“This main sea begins at the low-water-mark. But between the high-water-mark and the low-water-mark, where the sea ebbs and flows, the common law and admiralty have divisum imperium, an alternate jurisdiction; one upon the water, when it is full sea; the other upon the land, when it is an ebb.” 1 William Blackstone, Commentaries on the Laws of England 107 (1765).
divisum imperium
divisum imperium (di-vI-z[schwa]m im-peer-ee-[schwa]m), n. [Latin “a divided empire”] Divided jurisdiction; alternate jurisdiction, as of courts.
