But the same clause in the constitution which gives Congress the power of exclusive legislation over this District, also empowers it “to exercise like authority over all places purchased by the consent of the legislature of the state, in which the same shall be, for the erection of forts, magazines, arsenals, dock-yards, and other needful buildings.” If, then, Congress has any constitutional power to legalize slavery in this District, it has the same power to legalize it, (that is, to create it,) in all places in the state of Massachusetts, or New York, or any other, where it may have obtained territory from a state for a fort, magazine, arsenal, dock-yard, or other needful building. Where it has obtained land in the middle of a city,--Philadelphia, New York, Boston, or Chicago,--for a custom-house, it may create slavery there. The power to do this is conferred in precisely the same words as the power by which it has been held that slavery can be established in the District of Columbia. And now I will occupy the few minutes that are left me, in considering what seems to me the only plausible argument that can be urged in favor of the constitutionality of slavery in this District. It may be said, that when a territory is obtained by one nation from another, whether by conquest or by treaty, the laws which governed the inhabitants at the time of the conquest or cession, remain in force until they are abrogated by the laws of the conquering or purchasing power. For this principle, the authority of Lord Mansfield, in the case of _Campbell_ v. _Hall_, 1 Cowper, 208, may be cited. The decision of our own courts are to the same effect. (See _United States, appellant_, vs. _Juan Percheman_, 2 Gallison’s Reports, 501; _Johnson_ vs. _McIntosh_, 7 Peters, 51; 8 Wheat. 543.) I do not dispute the authority of this case. But it does not touch the question I am arguing; or, so far as it bears upon it at all, it confirms the views I would enforce. The principle is, that the existing laws remain in force _until_ they are abrogated. I agree to this. But in the case of the District of Columbia, there was a special agreement between Maryland and the United States, that as soon as the United States should legislate for the District, the laws of Maryland, _as such_, should cease to be operative here. On the 27th day of February, 1801, therefore, all the rights which the citizens of this District possessed, they possessed under the law of Congress, and not under the law of Maryland. On the day preceding, a citizen could have voted for governor or other state officers of Maryland; but on the day following, he could no longer vote for any such officer. On the day preceding, he could have voted for electors of President and Vice President of the United States; but on the day following, he was bereft of all such right of the elective franchise, and must accept such officers and legislators as the rest of the country might choose to elect for him. On the day