When, in 1858, the Admiral reached the allotted term of three-score years and ten, yet in perfect health, he executed his resolution of resigning to younger men the posts he held in the active scientific world, and concentrated his attention, at his quiet and literary retreat of St. John's Lodge, near Aylesbury, on reducing for the press the vast amount of professional as well as general information which he had amassed during a long, active, and earnest life: the material for this "Digest" outstanding as the last, largest, and most important part of it. Had he survived but a few months more, a preface in his own terse and peculiar style, containing his last ideas, would have rendered these remarks unnecessary; but he was cut off on the 8th of September, 1865, leaving this favourite manuscript to the affectionate care of his family and friends. By them it has been most carefully revised; and is now presented to the public, especially to his honoured profession, for the benefit of which he thought and worked during the long period which elapsed between his leaving the quarter-deck and his death; as his Charts (constructed from his numerous surveys), his twenty years' Essays in the _United Service Journal_, his efforts to render his astronomical researches accessible to seamen,--all testify. Admiral Smyth was what has been called a _commonplacer_. He had the habit of methodically storing up, through a long series of years, all that could profit the seaman, whether scientific or practical. A collector of coins, and in various ways an antiquary, he knew well, not merely that "many mickles make a muckle," but that it will sometimes chance that the turning up of one little thing makes another little thing into a great one. And he culled from the intelligent friends with whom he associated many points of critical definition which cannot be found elsewhere. Thus, in addition to naval terms, he has introduced others relating to fortification; to ancient and modern arms and armour; to objects of natural history occurring at sea, in travel, &c.: the whole forming such an assemblage of interesting and instructive matter as will prove valuable to both seaman and landsman.