"Now then, if water isn't absolutely incompressible, at least it compresses very little. In fact, according to the most recent calculations, this reduction is only .0000436 per atmosphere, or per every thirty feet of depth. For instance, to go 1,000 meters down, I must take into account the reduction in volume that occurs under a pressure equivalent to that from a 1,000-meter column of water, in other words, under a pressure of 100 atmospheres. In this instance the reduction would be .00436. Consequently, I'd have to increase my weight from 1,507.2 metric tons to 1,513.77. So the added weight would only be 6.57 metric tons."

"That's all?"

"That's all, Professor Aronnax, and the calculation is easy to check. Now then, I have supplementary ballast tanks capable of shipping 100 metric tons of water. So I can descend to considerable depths. When I want to rise again and lie flush with the surface, all I have to do is expel that water; and if I desire that the Nautilus emerge above the waves to one-tenth of its total capacity, I empty all the ballast tanks completely."

This logic, backed up by figures, left me without a single objection.

"I accept your calculations, captain," I replied, "and I'd be ill-mannered to dispute them, since your daily experience bears them out. But at this juncture, I have a hunch that we're still left with one real difficulty."

"What's that, sir?"

"When you're at a depth of 1,000 meters, the Nautilus's plating bears a pressure of 100 atmospheres. If at this point you want to empty the supplementary ballast tanks in order to lighten your boat and rise to the surface, your pumps must overcome that pressure of 100 atmospheres, which is 100 kilograms per each square centimeter. This demands a strength--"

"That electricity alone can give me," Captain Nemo said swiftly. "Sir, I repeat: the dynamic power of my engines is nearly infinite. The Nautilus's pumps have prodigious strength, as you must have noticed when their waterspouts swept like a torrent over the Abraham Lincoln. Besides, I use my supplementary ballast tanks only to reach an average depth of 1,500 to 2,000 meters, and that with a view to conserving my machinery. Accordingly, when I have a mind to visit the ocean depths two or three vertical leagues beneath the surface, I use maneuvers that are more time-consuming but no less infallible."

"What are they, captain?" I asked.

"Here I'm naturally led into telling you how the Nautilus is maneuvered."

"I can't wait to find out."

"In order to steer this boat to port or starboard, in short, to make turns on a horizontal plane, I use an ordinary, wide-bladed rudder that's fastened to the rear of the sternpost and worked by a wheel and tackle. But I can also move the Nautilus upward and downward on a vertical plane by the simple method of slanting its two fins, which are attached to its sides at its center of flotation; these fins are flexible, able to assume any position, and can be operated from inside by means of powerful levers. If these fins stay parallel with the boat, the latter moves horizontally. If they slant, the Nautilus follows the angle of that slant and, under its propeller's thrust, either sinks on a diagonal as steep as it suits me, or rises on that diagonal. And similarly, if I want to return more swiftly to the surface, I throw the propeller in gear, and the water's pressure makes the Nautilus rise vertically, as an air balloon inflated with hydrogen lifts swiftly into the skies."

"Bravo, captain!" I exclaimed. "But in the midst of the waters, how can your helmsman follow the course you've given him?"

"My helmsman is stationed behind the windows of a pilothouse, which protrudes from the topside of the Nautilus's hull and is fitted with biconvex glass."

"Is glass capable of resisting such pressures?"

"Perfectly capable. Though fragile on impact, crystal can still offer considerable resistance. In 1864, during experiments on fishing by electric light in the middle of the North Sea, glass panes less than seven millimeters thick were seen to resist a pressure of sixteen atmospheres, all the while letting through strong, heat-generating rays whose warmth was unevenly distributed. Now then, I use glass windows measuring no less than twenty-one centimeters at their centers; in other words, they've thirty times the thickness."

"Fair enough, captain, but if we're going to see, we need light to drive away the dark, and in the midst of the murky waters, I wonder how your helmsman can--"

"Set astern of the pilothouse is a powerful electric reflector whose rays light up the sea for a distance of half a mile."

"Oh, bravo! Bravo three times over, captain! That explains the phosphorescent glow from this so-called narwhale that so puzzled us scientists! Pertinent to this, I'll ask you if the Nautilus's running afoul of the Scotia, which caused such a great uproar, was the result of an accidental encounter?"

"Entirely accidental, sir.