ACTION. In law, the formal demand of one's right from another person, made and in sisted in a court of justice which has jurisdic tion of the person and the subject-matter of litigation. In a quite common sense, action includes all the formal proceedings in a court of justice attendant upon the demand of a right made by one person, or party, of another in such court, including an adjudication upon the right, and its enforcement or denial by the court.
The parties to an action are called plaintiff and defendant, and the former is said to sue or prosecute the latter, hence the word suit instead of action. In some few instances the redress sought by a civil action consists in the recovery of some specific article of property wrongfully and unlawfully taken by the defendant from the plaintiff, but most frequently the object of an action is to obtain compensation in money for an injury complained of, which compensa tion is technically called damages.
The action is said to terminate properly at judgment.
Civil actions are those actions which have for their object the recovery of private rights, or of damages for their infraction.
Criminal actions are those actions prose cuted in a court of justice, in the name of the government, against one or more persons ac cused of a crime.
Transitory actions are those civil actions the cause of which might have arisen in one place or county as well as another.
Local actions are those civil actions the cause of which could have arisen in some particular place or county only.
Personal actions are those civil actions which are brought for the recovery of personal prop erty, for the enforcement of some contract or to recover damages for the commission of an injury to the person or property.
Real actions are those brought for the re covery of lands, tenements and hereditaments. Mixed actions are those which partake of the nature of both real and personal actions.
In higher theoretical mechanics the word °action° is used to signify the value of a cer tain integral, whose form may vary according to the character of the problem in In the case of a single particle the action is the space integral of the momentum of the particle, or it is double the time integral of its kinetic energy.
In a system of such particles the total action is the sum of the actions of the constituent parti cles. It is probable that the physical principle corresponding to the mathematical expression called °action" will some day be exhibited to us in a simple form; but up to the present time no mathematician or physicist has succeed ed in doing this. The importance of °action" as a mathematical conception may be seen from the following theorem, which has long been known: °If the sum of the potential and kinetic energies of a system is the same in all its configurations, then, of all the sets of paths by which the parts of the system can be guided by frictionless constraint to pass from one given configuration to another, that one for which the action is least is the natural one, and requires no restraint." The theorem just stated is known as Maupertuis' "principle of least action." There is also a principle of stationary action, and one of varying action; but it is impossible to eluci date these without a prohibitive amount of mathematics. The last two principles were formulated by Sir William Rowan Hamilton.
In theoretical mechanics the word gac tion," is also used to signify a force acting upon a body, as in the expression °action and reaction." See FORCE; MOTION, LAW OF.
In applied mechanics the mechanism by which some operation is effected in a machine is often called the action of the machine; thus we speak of the action of a gun, meaning the mechanism governing the loading and firing of the gun or of the action of a piano, mean ing the combination of keys, hammers and other parts, by which the player causes the strings of the instrument to vibrate.
Consult Holmes, 'The Common Law' • Pol lock and Maitland, 'English Law' ; and Sohm, 'Institutes of Roman Law' (2d ed., 1901).