Courts of equity grant relief by injunction in those cases in which, but for their interposition, an equitable right would be infringed. In such cases courts of law can afford no remedy, for they cannot adjudicate upon an equity, and are powerless to prevent an invasion of it. Where then the rights of a party are wholly equitable in their nature, he can find no redress in the common law tribunals; but the mere existence of an equitable element in a suit being regarded by these courts as no bar to their procedure, they take jurisdiction, and, in deciding upon the legal merits of the case, must sometimes disregard the equity, because its recognition does not lie within their competence as courts of law. In such cases as these a court of equity, in the exercise of its distinctive jurisdiction, will interpose by injunction to protect the equity. This protection consists in restraining in behalf of the plaintiff the commission or continuance of some act of the defendant. An injunction is defined to be a writ, framed according to the circumstances of the case, commanding an act which the court regards as essential to justice, or restraining an act which it esteems contrary to equity and good conscience.

As examples of those cases where relief is afforded to rights which either are wholly equitable, or under the circumstances of the case are incapable of being asserted in courts of law, may be cited instances in which trustees are enjoined from using their legal title to oust the possession of those who are equitably entitled to the benefit and enjoyment of the trust estate; so tenants for life or mort-gageors in possession, who are not punishable at law for committing waste, will be enjoined in equity from doing so; and again, mortgage-ors in possession, though in some sense owners of the mortgaged estate, will yet be restrained by injunction from so reducing its value as to impair the security of the mortgagee. The administration and marshalling of assets, and the marshalling of securities, furnish other illustrations of the interposition of courts of equity by injunction to control the proceedings of creditors and others at law, and upon principles almost purely of an equitable nature. - A second class of cases includes those in which an equitable element is involved, but the matter of which otherwise is cognizable at law. If in such cases the courts of law have already taken jurisdiction, a court of equity will in a proper case restrain their further procedure.

Thus, when fraud, accident, or mistake has given one party to the suit an unfair advantage over his opponent, an equity arises in favor of the latter which will be protected by injunction. For example, if after judgment against the defendant at law a receipt is found, showing the payment of the very debt upon which he has been condemned, if there be no remedy in such a case at law, equity will enjoin, and so prevent, the execution of the judgment. Equity will also sometimes relieve against torts. The ground of interference here is, that between the complete right of the plaintiff and the largest remedy which he can receive at law for the wrong done him, there lies an equity which is not protected; this may rest either in the inadequacy of the money compensation which the plaintiff recovers, or in his right to be exempted from vexatious litigation. The equity jurisdiction in these cases is most frequently exercised in respect to waste, nuisances, and infringements of patent rights and of copyrights. The remedies at law in all these cases are similar.

To cite alone that of nuisances, they can at most only abate or afford compensation for existing nuisances, but are ineffectual to prevent such as are threatened or in progress; if, however, the complainant's right be clearly admitted or established at law, and the nature of the threatened injury be such that it cannot be compensated by damages, or will occasion a constantly recurring grievance, equity has jurisdiction to enjoin. Further, as examples of the equitable relief afforded by injunction, it may be mentioned that courts of equity will restrain the unjust conveyance of real property or the transfer of stocks during the pendency of suits which concern them; they will forbid the publication of private papers, letters, or manuscripts; they will enjoin a husband's transfer of property in fraud of the legal or equitable rights of the wife; and will compel the due observance of personal covenants where there is no effectual remedy at law. - In the cases thus reviewed, the court of equity issues the injunction by its remedial writ. The judicial writ is in the nature of an execution, and issues subsequently to a decree of the court.

Injunctions may be either temporary, when they are granted for a limited time, or until the filing of the defendant's answer, or the hearing of the court; or perpetual, when in the opinion of the court, after a hearing of the merits of the case, the plaintiff has established his right to such relief.