CHAPTER IV

“NEW PRINCIPLES OF GUNNERY” We have traced the smooth-bore cannon through the successive stages of its evolution. It is now proposed to give, in the form of a biographical sketch, an account of the inception of scientific methods as applied to its use, and at the same time to pay some tribute to the memory of the man who laid the foundations deep and true of the science of modern gunnery. One man was destined to develop, almost unaided, the principles of gunnery as they are known to-day. This man was a young Quaker of the eighteenth century, Benjamin Robins. For a variety of reasons his fame and services seem never to have been sufficiently recognized or acknowledged by his own countrymen. To many his name is altogether unknown. To some it is associated solely with the discovery of the ballistic pendulum: the ingenious instrument by which, until the advent of electrical apparatus, the velocities of bullets and cannon balls could be measured with a high degree of accuracy. But the ballistic pendulum was, as we shall see, only one manifestation of his great originating power. The following notes will show to what a high place Robins attained among contemporary thinkers; and demonstrate the extent to which, by happy combination of pure reason and experiment, he influenced the development of artillery and fire-arms. His _New Principles of Gunnery_ constituted a great discovery, simple and surprisingly complete. In this work he had not merely to extend or improve upon the inventive work of others; his first task was to expose age-long absurdities and demolish all existing theories; and only then could he replace them by true principles founded on correct mathematical reasoning and confirmed by unwearying experiment with a borrowed cannon or a “good Tower musquet.” Down to the time of Robins, gunnery was still held to be an art and a mystery. The gunner, that honest and godly man,[80] learned in arithmetic and astronomy, was master of a terrible craft;--his saltpetre gathered, it was said, from within vaults, tombs, and other desolate places;--his touchwood made from old toadstools dried over a smoky fire;--himself working unscathed only by grace of St. Barbara, the protectress of all artillerymen. The efficiency of his practice depended overwhelmingly on his own knowledge and on the skill with which he mixed and adjusted his materials. No item in his system was of sealed pattern; every element varied between the widest limits. There were no range-tables. His shots varied in size according to the time they happened to have been in service, to the degree of rusting and flaking which they had suffered, and to their initial variations in manufacture. His piece might be bored taper; if so, and if smaller at the breech end than at the muzzle, there was a good chance of some shot being rammed short of the powder, leaving an air space, so that the gun might burst on discharge; if smaller at the muzzle end the initial windage would be too great, perhaps, to allow of efficient discharge of any shot which could be entered. There was always danger to be apprehended from cracks and flaws. But the greatest of mysteries was that in which the flight of projectiles was shrouded. At this point gunnery touched one of the oldest and one of the main aspects of natural philosophy. The Greek philosophers failed, we are told, in spite of their great mental subtlety, to arrive at any true conception of the laws governing the motion of bodies. It was left to the period of the revival of learning which followed the Middle Ages to produce ideas which were in partial conformity with the truth. Galileo and his contemporaries evolved the theory of the parabolic motion of falling bodies and confirmed this brilliant discovery by experiment. Tartaglia sought to apply it to the motion of balls projected from cannon, but was held up by the opposing facts: the initial part of the trajectory was seen to be a straight line in actual practice, and even, perhaps, to have an upward curvature. So new hypotheses were called in aid, and the path of projectiles was assumed to consist of three separate motions: the _motus violentus_, the _motus mixtus_, and the _motus naturalis_. During the _motus violentus_ the path of the spherical projectile was assumed to be straight--and this fallacy, we may note in passing, gave rise to the erroneous term “point blank,” to designate the distance to which the shot would travel before gravity began to operate; during the _motus naturalis_ the ball was assumed to fall along a steep parabola; and during the _motus mixtus_, the path of the trajectory near its summit, the motion was assumed to be a blend of the other two. This theory, though entirely wrong, fitted in well with practical observation; the trajectory of a spherical shot was actually of this form described. But in many respects it had far-reaching and undesirable consequences. Not only did it give rise to the misconception of the _point en blanc_; it tended to emphasize the value of heavy charges and high muzzle velocities while at the same time obscuring other important considerations affecting range. So the gunner was primed with a false theory of the trajectory. But even this could not be relied on as constant in operation. The ranging of his shot was supposed to be affected by the nature of the intervening ground; shot were thought to range short, for some mysterious reason, when fired over water or across valleys, and the gunner had to correct, as best he could, for the extra-gravitational attraction which water and valleys possessed. In addition to all these bewilderments there was the error produced by the fact that the gun itself was thicker at the breech than at the muzzle, so that the “line of metal” sight was not parallel with the bore: a discrepancy which to the lay mind, and not infrequently to the gunner himself, was a perpetual stumbling-block. It is not surprising that, in these conditions, the cannon remained a singularly inefficient weapon. Imperfectly bored; discharging a ball of iron or lead whose diameter was so much less than its own bore that the projectile bounded along it and issued from the muzzle in a direction often wildly divergent from that in which the piece had been laid; on land it attained its effects by virtue of the size of the target attacked, or by use of the _ricochet_; at sea it seldom flung its shot at a distant ship, except for the purpose of dismasting, but, aided by tactics, dealt its powerful blows at close quarters, double-shotted and charged lavishly, with terrible effect. It was then that it was most efficient. Nor is it surprising that, in an atmosphere of ignorance as to the true principles governing the combustion of gunpowder and the motion of projectiles, false “systems” flourished. The records of actual firing results were almost non-existent. Practitioners and mathematicians, searching for the law which would give the true trajectories of cannon balls, found that the results of their own experience would not square with any tried combination of mathematical curves. They either gave up the search for a solution, or pretended a knowledge which they were unwilling to reveal. § In the year 1707 Robins was born at Bath. Studious and delicate in childhood, he gave early proof of an unusual mathematical ability, and the advice of influential friends who had seen a display of his talents soon confirmed his careful parents in the choice of a profession for him: the teaching of mathematics. Little, indeed, did the devout Quaker couple dream, when the young Benjamin took coach for London with this object in view, that their son was destined soon to be the first artillerist in Europe. That the choice of a profession was a wise one soon became evident. He was persuaded to study the great scientific writers of all ages--Archimedes, Huyghens, Slusius, Sir James Gregory and Sir Isaac Newton; and these, says his biographer, he readily understood without any assistance. His advance was extraordinarily rapid. When only fifteen years old he aimed so high as to confute the redoubtable John Bernouilli on the collision of bodies. His friends were already the leading mathematicians of the day, and there were many who took a strong interest in the brilliant and attractive lad. He certainly was gifted with qualities making for success; for, we are told, “besides his acquaintance with divers parts of learning, there was in him, to an ingenuous aspect, joined an activity of temper, together with a great facility in expressing his thoughts with clearness, brevity, strength, and elegance.” Robins’ mind was of too practical a bent, however, to allow him to stay faithful to pure mathematics; his restless energy required another outlet. Hence he was led to consider those “mechanic arts” that depended on mathematical principles: bridge building, the construction of mills, the draining of fens and the making of harbours. After a while, taking up the controversial pen again, he wrote and published papers by which a great reputation gradually accrued. In 1735 he blew to pieces, with a _Discourse on Sir Isaac Newton’s Method of Fluxions_, a treatise written against the mathematicians by the Bishop of Cloyne. And shortly after followed further abstruse and controversial studies: on M. Euler’s Treatise on Motion, on Dr. Smith’s System of Optics, and on Dr. Jurin’s Distinct and Indistinct Vision. His command of language now attracted the attention of certain influential gentlemen who, deploring the waste of such talent on mathematical subjects, persuaded their young acquaintance to try his hand at the writing of political pamphlets: party politics being at that time the absorbing occupation of the population of these islands. His success was great; his writings were much admired. And--significant of the country and the age--friendships and acquaintances were formed by the pamphleteer which were later to be of great value to the rising scientist. This phase of his activities, fortunately, did not last long. Kindling the lamp of science once more, he now started on the quest which was to make him famous. For thoughtful men of all ages, as we have already noted, the flight of bodies through air had had an absorbing interest. The subject was one of perennial disputation. The vagaries of projectiles, the laws governing the discharge of balls from cannon, could not fail to arouse the curiosity of an enthusiast like Robins, and he now set himself in earnest to discover them by an examination of existing data, by pure reason, and by actual experiment. Perusal of such books as had been written on the subject soon convinced him of the shallowness of existing theories. Of the English authors scarcely any two agreed with one another, and all of them carped at Tartaglia, the Italian scientist who in the classic book of the sixteenth century tried to uphold Galileo’s theory of parabolic motion as applied to military projectiles. But what struck Robins most forcibly about all their writings was the almost entire absence of trial and experiment by which to confirm their dogmatical assertions. This absence of any appeal to experiment was certainly not confined to treatises on gunnery; it was a conspicuous feature of most of the classical attempts to advance the knowledge of physical science. Yet the flight of projectiles was a problem which lent itself with ease to that inductive method of discovering its laws through a careful accumulation of facts. This work had not been done. Of all the native writers upon gunnery only four had ventured out of two dimensions; only four had troubled to measure definite ranges. All four asserted the general proposition that the motion of bodies was parabolic. Only one noticed that practice did not support this theory, and he, with misapplied ingenuity, called in aid the traditional hypothesis of a violent, a crooked, and a natural motion. Which wrong hypothesis enabled him, since he could choose for himself the point at which the straight motion ceased, to square all his results with his precious theory. Leaving the books of the practitioners, Robins had more to learn from the great circle of mathematicians who in the first part of the eighteenth century lent a lustre to European science. The old hypotheses were fast being discarded by them. Newton, in his _Principia_, had investigated the laws of resistance of bodies to motion through the air under gravity, by dropping balls from the cupola of St. Paul’s Cathedral; and he believed that the trajectory of a cannon ball differed from the parabola by but a small extent. The problem was at this time under general discussion on the Continent; and led to a collision between the English and the German mathematicians, Newton and Leibnitz being the two protagonists.[81] But, whatever the merits or outcome of the controversy, one thing seems certain. None of the great men of the day understood the very great accession of resistance which a fast-travelling body encountered in cleaving the air, or realized the extent to which the trajectory was affected by this opposing force. It was in fact universally believed and stated, that “_in the case of large shot of metal, whose weight many times surpasses that of air, and whose force is very great, the resistance of air is scarcely discernible, and as such may, in all computations concerning the ranges of great and weighty bombs, be very safely neglected_.”[82] In 1743 Robins’ _New Principles of Gunnery_ was read before the Royal Society. In a short but comprehensive paper which dealt with both internal and external ballistics, with the operation of the propellant in the gun and with the subsequent flight of the projectile, the author enunciated a series of propositions which, founded on known laws of physics and sustained by actual experiment, reduced to simple and calculable phenomena the mysteries and anomalies of the art of shooting with great guns. He showed the nature of the combustion of gunpowder, and how to measure the force of the elastic fluid derived from it. He showed, by a curve drawn with the gun axis as a base, the variation of pressure in the gun as the fluid expanded, and the work done on the ball thereby. Producing his ballistic pendulum he showed how, by firing a bullet of known weight into a pendulum of known weight, the velocity of impact could be directly ascertained. This was obviously a very important discovery. For an accurate measurement of the “muzzle velocity” of the bullet discharged from any given piece of ordnance was, and still is, the solution and key to many another problem in connection with it: for instance, the effect of such variable factors as the charge, the windage or the length of gun. In fact, as the author claimed, there followed from the theory thus set out a whole host of deductions of the greatest consequence to the world’s knowledge of gunnery. Then, following the projected bullet in its flight, he proceeded to tell of the continuous retardation to which it was subject owing to the air’s resistance. He found, he said, that this resistance was vastly greater than had been anticipated. It certainly was not a negligible quantity. The resistance of the air to a twenty-four pound cannon ball, fired with its battering charge of sixteen pounds of powder, was no less than twenty-four times the weight of the ball when it first issued from the piece: a force which sufficiently confuted the theory that the trajectory was a parabola, as it would have been if the shot were fired in vacuo. It was neither a parabola, nor nearly a parabola. In truth it was not a plane curve at all. For under the great force of the air’s resistance, added to that of gravity, a ball (he explained) has frequently a double curvature. Instead of travelling in one vertical plane it actually takes an incurvated line sometimes to right, sometimes to left, of the original plane of departure. And the cause of this departure he ascribed to a whirling motion acquired by the ball about an axis during its passage through the gun. The reading of the paper provoked considerable discussion among the learned Fellows, who found themselves presented with a series of the most novel and unorthodox assertions, not in the form of speculations, but as exact solutions to problems which had been hitherto unsolved; and these were presented in the clearest language and were fortified by experiments so careful and so consistent in their results as to leave small room for doubt as to the certainty of the author’s theory. Of special interest both to savants and artillerists must have been his account of “a most extraordinary and astonishing increase in the resistance of the air which occurs when the velocity comes to be that of between eleven and twelve hundred feet in one second of time”: a velocity, as he observed, which is equal to that at which sounds are propagated in air. He suggested that perhaps the air, not making its vibrations with sufficient speed to return immediately to the space left in the rear of the ball, left a vacuum behind it which augmented the resistance to its flight. His statement on the deflection of balls, too, excited much comment. And, in order to convince his friends of the reality of this phenomenon, which, though Sir Isaac Newton had himself taken note of it in the case of tennis balls, had never been thoroughly investigated, Robins arranged an ocular demonstration. One summer afternoon the experiments took place in a shady grove in the Charterhouse garden. Screens--“of finest tissue paper”--were set up at intervals of fifty feet, and a common musket bored for an ounce ball was firmly fixed in a vice so as to fire through the screens. By repeated discharges the various deflections from the original plane of departure were clearly shown; some of the balls whirled to the right, some to the left of the vertical plane in which the musket lay. But not only was the fact of this deflection established to the satisfaction of the visitors. A simple but dramatic proof was afforded them of the correctness of Robins’ surmise that the cause was the whirling of the ball in flight. A musket-barrel was bent so that its last three or four inches pointed to the left of the original plane of flight. The ball when fired would then be expected to be thrown to the left of the original plane. But, said Robins, since in passing through the bent part the ball would be forced to roll upon the right-hand side of the barrel; and as thereby the left side of the ball would turn up against the air, and would increase the resistance on that side; then, notwithstanding the bend of the piece to the left, the bullet itself might incurvate towards the right. “And this, upon trial, did most remarkably happen.”[83] Robins by now had gained a European reputation. Mathematical controversy and experiments in gunnery continued to occupy his time and absorb his energies, and it was not long before he was again at the rostrum of the Royal Society, uttering his eloquent prediction as to the future of rifled guns. Speaking with all the emphasis at his command he urged on his hearers the importance of applying rifling not only to fire-arms but to heavy ordnance. That State, he said, which first comprehended the advantages of rifled pieces; which first facilitated their construction and armed its armies with them; would by them acquire a superiority which would perhaps fall little short of the wonderful effects formerly produced by the first appearance of fire-arms. His words had little or no effect. Mechanical science was not then equal to the task. A whole century was to elapse before rifled ordnance came into general use. The genius of Whitworth was required to enable the workshops of the world to cope with its refined construction. Another subject which attracted Robins’ attention at this time was fortification, the sister art of gunnery, which now had a vogue as a result of the great continental wars. He was evidently regarded as an authority on the subject, for we find him, in 1747, invited by the Prince of Orange to assist in the defence of Berghen-op-Zoom, then invested and shortly afterwards taken by the French. Now befell an incident which, besides being a testimony to the versatility of his genius, proved to be of great consequence to him in his study of artillery. In 1740 Mr. Anson (by this time Lord Anson, and at the head of the Admiralty) had set out on his famous voyage to circumnavigate the world. For some time after his return the public had looked forward to an authentic account, on the writing of which the chaplain of the _Centurion_, Mr. Richard Walter, was known to be engaged. Mr. Walter had collected, in the form of a journal, a mass of material in connection with the incidents of the voyage. But on a review of this it was decided that the whole should be rewritten in narrative form by a writer of repute. Robins was approached, and accepted the commission. The material of the chaplain’s journal was worked up by him into a narrative, and the book was published in 1748. “It was an immediate success; four large editions were sold in less than a year; and it was translated, with its stirring accounts of perils and successes, into nearly all the languages in Europe.” Robins’ name did not appear in it, and his share in the authorship is to this day a subject of literary discussion. The acquaintance with Lord Anson thus formed was of great benefit to him, not only in securing for him the means of varied experiment with all types of guns in use in the royal navy, but by the encouragement which his lordship gave him to publish his opinions even when they were in conflict with the orthodox professional opinion of the day. To this encouragement was due the publication in 1747 of a pamphlet entitled, _A Proposal for increasing the strength of the British Navy, by changing all guns from 18-pounders downwards into others of equal weight but of a greater bore_; a paper which, indirectly, had considerable influence on the development of sea ordnance. In the