portion equal to that of the ball A., _i.e._, E.F. = C.D., (plate 23,
fig. 4), and elongated so that its weight should be equal to that of the
spherical shot B., it is evident that it would meet equal resistance
from the air, to the ball A., having, at the same time, as much power to
overcome resistance as the body B.
Elongated balls, by offering a larger surface to the sides of the
barrel, are less liable to be affected by any imperfections in the bore;
whereas the spherical ball, pressing only on its tangential point, will
give to any little hollows, or undulations, wherever they occur.
~Balls cannot be expanded.~
~Elongated projectiles easily expanded.~
A spherical ball cannot be expanded into the grooves, unless there be
very little windage, except by blows from the ramrod, the gas escaping
round the circumference of the ball, and giving it an irregular motion
while passing down the barrel; but an elongated projectile can be
readily expanded, and the facility of doing so is in proportion to the
difference of length between its major and minor axis.
DEVIATIONS OF PROJECTILES FROM SMOOTH-BORED GUNS.
~Causes of deviation of shot.~
Very great irregularities occur in the paths described by projectiles
fired from smooth-bored guns. It is a fact well known to all practical
artillerists, that if a number of solid shot or any other projectile be
fired from the same gun, with equal charges and elevations, and with
gunpowder of the same quality, the gun carriage resting on a platform,
and the piece being laid with the greatest care before each round, very
few of the shot will range to the same distance; and moreover, the
greater part will be found to deflect considerably (unless the range be
very short) to the right or left of the line in which the gun is
pointed.
~Four causes of deviation.~
The causes of these deviations may be stated as follows:--1st, Windage;
2nd, Rotation; 3rd, Wind; 4th, from Rotation of the Earth.
1st CAUSE, WINDAGE.
~Action from windage.~
~False direction.~
~Gives rotation.~
Windage causes irregularity in the flight of a projectile, from the fact
of the elastic gas acting in the first instance on its upper portion,
and driving it against the bottom of the bore; the shot re-acts at the
same time that it is impelled forward by the charge, and strikes the
upper surface of the bore some distance down, and so on by a succession
of rebounds, until it leaves the bore in an accidental direction, and
with a rotatory motion, depending chiefly on the position of the last
impact against the bore. Thus should the last impact of a (concentric)
shot when fired from a gun be upon the right hand side of the bore, as
represented, (plate 23, fig. 5); the shot will have a tendency to
deflect to the left in the direction. While at the same time a rotation
will be given to it in the direction indicated by the arrows.
2nd CAUSE, ROTATION.
~Rotation without translation.~
Every body may have a twofold motion, one by which it is carried
forward, and the other by which it may turn round on an axis passing
through its centre, called a motion of rotation.
When a body has only a motion of translation all the particles of which
it is composed move with equal swiftness, and also in parallel
directions; and by the first law of motion, every particle put in such
motion will constantly move with the same velocity in the same
direction, unless it be prevented by some external cause.
~Rotation.~
~Rotation and translation combined.~
By a motion of rotation, a body without changing its place, turns round
on an axis passing through its centre of gravity. A body may have at the
same time both a progressive and rotatory motion, without either
disturbing the other, and one may suffer a change from the action of
some external force, while the other continues the same as before.
~Force through centre of gravity, causes progressive motion only.~
If the direction of the force be through the centre of gravity, it
causes a progressive motion only, that is, if the body was at rest
before, it will move forward in the direction of the impressed force.
~Effect of force on a body in motion.~
If a body had a progressive motion before, then impressed force will
cause it to move faster or slower, or to change its direction, according
as the direction of this second force conspires with or opposes its
former motion, or acts obliquely on its direction.
~Rotation not disturbed by second force in direction of centre of
gravity.~
If a body, besides its progressive motion had a motion of rotation also,
this last will not be changed by the action of a new force passing
through the centre of gravity.
~Rotation of force does not pass through the centre of gravity.~
If the direction of the force does not pass through the centre of
gravity, the progressive motion will be altered, and the body will then
also acquire a rotatory motion round an axis passing through the centre
of gravity, and perpendicular to a plane passing through the direction
of the force and this centre.
CASES BEARING UPON THE FOREGOING THEORY.
~When ball is perfectly round, centre of gravity coincides with
figure, and no windage.~
1st Case. Suppose the ball to be perfectly round, its centre of gravity
and figure to coincide, and let there be no windage. In this case the
force of the powder not only passes through the centre of gravity of the
shot, but proceeds in a direction parallel to the axis of the bore, and
there would be but small friction due to the weight of the shot.
~If windage then rotation.~
2nd Case. But as there is a considerable amount of friction between the
bore and the projectile in the case where there is windage, the
direction of this force being opposite to that of the gunpowder, and
upon the surface of the ball, it will therefore give rotation to the
shot.
~Eccentricity causes rotation.~
3rd Case. Suppose the ball to be perfectly round, but its centre of
gravity not to coincide with the centre of figure. In this case the
impelling force passes through the centre of the ball, or nearly so, and
acts in a direction parallel to the axis of the piece; but if the centre
of gravity of the ball lie out of the line of direction of the force of
the powder, the shot will be urged to turn round its centre of gravity.
~Angular velocity.~
The angular velocity communicated to the body will depend, firstly, upon
the length of the perpendicular from the centre of gravity upon the
direction of the impelling force, and secondly, upon the law of density
of the material or the manner in which the metal is distributed. The
direction of rotations will depend upon the position of the centre of
figure with regard to that of gravity. (Plate 23, fig. 6.)
~Robins’ remarks.~
Robins remarks, bullets are not only depressed beneath their original
direction by the action of gravity, but are also frequently driven to
the right or left of that direction by the action of some other force.
If it were true that bullets varied their direction by the action of
gravity only, then it ought to happen that the errors in their flight to
the right or left of the mark, should increase in proportion to the
distance of the mark from the firer only.
~Deflection not in proportion to distance.~
But this is contrary to all experience, for the same piece which will
carry its bullet within an inch at ten yards, cannot be relied upon to
ten inches in one hundred yards, much less to thirty inches in three
hundred.
Now this irregularity can only arise from the track of the bullet being
incurvated sideways as well as downwards. The reality of this doubly
incurvated track being demonstrated, it may be asked what can be the
cause of a motion so different from what has been hitherto supposed.
~1st cause of increase, deflection.~
1st Cause. Is owing to the resistance of the air acting obliquely to the
progressive motion of the body, and sometimes arises from inequalities
in the resisted surface.
~2nd cause, from whirling motion.~
~Direction of a shot influenced by position of axis round which it
whirls.~
2nd Cause. From a whirling motion acquired by the bullet round its axis,
for by this motion of rotation, combined with the progressive motion,
each part of the bullet’s surface will strike the air in a direction
very different from what it would do if there was no such whirl; and the
obliquity of the action of the air arising from this cause will be
greater, according as the rotatory motion of the bullet is greater in
proportion to its progressive motion; and as this whirl will in one part
of the revolution conspire in some degree with the progressive, and in
another part be equally opposed to it, the resistance of the air on the
fore part of the bullet will be hereby affected, and will be increased
in that part where the whirling motion conspires with the progressive;
and diminished where it is opposed to it. And by this means the whole
effort of resistance, instead of being in a direction opposite to the
direction of the body, will become oblique thereto, and will produce
those effects we have already mentioned. For instance, if the axis of
the whirl was perpendicular to the horizon, then the incurvation would
be to the right or left. If that axis were horizontal to the direction
of the bullet, then the incurvation would be upwards or downwards. But
as the first position of the axis is uncertain, and as it may
perpetually shift in the course of the bullet’s flight, the deviation of
the bullet is not necessarily either in one certain direction, nor
tending to the same side in one part of its flight that it does in
another, but it more usually is continually changing the tendency of its
deflection, as the axis round which it whirls must frequently shift its
position during the progressive motion.
~Doubly incurvated track.~
It is constantly found in practice that a shot will deviate in a curved
line, either right or left, the curve rapidly increasing towards the end
of the range. This most probably occurs from the velocity of rotation
decreasing but slightly, compared with the initial velocity of the shot,
or, if a strong wind is blowing across the range during the whole time
of flight, the curve would manifestly be increased according as the
velocity of the ball decreased.
ILLUSTRATIONS OF ROBINS’ THEORY OF ROTATION.
~With ball and double string.~
1st Illustration. A wooden ball 4¹⁄₂ inches in diameter suspended by a
double string, nine feet long. It will be found that if this ball
receive a spinning motion by the untwisting of the string it will remain
stationary. If it be made to vibrate, it will continue to do so in the
same vertical plane. But if it be made to spin while it vibrates it will
be deflected to that side on which the whirl combines with the
progressive motion.
~By firing through screens.~
2nd Illustration. By firing through screens of thin paper placed
parallel to each other, at equal distances, the deflection or track of
bullets can easily be investigated. It will be found that the amount of
deflection is wholly disproportioned to the increased distance of the
screens.
~Bent muzzle.~
3rd Illustration. To give further light upon this subject, Mr. Robins
took a barrel and bent it at about three or four inches from the muzzle
to the left, the bend making an angle of 3° or 4° with the axis of the
piece.
By firing at screens it was found that although the ball passed through
the first screens to the left, it struck the butt to the right of the
vertical plane on which aim was taken in line of the axis of the unbent
portion of the barrel. This was caused by the friction of the ball on
the right side of the bent part of the muzzle, causing the ball to spin
from left to right.
ON ECCENTRIC PROJECTILES.
~How to find centre of gravity.~
Sir Howard Douglas, in his “Naval Gunnery,” states:--“The position of
the centre of gravity can be found by floating the projectile in
mercury, and marking its vertex. Then mark a point upon the shot
diametrically opposite to that point, which will give the direction of
the axis in which the two centres lie. Thus the shot can be placed in
the gun with its centre of gravity in any desired position.”
~Effect of eccentricity.~
“On making experiments, it appeared that not one shot in a hundred, when
floated in mercury, was indifferent as to the position in which it was
so floated, but turned immediately, until the centre of gravity arrived
at the lowest point, and consequently that not one shot in a hundred was
perfect in sphericity, and homogeneity. Shells can be made eccentric by
being cast with a solid segment in the interior sphere, left in the
shell, or by boring two holes in each shell, diametrically opposite to
one another, stopping up one with 5lbs. of lead, and the other with
wood. When the centre of gravity was above the centre of the figure, the
ranges were the longest, and when below, the shortest. When to the right
or left hand, the deviations were also to the right or left. The mean
range which, with the usual shot, was 1640 yards, was, with the shot
whose centres of gravity and of figure were not coincident, the centre
of gravity being upwards, equal to 2140 yards, being an increase of 500
yards.
~Ricochet of eccentric shot.~
“With respect to the ricochet of eccentric spherical projectiles, the
rotation which causes deflection in the flight, must act in the same
manner to impede a straight forward graze. When an ordinary well formed
homogenous spherical projectile, upon which probably very little
rotation is impressed, makes a graze, the bottom of the vertical
diameter first touches the plane, and immediately acquires, by the
reaction, a rotation upon its horizontal axis, by which the shot rolls
onwards throughout the graze, probably for a straight forward second
flight. But in the case of an eccentric spherical projectile, placed
with its centre of gravity to the right or to the left, its rotation
upon its vertical axis during the graze must occasion a fresh deflection
in its second flight, and it is only when the centre of gravity is
placed in a vertical plane passing through the axis of the gun, that the
rotation by touching the ground will not disturb the direction of the
graze, though the extent of range to the first graze will be affected
more or less according as the centre of gravity may have been placed
upwards or downwards. Whether the rebounds take place from water, as in
the experiments made on board the “Excellent,” or on land, as those
carried on at Shoeburyness, the shot, when revolving on a vertical axis,
instead of making a straight forward graze, suffered deflection which
were invariably towards the same side of the line of fire as the centre
of gravity; and at every graze up to the fourth, a new deflection took
place.
~Knowledge derived from experiments with eccentric shot.~
“The results of these very curious and instructive experiments fully
explain the extraordinary anomalies, as they have heretofore been
considered, in length of range and in the lateral deviations: these have
been attributed to changes in the state of the air, or the direction of
the wind, to differences in the strength of the gunpowder, and to
inequalities in the degrees of windage. All these causes are, no doubt,
productive of errors in practice, but it is now clear that those errors
are chiefly occasioned by the eccentricity and nonhomogeneity of the
shot, and the accidental positions of the centre of gravity of the
projectile with respect to the axis of the bore. The whole of these
experiments furnish decisive proof of the necessity of paying the most
scrupulous attention to the figure and homogeneity of solid shot, and
concentricity of shells, and they exhibit the remarkable fact that a
very considerable increase of range may be obtained without an increase
in the charge, or elevation of the gun.”
~No advantage in using eccentric projectiles.~
It is not to be expected that eccentric projectiles would be applicable
for general purposes, on account of the degree of attention and care
required in their service, nor would much advantage be gained by their
use, as the momentum is not altered, and it is only necessary to give
the ordinary shot a little more elevation in order to strike the same
object.
~Range of elongated projectiles at certain low elevations greater in
air than in vacuo.~
There is another point of great importance with regard to the range of
elongated projectiles. It is asserted by Sir W. Armstrong and others,
that at certain low elevations the range of an elongated projectile is
greater in the atmosphere than in vacuo, and the following is the
explanation given by the former of this apparent paradox. “In a vacuum,
the trajectory would be the same, whether the projectile were elongated
or spherical, so long as the angle of elevation, and the initial
velocity were constant; but the presence of a resisting atmosphere makes
this remarkable difference, that while it greatly shortens the range of
the round shot, it actually prolongs that of the elongated projectile,
provided the angle of elevation do not exceed a certain limit, which, in
my experiments, I have found to be about 6°. This appears, at first,
very paradoxical, but it may be easily explained. The elongated shot, if
properly formed, and having a sufficient rotation, retains the same
inclination to the horizontal plane throughout its flight, and
consequently acquires a continually increasing obliquity to the curve of
its flight. Now the effect of this obliquity is, that the projectile is
in a measure sustained upon the air, just as a kite is supported by the
current of air meeting the inclined surface, and the result is that its
descent is retarded, so that it has time to reach to a greater
distance.”
~Charge.~
The form and weight of the projectile being determined as well as the
inclination of the grooves, the charge can be so arranged as to give the
necessary initial velocity, and velocity of rotation; or if the nature
of projectile and charge be fixed, the inclination of the grooves must
be such as will give the required results. The most important
consideration is the weight and form of projectile; the inclination of
the grooves, the charge, weight of metal in the gun, &c., are regulated
almost entirely by it. The charges used with rifle pieces are much less
than those with which smooth-bored guns are fired, for little or none of
the gas is allowed to escape by windage, there being therefore no loss
of force; and it is found by experience that, with comparatively low
initial velocities, the elongated projectiles maintain their velocity,
and attain very long ranges.
NOTE.--The foregoing articles on “Theory,” are principally extracted
from “New Principles of Gunnery by Robins,” “Treatise on Artillery, by
Lieut.-Colonel Boxer, R.A.” “The Rifle Musket, by Captain Jervis,
M.P., Royal Artillery.” “Elementary Lecturers on Artillery, by Major
H. C. Owen and Captain T. Dames, Royal Artillery.”
THE END.
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Extended Table of Contents
Page
INTRODUCTION. i
CONTENTS iii
ERRATA. iv
HISTORY OF GUNPOWDER. 1
GREEK FIRE. 4
ON THE MANUFACTURE OF GUNPOWDER. 7
SALTPETRE, OR NITRE. 7
OLD METHOD. 7
NEW METHOD. 8
CHARCOAL. 9
SULPHUR. 11
PULVERIZING THE INGREDIENTS. 11
MIXING THE INGREDIENTS. 12
THE INCORPORATING MILL. 12
INCORPORATING THE INGREDIENTS. 13
BREAKING DOWN THE MILL CAKE. 14
PRESSING THE MEAL BY THE HYDRAULIC PRESS. 14
GRANULATING THE PRESS CAKE. 15
DUSTING LARGE-GRAIN POWDER. 16
DUSTING FINE-GRAIN POWDER. 17
GLAZING FINE-GRAIN POWDER. 17
STOVING OR DRYING POWDER. 17
FINISHING DUSTING. 17
EXAMINATION AND PROOF OF GUNPOWDER. 18
PROOF OF MERCHANT’S POWDER. 18
REMARKS ON THE PROOF OF POWDER BY THE EPROUVETTES. 19
OF THE SIZE OF GRAIN FOR GUNPOWDER. 19
OBSERVATIONS ON THE MANUFACTURE OF GUNPOWDER ON THE CONTINENT
AND AMERICA. 20
PRODUCTION AND PURIFICATION OF THE INGREDIENTS. 20
PULVERIZING AND MIXING THE INGREDIENTS. 20
INCORPORATING PROCESS. 21
GRANULATING. 21
STOVING OR DRYING. 21
NEW RIFLE POWDER. 22
ON MAGAZINES. 23
LIGHTNING CONDUCTORS. 24