If for a time international intercourse follows certain methods, these methods are regarded as binding in later intercourse, and departure from this procedure is held a violation of international right. That collection of customs known as "The Law Merchant" is an example of a source of this class. Of this it has been said, "Gradually, the usages of merchants hardened into a cosmopolitan law, often at positive variance with the principles of local law, but none the less acquiesced in for mercantile transactions, and enforced by tribunals of commanding eminence and world-wide reputation, such as the courts of the Hanseatic League and the Parloir aux Bourgeois at Paris."[42]
Sir W. Scott, in the case of the "Santa Cruz," 1798, said "Courts of Admiralty have a law and a usage on which they proceed, from habit and ancient practice."[43]
[§ 15. Precedent and Decisions]
The domestic courts of those states within the family of nations, may by their decisions furnish precedents which become the basis of international practice.
(a) Prize and Admiralty courts decisions form in themselves a large body of law. Jurisdiction in admiralty and maritime causes in the United States rests in the District Courts, the Circuit Courts, and the Supreme Court. The District Courts have original jurisdiction in civil causes of admiralty and concurrent jurisdiction with the Circuit and State Courts in suit of an alien, because of violation of international law or treaty of United States. The District Court also has full prize court powers. Appeals from prize courts decisions go directly to the Supreme Court for final judgment; appeals from admiralty decisions go to the Circuit Court for final judgment.[44] The prize courts of other powers vary in jurisdiction, nature, and procedure. British and American courts rely more particularly upon precedents, while the Continental courts follow more distinctly the general principles laid down in codes and text writers, and place less reliance upon previous interpretation of these principles as shown in court decisions.[45] Whatever the method of the prize court, its decision, if legally rendered, stands as valid in all states.[46]
(b) The decisions of domestic courts upon such matters as extradition,[47] diplomatic privileges, piracy, etc., tend to become a source of international law. In the United States the Supreme Court has original jurisdiction "in all cases affecting ambassadors, other public ministers, and consuls."[48]
(c) The decisions of courts of arbitration and other mixed courts are usually upon broad principles. Some of the principles involved may become established precedents, yet the tendency to render a decision, which by a compromise may be measurably acceptable to both parties, may lessen the value of the decision as a precedent. As arbitration is of necessity voluntary, there is generally a consensus upon certain points, even though the decision rendered may not become a precedent. The growth of the practice of arbitration of disputes is an indication of the general recognition of mutual confidence between states. The principles upon which the court of arbitration bases its decision, rather than the decision itself, furnish material valuable for international law.
[§ 16. Treaties and State Papers]
Treaties and state papers of whatever form[49] indicate the state of opinion, at a given time, in regard to the matters of which they speak. Since they are binding upon the parties to them, treaties may be regarded as evidence of what the states, bound by their terms, accept as law. When the same terms are generally accepted among nations, treaties become a valuable evidence of concrete facts of practice and proper sources of international law. The principles may be so well established by successive treaties as to need no further treaty specification. Treaties and state papers vary greatly in value as sources of international law, however.
(a) Treaties and state papers may lay down new rules or outline the operation of old rules. As instances of those laying down new rules may be taken the Clayton-Bulwer Treaty of April 19, 1850, the convention for the protection of Submarine Cables, March 14, 1884, the Geneva Convention of 1864; of those outlining and determining the operation of old rules, there are many instances, the most numerous in the treaties in regard to maritime affairs and consuls.