PROJECTILES. To accomplish the dam age or destruction of a target a projectile should have certain hardness, tenacity and weight. If it be soft and weak compared with the body struck, it will spread out laterally or break into pieces, and presenting an increased surface will meet with a greater resistance, and consequently will penetrate less than if it had retained its original form. High density gives to the mass the least possible volume, whereby the effect of the resistance offered by the air and by the body to he penetrated is diminished. - Different materials have been used for projectiles. Stone, lead, wrought-iron steel, cast-iron, and chilled iron possess peculiar properties which render each advantageous according to the object to be attained.
Prior to the invention of gunpowder, large masses of stone without regard to form were thrown from machines constructed for that purpose. This material was very generally em ployed until the year 1400; but its want of strength and density, qualities required in a projectile propelled by powder, necessitated its use in large masses and with comparatively small charges. Such projectiles were destruc tive against unbacked walls of masonry, but broke if ricocheted on earth. As late as 1807, stone balls of enormous calibre were used by the Turks in defending the passage of the Dardanelles.
Lead, as a material for projectiles, possesses the essential quality of density; but it is too soft to be used against very resisting objects, since it is flattened even against water. From its softness and fusibility, large projectiles of this material are liable to be dis figured, and partially melted, by the violent shock and great heat of large charges of powder. Its use is chiefly confined to small-arms and case-shot, which are generally di rected against animate objects. These defects of lead may be cor rected, in a measure, by alloying it with tin, antimony, etc. From the first introduction of cannon wrought iron projectiles have at different times been tried. This metal has
great density and tenacity, but has not a hard degree of hardness, can not be easily worked into the neces sary shapes, and where used in large masses becomes very expensive.
Steel possesses the qualities required in a pro jectile, but is very costly and difficult to manipu late.
The adoption of cast-iron for projectiles caused an important advance in artillery. It has great hardness, sufficient density and tenacity; is cheap, easy to mold, and can at slight cost be given exact forms. Recent improvements in the manufacture of this metal have so greatly increased the strength of projectiles made from it, that they can be used effectively against heavy armor. Cast iron, chilled by being cooled rapidly, has its hardness, crushing strength and density in creased. Projectiles so prepared are now employed with excellent results against the most powerful armor, and are found about as effective as those of steel and very much less costly. Compound projectiles, uniting the good and correcting the bad qualities of dif ferent metals, have sometimes been used Thus, at the siege of Cadiz, cast-iron shells filled with lead, forming projectiles of great strength and density, were thrown from mortars to a distance of three miles and three quarters.
Projectiles may be either spherical or elongated. Spherical projectiles are commonly used in smooth-bored cannon, and for this purpose have certain advantages over those of oblong form: (1) They touch the surface of the bore at only one point, and are therefore less liable to wedge in the bore and en danger the safety of the piece; (2) the cen tres of figure and inertia coincide; (3) the mass is embraced in the least possible colume; (4) as they turn over in their flight, the sur face presented to the resistance of the air is uniform and a minimum; (5) in ricocheting on land or water, their rebounds are more certain and regular, and less derivation occurs from the plane of fire.