There is nothing in the nature of things that I know of to prevent submarine warfare being carried on in the future to a very large extent. This development will probably follow triple lines: (1) Vessels for the defence of ports and harbours, with sufficient means of proceeding outside to give the defence a certain limited power of attack in the approaches; (2) Vessels primarily designed for attack, and therefore capable of proceeding to sea for considerable distances; and (3) Smaller vessels to be taken to sea in ships, as part of their equipment, and capable of being lowered to take part in a battle, and raised again, and re-stowed on board when no longer needed in action. All these types of vessel will need to be endowed with the power of passing easily and quickly from the floating to the submerged condition, and back again to the surface when necessary; but the boats of the second class in the foregoing category will doubtless be developed to an extent as yet anticipated by very few of us, in respect alike of their ability to proceed for great distances below water, and of their ability to steam satisfactorily afloat when submergence is needless. All who are acquainted with the structure of waves, so to speak, will be aware that wave disturbance diminishes very rapidly as we go down below the surface, and will consequently understand that when once we have succeeded in giving submarines a great range of under-water travel, we shall have endowed them with the capability of avoiding at pleasure in bad weather the tempestuous surface of the sea, with all the drawbacks to speed which stormy seas impose upon ships, and especially upon comparatively small vessels. In order to bring about this advantage, science has to effect, no doubt, immense improvements in the production of storage of air, or of its equivalent; but there is great reason to believe that the demand will bring the supply, as in so many other matters. Nor must it be forgotten that this is a branch of science for the development of which the ship proper, as we have hitherto known it, has offered few, if any, inducements. I do not know how the sight of an ordinary modern ship of war strikes the eyes of others, but for my part I never look at one, with its vast and monstrous assemblage of gaping mouths of funnels, pipes, and cowls, without thinking that our method of supplying breathing gas to men below in a ship is at present of a very elementary and unsatisfactory character. It is certainly the roughest and readiest method that could well be adopted. Nor is it without a sense of satisfaction that one knows that the submarine ship will at least sweep away these ugly and towering excrescences, and force us to resort much more than at present to the chemical and mechanical arts for the ventilation of vessels.