"If, then, this contract had an eye to the State of Virginia for its operation and effect, the _lex loci_ ceases to operate. In that case it must, to have its effect, conform to the laws of Virginia. It is insufficient under those laws to effectuate an emancipation, for want of a due recording in the county court, as was decided in the case of Givens _v._ Mann, in this court. It is also ineffectual within the Commonwealth of Virginia for another reason. The _lex loci_ is also to be taken subject to the exception, that it is not to be enforced in another country, when it violates some moral duty or the policy of that country, or is not consistent with a positive right secured to a third person or party by the laws of that country in which it is sought to be enforced. In such a case we are told, '_magis jus nostrum, quam jus alienum servemus_.'" (Huberus, tom. 2, lib. 1, tit. 3; 2 Fontblanque, p. 444.) "That third party in this instance is the Commonwealth of Virginia, and her policy and interests are also to be attended to. These turn the scale against the _lex loci_ in the present instance." The second or last-mentioned position assumed for the plaintiff under the pleas in bar, as it rests mainly if not solely upon the provision of the act of Congress of March 6, 1820, prohibiting slavery in Upper Louisiana north of thirty-six degrees thirty minutes north latitude, popularly called the _Missouri Compromise_, that assumption renews the question, formerly so zealously debated, as to the validity of the provision in the act of Congress, and upon the constitutional competency of Congress to establish it. Before proceeding, however, to examine the validity of the prohibitory provision of the law, it may, so far as the rights involved in this cause are concerned, be remarked, that conceding to that provision the validity of a legitimate exercise of power, still this concession could by no rational interpretation imply the slightest authority for its operation beyond the territorial limits comprised within its terms; much less could there be inferred from it a power to destroy or in any degree to control rights, either of person or property, entirely within the bounds of a distinct and independent sovereignty--rights invested and fortified by the guaranty of that sovereignty. These surely would remain in all their integrity, whatever effect might be ascribed to the prohibition within the limits defined by its language.