A discourse on the theory of gunnery / Delivered at the anniversary meeting of the Royal Society, November 30, 1778

by Sir John Pringle

Gentlemen,

Among the several experiments communicated to the society, during the course of the preceding year, none seeming so much to engage your attention, as those contained in the Paper, intituled, The force of fired gun-powder, and the initial velocity of cannon-balls, determined by experiments: with much pleasure therefore I acquaint you, that, on account of the pre-eminence of that communication, your Council have judged the author, Mr. Charles Hutton, worthy of the honour of the annual medal, instituted on the bequest of Sir Godfrey Copley Baronet, for raising a laudable emulation among men of genius, in making experimental inquiries. But, as on former occasions, so now, your Council, waving their privilege of determining the choice, have acted only as a select number deputed by you, to prepare matters for your final decision. I come then, on their part, briefly to lay before you the state of the Theory of Gunnery, from its rise to the time when its true foundation was laid, in order to evince how conducive those experiments may be to the improvement of an art of public concern, as well as to the advancement of natural knowledge, the great object of your institution. And if, upon a review of the subject, you shall entertain no less favourable an opinion of Mr. Hutton’s performance, than what your Council have done, it is their earnest request that you would enhance the value of this prize, by authorizing your President to present it to our ingenious brother in your name.

Artillery (in the large acceptation of the term) took place long before the invention of gun-powder. We trace the art to the remotest antiquity, since the Sacred Records acquaint us, that one of the kings of Judah, eight hundred years before the Christian æra, erected on the towers and bulwarks of Jerusalem engines of war, the contrivance of ingenious men, for shooting arrows and great stones for the defence of that city[1]. Such machines were afterwards known to the Greeks and Romans by the names of balista, catapulta and others, which had amazing powers, and were not less terrible in their effects than the cannon and mortars of the moderns. It appears that the balista was contrived to shower volleys of darts and arrows of a very large size upon the enemy, whilst the catapulta or onagra (as it was otherwise called) was fitted not only for that purpose, but for discharging stones of an enormous weight; I might say rocks, since some of them are reported to have weighed several hundred pounds. Batteries composed of numerous pieces of that kind of artillery, nothing could withstand. Yet, if we are rightly informed, their sole principle of motion consisted in the spring of a strongly-twisted cordage, made of animal substances singularly tough and elastic. These warlike instruments continued, not only during the time of the Roman empire, but to the 12th and 13th centuries, as we find from history; nor indeed is it probable that they were totally laid aside, till gun-powder and the modern ordnance, attaining a good degree of perfection, superseded their use. The very intelligent commentator of Polybius[2] is of opinion, that the military art rather lost than gained by the exchange of the catapulta for the mortar: but however that point may be determined in speculation, it is not likely that the ancient tormenta militaria will ever be revived; but that all nations will keep to the art of gunnery and study how to improve it; that is, they will adhere to a system of artillery, wherein the moving power depends on the expansive force of gun-powder, or of some other substance of a similar nature.

Upon the first application of this principle to the purposes of war, nothing perhaps was less thought of than to assist so empirical a practice by scientific rules; for, however aiding in these matters the ancient mechanicians might have been, who, like Archimedes, had invented or perfected some of the balistic machines, no praise seemed now due to the mathematicians for either the discovery or improvement of the new artillery. In fact, we find the practice of the art had subsisted about 200 years, before any geometer considered it as one that admitted a theory, or at least such a theory as was grounded on geometry.

It seems but just to trace and commemorate the inventors of the ingenious arts which furnish matter for discourses on these occasions; and not only the main inventors, but even those who first turned their thoughts upon the subject: for, though such men may not have produced any thing perfect, yet they may have suggested ideas to others of a less inventive, but of a more executive genius, and who, unprovided with those hints, would never have made any notable discovery. I must therefore observe, that the Italians were the first who emerged out of those thick clouds of ignorance and barbarism which had so long overspread this quarter of the world. They profited by the unhappy fate of Constantinople; for by liberally receiving the learned emigrants on that distressful occasion, they were largely repaid by their arts and sciences, and still more abundantly by their language, whereby they were enabled to read and to translate those ancient manuscripts, which the Greeks had saved out of the wreck of their country. The art of printing, which was established soon after, was the means of quickly disseminating those treasures of knowledge, and concurred with the fall of the eastern empire to form an epoch for the advancement of learning, unparalleled in the annals of letters.

The end of the 15th century, and the whole of the 16th, were chiefly employed by the Italians in the study and in the translation of the old Greek authors. The geometry of the ancient Greeks, as well as the arithmetic in numbers and species of the Arabians, were cultivated; but both remained, as it were, sciences by themselves, unassisting to, or at best but weak and reluctant auxiliaries to the philosophy of the schools: and indeed how could the abstracted doctrines of numbers and quantities be strained to co-operate with a system, in which neither the laws of motion, nor any but the superficial, and often delusive properties of matter, were to be met with? The genius of the Greeks, all acute and brilliant as it was, had never been properly directed to the interpretation of nature, and was indeed unfit (as Lord Bacon pronounced) for a study that made so slow and painful a progress, by re-iterated and varied experiments and observations. It was no wonder then, if the mixed mathematics, as they are called, descended to the moderns in a state no-wise corresponding to the elegance and certainty of those parts of the science which were elementary and pure; and that those mixed parts should have been found defective and erroneous, in proportion (if I may so express myself) to the physical considerations that were to be taken into the inquiry. The imperfection of the ancients, with regard to natural philosophy, was not perceived at that time; nay, at the period we are treating of, the learned were firmly persuaded of the contrary, and that all that was wanting to be known concerning the laws of nature, and the properties of matter, was to be taken either directly, or by deduction, from the physics of Aristotle. It was not till the 17th century was somewhat advanced, that men of science began to listen to Lord Bacon and Galileo, the great founders of the experimental and the true philosophy.

Mean while, in the beginning of the 16th century, unqualified as the Italians then were for entering upon physico-mathematical inquiries[3], they nevertheless made the attempt, and in particular took the theory of projectiles into consideration. Some imagined that a body impelled with violence, such as a ball discharged from a cannon, moved in a right line till the force was spent, and that then it fell in another right line perpendicularly to the earth. Upon this principle, absurd as it was, we find one of the earliest authors grounding his whole theory of gunnery[4]; whilst others, dissenting from his hypothesis, admitted only the straight line, in which the ball moved for some time after coming out of the piece, and that other straight line in which it fell to the ground; but asserted that these two were connected by a curve line, and that this curve was the segment of a circle. Nicolas Tartaglia of Brescia, a mathematician of the first rank in those days, and still celebrated for his improvements in algebra, hath been supposed to be the author of this doctrine, no less erroneous than the former, and for which two of his books have been quoted[5]. Those I have never seen; but from another of his works, professedly written on this subject, and translated into English under the title of Colloquies concerning the art of shooting in great and small pieces of artillery[6], him I find, contrary to the opinion of his contemporaries, maintaining that no part of the track of a cannon-ball is in a right line, though the curvature in the first part of its flight be so small, that it needeth not to be attended to. But Tartaglia is far from supposing, that the line in question hath any relation to a parabola, or to any regular curve. It would seem then, that if this mathematician had at first been so far mistaken, as to fancy that some part of the course of a projectile was in a straight line, he had afterwards changed his opinion, and was perhaps singular in what he finally embraced.

From numerous instances one would imagine, that in those days, so far were men of science from making experiments themselves, that they even shut their eyes against what chance would have presented to their sight. For, whoever had minded the roving shot of an arrow, the flight of a stone from a sling, or had attended to a stream of water issuing from the spout of a cistern, might have been convinced, that the path of every projectile was in a continued curve, whatever little he otherwise knew concerning the properties of that one.

But had the observation of the philosophers gone so far, they had still been at a distance from the truth. They might have perceived a likeness between the track of those bodies in motion and a parabola, and concluded, from analogy, that all projectiles delineated that curve in the air; but they could never have realized their conjectures by mathematical demonstration, without previously knowing the law of acceleration in falling bodies: a discovery reserved for the next century, and for Galileo[7], one of the greatest ornaments of it.