Reference: John Bouvier, A Law Dictionary Adapted to the Constitution and Laws of the United States of America and the Several States of the American Union, Childs & Peterson, c1856.)
RES NULLIUS. A thing which has no owner. A thing which has been abandoned by its owner is as much res nullius as if it had never belonged to any one.
(The first possessor of such a thing becomes the owner, res nullius fit primi occupantis. Bowy. Com. 97.