target at 200 yards, making an irregular hole about 2 feet in diameter. The same charge at 800 yards did not make a clean breach. The Whitworth shell burst in the backing of the same target has been referred to. Experiments on the effect of the 15-inch gun are now in progress. Its hollow 375-pound shot (3-inch walls) was broken without doing serious damage to 10-1/2-inch laminated armor backed with 18 inches of oak. The comparative test of solid and laminated armor has already been mentioned. The best 4-1/2-inch solid plates, well backed, are practically proof against the guns of English iron-clads, namely, 68-pounder smooth-bores and Armstrong 110-pounder rifles, the service charge of each being 16 pounds.
Rifling and Projectiles. The spherical shot, presenting a larger area to the action of the powder, for a given weight, than the elongated rifle-shot, has a higher initial velocity with a given charge; and all the power applied to it is converted into velocity, while a part of the power applied to the rifle-shot is employed in spinning it on its axis. But, as compared with the rifle-shot, at long ranges, it quickly loses, 1st, velocity, because it presents a larger area to the resisting air; 2d, penetration, because it has to force a larger hole through the armor; and 3d, accuracy, because the spinning of the rifle-shot constantly shifts from side to side any inaccuracy of weight it may have on either side of its centre, so that it has no time to deviate in either direction. Practically, however, iron-clad warfare must be at close quarters, because it is almost impossible to aim any gun situated on a movable ship's deck so that it will hit a rapidly moving object at a distance. It is believed by some authorities that elongated shot can be sufficiently well balanced to be projected accurately from smooth-bores; still, it is stated by Whitworth and others that a spinning motion is necessary to keep an elongated shot on end while passing through armor. On the whole, so far as penetrating armor is concerned, the theory and practice favor the spherical shot. But a more destructive effect than mere penetration has been alluded to,—the bursting of a shell within the backing of an iron-clad vessel. This can be accomplished only by an elongated missile with a solid head for making the hole and a hollow rear for holding the bursting charge. The rifle-shot used in America, and the Armstrong and some other European shot, are covered with soft metal, which in muzzle-loaders is expanded by the explosion so as to fill the grooves of the gun, and in breech-loaders is planed by the lands of the gun to fit the rifling,—all of which is wasteful of power. Whitworth employs a solid iron or steel projectile dressed by machinery beforehand to fit the rifling. But as the bore of his gun is hexagonal, the greater part of the power employed to spin the shot tends directly to burst the gun. Captain Scott, R.N., employs a solid projectile dressed to fit by machinery; but the surfaces of the lands upon which the shot presses are radial to the bore, so that the rotation of the shot tends, not to split the gun, but simply to rotate it in the opposite direction.
Mounting Heavy Ordnance, so that it may be rapidly manoeuvred on shipboard and protected from the enemy's shot, has been the subject of so much ingenious experiment and invention, that in a brief paper it can only be alluded to in connection with the following subject:—
