GITNNERY. Ignorance of the laws of gravity and of other phy,5ical circumstances affecting the flight of projectiles, prevented any correct theory of gunnery being arrived.
at in the earliest stages of artillery. The first author professedly treating on the flhrht of cannon-shot was Nicholas Tartaglia. a distinguished Italian mathematician, who, in 1537, published his work, La _nova Scientia. He had no practical acquaintance with his'subject, but his guesses were shrewd and often marvelously near the truth. Among other tlffugs he ascertained that no portion of the track described by a ball is a right line, and as a practical aid to artillerists, he devised the gunner's guadr«nt _liter Tartaglia, many philosophers, especially of Italy, theorized on the question, and various tables of ranges, elevations, charges, etc., had been published, all more or less fallacious, when a nearer approach to accuracy appeared in Galileo's Dialogues am Motion, printed in 16:38. The officers who had charge of artillery in actual use were too little gifted with scientific education to deduce theory from practice; and up to the time of Robins, who wrote in 1742, but four Browne, Eldred, and Alderson, of whom the last three were Englislimen-ahave left treatises of any value on the use of their weapons.
Galileo, in his contributions to physics, had shown that cannon-shot, or any other projectiles, being affected by the downward force of gravitv, would travel in the curve of a parabola. unless affected by the resistance of the air. philosopher pointed out modes by which the disturbances caused by this resisting medium might be ascertained; but subsequent writers, with the exception of Newton and Bernoulli!, till the time of Robins, chose to assume that the atmospherical resistance was but nominal, mid. boldly asserted that all shot described paritbolas in their course. In 1742 Benjamin Robins, who must be considered the real founder of the science, published his. _Rut Principles of Gunnery, a work the result of long and almost exhaustive expclitnents. He treated of the atmospheric resistance, of the force of gunpowder, of the effects of varying length and weight in guns, and of almost everything which in any •w:,y related to the motion of projectiles, carrying the theory of gunnery nearly to perfection. As one result 'of his experiments, Robins established the law that common slim. encountered a resistance from the air during their passage, which increased as the squarc of the velocity, or very nearly so; and that their courses differed widely front parabolas. By means of the ballistic pendulum (q v.) he measured the speed of halls at the '.'ery cannon's mouth. Euler, in the latter part of the 18th c., added much to the knowledge of the subject by his com mentaries on the work of Robins, as did also the mathematician Hutton.
The theory of gunnery, so far as it can be deduced from the universal laws of motion, without regard to the resistance of the air, fails under the more general bead of projec tiles (q.v.). But except in firing bombs, which from their low velocity are not so much affected by the resistance of the air, the niece mathematical theory is of little service. All the real practical rules have been tkaneed from experiment. The following are a few of the more important results thins arrived at: For a given charge and weight of projectile, there is a certain length of bore that gives the greatest velocity; the cause being, that with a less length some of the powder is discharged undecomposed, and with a greater, the combustion is finished before the ball leaves the muzzle, so that it has to contend with the friction of the gun without receiving additional impulses. Increase of length, accompanied by proportionate increase of charge, gives increased velocity; but the greater velocity is only in proportion to the cube root of the increased length.
The resistance of the air does not arise merely from the projectile having to displace its own bulk of it as it advances; for in the ease of a body moving with great velocity, the air becomes condensed in front of it, while that behind is highly ruffled. The dis placed air behind does not return freely to fill up the vacuum, until the speed of the ball is reduced to 1400 ft. per second;,, the maximum profitable velocity is calculated to be 1000 ft. and that, or any higher speed, is believed to be reduced to 1400 ft. after a course of WO ft.
The resistance offered to bodies by the air is as their surfaces, i.e., in the case of round or cylindrical shot, as the squares of the diameters; whilst the power of the bodies themselves to overcome resistance is as their weights, or as the cubes of their diameters. Of course balls of like size but different density will produce widely different results. Hence the greater range of solid as compared to hollow shot. Solid shot fired with equal velocities and elevations, range as their weight, the heavier overcoming atmos pheric resistance better than the lighter. Shot of equal weight and diameter will range according to their velocities; but not in direct proportion, for the retarding power varies as the square of the velocity. Velocities of shot of equal diameter are as the square roots of the charges, The diminution in speed caused by atmospheric resistance may be judged of from the following table of the speed of a 32-pounder at different parts of its course; it being premised a body in vacuo, once started, should move ad infinitum, without decrease of velocity: Initial velocity 1600 feet per second. Velocity 500 yards from gun 1126 " " 1000 " 1000 " " 1500 " 608 "