"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 homogeneity 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 .07 to .08 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 1,507 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. I can understand your rising to the surface; but diving below the surface, does not your submarine contrivance encounter a pressure, and consequently undergo an upward thrust of one atmosphere for every thirty feet of water, just about fifteen pounds per square inch?"
"Just so, sir."
"Then unless you quite fill the Nautilus, I do not see how you can draw it down to those depths which at times you reach."
"Professor, you must not confound statics with dynamics, or you will be exposed to grave errors. There is very little labor spent in attaining the lower regions of the ocean, for all bodies have a tendency to sink. When I wanted to find out the necessary increase of weight required to sink the Nautilus, I had only to calculate the re-
