owes to him the duty of diligence, prudence, and skill, which, as carrying on a public employment, he owes to all his passengers;' and that he cannot escape.liability for a negligent performance of that duty resulting in injury by urging that- the pass or • commission was issued, or the gratuitous passage permitted, by him, in violation of law.” As authority for this proposition the court cited Carroll v. Staten Island R. R. Co., 58 N. Y. 126; Del., Lack. & Western R. R. Co. v., Trautwein, 52 N. J. Law, 169; 7 L. R. A. 435; 5.Am. & Eng. Encyc. Law (2d ed.), 508, and other authorities.
It is plain that the decision adverse to the plaintiff in error was upon two independent grounds, the second ground being avowedly based upon the hypothesis that the court might be wrong,in its decision upon the'first.
Whether the Hepburn Act prohibits a carrier from giving free interstate transportation to the employés of the' Railway Mail Service when they are not on duty but are traveling for their own benefit or pleasure, is of course, a Federal question.
But whether — -assuming that question to be answered in the affirmative — the relation of carrier and passenger arises in the case of gratuitous passage under circumstances such as are presented in this case, is (in the absence of an act of Congress regulating the matter) a question not of Federal but of state law.
It is settled by numerous decisions of this court that where the' decision in the state court adverse to the plaintiff in error proceeds upon two independent grounds, one of which) not involving a Federal question, is sufficient to sustain the judgment, the writ of error will be dismissed or the judgmént affirmed, according to circumstances. Murdock v. City of Memphis, 20 Wall. 590, 635, 636; De Saussure v. Gaillard, 127 U. S. 216, 234; Hale v. Akers, 132 U. S. 554, 565; Hopkins v. McLure, 133 U. S. 380; Johnson v. Risk, 137 U. S. 300; Beaupre v. Noyes,