Numerous and deep harbors are a source of strength and wealth, and doubly so if they are the outlets of navigable streams, which facilitate the concentration in them of a country's internal trade; but by their very accessibility they become a source of weakness in war, if not properly defended. The Dutch in 1667 found little difficulty in ascending the Thames and burning a large fraction of the English navy within sight of London; whereas a few years later the combined fleets of England and France, when attempting a landing in Holland, were foiled by the difficulties of the coast as much as by the valor of the Dutch fleet. In 1778 the harbor of New York, and with it undisputed control of the Hudson River, would have been lost to the English, who were caught at disadvantage, but for the hesitancy of the French admiral. With that control, New England would have been restored to close and safe communication with New York, New Jersey, and Pennsylvania; and this blow, following so closely on Burgoyne's disaster of the year before, would probably have led the English to make an earlier peace. The Mississippi is a mighty source of wealth and strength to the United States; but the feeble defences of its mouth and the number of its subsidiary streams penetrating the country made it a weakness and source of disaster to the Southern Confederacy. And lastly, in 1814, the occupation of the Chesapeake and the destruction of Washington gave a sharp lesson of the dangers incurred through the noblest water-ways, if their approaches be undefended; a lesson recent enough to be easily recalled, but which, from the present appearance of the coast defences, seems to be yet more easily forgotten. Nor should it be thought that conditions have changed; circumstances and details of offence and defence have been modified, in these days as before, but the great conditions remain the same. Before and during the great Napoleonic wars, France had no port for ships-of-the-line east of Brest. How great the advantage to England, which in the same stretch has two great arsenals, at Plymouth and at Portsmouth, besides other harbors of refuge and supply. This defect of conformation has since been remedied by the works at Cherbourg.