quite as important as invulnerability.  Light armor is a complete protection against the most destructive shells, and the old wooden frigates could stand a long battle with solid shot.  But without superior speed, the most invulnerable and heavily armed vessel could neither keep within effective range of her enemy, nor run her down as a ram, nor retreat when overpowered.  And a very fast vessel can almost certainly run past forts, as they are ordinarily situated, at some distance from the channel, without being hit.  Indeed, the difficulty of hitting a moving object with heavy cannon is so great that slow wooden ships do not hesitate to encounter forts and to reduce them, for a moving ship can be so manoeuvred as to hit a stationary fort.

The disadvantages of large ships are, first, great draught.  Although draught need not be increased in the same degree as length, a stable and seaworthy model cannot be very shallow or flat-bottomed.  Hence the harbors in which very large vessels can manoeuvre are few, and there must be a light-draught class of vessels to encounter enemies of light draught, although they cannot be expected to cope very successfully with fast and heavy vessels.  Second, a given sum expended exclusively in large vessels concentrates coast-defences upon a few points, while, if it is devoted to a greater number, consisting partly of small vessels, the line of defences is made more continuous and complete.

System of Protection.  But the effectiveness of war-vessels need not depend solely upon their size.  First, twice or thrice the power may be obtained, with the same weight of boilers and machinery, and with considerable economy, by carrying very much higher steam, employing simple surface-condensers, and maintaining a high rate of combustion and vaporization, in accordance with the best commercial-marine practice.  Second, the battery may be reduced in extent, and the armor thus increased rather than diminished in thickness, with a given buoyancy.  At the same time, the fewer guns may be made available in all directions and more rapidly worked, so that, on the whole, a small ship thus improved will be a match in every respect for a large ship as ordinarily constructed.  Working the guns in small revolving turrets, as by Ericsson’s or by Coles’s plan, and loading and cooling them by steam-power, and taking up their recoil by springs in a short space, as by Stevens’s plan, are improvements in this direction.  The plan of elevating a gun above a shot-proof deck at the moment of aiming and firing, and dropping it for loading or protection by means of hydraulic cylinders, and the plan of placing a gun upon the top of the armor-clad portion of the ship, covering it with a shot-proof hood, and loading it from below, and the plan of a rotating battery, in which one gun is in a position to fire while the others attached to the same revolving frame are loading,—­all these obviously feasible plans have the advantages of avoiding port-holes