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sideration of the principles involved in these changes, which is all that we can attempt, may, however, be of interest.
The substitution of the rifled bore, with the elongated projectile, for the smooth or plane cylindrical bore with the spherical bullet, may be regarded as the main element. And yet the invention of the rifle and elongated shot was not new even in 1851. To take one instance, Captain Norton had for some twenty or thirty years, and others for a longer or shorter period, been advocating elongated and expanding projectiles, which are now universally adopted for the small-arms of every European army, without receiving the least encouragement. This is one of the many examples of inventions, which, coming before the world was ready for, or required them, have fallen still-born. Indeed, the mathematician Benjamin Robins, who may almost be considered the father of modern gunnery, as far back as 1747, published a short work explaining the true use of the spiral grooves of the rifle and their great value in insuring accuracy, and suggested how advantage might be taken of them to enable us to employ elongated (egg-shaped) projectiles which would give increased range and accuracy. He concludes with the following remarkable prediction:
I shall, therefore, close this paper with predicting that whatever state shall thoroughly comprehend the nature and advantage of rifled-barrel pieces, and, having facilitated and completed their construction, shall introduce into their armies their general use with a dexterity in the management of them, they will, by this means, acquire a superiority, which will almost equal anything that has been done at any time by the particular excellence of any one kind of arms, and will perhaps fall but little short of the wonderful effects which histories relate to have been formerly produced by the first inventors of fire-arms.
His advice was neglected for a hundred years. Might we not with safety refer to the Austrians at Solferino, and the Chinamen of the Taku forts, for confirmation of the truth of his prophecy? It appears as if the strong impulse which is necessary to force on a change had never till lately been called into action; though, at the same time, in the case of large guns-heavy ordnance- another cause must be allowed to have exercised a certain amount of weight. Without the means afforded by the steam-hammer and other modern mechanical and manipulative contrivances, it would be impossible to construct such guns as those of Sir W. Armstrong or Mr. Whitworth, or their ammunition. This, however, does not apply to the more simple constructions followed on the Continent, and which might have been as effectively employed fifty years ago.
We will now attempt, though necessarily in a very superficial manner, to elucidate the reasons for a rifle being a
more accurate and far-reaching weapon than the old smooth bore; for without some knowledge of these, the changes can scarcely be appreciated. Neglecting the form of the outside at present, let us consider the interior only, and following the Irishman's receipt for making a gun, as the first stage, "take a long hollow," and we have the long cylindrical bore, closed at one end, in which the charge of powder is ignited, and which, becoming very rapidly, though not instantaneously, converted into gas, drives the projectile-a spherical bullet-before it in one direction, and the gun in the other.* Unless the gun be a breech-loader, the bullet must necessarily, for ease in loading, be rather smaller than the bore. Through this interstice, termed windage, a great deal of the gas escapes uselessly; whence there is a great loss of initial velocity. And further, the bullet goes bounding along the bore, striking first against one side and then the other, and leaves it, not in the direction of the axis of the piece, but in some other direction, depending on the side it struck last, which is one cause of inaccuracy; but it also, either from having rubbed against one side of the bore more than the other, or from its not being perfectly homogeneous, when the centres of figure and gravity do not. coincide, carries with it a spinning or whirling motion, which is another and more important cause of inaccuracy. For this rotation causes great deflection, in the following manner:- Owing to its rapid motion, the air becomes more condensed in front of the bullet than behind; in fact, when the velocity is more than 1,344 feet per second (the rate at which air will rush into a vacuum), there is a complete vacuum behind it. If we imagine the bullet to combine with its motion of translation, a rotation from left to right as we look down upon it while facing in the direction in which it is going; that is, representing the bullet in plan by a shilling, in the direction that the superscription runs; then the air being denser before than behind, there will constantly be a greater friction on the anterior than on the posterior half of the bullet, -a friction that is opposing the motion of rotation of the front half to the right, and therefore tending to deflect or make the
The permanent gases generated occupy, it is computed, at the temperature supposed to be produced-3,000° Fahr.,-a volume of about 2,000 times the bulk of the powder. But this point, as well as whether, at this high temperature, Marriott's law of the elasticity varying as the density holds good, has never been accurately determined. If, however, we take Dr. Hutton's estimate, which is rather a low one, that the first force of fired gunpowder is equal to 2,000 atmospheres (30,000 lb.) on the square inch, and that, as Robins computed, the velocity of expansion is about 7,000 feet per second, we have some idea of the force.
shot roll off to the left. But at the same time one halfsupposing the bullet to be cut in two, in the opposite direction, by the plane of the trajectory-is moving in the same direction with, and the other half against, the motion of translation. That is, in the case just considered, the left half would be rotating in the same direction as the motion of translation, the right half in the opposite direction; consequently, the motion of the right half would be assisting, and the motion of the left retarding, the air in escaping past it. The bullet, therefore, constantly creating and meeting a denser medium on the left than on the right, has a tendency to deflect to the right. This tendency, which is in the opposite direction, is stronger than the one before mentioned, and the ball is deflected to the right -in a curve, as the velocity of rotation diminishes less rapidly than the velocity of translation.* In the same way the range is increased or diminished according as the rotation of the fore part is upwards or downwards.
From these remarks may be gathered the general causes which give uncertainty to the direction of the flight of a spherical ball from the smooth-bored gun; viz., uncertain rotation and the resistance of the air. In the rifle we have a means of counteracting these by imparting a constant and fixed rotation. The rifled barrel, instead of being a plain cylinder, has spiral grooves cut in it. The ball fits these grooves, and in being forced out by the powder, is constrained, in the same way as a screw in being withdrawn from a nut, to rotate round an axis which is the same as that of the bore of the gun. This rotation is constant, and the tendency is for the axis of a rotating body to remain parallel to its original direction,† as may be easily seen with a spinning-top; and, moreover, the axis being coincident -at all events, during the early part of the flight - with the line of the trajectory, the causes of deflection before considered do not come into play, while, at the same time, any irregularities of surface are brought first to one side and then to the other; and any deflections which might be caused by them are neutralized.
Having now shown how the inaccuracy is overcome, let us examine how the range is increased. The obstacle to an in
* Robins showed this very well by an experiment with a bent musketbarrel; the ball, instead of following the direction to which the end of the barrel was bent, was incurvated in the opposite direction, and crossed the direction of the straight portion. The ball, in fact, rubbing against the bent portion, received a strong rotation in the opposite direction, and, as explained, was deflected.
+ See Mechanical Summary, p. 277,-" Guns and Iron-cased Ships,"-a new form of projectile.
crease of range is the resistance of the air, which, with high velocities, is very great, as may be gathered from the following experimental resistances to a ball two inches in diameter, extracted from a table given by Dr. Hutton. With a velocity of 100 feet per second, it was 174 lb.; with 200 feet, 709 lb.; with 900 feet, 94-106 lb.; and with 2,000 feet, 102-362 lb. As the resistance is nearly proportional to the surface exposed to it, so, to gain increased ranges, it is necessary to increase the weight of the ball in a greater ratio than the surface exposed. For if two balls, one twice the weight of the other, exposing the same surface to the resistance of the air, are projected with the same velocities, the heavier having twice the momentum or store of motion, has twice the power of overcoming the resistance; that is, twice the range. With smoothbored guns and spherical shot, the only way of accomplishing this (increased density being practically out of the question), is to increase the diameter of the shot, when the weight increasing as the cube, and the surface as the square of the diameter, the desired result is obtained, as far as the other circumstances will admit.
With high velocities (as was shown by Dr. Hutton), the resistance rapidly rises in a variable ratio, which increases more and more above the square of the velocity; so that, beyond a certain point, the increase is of no avail.
In the rifle, however, the power of impressing a rotation gives us an advantage in overcoming the resistance of the air. For, as the tendency is for the axis of a rotating body to remain parallel to its original direction, if we project an elongated shot, it will be maintained with its point foremost during the flight, and, in proportion to its weight, will present a very small surface to the resistance of the air. Thus, if we compare Mr. Whitworth's 3-pounder with the old 3-pounder, the weights of the shot are the same, but the diameter of the spherical shot is 2.91 inches, and of the Whitworth 1.5 inch; the surfaces are, therefore, as 8:47 to 2:25; that is, the Whitworth, with an exposed surface of only about one-fourth that of the 3-pounder, has the same weight wherewith to overcome the resistance offered by the atmosphere. Hence the enormous range that was obtained,-9,688 yards, or upwards of 5 miles. It must not, however, be inferred from this that the projectile may be indefinitely increased in length, and increased ranges thereby obtained. For as the powder is by no means instantaneously converted into gas, we very soon arrive at a limit beyond which it is useless to increase the charge; for it would not be wholly exploded before the shot left the gun, and we arrive at a point where the velocity is decreased without any corresponding gain. It is perhaps right to notice here the
erroneous idea, that an elongated rifle projectile has a much greater initial velocity than a round shot. A little consideration will show that this is not the case. With the same pressures acting through the same spaces, that is, similar charges fired under like conditions, the velocities of the shot will be inversely as the square roots of their weights. Besides which, in the case of the rifle, there is the work lost in friction and in giving the rotation. Where the rifle does gain, is in this; that whereas, cæteris paribus, the initial velocities are inversely as the squares of the weights, the resistances of the air rise in a much higher proportion than the squares of the velocities, when these are high. A limit is, therefore, reached beyond which it is useless to increase the velocity of the round shot, and which it is possible nearly to attain with the rifle projectile. The following table, extracted from the "Lectures on Artillery," by Major Owen, R.A., and Captain Dames, R.A., at the Royal Military Academy (from which work we also, by their kind permission, copy the drawings of the gun and fuzes), will illustrate these remarks, showing, as it does, that at first the higher velocity of the 12-pounder round shot gives it the advantage over the Armstrong.
This table, moreover, does not fully express the difference in initial velocities of the two shot; for, paradoxical as it may appear, the ranges of the elongated projectile are, up to about 6 of elevation, absolutely greater in the resisting atmosphere than they would be in vacuo; for the elongated shot, from its rotation, retains the same inclination to the horizontal plane throughout the flight, and consequently acquires a continually increasing obliquity to the curve of its flight. And the effect of this obliquity is, that the projectile is in a measure sustained upon the air, just as a kite is supported by the current of air meeting the inclined surface; and its descent being retarded, it has time to reach a greater distance. At least this is Sir W. Armstrong's explanation, and there is no doubt that whereas the 12-pounder with an initial velocity of about 1,600 feet per