Immediately after his return from France to Holland in April 1599, Grotius published his “Limeneuretica, sive Portuum investigandorum Ratio,” a treatise for the instruction of seamen in ascertaining the exact situation of a ship at sea. This work was merely a translation, and has been of course long since superseded by modern discoveries; but it is worthy of remark, as a proof of the extraordinary acquirements of a youth of sixteen, that he should have added to his critical and scholastic knowledge so competent an acquaintance with magnetism and practical navigation as the translation of such a work implies. In the course of the same year he enrolled himself on the list of Advocates at the Hague, and before he was eighteen years of age commenced the actual practice of his profession. In this occupation he was eminently successful, though he always disliked it, and lamented the time which it claimed from more congenial pursuits. His reputation and practice, however, daily increased, until in the year 1607, being recommended by the suffrages of the courts, and nominated by the States of Holland, Prince Maurice conferred upon him the important and responsible office of Advocate-General of the provinces of Holland and Zealand. Soon after this appointment, he married Mary Reygersburgh, the daughter of an opulent family in Zealand, with whom he lived in the most complete harmony. In the year 1608, while he held the office of Advocate-General, Grotius composed his ‘Mare Liberum,’ the general design of which was to show, upon the principles of the law of nations, that the sea was open to all without distinction, and to assert the right of the Dutch States to trade to the Indian seas, notwithstanding the claim of the Portuguese to an exclusive title to that commerce. This tract was published without the consent of Grotius; and at a subsequent period of his life he expressed his disapprobation of it. “My intention,” he says, “was good; but the work savours too much of my want of years.” Many years afterwards, Selden published his profound work on maritime rights, entitled ‘Mare Clausum,’ in which he incidentally notices this treatise of Grotius with much respect, though he advocates a contrary doctrine. Soon after the appearance of his ‘Mare Liberum,’ Grotius published a ‘Dissertation on the Antiquity of the Batavian Republic,’ for which he received the thanks of the States of Holland, accompanied by a present.