“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
introduction to this paper the author explains that its subject-matter
is the result of the speculations and experiments of earlier years;
and he describes the incident which at the later date induced its
publication. It appears that at the capture of the _Mars_, man-of-war,
a manuscript was discovered on board which contained the results and
conclusions of some important gunnery trials which the French had been
carrying out. This manuscript, being shown to Robins by Lord Anson,
was found to contain strong confirmation of his own views both as to
the best proportions of guns and the most efficient powder-charges
for the same. He had not published these before, he plaintively
explains, because, “not being regularly initiated into the profession
of artillery, he would be considered a visionary speculatist.” But
fortified by the French MS. he no longer hesitated to submit his
proposal to the public.
Briefly, the paper is an argument for a more efficient disposition
of metal in ordnance. Robins states his case in language simple and
concise. Large shot, he says, have naturally great advantages in
ranging power over small shot; in sea fighting the size of the hole
they make and their increased power of penetration gives them a greatly
enhanced value. Hence the endeavour made in all cases to arm a vessel
with the largest cannon she can with safety bear. And hence the
necessity for so disposing the weight of metal in a ship’s ordnance to
the best advantage; all metal not usefully employed in contributing to
the strength of the pieces being not only useless but prejudicial to
efficiency.
He then proceeds to prove (not very convincingly, it must be admitted)
that there is a law of comparison to which the dimensions of all guns
should conform, and by which their weights could be calculated. For
every pound of bullet there should be allowed a certain weight of metal
for the gun. So, taking the service 32-pounder as having the correct
proportions, the weight and size of every other piece can be found
from this standard. He observes, however, that in actual practice the
smaller the gun, the greater its relative weight; the 6-pounder, for
example, weighs at least eighteen hundredweight, when by the rule it
should weigh ten. The proposal is therefore to utilize the redundant
weight of metal by increasing the calibre of the smaller guns. At the
same time it is proposed to limit the stress imposed on all guns by
reducing the powder-charge to one-third the weight of the bullet, for
all calibres; this smaller charge being almost as efficient for ranging
as the larger charges used, and infinitely less dangerous to the gun.
The publication of the pamphlet came at an opportune moment. A new
spirit was dawning in the navy, a new enthusiasm and search for
efficiency were abroad, which in the next half-century were to be
rewarded by a succession of well-earned and decisive victories.
Interest in the proposed change in armament was widespread, both in and
outside the royal service. And a significant commentary on the proposed
regulation of powder-charges was supplied, this very year, by Admiral
Hawke, who reported that in the fight off Ushant all the breechings
of his lower-deck guns broke with the repeated violence of recoil,
obliging him to shoot ahead of his opponent while new breechings were
being seized.
Some time was to elapse before the arguments of Robins gave signs of
bearing fruit. Experiments carried out at Woolwich in the seventies
by Dr. Hutton with all the facilities ensured by the patronage of a
ducal master-general of ordnance merely extended and confirmed Robins’
own results. In ’79 the carronade made its appearance, to attest in
dramatic fashion the value, at any rate for defensive work, of a large
ball, a small charge, and an unusually small windage. As offensive
armament it represented, of course, the _reductio ad absurdum_ of the
principles enunciated by Robins; its dominant feature of a ball of
maximum volume projected with a minimum velocity was, in the words of
an American authority, “manifestly as great an error as the minima
masses and the maxima velocities of the long gun system, to which the
carronade was thus directly opposed.” Nevertheless, the carronade
(whose history we deal with in a later chapter) did excellent work.
Mounted upon the upper decks and forecastles of merchantmen and the
smaller classes of warships, it emphasized, by the powerful and often
unexpected blows which it planted in the ribs of such adversaries
as ventured within its range, the comparative inefficiency of the
smaller types of long gun with which our ships of war were armed.
To the clearest-sighted of our naval captains the relative merits
and defects of the carronade and the small long gun were evidently
clear. In the year 1780 we find Kempenfelt advocating, in a letter
to Sir Charles Middleton, a weapon with a little more length and
weight than a carronade: something between it and a long gun. Robins’
arguments against the still prevalent types of small pieces have proved
convincing to him, and he transcribes the whole of the _Proposal_ for
the consideration of his superior. “Here you have, sir,” he writes,
“the opinion of the ablest artillery officer in England at that time,
and perhaps in Europe.”
Once more the versatile and gifted pen was called in aid of politics.
In 1749 he was persuaded to write what his biographer describes as a
masterpiece of its kind: _An apology for the unfortunate affair at
Preston-Pans in Scotland_.[84] But soon an opening worthier of his
talents presented itself. The East India Company, whose forts in India
were as yet ill-adapted for defence, required the services of an expert
in military fortification. An offer was made, and, as Engineer-General
to the Company, Robins left England for the East at the end of ’49,
to the great sorrow of all his acquaintance. They were not to see him
again. In the summer of the following year he died of a fever, pen in
hand, at work upon his plans in the service of the Company.
* * * * *
So ended a short, a brilliant, and a very honourable career. Benjamin
Robins possessed in an exceptional degree the power, inherent in so
many of his countrymen, of applying the truths of science to practical
ends. An individualist deriving inspiration from the great masters of
the past, he followed the bent of his enthusiasms in whatever direction
it might lead him, till ultimately his talents found expression in a
field undreamed of by himself or by his early friends. In the realm of
gunnery he was an amateur of genius. Partly for that reason, perhaps,
his views do not appear to have been considered as authoritative by
our own professionals; the prophet had more honour in Berlin, Paris
and Washington. Speaking of the rifle, the true principle of which was
admittedly established by him, the American artillerist Dahlgren wrote
in 1856: “The surprizing neglect which seemed to attend his labours was
in nothing more conspicuous than in the history of this weapon. Now
that whole armies are to wield the rifled musket with its conical shot,
one is surprized at the time which was permitted to elapse since that
able experimenter so memorably expressed his convictions before the
Royal Society, in 1746.”
Of the value of his work to the nation there is now no doubt. Of
the man himself an entertaining picture is given in his biography,
published, together with his principal papers, by Dr. Hutton, from
which many of the foregoing notes have been taken. Among other eminent
men who have given their life and labours to the public service, and
whose efforts in building up the past greatness of England have been
generously acknowledged, let us not forget to honour that distinguished
civilian, Benjamin Robins.
[Illustration: TUDOR SHIPS UNDER SAIL
From the same MS. as plate facing page 60]