Should a vessel be heavily down by the head or stern, a floating dock can be tilted to lift it, and should the vessel be heeling over, the dock itself can be inclined so that it shall receive it without difficulty. Yet another advantage is that the floating dock can be used in any kind of ordinary weather. Lying at its moorings it is head on to wind and sea. The amount of surface it opposes to the direct action of wind and sea is comparatively slight. The very massiveness of its structure reduces longitudinal and lateral motion to a minimum, especially when submerged. Even with a fairly heavy sea running, a damaged and leaking vessel can be brought upon the dock where its weight, added to that of the dock itself, makes the combined structure additionally stiff, so that the necessary repairs can be undertaken in safety as soon as the vessel is lifted, and with as much ease as if the dock and its burden were in still water. Floating docks also can be used at any state of the tide, but he would be a rash man who attempted to warp a vessel into an ordinary dry dock with the tide running past the entrance with any degree of strength. [Illustration: OLD FLOATING DOCK AT ROTHERHITHE, circa 1800.] The earliest type of the modern floating dock is that known as the box dock. It consists of a pontoon divided into cells or compartments, and having on either side a large wall also divided into compartments arranged in tiers, the ends of the structure between the walls being open. The earliest of these docks were made of wood, and compared with those of later date were of small dimensions. One of the most noteworthy wooden docks was that at Rangoon, launched in February 1866, and having a length of 300 feet, with a breadth of 90 feet, and an inside breadth of 70 feet, and able to take vessels drawing from 15 to 16 feet of water. There is also at Altona a wooden floating dock built in 1868 and still in active use; it is 138 feet in length, and can lift vessels up to 420 tons register. The early floating docks were usually in transverse section like the capital letter =[U]=, and followed fairly closely the form of the round-bottomed ships of the time. As the girder principle, however, became introduced in shipbuilding it was recognised that floating docks must be constructed approximating to that shape, and modern floating docks are now built rectangular in transverse section, though in constructional details this form is a modification of the =[U]= shape.