The famous river Thames owes part of its stream, as well as its appellation, to the Isis; rising a little above Winchelcomb, and being increased with several rivulets, unites both its waters and its name to the Thame, on the other side of Oxford; thence, after passing by London, and being of the utmost utility, from its greatness and navigation, it opens into a vast arm of the sea, from whence the tide, according to Gemma Frisius, flows and ebbs to the distance of eighty miles, twice in twenty-five hours, and, according to Polydore Vergil, above sixty miles twice in twenty-four hours.