The lighthouse on Middle Bay Island, within the bar of Charleston Harbor, has been ceded to the United States and is bounded to the north by a small inlet passing between said island and Morris Island; to the south, by an inlet called Folly Inlet; to the east, by the Atlantic Ocean; and to the west, by a sound or creek passing between the said Middle Bay Island and the other island aforesaid; together with the lands and tenements thereunto belonging and together with the jurisdiction of said island as far as such jurisdiction shall be incident and essential for the erection of forts, magazines, arsenals, dockyards and other needful buildings, the appointment of officers and the general regulation of the lighthouse, forts, magazines, arsenals and dockyards, in fee simple in as full, ample and effectual manner as the premises could be granted, aliened, transferred, conveyed and confirmed by any deed or devise in due form of law. But said island was so ceded upon the special proviso and condition, nevertheless, that the United States shall sufficiently support, maintain, keep in good repair and rebuild, when necessary, the lighthouse, from time to time and at all times hereafter and shall also erect, or cause to be erected, proper leading marks to and for, or as appending to, the lighthouse and cause buoys to be stationed in fit places for further and better facilitating and securing the navigation and that all expenses which shall accrue in, for and about the lighthouse or the leading marks and buoys above mentioned shall be defrayed out of the treasury of the United States.