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.”

“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. Effect of eccentricity.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.

PLATE 1.

FIG. 1.

Powder Mill.

FIG. 2.

Old Eprouvette Pendulum

FIG. 3.

New Pattern Eprouvette

Harry Vernon delt.

Day & Son Lith^rs. to the Queen.

PLATE 2.

Enlarged section of Valve

Hydraulic Press

Harry Vernon delt.

Day & Son Lith^rs. to the Queen.

PLATE 3.

Robins’ Balistic Pendulum

Harry Vernon delt.

Day & Son Lith^rs. to the Queen.

PLATE 4.

FIG. 1.

Bow unstrung

FIG. 2.

Bow strung

FIG. 3.

Hand or Arrow Rocket

FIG. 4.

Five barrelled Matchlock

FIG. 5.

Revolving Barrelled Matchlock

CHINESE EXPLOSIVE AND OTHER WEAPONS.

FIG. 6.

Asiatic Bow

Harry Vernon delt.

Day & Son Lith^rs. to the Queen

PLATE 5.

FIG. 1.

Matchlock

FIG. 2.

Breech loading Gingal (Chamber in)

FIG. 3.

Breech loading Gingal (Chamber out)

CHINESE EXPLOSIVE ARMS.

Harry Vernon delt.

Day & Son Lith^rs. to the Queen.

PLATE 6.

FIG. 1.

FIG. 2.

FIG. 3.

FIG. 4.

Harry Vernon dele.

MACHINES FOR THROWING DARTS AND STONES.

Day & Son Lith^rs. to the Queen.

PLATE 7.

ONAGER (SLUNG).

Harry Vernon delt.

Day & Son, Lith^rs. to the Queen.

PLATE 8.

Onager (unslung).

Harry Vernon delt.

Day & Son Lith^rs. to the Queen.

[Larger illustration]

PLATE 9.

Balista

Arthur Walker C.^t 79.^th delt.

Day & Son Lith^rs. to the Queen.

PLATE 10.

Catapulta.

Dessiné par Arthur Walker.

Day & Son Lith^rs. to the Queen.

PLATE 11.

FIG. 1.

Staff slings, Longbows, Crossbows and Flail.

FIG. 2.

Onager.

FIG. 3.

Trepied.

Harry Vernon delt.

Day & Son Lith^rs. to the Queen.

PLATE 12.

Detail of Springs.

Balista.

Harry Vernon Staff Serj^t. del.

Day & Son Lith^rs. to the Queen.

PLATE 13.

FIG. 1. FIG. 2.

A Cross bow man and Slinger.

FIG. 3.

Harry Vernon delt.

Day & Son Lith^rs. to the Queen.

PLATE 14.

FIG. 1.

FIG. 2.

FIG. 3.

FIG. 4.

Cross-bows and Quarrels.

Harry Vernon delt.

Day & Son Lith^rs. to the Queen.

[Larger Fig. 1.]
[Larger Fig. 3.]

PLATE 15.

Harry Vernon delt.

A Cross bow man and his Paviser.

Day & Son Lith^rs. to the Queen.

PLATE 16.

FIG. 1.

Gun and Querrel Temp:
Edward 3^rd. Sloane M^ss.

FIG. 2.

Small chambered Cannon
from the Santini M^ss.

FIG. 3.

Santini M^ss.
Early part of 15^th Cent^y.

FIG. 4.

Mode of mounting
from Froissart.

FIG. 5.

Method of obtaining elevation.

FIG. 6.

Mode of Mounting
from Valturius.

FIG. 7.

From the wreck of the “Mary Rose” Temp: Henry 8^th.

FIG. 8.

Hooped Cannon in wooden bed.

FIG. 9.

Ancient Screw piece.

FIG. 10.

Ancient Screw Breech loader.

FIG. 11.

Chinese Field piece Peiho 1860.

FIG. 12.

Ancient howitzer Cannon for
throwing balls Filled with powder

Arthur Walker delt.

Day & Son Lith^rs. to the Queen.

PLATE 17.

FIG. 1.

Giorgio Martini, 15^th. Century, latter part.

FIG. 2.

Queen Elizabeth’s Pocket Pistol.

Mons Meg.

Chamber. Pierrier or Paterera__16^th. Century.

H. Cautly del.

Day & Son Lith^rs. to the Queen.

PLATE 18.

FIG. 1.

Cart of War.__Temp: Henry 8^th.

FIG. 2.

“Moolik i Meidan.”

FIG. 3.

Bombard and Carriage.__15^th. Cent^y.

FIG. 4.

Long Serpentine of Wrought Iron.__15^th. Cent^y.

R.G. Coles del.^t

Day & Son Lith^rs. to the Queen.

PLATE 19.

FIG. 1.

FIG. 2.

FIG. 7.	FIG. 11.	FIG. 12.	FIG. 3.	FIG. 4.	FIG. 5.	FIG. 8.
			FIG. 6.

[Larger Figs. 3-8, 11, 12]

FIG. 9.

Musketeer 16^th. Cent^y.

FIG. 10.

Earliest form of Hand Gun.

Arthur Walker, delt.

Day & Son Lith^rs. to the Queen.

PLATE 20.

14	15	16	18	19
		17

Day & Son Lith^rs. to the Queen.

[Larger Figs. 1-19]

PLATE 21.

FIG. 1.

FIG. 2.

FIG. 3.

FIG. 4.

FIG. 5.

Arthur Walker del.

Day & Son Lith^rs. to the Queen.

[Larger Figs. 1-5]

PLATE 22.

FIG. 1.

FIG. 2.

FIG. 3.

FIG. 4.

Arthur Walker L^t. 79^th. del.

Day & Son Lith^rs. to the Queen.

[Larger Figs. 1-4]

PLATE 23.

FIG. 1.

FIG. 2.

FIG. 3.

FIG. 4.

FIG. 5.

FIG. 6.

Harry Vernon Staff Serj^t. del.

Day & Son Lith^rs. to the Queen.

[Larger Figs. 1-6]