Page:The American Cyclopædia (1879) Volume VIII.djvu/340

 326 GUNNERY first less curved than those of elongated shot ; bat in the latter part of the flight, at consider- able ranges, this relation is reversed. This is because the initial velocity of round shot is almost always greater, and the terminal velo- city less, than that of elongated shot ; the cur- vature everywhere being very nearly propor- tional to the velocity. The so-called "dan- gerous space " is that part of a projectile's path which is not higher above the earth than 5 ft. 10 in., or the stature of a man. The danger- ous space is evidently greater at short than at long ranges, since it depends upon the angle which the descending branch of the trajectory makes with the earth, being greater the less the angle of descent ; and the longer the range the greater is the angle of descent ; for, to ob- tain the longer range, the muzzle of the gun must be more elevated, and the descending branch, owing to the resistance of the air, al- ways makes a larger angle with the earth than the ascending branch. The force of a pro- jectile is measured by the product of its mass into the square of its velocity. The force, although a prime factor in the efficiency of a projectile, is not the only one ; for cases may arise in which the energy is too great. Thus in firing at a wooden vessel, a shot with a slow motion, making a large irregular hole, and hurling splinters, will be more destructive than a swift shot, cutting cleanly through, with com- paratively little injury. In curved fire from mor- tars and howitzers, a low velocity is not only necessary, but desirable. Most of the effects of projectiles are accomplished by penetrating the objects against which they are directed, and their work will generally be most effectively accomplished when their energy is moderately in excess of that required for complete pene- tration. In this connection the penetration of iron vessels becomes of great interest and im- portance. The most systematic experiments to ascertain the effect of shot on iron targets have been summarized by Capt. W. H. Noble of the English artillery, who deduces the fol- lowing rules: 1. If two shot, having the same diameter and form of head, strike with equal energy, the penetration will be the same, though one may be a light round shot, striking with a high velocity, and the other a long heavy shot, with a low velocity. 2. A plate will be equal- ly penetrated by shot of different diameters, provided the energy on striking is proportional to the diameter. Thus, a 12-inch shot must have twice as much energy as a 6-inch shot, in order to penetrate the same plate. 3. The resistance of plates to penetration varies as the^ square of the thickness. These rules are subject to certain qualifications, depending upon the shape of the head of the shot. A hemispherical head is disadvantageous, because it tends to bulge laterally, and the same is par- tially true of a flat-fronted shot. The best form is the pointed ogive, which passes through without materially bulging, and makes a hole no larger than it's true diameter. The flat- fronted shot usually rips out a piece, called a button, in the shape of the frustum of a cone, the larger base being detached from the back of the plate. This is carried into the wooden backing, giving an increased resistance as com- pared with the ogive. Spherical projectiles are liabte to flatten against the target and break in pieces. It is apparent that when flat- tening occurs the increased diameter involves the necessity of making a larger hole in order to penetrate. The striking velocity may be so great that the projectile will be dashed to pieces by its impact, and its energy partially absorbed in its own destruction, instead of that of the target. This is especially true of spher- ical shot, fired with heavy charges at short range against thick plates. In comparing the effects of spherical and elongated projectiles against iron plates, many quantities must be considered, some favoring one form and some the other; but the final result is strongly in favor of the elongated form. For penetrating earth and battering masonry, similar consider- ations are applicable. Concerning the effec- tive range of guns, there is much popular mis- apprehension. To the scientific gunner the maximum range is of so little moment that its extent for common infantry bullets or for the heaviest seacoast projectiles is unknown. The longest range known to us was attained by one of Sir Joseph Whitworth's projectiles, viz., about 11,100 yards, not quite 6 miles. The efficiency is greatest near the muzzle, and di- minishes as the range increases. A range may be considered effective at which there is a rea- son able probability of doing inj ury. For bullets the effective range will depend upon the way in which the enemy's troops are deployed. Against a skirmish line it cannot much exceed 500 yards, but against massed troops it may be as great as 1,500 yards. With field projectiles an enemy may be harassed at 2,500 yards, or even 3,000. In the bombardment of cities the extreme range is sometimes resorted to, on the assumption that a projectile falling any- where within the line of fortification may work damage. Effective range turns upon the higher question of probabilities of fire. Thus far we have discussed projectiles only, since their properties constitute the basis of gunnery. Gunpowder is merely the agent for giving them energy, and the gun for giving them direction. When we examine the rela- tions among the three elements, the problem is highly complicated. We have two forces : the inertia of the shot, and the elastic force of the gases evolved by the powder. It is supposed that the metal contained in a given projectile is cast into a solid cylinder, having the diameter of the bore of the gun. Its length is called the column of metal of the projectile, and constitutes a measure of its in- ertia. Equal velocities will be imparted to different projectiles when the mean intensity of the forces acting upon them during a given time is proportional to their respective columns