The principle, however, upon which the commissioner of the United States defended his claim to attach such an extent of country to the discovery of Captain Gray, was, that it was at once _reasonable_ and _moderate_; reasonable, because there must be some rule for determining the local extent of a discovery, and none was more proper than taking the water-courses which nature had laid down, both as the fair limits of the country, and as indispensable to its use and value; moderate, because the natives of Europe had often, under their rights of discovery, carried their claims much further. As to the reasonableness of the rule, if Mr. Rush meant that rivers were the natural and most convenient boundaries of territories, this proposition would command a ready assent: but the result of the principle which he set up as to the extent of the discovery, would be to make the high-lands, and not the water-courses, the territorial limits. In respect, however, to the moderation of the principle, when the magnitude of the great rivers of America, the Amazons for example, or the Mississippi, is taken into consideration, the absolute moderation of the rule would be questionable. But its moderation was insisted upon in comparison with the extensive grants of the European sovereigns. The comparative moderation, however, of a principle will not be sufficient to give it validity as a principle of international law, if it should be not in accordance with the practice of nations.
But Mr. Monroe, under whose administration as President of the United States this principle was advanced by Mr. Rush, had, in the negotiations which he, in conjunction with Mr. Pinckney, carried on in 1805 with Spain, propounded a very different principle, viz.: "that whenever any European nation _takes possession of any extent of sea coast_, that possession is understood as extending into the interior country, to the sources of the rivers emptying within that coast, to all their branches, and the country they cover, and to give it a right in exclusion of all other nations to the same."
Now Vattel (i., § 266) observes,--"When a nation takes possession of a country, with a view to settle there, it takes possession of everything included in it, as lands, lakes, rivers, &c."
