“The Nautilus is composed of two hulls, one inside, the other outside, joined by T-shaped irons, which render it very strong. Indeed, owing to this cellular arrangement it resists like a block, as if it were solid. Its sides cannot yield; it coheres spontaneously, and not by the closeness of its rivets; and the homogenity of its construction, due to the perfect union of the materials, enables it to defy the roughest seas. “These two hulls are composed of steel plates, whose density is from .7 to .8 that of water. The first is not less than two inches and a half thick and weighs 394 tons. The second envelope, the keel, twenty inches high and ten thick, weighs alone sixty-two tons. The engine, the ballast, the several accessories and apparatus appendages, the partitions and bulkheads, weigh 961.62 tons. Do you follow all this?” “I do.” “Then, when the Nautilus is afloat under these circumstances, one-tenth is out of the water. Now, if I have made reservoirs of a size equal to this tenth, or capable of holding 150 tons, and if I fill them with water, the boat, weighing then 1507 tons, will be completely immersed. That would happen, Professor. These reservoirs are in the lower parts of the Nautilus. I turn on taps and they fill, and the vessel sinks that had just been level with the surface.” “Well, Captain, but now we come to the real difficulty.