General Cullum briefly describes the various bridge-systems employed in the different services of the world, including the galvanized iron boat system, the Blanchard metal cylinder system, the Russian and Fowke's systems of canvas stretched over frames, the Birigo system, the French _bateau_ system, the various trestle systems, and many others. The French wooden _bateau_ is the pontoon chiefly used in our service, and it is specially commended by its thoroughly proved efficiency, and by its utility as an independent boat. Its great weight and the consequent difficulty of its transportation are the great drawbacks, and to this cause may well be ascribed much of the fatal delay before the Fredericksburg crossing. It is a hopeless problem to devise any bridge-equipage which shall overcome all serious objections. All that should be expected is to reduce the faults to a practical minimum, while meeting the general wants of the service in a satisfactory manner. The lack of mobility in any bridge-train which can be pronounced always trustworthy may, perhaps, compel the adoption, in addition to the _bateau_-train, of a light equipage for use in quick movements. This will, however, create complication, which is nearly as objectionable here as in the calibre of guns. Thus it is that any solution may prove not exactly the best one for the particular cases which may arise under it. All that should be demanded is, that, by the application of sound judgment to the data which experience and invention afford, our probable wants may be as well met as practicable. Some system we must have; and, on the one hand, zeal for mobility, commendable as it is, must not be permitted to invite grand disasters through failures of the pontoons to do their allotted work; while, on the other hand, a morbid desire to insure absolutely trustworthy solidity of construction must be restrained from imposing needless burdens, which may habitually make our crossings Fredericksburg affairs. Between these extremes lies the right road. American skill has hardly exhausted its resources on this problem. The suspension-bridge train, a description of which General Meigs has published, is deserving of consideration for many cases in campaigns. General Haupt's remarkable railroad-bridges thrown over the Rappahannock River and Potomac Creek, the latter in nine working-days, were structures of such striking and judicious boldness as to justify most hopeful anticipations from the designer's expected treatise on bridge-building. Our national eminence in the art of building wooden trussed and suspension bridges is proof enough that whatever can be done to improve on the military bridge-trains of Europe may be expected at our hands. We shall not lack inventiveness; let us be as careful not to lack judgment, and by all means to be fair and honest in seeking for the best system. When the experience of this war can be generalized, a more positive pontoon-system will be exacted for our service.