“Where the act uses the word ‘piratical,’ it does so in a general sense; importing that the aggression is unauthorized by the law of nations, hostile in its character, wanton and criminal in its commission, and utterly without any sanction from any public authority or sovereign power. In short, it means that the act belongs to the class of offenses which pirates are in the habit of perpetrating, whether they do it for purposes of plunder, or for purposes of hatred, revenge, or wanton abuse of power.” U. S. v. The Malek Adhel, 2 How. 232, 11 L. Ed. 239.