624, or in the large edition Section 1677.] The nature of the cause frequently prescribes the rule of competency.
Thus all the questions which concern maritime commerce evidently fall under the cognizance of the Federal tribunals.

*g Almost all these questions are connected with the interpretation of the law of nations, and in this respect they essentially interest the Union in relation to foreign powers.

Moreover, as the sea is not included within the limits of any peculiar jurisdiction, the national courts can only hear causes which originate in maritime affairs.
[Footnote g: As for instance, all cases of piracy.] The Constitution comprises under one head almost all the cases which by their very nature come within the limits of the Federal courts.

The rule which it lays down is simple, but pregnant with an entire system of ideas, and with a vast multitude of facts.

It declares that the judicial power of the Supreme Court shall extend to all cases in law and equity arising under the laws of the United States.
Two examples will put the intention of the legislator in the clearest light: The Constitution prohibits the States from making laws on the value and circulation of money: If, notwithstanding this prohibition, a State passes a law of this kind, with which the interested parties refuse to comply because it is contrary to the Constitution, the case must come before a Federal court, because it arises under the laws of the United States.