NOTE.--The preceding articles on the Rifle, Rifling, and Rifle Projectiles are mainly compiled from: “New Principles of Gunnery, by Robins,” “Scloppetaria,” “Remarks on National Defence, by Col. the Hon. A. Gordon,” “Dean’s Manual of Fire Arms,” “Rifle Ammunition, by Capt. A. Hawes,” “Rifles and Rifle Practice, by C. M. Wilcox,” “Papers on Mechanical Subjects, by Whitworth,” “The Rifle Musket, by Capt. Jarvis, Royal Artillery,” “Des Armes Rayees, by H. Mangeot,” “Cours Elementaire sur les Armes Portatives, by F. Gillion,” and “Cours sur les Armes a feu Portatives, by L. Panot.” THEORETICAL PRINCIPLES. DEFINITIONS. ~Matter.~ Matter,--everything which has weight. ~Body.~ Body,--a portion of matter limited in every direction. ~Mass.~ Mass,--the quantity of matter in any body. ~Particle.~ Particle,--or material point, is a body of evanescent magnitude, and bodies of finite magnitude are said to be made up of an indefinite number of particles, or material points. ~Inertia.~ Inertia,--passiveness or inactivity. ~Attraction.~ Attraction,--a fundamental law of nature, that every particle of matter has a tendency to be attracted towards another particle. ~Density.~ Density,--is in proportion to the closeness of the particles to each other. ~Volume.~ Volume,--the space bounded by the exterior surface of a body, is its apparent volume or size. ~Elasticity.~ Elasticity,--a body that yields to pressure, and recovers its figure again; hence air and gasses are elastic bodies; lead a non-elastic body. ~Motion.~ Motion,--is the changing of place, or the opposite to a state of rest. ~Velocity.~ Velocity,--is the rate of motion; there are four rates of motion, viz., Uniform, Variable, Accelerated, and Retarded. ~1st. Uniform.~ 1st. Uniform,--when a particle traverses equal distances, in any equal successive portion of time. ~2nd. Variable.~ 2nd. Variable,--when the spaces passed over in equal times, are unequal. ~3rd. Accelerated.~ 3rd. Accelerated,--when the distances traversed in equal times are successively greater and greater. ~4th. Retarded.~ 4th. Retarded,--when the distances traversed in equal times are successively less and less. Acceleration or Retardation, may also be equal or unequal, that is uniform or variable. ~Friction.~ Friction,--arises from the irregularities of the surfaces which act upon one another. ~Force.~ Force,--any cause which produces, or tends to produce a change in the state of rest, or of motion of a particle of matter. ~Measure of force.~ Forces are measured by comparison with weights. Thus any forces which will bend a spring into the same positions as weights of 1lb., 2lbs., 3lbs., &c., are called respectively forces of 1lb., 2lbs., 3lbs., &c., &c. ~Momentum.~