The ordinary form of “gun” is shown by fig. 6. The knob at the right-hand side of the cut is called the “button,” the next division the “vent field,” beyond this to the rim the “first reinforce,” further on, the “second reinforce,” from which a cylindrical bar projects on each side for attaching the gun to the carriage, called “trunnions.” Beyond this to the next rim is called the “chace,” and beyond this again to the end the “muzzle.” Guns are chiefly used to throw solid round shot of cast-iron, accurately turned to a sphere, and the weight of these determines the character of the gun, as a thirty-two pounder, &c., the words “heavy” and “light” designating the thickness and consequent weight of the metal composing it. There is a smaller and shorter kind of gun, called a “carronade,” which is held to the carriage by a projection underneath, having a hole for a bolt to secure it, instead of trunnions. Another kind of gun, called a “howitzer,” is of shorter proportions than the ordinary gun and larger in the bore; it is chiefly intended to throw shells at a slight elevation. The mortar is still shorter, and of much thicker metal; it is held to a sort of platform by trunnions at its extreme end, and is intended to throw shells to great distances, and at a great elevation. Illustration: FIG. 7. SHELL CASTING. Illustration: BULLET-CASTING, WOOLWICH ARSENAL. Illustration: FIG. 8. (‡ BULLET MOULD.) Illustration: FIG. 9. (‡ BULLETS.) Illustration: FIG. 10. (‡ NIPPERS.) Illustration: PREPARING LEAD FOR BULLETS.