Jules Verne: Twenty Thousand Leagues Under the Seas

FIRST PART CHAPTER 13: Some Figures (continued)

"The two hulls are manufactured from boilerplate steel, whose relative density is 7.8 times that of water. The first hull has a thickness of no less than five centimeters and weighs 394.96 metric tons. My second hull, the outer cover, includes a keel fifty centimeters high by twenty-five wide, which by itself weighs 62 metric tons; this hull, the engine, the ballast, the various accessories and accommodations, plus the bulkheads and interior braces, have a combined weight of 961.52 metric tons, which when added to 394.96 metric tons, gives us the desired total of 1,356.48 metric tons. Clear?"

"Clear," I replied.

"So," the captain went on, "when the Nautilus lies on the waves under these conditions, one-tenth of it does emerge above water. Now then, if I provide some ballast tanks equal in capacity to that one-tenth, hence able to hold 150.72 metric tons, and if I fill them with water, the boat then displaces 1,507.2 metric tons-- or it weighs that much--and it would be completely submerged. That's what comes about, professor. These ballast tanks exist within easy access in the lower reaches of the Nautilus. I open some stopcocks, the tanks fill, the boat sinks, and it's exactly flush with the surface of the water."

"Fine, captain, but now we come to a genuine difficulty. You're able to lie flush with the surface of the ocean, that I understand. But lower down, while diving beneath that surface, isn't your submersible going to encounter a pressure, and consequently undergo an upward thrust, that must be assessed at one atmosphere per every thirty feet of water, hence at about one kilogram per each square centimeter?"

"Precisely, sir."

"Then unless you fill up the whole Nautilus, I don't see how you can force it down into the heart of these liquid masses."

"Professor," Captain Nemo replied, "static objects mustn't be confused with dynamic ones, or we'll be open to serious error. Comparatively little effort is spent in reaching the ocean's lower regions, because all objects have a tendency to become 'sinkers.' Follow my logic here."