Like ships, floating docks may be classified historically wording to the materials from which they are constructed, i.e., timber, iron, steel, and possibly reinforced concrete. The earliest floating dock of which any history has come down to us was, like the ships of that date, constructed of timber, and in point of fact this particular dock commenced its career as a ship. At the time to which I refer, that of Peter the Great of Russia or Charles II of England, the captain of a British merchantman in the Baltic found it necessary to do some repairs to the bottom of his ship. Had he been in home waters, he would have beached the ship at high tide, and by means of tackles attached to her mastheads have careened her or pulled her down to such an angle that any of her under-water structure would be exposed at low water, and thus have effected the necessary repairs. In the tideless waters of the Baltic such a procedure was impracticable, and still the repairs had to be carried out. In the port in which these occurrences took place, there happened to be an old hulk much larger than the vessel to be repaired, and this the British captain bought and gutted. He then fitted a gate at the after end, cutting away her stern proper to enable this to be done, and filled in ballast so that the hulk rested on the bottom with her upper works above the surface of the sea. Warping his own ship inside the hulk, he shut the stern gate and pumped the water out. His ship was then inside a primitive graving dock, which, however, owing to the water being pumped out, was afloat. Thus it was that the first idea of a floating dock was evolved. The name of the hulk was the "Camel," and a lifting pontoon to this day is known as a camel. I have a print of a floaking clock on this principle dated 1829, which a,ppenrs to imply that not much progress was made in the century and a half following the original evolution of the floating dock idea. In fact, as far as one can trace, nothing further was done until it occurred to some engineer, whose name has not come down to posterity, to build a dock with the ends open, and to get the required buoyancy by making the platform upon which the vessel rested hollow. He was met at once with the problem of how to obtain stability for his dock, as if a structure be totally submerged it has no stability unless the centre of gravity happens to be below the centre of buyancy-a state of affairs which cannot exist when a ship is being lifted on a submerged pontoon. In early docks there were two rows of stability boxes, one on either side of the pontoon, which were attached to the pontoon by screws. In the course of lifting a ship by pumping water out of the pontoon, the boxes were lifted too, and when they were nearly out of the water the screws were turned, so that they were lowered to their normal water line, and the pontoon pumped up again. Thus, by successive stages, the vessel was lifted.